ie250 ih r

QAF 011b | Rev. 10 | 26-12-13

©2014 Haward Technology Middle East

This document is the property of the course instructor and/or Haward Technology Middle East. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of Haward Technology Middle East.

P.O. Box 26070, Abu Dhabi, UAE Tel: +971-2-59 69 400 Fax: +971-2-59 69 401 Email: [email protected] http://www.haward.org

Distribution Network Automation Volume 1

Haward Technology Middle East

April 06-10, 2014 Dharan, KSA Course Instructor Mr. Sydney Thoresson

Liquid & Gas Flowmetering

To the Participant

The Course Notes are intended as an aid in following lectures and for review inconjunction with your own notes; however they are not intended to be acomplete textbook. If you spot any inaccuracy, kindly report it by completingthis form and dispatching it to the following address, so that we can take thenecessary action to rectify the matter.

Haward Technology Middle EastP.O. Box 26070Abu Dhabi, UAE

Tel.: +971 2 59 69 400Fax: +971 2 59 69 401Email: [email protected]

Name

Address

E-mail

Course Title

Course Date

Course Location

Descriptionof Inaccuracy

Disclaimer

The information contained in these course notes has been compiledfrom various sources and is believed to be reliable and to representthe best current knowledge and opinion relative to the subject.

Haward Technology offers no warranty, guarantee or representationas to its absolute correctness or sufficiency.

Haward Technology has no responsibility in connection therewith;nor should it be assumed that all acceptable safety and regulatorymeasures are contained herein, or that other or additionalinformation may be required under particular or exceptionalcircumstances.

Table of Contents Section 1 Introduction to

Process Measurement Section 2 Flow Measurement

Section 3 Differential Pressure

Flowmeters

Section 4 Variable Area Flowmeters

Section 5 Oscillatory Flow Measurement

Section 6 Rotary Inferential Flowmeters

Section 7 Electromagnetic Flowmeters

Section 8 Positive Displacement Flowmeters

Section 9 Ultrasonic Flowmeters

Section 10 Mass Flowmeters

and Selection

Section 11 Miscellaneous Devices

Section 12 Flowmeter Calibration

Table of Contents Section 13 Flowmeter Installation Guidance Section 14 Flowmeter Costs and Flowmeter

Selection

Section 15 Introduction to Multiphase Flow Measurement

Section 16 Basic Concepts of

Multiphase Flow and Multiphase Flowmeter

Section 17 Current Main Suppliers of Multiphase Flowmeters

Section 18 Level Measurement

Section 19 Selection of Flowmeters

Section 20 OIML Recommendation 117

Section 21 Terminal Custody Transfer

Section 22 Lease Automatic

Custody Transfer

Table of Contents

Section 23 Truck Custody Transfer

Section 24 Leak Detection Systems

Section 25 API Standards

Section 26 Standards Organizations, Flow Measurement Standards and References

Section 27 Contoured Devices

Section 28 a. Computer System Control A b. Computer System Control B

Section 1

Introduction to Process Measurement

of 10

Section 1 IE250-IH


Liquid & Gas Flow Metering

Course Objectives

Upon the successful completion of this course, each participant will be able to:

Apply an in-depth knowledge and skills in liquid and gas multiphase and single-phase flowmetering, ultrasonic flowmetering, custody measurement and loss control of petroleum products

Select and calibrate an ultrasonic flowmeter for the required application and deal with related operational and measurement concerns

Choose the correct flowmeter or combination of flowmeters for a particular multiphase application and be able to resolve any ensuing problems in relation to unreliability or inaccuracy of flowmeter readings

Compare the performances of existing multiphase meters such as Agar, Weatherford, Roxar, Schlumberger and Haimo and recognize their importance in flowmetering

Determine the different types, methods and techniques used in custody transfer and understand the various pipeline meter considerations

Employ systematic techniques in leak detection and loss control during custody transfer and list the various API standards applicable to flowmetering and custody measurement

of 10

Section 1 IE250-IH


Table of Contents Section 1 Introduction to Process Measurement Section 2 Pressure Measurement Section 3 Temperature Measurement Section 4 Flow Measurement Section 5 Differential Pressure Flowmeters Section 6 Variable Area Flowmeters Section 7 Oscillatory Flow Measurement Section 8 Rotary Inferential Flowmeters Section 9 Electromagnetic Flowmeters Section 10 Positive Displacement Flowmeters Section 11 Ultrasonic Flowmeters Section 12 Mass Flowmeters Section 13 Miscellaneous Devices Section 14 Flowmeter Calibration Section 15 Flowmeter Installation Guidance Section 16 Flowmeter Costs and Flowmeter Selection Section 17 Quality Assurance and Standards Section 18 Introduction to Multiphase Flow Measurement Section 19 Basic Concepts of Multiphase Flow and Multiphase Flowmeters Section 20 Current Main Suppliers of Multiphase Flowmeters Section 21 Selection of Flowmeters Section 22 Future Developments in Flow Measurement Section 23 Numerical Exercises Section 24 Standards Organisations, Flow Measurement Standards and References Section 25 Cavitation and Flashing Section 26 Pipeline Requirements and Installation Notes for Dry-type

Differential Transmitters Section 27 Contoured Devices

of 10

Section 1 IE250-IH


Section 1

Introduction to Process Measurement

Process Measurement

Conversion of a physical parameter • temperature/pressure/level/flow

To a standard, widely-recognised signal • Pneumatic

‐ 3 - 15 psi; 20 - 100 kPa • Electrical level (voltage/current)

‐ 4 - 20 mA; 0 - 10 V • Digital code

‐ HART/Profibus PA; Foundation Fieldbus

Analog Inputs

of 10

Section 1 IE250-IH


Measurement Accuracy

How closely does the output signal represent the actual parameter?

(what is the uncertainty of the measurement)

Expressing Accuracy

% of Reading % of Full-scale

Accuracy

of 10

Section 1 IE250-IH


Range of Operation

High and Low Operating Limits between which the device will operate

correctly.

Hysteresis

Accuracy of device dependent on previous value and the direction of variation.

of 10

Section 1 IE250-IH


Linearity

How close the curve is to a straight line.

Repeatability

How close a second measurement is to the first under the same

operating conditions and the same input.

Response

Output of a device expressed as a function of time due to an applied

input.

of 10

Section 1 IE250-IH


Typical Response to a Step Input

Effects of Temperature

Accuracy (uncertainty) may be specified over a certain temperature range (e.g. 10o - 60oC)

Temperature effect may be quoted as x %/oC

Effects of Time

Shows an instrument’s ability to maintain its stability over time Typical periods quoted as 60, 90, 180, 360 days, etc

• 10 - 12 years for recent instruments

of 10

Section 1 IE250-IH


Traceability

Capability of providing an unbroken paper chain back to the original, primary standard

Relative or total? Is the accuracy/uncertainty only relative to the next higher instrument a in the chain, or absolute, including all uncertainties back to the primary a standard?

Confidence Level

The percentage of devices which meet specification is called the ‘confidence level’

• A top manufacturer may specify that 99% of instruments meet the specification

Not all instruments meet the specification

Resolution

The ability to ‘resolve’ a minimum difference between two readings On an analog meter, the scale difference between two adjacent lines In a digital instrument, the smallest step between one reading and the

next higher or lower value

Noise Level

Most process instruments have an output with random variations These variations interfere with the reading

Calibration

A comparison of a measurement against an equal or better device, and adjusting the instrument to agree with the better device.

Budget

Important Selection Consideration! Price usually dictates performance

of 10

Section 1 IE250-IH


What are we Measuring?

meters (m) - length or distance kilograms (kg) - mass seconds (s) - time Amperes (A) - electrical current Degrees Kelvin (oK) - temperature Moles (mol) - amount of any substance Candela (cd) - intensity of light

Instrumentation Representation on Flow Diagrams

of 10

Section 1 IE250-IH


Letter Codes and Balloon Symbols

Symbols for Transducers, etc.

COURSE RECAP Day 1

0730 - 0800 Registration & Coffee

0800 - 0815 Welcome & Introduction

0815 – 0830 PRE-TEST

0830 - 0930 Flowmetering Overview Introduction to Pipeline Flowmetering with Highlighted Problem Areas

0930 - 0945 Break

0945 - 1045 Introduction to Process Measurement Accuracy, Hysteresis, Linearity, Repeatability, Response, Traceability, Confidence, Resolution, Calibration, Process Symbols

1045 – 1230 Measurement of Pressure Static, Dynamic, Total Pressures, Commercial Pressure Gauges

1230 - 1245 Break

1245 - 1330 Measurement of Temperature and Density Commercial Gauges

1330 - 1420 Flow Measurement Laminar Flows & Turbulent Flows, Velocity Distributions, Reynolds Number Worked Examples, Volume, Mass, Total Flows, Viscosity, Cavitation

1420 – 1430

Recap Using this Course Overview, the Instructor(s) will Brief Participants about the Topics that were Discussed Today and Advise Them of the Topics to be Discussed Tomorrow

1430 Lunch & End of Day One

Day 2

0730 - 0915

Fluid Mechanics of Pipe Flows

Fitting Losses ● Newtonian & Non-Newtonian Flows ● Flowmeter

Classification ● Worked Examples

0915 - 0930 Break

0930 - 1045

Flowmeter - Differential Pressure Type

Elementary Theory Based on Bernoulli’s Equation & Continuity ● Orifice

Meters ● Critical Flow Element ● Laminar Flow Element

1045 – 1230

Flowmeter - Differential Pressure Type (cont’d)

Venturi Meters ● Flow Nozzles ● Low Loss Devices ● Variable Orifice

Meters ● Variable Area Meters ● Pitot Tubes & Pitot Static Tubes ●

Target Flowmeters ● Drain Holes and Vents

1230 - 1245 Break

1245 - 1420 Flowmeter – Variable Area Operating Constraints & Performances, Advantages and Disadvantages

1420 – 1430


1430 Lunch & End of Day Two

Day 3

0730 - 0830

Flowmeter - Fluid Oscillatory Flowmeters

Fluidic Meters ● Vortex Shedding Meters ● Operating Constraints &

Performances ● Advantages & Disadvantages

0830 - 0930 Flowmeter - Rotary Inferential Meters

Turbine Flowmeters ● Miscellaneous Designs ● Advantages & Disadvantages

0930 - 0945 Break

0945 - 1130

Flowmeter - Electromagnetic Flowmeters

Principle of Operation ● AC & Pulsed DC Types ● Applications &

Operating Constraints and Performances ● Advantages & Disadvantages

1130 - 1230 Flowmeter – Positive Displacement Flowmeters Helical Gear Meter, Nutating Disc Meter, Piston Meter, Rotary Meter, Advantages & Disadvantages, Applications, Worked Examples

1230 - 1245 Break

1245 - 1330 Flowmeter - Ultrasonic Flowmeters

Doppler Type ● Time-of -Flight Type ● Clamp-on Type ● Applications ● Advantages & Disadvantages

1330 - 1420

Flowmeter - Mass Flow Measurement

Coriolis Flowmeters ● Hot Wire Anemometer & Thermal Profile Meter ●

Applications ● Advantages & Disadvantages

1420 – 1430


1430 Lunch & End of Day Three

Day 4

0730 - 0830 Flowmeter – Miscellaneous Devices Cross Correlation Methods, Tracer Methods, Weighing Methods Velocity Profile Integration Techniques, Laser Doppler Systems

0830 – 0930

Flowmeter Calibration

Gravimetric Methods for Liquid Flowmeters ● Volumetric Methods for Liquid

Flowmeters ● Use of Pipe Provers ● Methods for Gas Flowmeters ●

Critical Flow Nozzle ● Velocity Traversing Technique ● Clamp-on Ultrasonic Flowmeter

0930 - 0945 Break

0945 - 1030

Flowmeter Installation Guidance

Introduction ● Pipe-Flow Disturbances & Other Sources of Error Effects of

Installation on Specific Flowmeters ● Remedial Actions & Use of Flow Conditioners

1030 – 1130 Flowmeter Costs and Flowmeter Selection

Initial Considerations ● Flowmeter Selection Procedure ● Additional Factors

1130 - 1230

Quality Assurance and Standards

Traceability & Hard Standards ● Flow Standards ● UK National

Measurement Systems ● Accreditation Process

1230 - 1245 Break

1245 - 1420 Introduction to Multiphase Flow Measurement Description of Multiphase Flows, Definitions of Various Associated Terms, Flow Pattern Classification, Flow Regimes, Multiphase Measurement

Problems, Multiphase Meter Classification

1420 – 1430


1430 Lunch & End of Day Four

Day 5

0730 - 0830 Basic Concepts of Multiphase Flows & Multiphase Flowmeters Response of Single-Phase Flowmeters in Multiphase Flows, Wet Gas Flow Measurement, Application of Two Flowmeters for Multiphase Flows

0830 - 0930 Current Main Supplier of Multiphase Flowmeters Overview of Different Devices & their Limitations/Advantages

0930 - 0945 Break

0945 - 1230

Selection of Flowmeters

Classification of Flowmeter Types ● Selection Considerations ● Installation

Planning & Installation ● Faults & Failures ● Application Tables

1230 - 1245 Break

1245 - 1345

Future Developments in Flow Measurement

Flowmeter Developments ● Secondary Instrumentation ● Signal

Acquisition & Processing from Single-Phase Flowmeters ● Utilization of Unconditioned Signals from Single Phase Flowmeters in Multiphase Flows

1345 – 1400 Course Conclusion Using this Course Overview, the Instructor(s) will Brief Participants about the Course Topics that were Covered During the Course

1400 - 1415 POST-TEST

1415 – 1430 Presentation of Course Certificates

1430 Lunch & End of Course

Section 2

Flow Measurement

of 20

Section 2 IE250-IH


Section 2

Pressure Measurement

Principles

Pressure = Force per unit area Units are psi, mm Hg and kPa, etc. Absolute Pressure referenced to a vacuum Gauge Pressure referred to ambient atmospheric pressure Differential Pressure compares two different pressures

Pressure Units

of 20

Section 2 IE250-IH


Pressure Sources Static Pressure

Due to weight of the molecules “pressing down”. Dynamic Pressure

Relative movement when a body is moving through the fluid.

Static Pressure

Dynamic Pressure

of 20

Section 2 IE250-IH


Pressure Variations

Total Pressure

Pressure Transducers – Mechanical

Bourdon Tube Helix and spiral tubes Spring and Bellows Diaphragm Manometer Single and Double Inverted Bell

of 20

Section 2 IE250-IH


C - Bourdon Tube

Bent tube will change its shape when exposed to variations in internal or external pressure

Orientation dependent for correct results Wide Operating range

C - Bourdon Pressure Element

Advantages of C – Bourdon

Inexpensive Wide Operating Range Fast response Good sensitivity Direct Pressure measurement

of 20

Section 2 IE250-IH


Disadvantages of C-Bourdon

Intended for indication only Non-linear transducer Hysteresis on cycling Sensitive to temperature variations Limited life under shock/vibration Some materials clog the tube Unstable zero point

Application Limitations

Use in air if calibrated for air Use in liquid if calibrated for liquid Bleed air from the liquid lines If for Oxygen, device cannot be calibrated if it leaves oil traces oil

Helix and Spiral Tubes

With one end sealed, pressure causes the tube to straighten out Spiral suitable up to 28 000 kPa Helical suitable up to 500 000 kPa

Spiral Bourdon Element

of 20

Section 2 IE250-IH


Helix Bourdon Element

Advantages - Spiral/Helix

Increased accuracy and sensitivity Higher over-range protection

Disadvantages - Spiral/Helix

Very Expensive

Spring and Bellows

Expandable element Free end responds to pressure Spring used to oppose force Linkage to pointer for indication Primarily for ON / OFF control Provides contacts for electrical circuits Responds to pneumatic or hydraulic pressure changes

of 20

Section 2 IE250-IH


Spring and Bellows Switch

of 20

Section 2 IE250-IH


Spring and Bellows Gauge

Advantages - Spring/Bellows

Simple construction Easily maintained Inexpensive

Disadvantages - Spring/Bellows

Sensitive to temperature variations Work hardening of bellows Hysteresis Poor over-range protection

Diaphragm

Sensor measurement dependent on deflection of diaphragm Flexible disc Flat or with concentric corrugations Sheet metal with high tolerance dimensions

of 20

Section 2 IE250-IH


Simple Corrugated Diaphragm

Advantages – Diaphragm

Provide isolation from process fluid Good for low pressure Inexpensive Wide range Reliable and proven Used to measure gauge, atmospheric and differential pressure

Manometer

Simplest form is U-shaped, liquid filled tube Reference and measured pressure applied to ends of tube Difference in pressure causes difference in liquid level between sides

of 20

Section 2 IE250-IH


Simplest Form of Manometer

Typical Applications

Mainly spot checks or calibration • Modern calibration using electronic meters

Low range measurements • Higher measurements require mercury

‐ toxic, therefore hazardous

Advantages – Manometer

Simple operation and Construction Inexpensive

Disadvantages - Manometer

Low pressure range (water) Higher pressure range requires mercury Readings are localised

of 20

Section 2 IE250-IH



Size limits operation to low range Difficult to integrate into continuous control system

Single and Double Inverted Bell

Measures pressure difference between sides of bell shaped compartment To reference to surrounding conditions

• Lower compartment vented to outside • Gauge pressure measured

Inverted Bell d/p Detector

The bell instrument is used where very low pressures are to be measured, typically 0 - 250 Pa

of 20

Section 2 IE250-IH


Pressure Transducers and Elements

Strain gauge Vibrating wire Piezoelectric Capacitance Linear Variable Differential Transformer Optical

Strain Gauges

Metal wire or semiconductor chip Change in resistance as metal is deformed by pressure Temperature sensitive

• Temperature compensation required • Often use Wheatstone bridge

Wheatstone Circuit for Strain Gauges

of 20

Section 2 IE250-IH


Typical Application

Force • Applied to diaphragm • Through silicone fill fluid • To polysilicon sensor

Reference side exposed to atmospheric pressure for gauge transmitters

Advantages - Strain Gauges

Wide range, 7.5 kPa to 1 400 MPa Accuracy of 0.1% Small in size Stable devices with fast response No moving parts Good over-range capability

Disadvantages - Strain Gauges

Unstable due to bonding material Temperature sensitive Thermo-elastic strain causes hysteresis

Vibrating Wire

Electronic oscillator circuit causes natural frequency oscillation of wire Wire under tension in diaphragm Pressure changes cause changes in natural frequency

Advantages - Vibrating Wire

Good accuracy and repeatability Stable Low hysteresis High resolution Absolute/gauge/differential measurement

of 20

Section 2 IE250-IH


Disadvantages - Vibrating Wire

Temperature sensitive Affected by shock and vibration Non-linear Physically large

Piezoelectric

Crystals elastically deformed when force applied Measure rate of change of deformation Electrical output proportional to applied acceleration

Advantages – Piezoelectric

Accuracy 0.075% Very high pressure measurement, up to 70 MPa Small size Robust Fast response, < 1 nanosecond Self-generated signal

Disadvantages - Piezoelectric

Dynamic sensing only Temperature sensitive

Capacitance

Diaphragm movement causes capacitance change Sensor energised by a high frequency electrical oscillator Relative capacitance measured by bridge circuit

of 20

Section 2 IE250-IH


Capacitance Measurement

Advantages – Capacitance

Accuracy 0.01 to 0.2% Range of 80Pa to 35MPa Linearity Fast response

of 20

Section 2 IE250-IH


Disadvantages - Capacitance

Temperature sensitive Stray capacitance problems Vibration Limited overpressure capability Cost

Cross Section of the Rosemount -CellTM Sensor

Linear Variable Differential Transformer (LVDT)

Movement of high permeability material within transformer coils Pressure transferred via diaphragm, bellows or bourdon tube

of 20

Section 2 IE250-IH


Linear Variable Differential Transformer

Disadvantages

Mechanical wear Vibration

Optical Pressure Sensor

of 20

Section 2 IE250-IH


Optical

Opaque vane mounted to the diaphragm Vane moves in front of infra-red beam Received light indicates position of the diaphragm

Advantages – Optical

Temperature corrected Good repeatability Negligible hysteresis

Disadvantages - Optical

Expensive

Installation considerations

Location of Connections Isolation Valves Impulse Tubing Test and Drain Valves Construction Temperature Remote Diaphragm Seals Precautions with Remote Diaphragm Seals Process Flanges Additional Hardware

Location of Process Connections

Top of process line for gases Side of lines for other fluids

Isolation Valves

Between process fluid and measuring equipment if device is to be taken out

of 20

Section 2 IE250-IH


Use of Impulse tubing

Impulse piping • Short as possible • Self draining by sloping lines towards the process

Self venting instruments If solids can accumulate place tees and plug fittings in place of elbows

Test and Drain Valves

Blowdown valve needed for toxic or corrosive fluid

Sensor Construction

Mechanical and thermal isolation: • Away from process flange • Position in neck of electronics housing

Temperature Effects

Wheatstone bridge often used to compensate for temperature effects

Remote Diaphragm Seals

Remote seals needed if: • Corrosion is possible • Fluid viscosity may cause clogging • Process temperature is outside normal operating temperature of

transmitter • Fluid may solidify • Fluid needs to be flushed • Maintaining sanitary or aseptic conditions • Making density or other measurements

of 20

Section 2 IE250-IH


Precautions with Remote Seals

Large diameter/short capillary • minimises temperature effects

In two seal system use same • fluid • diaphragm diameter • capillary length

Fluid to cope with extremes of temp and pressure

Process Flanges

Coplanar flange • Becoming more standard

Traditional flange • traditional biplanar configurations

Level flange • Permits direct process mounting

Additional Hardware

If pulsation dampeners are required the material and fill fluids must be compatible with the process fluid

Siphons of correct material required for vapours above 60oC

Impact on the Control Loop

Longer response due to material build-up on sensing element Over-ranging causing incorrect readings

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 3

Differential Pressure Flowmeters

of 14

Section 3 IE035-IH


Section 3

Temperature Measurement

Principles

Transfer of heat energy from the process material to the measuring device

Two main types • Contact (Thermocouples, RTDs and Thermistors) • Non-contact (Infra red and Acoustic)

Thermocouples

Two wires of dissimilar metals • Iron/constantan connected at one end

Application of heat to junction • Creates a voltage between the two wires

A reference junction is placed in series with the sensing junction

of 14

Section 3 IE250-IH


Extension/Compensating Cable

Extension cable • same metals as thermocouple junction • used with base metal thermocouples

Compensating cable gives the same effect • copper alloy in both conductors • cheaper alternative • used with noble metal thermocouples

Averaging Temperatures

Temperature Difference

of 14

Section 3 IE250-IH


Construction

Installation Techniques

Use largest size thermocouple wire possible Avoid stress and vibration Use transmitters if possible

• Thermocouples are mV signals • Susceptible to noise • 4 - 20 mA signals almost noise-immune

Detection of Thermocouple Faults

Short in the extension wires may not be detected Measure resistance continuously to note any changes

Application Details

Thermopaste minimises air-gap problems Clean bore of thermowell when changing

New thermocouple of different mass/length to old one means longer response time

Grounding requires care

of 14

Section 3 IE250-IH


Thermocouple Voltage Curves

Applications

R-type thermocouples are suitable in oxidising atmospheres easily contaminated in others

T-type can be used in oxidising or reducing atmospheres J-type can be used in reducing atmospheres. Least expensive K-type can be used in oxidising atmospheres

of 14

Section 3 IE250-IH


Advantages

Low cost Small size Robust Wide range of operation Reasonably stable Reasonable output for large temperature changes Fast response

Disadvantages

Weak output, mV Limited accuracy

• Usually accepted as being 3% Sensitive to electrical noise Non-linear

• Complex conversion from emf to temp

• Not an issue with -processor inputs


Small temperature changes mean very small voltage changes Susceptible to noise Non-linear Calibration changes over time Cannot be used bare in conductive fluids

of 14

Section 3 IE250-IH


Thermocouple Colour Coding

Platinum Resistance Thermometers (RTD)

Platinum construction (usually) Electrical resistance increases with temp

Temperature coefficient in ohms/°C

• Usual figure of = 0.385/OC Fairly linear but temperature coefficient does vary Pt100 and Pt1000 Ni100 and Ni1000

of 14

Section 3 IE250-IH


Two/Three/Four Wire Measurement

of 14

Section 3 IE250-IH



Pt100 housed in thermowell 2-wire used in HVAC applications

• Provided very short runs used 3-wire used in industrial applications 4-wire in high precision environment

Advantages

Good sensitivity Standard copper wire

• From Pt100 to indicator/controller Mostly linear

• Up to 1000C • Non-linear (but predictable) after that

Disadvantages

Somewhat fragile • Pt wire wound on glass

‐ Similar expansion coefficients Self heating considerations Susceptible to noise

Comparative Transfer Curves

of 14

Section 3 IE250-IH


Thermistors

Semiconductor device formed from metal oxides Negative temperature coefficient Size from 1mm to a few cm disc Small temperature change easy to detect

Thermistor Resistance vs Temperature

of 14

Section 3 IE250-IH


Typical Thermistor Packaging

Selection and Sizing

-73 °C to 316 °C Many cannot be used above 120 °C

Advantages

Small size Fast response High sensitivity No cold junction compensation Inexpensive Polarity insensitive Wide selection of sensors

of 14

Section 3 IE250-IH


Disadvantages

Unstable due to drift and de-calibration Not easily interchangeable Non-linear Narrow span Fragile High resistance, noise problems

Liquid-in-glass Thermometer

of 14

Section 3 IE250-IH


Class II B Vapour Filling

Bi-metal Strip

of 14

Section 3 IE250-IH


Non-contact Pyrometers

Infra-red pyrometers Acoustic Pyrometers

Objects Above Absolute Zero Radiate

of 14

Section 3 IE250-IH


Structure of Humicap Sensor

Protect Thermocouple Signal

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 4

Variable Area Flowmeters

of 6

Section 4 IE250-IH


Section 4

Flow Measurement

Types of Flow

Newtonian vs Non-Newtonian Flow

of 6

Section 4 IE250-IH


Laminar Flow

Fluid moves smoothly in orderly layers. Little or no mixing of fluid across flow stream.

Turbulent Flow

Does not move smoothly in orderly layers. Large amount of mixing of fluid across flow stream.

Flow Profiles

Swirl

Occurs as fluid passes through elbows or some other form of pipeline geometry.

Reynolds Number

Reynolds Number defines the flow conditions at a particular point. Useful indicator of laminar and turbulent flow.

of 6

Section 4 IE250-IH


Reynolds Number

Volumetric Flow Rate

Represents the volume of fluid which passes through a pipe per unit of time.

Mass Flow Rate

Mass flowrate is a measure of the actual amount of mass of the fluid passing through a pipe per unit of time.

Totalised Flow

An accumulation of the amount of fluid that has past a point in a pipe.

Viscosity

Defines the resistance which the fluid has against flowing.

Dynamic Viscosity has the units of cP (CentiPoise).

Kinematic Viscosity = / has the units of cSt (CentiStokes).

of 6

Section 4 IE250-IH


Density

The density of a fluid is the mass of the fluid per unit volume. Density is affected by temperature and pressure variations.

Specific Gravity

The weight of a substance may vary for the same volume or size. The Specific Gravity is the ratio between the density of a substance to

the density of water.

Pulsations

To maintain good measuring conditions, pulsations in the flow stream should be recognised and (if possible) avoided.

Cavitation

Occurs when pressure is reduced below vapour pressure of the liquid. Vapour cavities, or bubbles subsequently form.

Non-Newtonian

Normal behaviour of fluids is such that as temperature increases, viscosity decreases.

Non-Newtonian fluids do not conform to the normal behaviour of liquids. They may become thinner or thicker when agitated or stiffen when

deformed.

Vena Contracta

The cross-sectional area of a fluid decreases as it is forced through a restriction.

This area continues to decrease for a short time after the restriction. The Vena Contracta is the minimum cross-sectional area of the fluid.

of 6

Section 4 IE250-IH


Vena Contracta

Rangeability

of 6

Section 4 IE250-IH


Turndown

Flow Measurements

Velocity Volumetric Flow Mass Flow Total Flow

Volumetric Flow

Mass Flow W = Q . p Where: Q is the volumetric flow rate. p is the density of the fluid. W is the mass of the flow rate.

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 5

Oscillatory Flow Measurement

of 13

Section 5 IE250-IH


Section 5

Differential Pressure Flowmeters

Basis of Operation

Pressure is measured on both sides of an imposed restriction in the path of normal flow.

Some Useful Equations

V = k . (Dp/r)

Q = k . A . (Dp/r)

W= k . . A . (Dp/r) V = Velocity Q = Volumetric flow rate

= Fluid density W = Mass flow rate

p = Differential pressure A = Cross-sectional area of the pipe k = a constant

of 13

Section 5 IE250-IH


Head Loss

Primary Element

Standard Orifice Plate is smooth disc with a round, sharp-edged inflow aperture and mounting rings.

of 13

Section 5 IE250-IH


Differential Pressure Profile with Orifice Plate

Orifice Type

Three main types of orifices: • Concentric square edged. • Concentric quadrant edged. • Eccentric or segmental square edged.

New type is 4-hole conditioning orifice plate See details later for this.

of 13

Section 5 IE250-IH


Concentric Orifice Plate

Quadrant Edge Orifice Plate

of 13

Section 5 IE250-IH


Segmental Orifice Plate

Advantages

Simple, inexpensive Requires no calibration (new) Easily fitted between flanges No moving parts Large range of sizes and opening ratios Suitable for most gases and liquids Well understood and proven Price not much more for large lines

Disadvantages

Accuracy typically > 1.5% Low turndown, typically 4:1

Accuracy is affected by , P and Damage to restriction affects accuracy Unrecoverable pressure loss Viscosity limits measuring range Straight runs of pipe required upstream

of 13

Section 5 IE250-IH



Inaccuracies due mainly to process conditions; temperature and pressure variations

Upstream and downstream piping Standard concentric orifice plates should not be used for slurries and

dirty fluids

Venturi Tube

Fluid accelerated through a nozzle shaped inflow piece (converging cone) which induces a local pressure drop.

Fairly high cost of Venturi Tube.

Venturi Tube

of 13

Section 5 IE250-IH


Venturi Tube Advantages

Less significant pressure drop across restriction Less unrecoverable pressure loss Requires less straight pipe

Disadvantages

More expensive Bulky, requires large section for installation

Flow Nozzles

Similar to venturi but shape of ellipse. Higher flow capacity than orifice plates.

Flow Nozzle used Mainly in High Velocity Applications

Advantages

High Velocity Higher turbulence Suspended solids More cost effective than venturi Smaller than venturi

of 13

Section 5 IE250-IH


Disadvantages

More expensive Higher unrecoverable pressure loss

Dall Tube

More compact than venturi Higher differential pressure for less unrecoverable pressure loss Low loss meter

Dall Tube Low Loss Meter

Advantages

Shorter length Lower unrecoverable pressure loss

of 13

Section 5 IE250-IH


Disadvantages

More complex to manufacture Sensitive to turbulence Accuracy based on flow data


Should be calibrated with piping section in which it is to be used Calibrate over full range of flows

Pitot Tube

Measures flow based on differential pressure Primarily gas flows, but also liquid flows Small tube directed into the flowstream to get total pressure Second measurement of static pressure Difference gives dynamic pressure

of 13

Section 5 IE250-IH


Basic Form of Pitot Static Tube

Advantages

Low cost Low permanent pressure loss Ease of installation into existing systems

Disadvantages

Low accuracy Low rangeability Clean liquid, gas or vapour only

Multiport Pitot Averaging

Multi-impact opening type and improves accuracy of this type of measurement.

Used to compensate for changes in the velocity profile.

of 13

Section 5 IE250-IH


Multiport “Annubar” Pitot Averaging System

Elbow

Pipe Elbow can be used as primary device Viable differential pressure device Tappings at 22.5º provide more stable readings 45º tappings more suited to bidirectional flow measurement

Elbow Meter Geometry

of 13

Section 5 IE250-IH


Flow in a Pipe Bend

Advantages

Simplified installation Inexpensive

Disadvantages

Low accuracy

Primary Element Advantages

No moving parts Large range of sizes and opening ratios Suitable for most gases and liquids Well understood and proven. Price does not dramatically increase with size

of 13

Section 5 IE250-IH


Primary Element Disadvantages

Accuracy affected by density; pressure and viscosity Erosion and physical damage to restriction affects measurement Unrecoverable pressure loss Viscosity limits measuring range Require straight runs of pipe Square law characteristics

Secondary Element

Differential Pressure transmitter Most common inaccuracy is not allowing enough straight pipe

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 6

Rotary Inferential Flowmeters

of 2

Section 6 IE250-IH


Section 6



Low viscosity liquids at high velocities.

Flow stream displaces a float placed in the stream.

of 2

Section 6 IE250-IH


Viscosity Limits of Rotameters Depend on Float Shape


Actual flow has to be converted into standard flow Not affected by piping configurations For 25mm bore the cost comparable to magmeter

Advantages

Inexpensive Wide range of applications Very basic operation Easy installation and simple to replace Linear scale

Disadvantages

Limited accuracy Subject to density, viscosity and temperature changes Fluid must be clean Erosion of device Expensive for large diameters Operate in vertical position only Viscosity > 200 cP

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 7

Electromagnetic Flowmeters

of 6

Section 7 IE250-IH


Section 7

Oscillatory Flow Measurement

Vortex Meter

Relationship between K-factor and Reynolds number

of 6

Section 7 IE250-IH


Round Bluff Bodies

Delta Shaped Bluff Bodies

Two Part Bluff Body

of 6

Section 7 IE250-IH


Rectangular Bluff Body

Construction of Typical Vortex Precession (Swirl) Meter

of 6

Section 7 IE250-IH


Coanda Flowmeter

Generates internal oscillations similar to an electronic oscillator. Oscillations are generated by feeding part of the mainstream flow back

into itself.

Diagram of Mode of Operation of Feedback Oscillator

Secondary Element

A number of devices can be used to measure the vortex frequency • Thermistors • Pressure Sensors • Magnetic Pick-up • Strain Gauge • Piezoelectric • Capacitive

of 6

Section 7 IE250-IH



Fully developed flow is required for good measure-ment. Meter should be installed upstream of any disturbance. Straight lengths of pipe can be reduced by fitting a flow straightener.

Advantages

Suitable for liquid, gas or steam Can be used for non-conductive fluids No moving parts, low maintenance Sensors available for gas and liquid

Not affected by , , P or temperature Low installation cost Good accuracy Linear response

Disadvantages

Uni-directional measurement only Clean fluids only Not suitable with partial phase change Not suitable for viscous liquids Straight pipe runs required for installation

Application Limitation

Upstream and downstream requirements of straight pipe vary according to a number of factors

• Severity and nature of disturbance upstream • Severity and nature of disturbance downstream • Type of vortex bluff body (the specific design of the meter) • The accuracy required

of 6

Section 7 IE250-IH


Straight Pipe-run Arrangements

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 8

Positive Displacement Flowmeters

of 3

Section 8 IE250-IH


Section 8

Rotary Inferential Flowmeters

Turbine Flowmeter Vortex Meter

Basis of Operation

Turbine meters have rotor-mounted blades that rotate when a fluid pushes against them

The rotational speed of the turbine is proportional to the mean velocity of the fluid


Sized by volumetric flow rate The main factor affecting the meter is viscosity Turbine meters are specified with minimum and maximum linear flow

rates

of 3

Section 8 IE250-IH


K-Factor

The K-factor is the number of pulses per unit volume.

Typical Calibration Curve

of 3

Section 8 IE250-IH


Advantages

High accuracy/repeatability/ rangeability for a defined viscosity and measuring range

Fairly high temperature range Very high pressure capability: 600 bar Measurement of non-conductive liquids Capability of heating measuring device Suitable for very low flow rates

Disadvantages

Not suitable for high viscosity fluids Viscosity must be known 10D upstream and 5D downstream of straight pipe is required Not effective with swirling fluids Only used for clean liquids and gases Pipe system must not vibrate Specifications critical for measuring range, and viscosity

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 9

Ultrasonic Flowmeters

of 5

Section 9 IE250-IH


Section 9


Electromagnetic Flowmeters BASIS OF OPERATION

Electromagnetic flowmeters use Faraday’s law to sense liquid velocity Faraday’s law:

• moving a conductive material at right angles through a magnetic field induces a voltage proportional to the velocity of the conductive material.

Conductive material is the liquid

Electromagnetic Meter

of 5

Section 9 IE250-IH


of 5

Section 9 IE250-IH


Magnetic Flowmeters

Accurate, and have a linear relationship between flow and output voltage

High accuracy units to 0.2%


Two main requirements are maximum and minimum velocity

Downsizing the meter increases flow-rate (velocity) through the meter

of 5

Section 9 IE250-IH


Application Velocity range, m/s

Normal service 0.6 - 12

Abrasive slurries 3.0 – 5.0

Non-abrasive slurries 1.5 – 7.5

Selection and Sizing - Liners

Meter can be lined with insulating material to prevent damage to electrodes

Liner is chosen for resistance to: • Chemical corrosion • Erosion • Abrasion • Pressure • Temperature


Pipeline must be full • Sufficient back pressure must be maintained

5 diameters of straight pipe upstream 3 diameters of straight pipe downstream Earthing is another important aspect

Advantages

No restrictions to flow • No pressure loss

No moving parts Good resistance to corrosion Independent of viscosity, density, pressure and turbulence Good accuracy Bi-directional Large range of flow rates/diameters

of 5

Section 9 IE250-IH


Disadvantages

Expensive

Limited to conductive liquids

Minimum conductivity about 5 micro Siemens /cm

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 10

Mass Flowmeters and Selection

of 4

Section 10 IE250-IH


Section 10



Meters measured flow rate by repeatedly passing a known quantity of fluid from the high to low pressure side of the device in the pipe

The number of times the known quantity is passed gives information about the totalised flow

The rate at which it passes is the volumetric flow rate

Rotary Vane

Spring loaded vanes slide in and out of a channel in a rotor. They make constant contact with the eccentric cylinder wall. As rotor turns, a known volume of fluid is trapped between the vanes

and the outer wall. Flow rate is based on volume per revolution.

Rotating Vane Meter

of 4

Section 10 IE250-IH



This type of meter is used extensively in the petroleum industry for such

liquids as gasoline and crude oil metering

Custody transfer

Advantages

High accuracy of 0.2% Suitable for high temperature service, up to 180oC Pressures up to 7MPa

Disadvantages

Clean liquids Head loss Expensive High Wear

Lobed Impeller

his type of meter uses two lobed impellers The impellers are meshed to rotate in opposite directions within the

inclosure A known volume of fluid is transferred for each revolution

Rotating Lobe Meter

of 4

Section 10 IE250-IH


Advantages

High operating pressures, up to 8 MPa High temperatures, up to 200oC.

Disadvantages

Clean liquids Head loss Expensive High wear

Oval Gear Meters

Two oval gears are intermeshed, trapping fluid between themselves and the outer walls of the device

Fluid pressure causes gears to rotate Revolution count determines volume of fluid moving through the device

Positive Displacement Meter

Advantages

High accuracy of 0.25% High operating pressures, up to 10MPa High temperatures, up to 300oC Wide range of materials for construction

of 4

Section 10 IE250-IH


Disadvantages

Pulsations caused by alternate drive action


Positive displacement meters can be damaged by overspeeding Primarily suited for clean lubricating and non-abrasive applications Filters/air eliminators required Limitations on operating temperature Meter is driven by the flow

Advantages

Can measure non-conductive liquids Very high accuracy Unaffected by viscosity High turndown of up to 10:1 Can be used in a pump dosing mode

Disadvantages

Clean fluids only, limited life due to wear Some irrecoverable pressure loss Requires viscous fluid Limited operating range Mechanical failure likely to cause blockage in pipe Cost

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 11

Miscellaneous Devices

of 3

Section 11 IE250-IH


Section 11

Ultrasonic Flowmeters

Ultrasonic Flow Measurement

Two types of ultrasonic flow measurement: • Transit time measurement • Doppler effect

Transit Time

The transit time flowmeter device sends pulses of ultrasonic energy diagonally across the pipe.

Transit time is measured from when the transmitter sends the pulse to when the receiver detects the pulse.

Transit Time Measurement

of 3

Section 11 IE250-IH



Fitted section of pipe Clamp on Transducers installed in-situ


Clamp-on designs limited due to differing mediums in which ultrasonics pass through

Sound-conductive path is required between transducer and process fluid inside the pipe

Couplings are available but expensive

Doppler Effect

Relies on objects with varying density in flowstream to return ultrasonic energy

Using Doppler effect meter, a beam of ultrasonic energy is transmitted diagonally through the pipe

This energy is reflected back in varying amounts due to particles in the stream with different densities

of 3

Section 11 IE250-IH



The Doppler flowmeter relies on reflections from particles/bubbles in the flowstream

It requires solids or bubbles in flow

Advantages

Suitable for large diameter pipes No obstructions, no pressure loss No moving parts, long operating life Fast response Installed on existing installations Not affected by liquid properties

Disadvantages

Accuracy is dependent on flow profile Fluid must be acoustically transparent


Turbulence or swirling in the process fluid can affect the ultrasonic signals.

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 12


of 10

Section 12 IE250-IH


Section 12

Mass Flowmeters

Mass Flowmeters

Mass flow measurement gives a more accurate account of fluids

Mass flow measurement is not affected by density, pressure and temperature

The Coriolis Effect

Based on Newtons Second Law of Motion.

Force = Mass x Acceleration.

Manipulation of the formula allows us to determine the mass of fluid, for a known force and acceleration.

The Coriolis effect causes a retarding force on a rotating section of pipe

when flow is moving outward.

This conversely produces an advance on the section of pipe for flow moving toward the axis of rotation.

of 10

Section 12 IE250-IH


Application of Coriolis Force to a Flowmeter

Coriolis Flowmeter Construction

of 10

Section 12 IE250-IH


Straight Through Flowmeter

A development to the looped type Coriolis meter is the straight through

pipe version This has an advantage of lower pressure loss Rotational movement is provided by vibrating the pipes Coriolis force develops in the pipes Pipes are vibrated at their resonant frequencies Sensors are used to detect the movement of the pipe

Basic Principle of ‘Straight Through’ pipe

of 10

Section 12 IE250-IH


Advantages

Direct, in-line mass flow measurement Independent of temperature, pressure, density and temperature

information Sensor capable of transmitting mass flow, density and temperature

information High density capability Conductivity Independent Suitable for hydrocarbon measurements Suitable for density measurement

Disadvantages

Cost Affected by vibration Installation costs


High temperature Vibration Amount of gas in liquid Restricted to low flow rates Limited to pipe sizes up to 150 mm

Coriolis Mass Flowmeter

of 10

Section 12 IE250-IH


Net Oil Computing

The NOC determines water cut by comparing the measured emulsion density to standardized reference densities of free oil and water.

Density is inversely proportional to the square of the flow tube

frequency.

The NOC combines flow and density outputs from the transmitter to compute and display the emulsion volume in cubic meters or U.S. barrels.

of 10

Section 12 IE250-IH


The net oil application of the Coriolis meter employs a computer, which stores the manually entered oil and water base densities.

Because different wells may be flowing consecutively through the same

meter, there is a facility to storethe individual base densitiesof several different wells which may exhibit different base density values for their components.

Thermal Mass Flowmeters

The two main types of thermal mass flow measuring devices are: • Thermal Anemometer • Temperature rise flowmeter

of 10

Section 12 IE250-IH


Advantages

Fast response times, <0.5 ms

Disadvantages

Require 10D of straight pipe upstream

Have similar limitations to pitot tubes

Temperature Rise Flowmeter - Insertion Type

Work on the principle of heating the flowstream.

Heating flowstream at one point, allows measurement of temperature both upstream and downstream of heating point.

Principle of Temperature Rise Method

of 10

Section 12 IE250-IH


Disadvantages

Suitable for low gas flows only Subject to erosion and corrosion More tapping points, increased chances of leakage

Temperature Rise Flowmeter - External Type

Newly developed methods for insertion type sensing has seen heating and sensing elements moved to the outside of the pipe

This overcomes problems with tapping points

Thermal Flowmeter with External Elements and Heater

of 10

Section 12 IE250-IH


Bypass Type Thermal Mass Flowmeter

Advantages

Non-contact, non intrusive sensing No obstruction to flow Reduced Maintenance

Disadvantages

Suitable for low gas flows only Subject to erosion and corrosion

Flow Meter Remains Full

of 10

Section 12 IE250-IH


Parallel Arrangement

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 13


of 3

Section 13 IE250-IH


Section 13

Miscellaneous Devices Cross Correlation Techniques

Figure shows the operating principle. At least two transducers are positioned at points a known distance apart which are then used to determine the time taken for the passage of some naturally occurring event in the flow such as turbulent eddies or particulates.

The correlation meter can be applied in two phase flow conditions. If the phases are tagged with, for example, different radioactive tracers, then phase velocities, phase slip and bulk mean velocity can be determined. Successful results have been reported at oil wellhead installations, where water, oil and gas flow as a complex mixture.

of 3

Section 13 IE250-IH


Tracer Techniques

These techniques rely on adding a marker or tracer at one point in the flow and detecting the presence of the tracer at a second point, a known distance downstream. For liquids, tracers include salt solutions, dyes or radioactive substances. For gases, the radio-active tracer is the most commonly used.

The main advantages: They are (virtually) non-invasive. Associated equipment is rugged and portable. Readings can be taken where plant access is difficult. The in-situ calibration of meters is thus easy to accomplish.

Liquid and Gas Flow Metering

The main disadvantages: The methods are not appropriate for continuous flowrate measurements. In most cases the methods do not give an instant result. Subsequent

laboratory data analysis is required. The criterion of good mixing must be met. The tracer method injects a suitable tracer for a short period of time at

the upstream section and records the dilution effect at a section a known distance downstream.

An approximation of the mean flow velocity can be obtained by measuring the time for the tracer to travel the distance between the two sections and for its concentration to reach a maximum. By measuring the time interval of the profile centroids, the flowrate can be obtained from: Q = flow area x {distance between sample points } / {time between profile centroids }

Tracer methods are applicable to a very broad range of metering problems in both industrial and research environments and instances where they can be used include:

On-line calibration of installed flowmeters.

Measurement of open channel flows.

Investigations of systems and plants not provided with installed flowmeters.

Diagnosis of plant malfunction.

of 3

Section 13 IE250-IH


Weighing Techniques

Only applicable to batch type processes and not for continuous processes. In industrial plant the weighing system can replace the flowmeter

completely and can achieve a cost effective alternative to mass meters. For the non-continuous metering of mixtures, solids and other difficult

fluids, commercially available load cell systems are standard practice.

Velocity Area Integration Methods

Involves the measurement of flow velocity at a number of points on one cross section of a pipe.

Mean velocity and hence the flowrate can be calculated using integration.

Velocity measurements can be made by either an array of individual devices or by one device, such as a Pitot tube, annubar or a laser anemometer with a traversing mechanism.

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 14

Flowmeter Costs and Flowmeter Selection

of 11

Section 14 IE250-IH


Section 14

Flowmeter Calibration A. Calibrators for Liquid Flowmeters

One characteristic of a liquid is that it can usually be contained in an open vessel, although if the liquid is volatile or hazardous suitable precautions have to be taken.

Calibration standards are usually of the 'bucket and stopwatch' type with the bucket either being weighed or the volume known.


‘Standing start and stop’ method Flow through the meter is accelerated as quickly as possible from rest to the full test flowrate. At the end of the test the flow is rapidly stopped.

‘Flying start and finish’ method Requires some sort of diverter in conjunction with a sump or reservoir into which the liquid flows and then is diverted into the measuring vessel for the appropriate time.

of 11

Section 14 IE250-IH



A flowmeter can be calibrated gravimetrically by statically weighing the quantity of liquid collected in a weighing vessel.

The vessel is weighed empty and then full and the difference in readings, corrected for the effect of air buoyancy provides the mass of liquid collected. If a volume flowmeter is to be calibrated this mass is divided by the density of the liquid at the flowmeter.

of 11

Section 14 IE250-IH


Liquid and Gas Flow Metering Pipe Provers

To calibrate meters on line, a pipe prover can be used in Figure 6. A length of pipe is fitted with switches so that the volume between the switches is known. If a displacer ( or pig ) is introduced to the flow, the time it takes to travel between the switches will give a measure of the flowrate.

These devices are used extensively to measure all types of high value fluid from LPG to high viscosity crude oil and are produced in all sizes from 3-36 inches diameters.

Unidirectional sphere prover Displacer only travels in one direction along the pipe. Displacer is an elastomer (neoprene, polyurethane, etc) sphere which

is usually hollow. Centre is filled with liquid and inflated until it is larger than the pipe bore to make a good seal to the pipe wall.

The pipe is normally steel with internal surface usually coated to provide a smooth low friction lining and to protect against corrosion.

At each end of the calibrated length of pipe a detector switch is located through the pipe-wall which triggers the switch when the sphere passes under it.

At the end of this prover is the sphere handling valve. This arrangement is designed to hold the sphere. When required the sphere can be launched into the flow and carried round the loop. At the end of the loop the sphere is captured and returned to the launch position ready for another run.

of 11

Section 14 IE250-IH


Liquid and Gas Flow Metering Bi-directional sphere prover

To reduce the pipe length, the bi-directional prover was developed. Similar in layout to the previous type, the flow can circulate around the

loop in both directions. A four-way valve changes the flow path without breaking the flow.

Piston provers For difficult fluids which may destroy lining, or leak past the

conventional sphere, piston provers have been produced. In this case the calibrated pipe is a smooth pipe of stainless steel or

plated carbon steel. The displacer is a piston with multiple seals. Switches can be conventional plungers or non-contacting type. These provers are bi-directional and controlled using a four-way valve.

Small volume (or compact provers)

These normally have a volume about one-tenth of a conventional design. They are normally piston provers with the detectors mounted external to

the pipe to ensure a high resolution for a small distance travelled.

of 11

Section 14 IE250-IH


B. Calibrators for Gas Flowmeters

Calibration method is determined by the meter type, the ranges of flow and flow conditions, pressure and the accuracy of calibration required.

A primary standard method is one in which reference flowrate is determined by measurements of mass, length, temperature and time.

A secondary standard method is one in which reference flowrate is determined using a flowmeter which has been calibrated by a primary method.

Liquid and Gas Flow Metering Displacement Methods

A number of devices are used for gas calibration based on the principles of the pipe prover. The biggest drawback of any prover system is the friction at the displacer/pipe seal. Mercury seal provers use a very light displacer, with a mercury ring acting as the seal sliding in a glass pipe.

Some high pressure, more conventional, provers exist where the density/pressure of the gas keep seal friction below critical levels.

Soap film burettes are a common calibration device. This method is used to measure small gas flows within the range 10-7 to 10-4 m3/s at conditions close to ambient. What is created is a pipe prover with the displacer formed by a soap film or bubble.

To calibrate a flowmeter the system is set up as shown in Figure 10. Gas flow from the meter on test passes through a vertically mounted burette. As the gas enters the burette a soap film is formed across the tube and travels up the tube at the same velocity as the gas. By measuring the time of traverse of the soap film between graduations at either end of this burette the rate of flow of the gas may be obtained.

of 11

Section 14 IE250-IH


Liquid and Gas Flow Metering Critical Flow Venturi-nozzle

If the pressure drop between the inlet and the throat of a nozzle or restriction is increased until sonic velocity is reached at the throat, then for a given value of the upstream pressure and temperature, the mass flowrate through the nozzle will be constant. The expression for the mass flowrate m of the gas is:

m = Cd C* At P0 / ( RT0 )1/2

of 11

Section 14 IE250-IH



The mass flowrate under sonic conditions is independent of downstream pressure and temperature and dependent only on the geometry of the nozzle, the properties of the gas, and the upstream pressure and temperature.

This feature makes the device particularly suitable for calibrating meters. Internationally agreed standard flowmeter.

A standard sonic Venturi is shown in Figure 12.

of 11

Section 14 IE250-IH


On-site Flowmeter Calibration Tracer methods

For the transit time method a pulse of tracer fluid is injected into the main flow stream, and the time taken for the tracer to pass between two detection points is noted. If the volume of pipe between the detectors is known the volumetric flow of the flow can be determined.

For the dilution method a tracer fluid which is detectable in low concentrations, is injected into the flow (Figure 15) at a known flow rate q m3/s. The mainstream flow is then sampled at a distance downstream of the injection point far enough to have allowed homogeneous mixing to have taken place, and the concentration, C, of the tracer is measured. The flowrate can be derived from:

Q = q / C Flowrate can be determined to within 0.5 per cent.

of 11

Section 14 IE250-IH


Velocity Traversing Methods

Flowrate is estimated by measuring a number of point velocities at discrete positions in a cross-section of the flow, and then integrating these over the flow cross-section (Figure 16). The most commonly used instruments are anemometers, insertion meters and Pitot tubes.

Main disadvantages of these methods are that they are time consuming, and difficulties are encountered with unsteady flows. For gas velocities in the range 0.3 to 3.0 m/s uncertainties of 4 per cent are attainable using vane anemometers and for velocities in the range 6-120 m/s 2 % can be achieved using Pitot tubes.

of 11

Section 14 IE250-IH


Clamp on Ultrasonic Meters

Clamp on ultrasonic meters can also be used for in-situ calibrations but many factors have to be considered such as flow profile, pipe material and internal condition and fluid properties.

Accuracies of no better than 2 - 10% can be assumed.

The Importance of Calibration Fluid

It is important, especially for liquids, to calibrate in the same fluid as that which the meter will normally see.

For liquid meters, especially those required to meter hydrocarbons, the choice of calibration fluid is particularly important.

Figure 17 shows results for large turbine meter for water and three petroleum products of different viscosities. It is important therefore to calibrate these meters using the actual working liquid and for this reason, turbine meters for crude oil are often calibrated on site using a dedicated pipe prover and the actual operating liquid.

of 11

Section 14 IE250-IH


Calibration Conditions

The pressure and temperature at which a flowmeter is to operate are important factors, particularly for gas meters.

Pressure and temperature not only affect the dimensions such as the throat diameter of a nozzle or the clearances in a positive displacement meter, but in the case of gas flow can have a significant effect on the gas density and viscosity as well.

To ensure that the velocity profile is fully developed and symmetrical it is essential that the calibration system gives adequate straight pipe upstream of the test meter.

Calibration Accuracy

Liquid flowmeter calibration facilities should be able to measure flowrates to uncertainty levels between 0.5 and 0.05 per cent depending upon the size, cost and complexity of the system.

Calibration systems for gas flowmeters should be able to measure flowrate to uncertainty levels of 0.5 per cent.

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 15

Introduction to Multiphase Flow Measurement

of 11

Section 15 IE250-IH


Section 15


Liquid and Gas Flow Metering Most flowmeters are designed to operate in ideal conditions. In practice the meter is likely to generate a measurement error. Common sources of this "installation error" include:

Upstream and downstream disturbances such as bends or valves Flow pulsations Acoustic noise sources and vibration Particles or bubbles in the flow

Flow Disturbances & Other Sources of Error

A disturbed region is generated downstream of pipework fixtures such as bends or valves.

Most flowmeters are intended for use in undisturbed (fully developed) flow, with a large length of straight pipe upstream of the meter. However, in reality, it is rarely possible to achieve this and most flowmeters are exposed to disturbed flow.

Classification of Flow Disturbances Pipework fixtures disturb the flow by:

Changing the distribution of flow in the pipe (distortion of the axial velocity profile)

Causing the flow in the pipe to swirl Changing the turbulence of the flow in the pipe

of 11

Section 15 IE250-IH


Distortion of the Axial Velocity Profile

The flow in a pipe is fastest in the centre and slowest at the walls. This produces a fully developed velocity profile, as shown in Figure 1.

If, for example, the fluid passes through a valve, the flow will be skewed to one side of the pipe generating higher velocities near the wall. Other disturbances may act to increase the velocity at the pipe centre and decrease it near the walls creating a peaked velocity profile.

Liquid and Gas Flow Metering Swirl

In fully developed flow all of the fluid travels parallel to the pipe walls. Some pipework fixtures can impart rotational movement on the flow, generally referred to as swirl.

Some disturbances generate single vortex swirl, others double,

triple or even quadruple swirl (see Figure 2).

of 11

Section 15 IE250-IH


Generation of Turbulence

In nearly all cases of interest to Engineers the flow in pipes includes random turbulent fluctuations. In fully developed flow these turbulent fluctuations are usually less than about 3% of the local mean fluid velocity. Passing fluid through pipework fixtures effectively stirs up the flow, usually causing increased turbulence.

Downstream Flow Conditions

Standards and manufacturers recommendations usually specify only a short length of straight pipe downstream of the meter, as being necessary.

This is not universally correct, some types of meter can be grossly affected by swirl or velocity profile distortion introduced as much as 3D downstream of the meter.

Generation and Decay of Flow Disturbances General Rules of Thumb

In general disturbing elements that are in the same plane generate peaked, flattened or skewed velocity profiles. Examples include single bends, S-bends, U-bends, expansions and contractions (see Figure 3).

The most typical situation in which swirl occurs is two 90° bends in planes at right angles to each other. Several severe swirl producing pipe configurations are shown in Figure 4.

of 11

Section 15 IE250-IH


of 11

Section 15 IE250-IH


The following rules of thumb can be applied:

Distortion of axial velocity profiles generally decays to near zero in about 20 to 30 pipe diameters (20 - 30D)

Single vortex swirl can persist for more than 100D. Double and multiple

vortex swirl decays within 20D

Turbulence generally decays to fully developed levels in less than 20D

Pipe Contractions and Expansions

Contractions produce an initially flattened velocity profile. Further downstream this will become peaked, before finally becoming fully developed.

Expansions produce the opposite effect - peaked, flattened then fully developed.

Pipework Mismatches, Weld Root Intrusions and Gaskets

Mismatches of pipework can often occur at flanges creating a step change in pipe diameter and will produce flattened or peaked profiles.

Misaligned flanges will skew the velocity profile. Weld intrusions into the pipe bore can significantly alter the flow.

Single Bends and Elbows

Flow passing through a single bend is forced to the outside of the bend producing an asymmetrical velocity profile at the bend outlet. The flow also moves round the walls of the pipe from the outside towards the inside generating symmetrical double vortex swirl.

Double Bends

S-bends produce a flattened profile and quadruple vortex swirl, both of which tend to decay quite quickly.

Out-of-plane double bends generate a flattened velocity profile and single vortex swirl. The closer the two bends, the greater this swirl will be. The swirl generated by double out-of-plane bends can persist for more than 100D.

of 11

Section 15 IE250-IH


Valves

Gate valves, sluice valves and ball valves skew the velocity profile when partially closed. Butterfly valves always disturb the flow, even when fully open.

Many non-return valves have a flap that hangs free in the flow. The disturbance generated by this arrangement depends on the angle of the flap and hence the flow rate.

Fiscal flowmetering installations in the oil industry generally use ball valves with machined bores that present no disturbance to the flow when fully open.

Other Installation Disturbances

Measurement errors generated by flow disturbances can be in excess of 50% for some meters. Flowmeters installed in disturbed flow therefore tend to provide realistic looking readings. This can make it difficult to spot that the meter is in error. Other potential sources of installation error include:

• Low or High Temperatures and Pressures • Noise and Flow Pulsations • Pipe Roughness, Corrosion and Deposition • Particulates, Bubbles, Droplets • Cavitation Flashing and Multiphase Flows

Installation Effects on Specific Meters Orifice Plates, Nozzles and Venturis

Guidance on installation is given in IS05167. Installation effects for differential pressure flowmeters are often given in terms of the percentage shift in the discharge coefficient, C.

A 1% shift in C will result in a flow measurement error of almost exactly 1 %.

Flow disturbances can result in errors of 10% or more. In general, orifice plates are most affected, then nozzles, and Venturis are least affected.

Most flow disturbances produce a positive error (over-reading) except for single vortex swirl

Low ratio meters are generally least affected by flow disturbances except for single vortex swirl.

Single vortex swirl causes a positive error in Venturis. For orifice plates and nozzles single vortex swirl causes a negative error

in low ratio meters and a positive error in high ratio meters.

of 11

Section 15 IE250-IH


As single vortex swirl can persist for more than 100D this is often considered to be the worst kind of flow disturbance.

Roughness effects, especially within the meter itself, can be significant. Erosion, corrosion and the build up of grease or sealant on the upstream face of an orifice plate may be an issue.

Erosion of the sharp edge of the orifice of an orifice plate can cause large errors.

Orifice plates and nozzles with corner tappings are most affected, then flange tappings, then D-D/2 tappings.

A large pressure difference across an orifice plate can cause it to bow or buckle, generating an error. Also large pressure differences may produce cavitation.

Orifice plates can be unintentionally installed backwards. This can result in measurement errors of between -10% to -20% depending on the plate.geometry.

Liquid droplets and solid particles in the flow will produce positive errors, increasing with droplet/particle concentration and density to +50% or more.


Electromagnetic flowmeters are usually provided with manufacturer's recommendations for installation.

Different designs of flowmeter have different characteristics and further

guidance is given in ISO 6817 In general electromagnetic flowmeters are relatively unaffected by

flow disturbances and a straight length of about 10D upstream is usually sufficient to keep the error caused by a bend or elbow to less than 1%.

Electromagnetic flowmeters are most sensitive to changes in velocity profile near their electrodes. This makes the orientation of the meter important. A meter installed close to a bend with its electrode in the plane of the bend will respond in a different manner to a meter with its electrodes perpendicular to the plane of the bend.

Swirl has little effect on electromagnetic meters. Meters with large electrodes, multiple electrodes and strong magnetic

fields are generally less affected by flow disturbances. Fouling of the electrodes can cause problems in some fluids. Electromagnetic flowmeters are often installed with their electrodes in

the horizontal plane to avoid contact with bubbles at the top of the pipe or particulates in the bottom.

of 11

Section 15 IE250-IH


Ultrasonic Meters

The response of ultrasonic flowmeters is dependent on the design and configuration of the meter. Figure 8 shows the response of three different flowmeters downstream of a single bend.

Manufacturers are likely to provide information on installation requirements.

The sensitivity of ultrasonic flowmeters to flow disturbances varies with the design of the meter. Single path meters can be in error by more than 10% if installed close to a bend.

In general, the more ultrasonic paths, the less sensitive the meter will be to flow disturbances.

Orientation of meter is important. The response of a meter to an asymmetrical flow disturbance will vary depending on whether its paths are horizontal, vertical or somewhere in-between.

As a rough guide, single path meters may need 30-40D of straight pipe downstream of a fixture, twin path meters 15-20D and only multipath meters may be satisfactory with much less.

When used in gas, ultrasonic flowmeters can be affected by acoustic noise, often generated by flow conditioners, valves or other fixtures.

The accuracy of clamp-on meters can suffer if the pipe onto which they are clamped is rough or ovoid. It is essential that the ultrasonic transducers are properly aligned and to ensure that the contact grease maintains a good interface with the transducers.

The transducer ports should be installed horizontally to prevent a build up of particulates or bubbles. Cavitation may also be an issue in these ports for low pressure, high flow rate applications.

Particulates, droplets and bubbles can affect ultrasonic flowmeters either by dissipating the ultrasonic pulses or distorting the velocity profile in the metering spool.

Turbine meters

The response of axial turbine meters to flow disturbances is very dependent on the design of the meter.

In general turbine meters are relatively insensitive to skewed velocity profiles and multiple vortex swirl. Peaked and flattened profiles may have a limited effect, but single vortex swirl is likely to cause errors of the order of 10%

Intuitively, if the direction of the swirl matches the rotation of the rotor of the meter one would expect an over-reading.

Swirl generated downstream of turbine meters can also induce errors. Audible noise and flow pulsations affect some meters, usually causing an

over- reading.

of 11

Section 15 IE250-IH


Vortex meters

Vortex meters are affected by all flow disturbances and can give positive or negative errors of up to 3%, if sufficient length of straight pipe is not provided upstream of the meter.

For most pipe fittings an upstream straight pipe length of between 10D and 30D is required.

Where swirling flow is likely to be produced, up to 70D may be necessary.

Vibration and pulsations in the flow may affect vortex shedding and the counting mechanism. An effect has been observed in which vortex meters "lock on" to the pulsation frequency.

Variable area meters

Variable area meters are known to be less sensitive to swirl or asymmetry than the majority of flowmeters

Upstream pipe configuration is relatively unimportant, but control valves should be placed downstream of the meter


Displacement meters are very tolerant of both upstream and downstream flow conditions and are unaffected by swirl or asymmetry.

Coriolis Flowmeters

Do not require a well developed flow profile. It is vital to avoid the vibration of adjacent pipework.

Thermal Mass Flowmeters

Errors in excess of 10% are likely for a probe type meter close to a bend. These meters are not particularly sensitive to vibration, but the probe

type meters should be adequately fixed to the pipe wall to prevent resonance.

Remedial Action Calibration of the Metering System

If the installation error can be measured or calculated, it can be accounted for and hence eliminated. Instead of calibrating the

of 11

Section 15 IE250-IH


flowmeter on its own, it might be better to calibrate the meter complete with the upstream and downstream pipework.

In-situ Calibration Techniques

The measurements of an installed flowmeter may be compared against those of another meter in the same flow. This has the advantage that two different types of meter can be selected which have different sensitivities to flow disturbances. The disadvantages of this approach are additional cost and meters may interfere with each other.

Flow Conditioners and Flow Straighteners

These are often positioned between a flow disturbance and a flowmeter in order to reduce the length of straight pipe required to ensure that the flow entering the flowmeter is acceptable.

Disadvantage with these is that they increase the pressure loss through

the metering system and can be fouled or blocked.

Types of Straightener

Most popular is the tube bundle. Figure 10. Length to diameter ratio of the tubes is usually > 10. Increasing the

length increases the pressure drop across the straightener. Other designs include the Etoile and AMCA, both of which are most

commonly used in gas.

of 11

Section 15 IE250-IH


Types of Conditioner

These generally comprise a perforated plate, sometimes with a flow straightening element downstream. Flow conditioners generally improve the axial velocity profile as well as removing swirl.

An NEL Spearman flow conditioner in Figure 11. Other designs include the Sprenkle, Zanker, Mitsubishi, Gallagher and K-Lab Laws conditioners.

Zanker and NEL designs are the easiest type to install and can be slid between two flanges without disturbing any other fittings.

Flow conditioners are not recommended for use with wet gas ( but Emerson 4-hole orifice works well).

Conclusions

Installation errors can be caused by flow disturbances or other aspects Flow disturbances are generated by bends, valves etc. Different flowmeter designs respond in different ways to installation

effects Remedial actions include:

Selection of an alternative meter Redesign of pipework surrounding the meter Recalibration of the metering system to account for the error Use of a flow straightener or conditioner

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 16

Basic Concepts of Multiphase Flow and Multiphase Flowmeter

of 2

Section 16 IE250-IH


Section 16

Flowmeter Costs and Flowmeter Selection


Best flowmeter might be the most reliable meter at the lowest cost when giving the user the required performance, but fluid properties and ambient effects need close consideration.

Cost includes the initial purchase of the flowmeter, installation, running, calibration and maintenance costs.

A recent survey showed about 50% of failures were due to poor application, 43% had installation defects and only 7% were due to equipment or design defects.

Initial Considerations

Sometimes, the plant operator may only wish to know whether the fluid in the pipework network is moving slowly, quickly or not at all. Under these circumstances, a flow indicator is needed, at a fraction of the cost of most flowmeters. If alarm limits for high or low flow are required, then indicators can be fitted with a simple microswitch to sound the required alarm.

If an indication of flowrate to within 10% is needed, it may still be unnecessary to purchase a flowmeter. As an example, many installations have changes of section or bends somewhere in the system. By inserting pressure tappings at selected points, a simple differential pressure transmitter would then employ the pipework as a crude Venturi or elbow meter.

If better accuracy is required or the signal is used to control the process, then flowmeter selection needs to be carried out.

of 2

Section 16 IE250-IH


Initial Considerations

The user must know: Physical and chemical fluid properties Range of flowrates expected or required Fluid temperature and pressure ranges to be covered Ambient temperature range expected Duration of operation (continuous or intermittent) Location of meter or metering station Accessibility for maintenance Required accuracy Resources available

Flowmeter Selection Procedure

There are many factors to be considered: Installation considerations Performance considerations Fluid property considerations Environmental considerations Economic considerations

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 17

Current Main Suppliers of Multiphase Flowmeters

of 3

Section 17 IE250-IH


Section 17


Calibration

Calibration is a set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring system and the corresponding values realised by standards.

The establishment of the relationship can be the production of an error figure or the definition of corrections. Another word is 'Proving'. Proving is normally meant to be a calibration where the 'relationship' is a proof of conformance to a specification.

Traceability

The property of the result of a measurement whereby it can be related to national or international standards, through an unbroken chain of comparisons all having stated uncertainties.

This ensures that that each standard or measure used for calibration purposes has itself been compared against a standard of higher quality up to the level at which the higher quality instrument is the accepted National Standard.

Mass

The ultimate primary standard of mass is the international prototype of the kilogram, a solid cylinder of platinum- iridium preserved at the International Bureau of Weights and Measures at Sevres, Paris.

All standards of mass in use in the UK are derived from the secondary platinum-iridium copy (No 18) of the prototype kilogram, and kept at NPL.

of 3

Section 17 IE250-IH


Length

The UK standard is held by NPL and is based on the 633 nm red light helium-neon lasers stabilised by saturated absorption by iodine. When the operating conditions are specified in detail a reproducibility of wavelength of 1 part in 1011 can be achieved.

All advanced countries have established their own standards of length and inter-comparison ensures international agreement.

Time

The UK National Standard for the second, the interval of time, and for frequency is the long beam Caesium resonator developed at NPL.

Inter-comparison with other similar high quality standards ensures international agreement and definition of the measure of time.

Temperature

Temperature is defined by fixed physical state changes of specific elements or compounds.

Temperatures between the fixed points are defined by the resistance of platinum wire and its known change with temperature between the fixed points.

Flow Standards

A flow measurement standard is derived from and dependent on a combination of other more basic standards of mass, length, time, pressure and temperature. It may be either gravimetric or volumetric.

It is not usually a device which can be easily transferred from one location to another nor, because of its size and complexity, is it something which can be kept in a glass case.

of 3

Section 17 IE250-IH


National Measurement System (NMS)

Within every modern state there exists a National Measurement System. Without such a system internal and external trade and manufacture could not function.

It is the function of the National Measurement system to establish the measurement standards to which reference and working standards within the country are traceable and ensure these standards can be recognized internationally.

Accreditation

Accreditation is the process in which a third party inspects and approves a calibration or test laboratory to ensure it meets its stated capability for the measurements it offers.

Certification

This is the process by which a company, product or instrument is certified as complying with, or calibrated to, a specified standard by a third party.

This implies that the process or product has been inspected and deemed to meet the requirements of the relevant standard or specification.

Items carrying the TUV mark will have had the process of production certified.

Items CE marked indicates that the supplier confirms the item complies with the relevant directive(s).

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 18

Level Measurement

of 13

Section 18 IE250-IH


Section 18

Introduction to Multiphase Flow Measurement

Description of Multiphase Flows

Multiphase flow, in the hydrocarbon production industry, is concerned with the simultaneous flow of mixtures of oil, water and gas.

When attempting to meter such flows it is important to understand their nature, since this impacts on the most appropriate methods for metering and on the accuracy of metering.


Multiphase flow of oil, water and gas potentially covers the full ranges of flowrates of all three phases. This will therefore include the range of gas volume fractions from 0% to 100% and water cuts from 0% to 100%.

Within these ranges, the characteristics of the flows can change dramatically, as a result of the relative velocities of the gas and liquid (and of the oil and water), the viscosity and the density differences.

Definitions Associated with Multiphase Flow

Continuous phase This is usually the predominant phase e.g in an oil flow in which separated water drops or gas bubbles are suspended. In exceptional cases, such as foams, however, the oil may account for only a few per cent of the flow, but still be the continuous phase in which the gas bubbles are suspended.

of 13

Section 18 IE250-IH



Velocity ratio The ratio of the mean gas velocity to the mean liquid velocity:

K = Ug / Ul = ( Mg / gAg ) / ( Ml / lAl) where Ag + Al = A the total cross-sectional area of the flow.

Quality Quality is the mass dryness fraction:

x = Mg / M

Void fraction

The void fraction is the fraction of the pipe area at a given cross-section which is occupied by the gas phase. This can vary considerably, e.g. in plug or slug flow but usually the variations are at such high frequencies that a time-averaged value can be used.

= Ag / A = ( x / g ) / { x / g + K ( 1 – x ) / l }

Density of the mixture If a density is required for use in flow equations for flowmeters in

multiphase flow then effective density e should be used where:

1 / e = { x / g + K( 1 – x ) / l } { x + ( 1 – x ) / K } = x2 / g +

( 1 – x )2 / ( 1 - )l

Note that for homogeneous flow, the velocity ratio K = 1, so that:

hom = m = 1 / { x / g + (1 – x ) / l }

Gas velocity The velocity of the gas phase in the pipe, Ug, can be determined from other variables as:

Ug = M { x / g + K(1 – x ) / l } / A

Homogeneous flow In reality it is difficult to define what constitutes homogeneous flow. In practice, however, the term is taken to mean a flow in which the two phases are uniformly and so well mixed that there is no relative slip between them, so that Ul = Ug = Uhom

of 13

Section 18 IE250-IH



Homogeneous velocity As defined above under homogeneous flow, the homogeneous velocity is:

Uhom = M { x / g + (1 – x ) / l } /A Slip

Slip is the difference between the mean velocities of the gas and the liquid phases:

UR = Ug - Ul

Superficial phase velocities

The superficial velocity is the velocity each phase would have if it flowed alone in the same pipe:

Ugs = Mg / g A = x M / g A

Uls = Ml / l A = ( 1 – x ) M / l A

Flow Patterns In Horizontal Two-Phase Flow

Two-phase flow patterns in a horizontal pipeline can be broadly categorised into four distinct flow regimes:

stratified, slug, annular and bubble flow

Between each of these flow regimes there are boundaries which may be

quite sharp (e.g. between stratified and slug flow) but are generally fairly indistinct transition regions.

of 13

Section 18 IE250-IH


Liquid and Gas Flow Metering Stratified flow

Here the gas and liquid flow in distinct separate layers. The liquid occupies the lower part of the pipeline and the gas occupies the upper part.

Within this configuration there may be waves on the liquid surface and occasional splashing of liquid onto the upper walls, or entrainment of liquid into the gas phase.

The liquid-gas interface may be smooth, rough or wavy. Stratified flow with a wavy gas-liquid interface is sometimes described

as wavy flow.

of 13

Section 18 IE250-IH


Liquid and Gas Flow Metering Slug flow

Slug flow is characterised by an intermittent behaviour. Observing a fixed point in the pipeline will show an alternation of high

and low liquid holdup. This corresponds to 'slugs' and a film region between the slugs.

The slug itself may contain a considerable fraction of entrained gas, which may vary along the length of a slug.

At higher liquid flowrates the flow may appear to be predominantly liquid phase with large asymmetric gas bubbles; this pattern is sometimes described as 'plug' flow.

Bubble flow

Bubble flow occurs at still higher liquid velocities where the entire pipe is continuously filled with liquid which contains entrained bubbles of gas.

Due to the effect of gravity, the bubbles will tend to collect in the upper part of the pipe.

There may be some variation in the fraction of gas bubbles with time, close to the transition points to slug or to annular flow.

Annular flow

Annular flow occurs when the liquid flows as a film on the pipe walls and the gas forms a core inside this liquid.

Again, under the effect of gravity, there will tend to be more liquid at the bottom of the pipe than the top.

A large fraction of the liquid phase may be entrained into the gas core and there may be waves or pulses of liquid particularly on the liquid layer at the bottom of the pipe.

Stratified / annular flow occurs when the gas velocity is sufficiently great to entrain liquid from a stratified flow, but insufficient to sustain a continuous liquid film.

Slug / annular flow occurs when the flow is intermittent as in the definition of slug flow, but with such a degree of gas flow in the slug body that there is a possibility of a continuous gas core.

of 13

Section 18 IE250-IH



Annular / slug flow is where the flow appears to be annular, but with a sufficient intermittent flow of liquid that there is not the possibility of a continuous gas core. This occurs with both greater liquid velocity and greater gas velocity than for slug/annular flow.

Bubble / slug flow occurs at higher gas velocities than bubble flow

where the greater volume of gas gives rise to agglomeration of bubbles with some degree of intermittency, but not to the extent of forming slug and film regions as seen in slug flow.

Flow Patterns in Vertical Two-Phase Flow

Two-phase flow patterns in a vertical pipe can be classified into: bubble, slug, churn and annular.

Between each of these flow regimes there are boundaries which are generally indistinct.

An additional flow pattern, wispy annular flow, can be observed at conditions of high mass flux, although this is unlikely to occur in multiphase hydrocarbon production systems.

of 13

Section 18 IE250-IH



Bubble Flow The liquid phase is continuous, and a dispersion of bubbles within the

liquid phase. Slug (or plug) flow At higher gas flowrates than for bubble flow, coalescence of the bubbles

occurs, and leads to the creation of characteristically bullet-shaped (Taylor) bubbles, which are separated by regions containing dispersions of smaller bubbles.

The liquid phase flows down the outside of the large bubbles in the form of a falling film, but the net flow of both liquid and gas is upwards.

Churn flow Increasing the flow velocity beyond that for slug flow leads to an

unsteady flow regime in which there is an oscillatory motion of the liquid upwards and downwards in the tube (hence the name churn flow).

Annular flow The liquid flows on the wall of the tube as a film, and the gas flows in

the centre. Usually some of the liquid phase is entrained as small droplets in the gas core.

Three-Phase Flow Pattern Effects in Vertical Flow

Unlike horizontal three-phase flows, there is no observed effect of the presence of oil and water phases on the flow patterns. This is because the mixing between oil and water maintains similar velocities of both phases, and gravity does not act to separate the oil and water.

The transitions between flow patterns are also unaffected by the water cut. In vertical flows, the transitions are dependent on momentum flux (product of density and superficial velocity squared). Hence the effects of liquid density changes between different water cuts is eliminated.

Multiphase Measurement Challenges

Pressure Drop Pressure drop is one of the most difficult 'simple' parameters of multiphase flow to make a meaningful average measurement. Empirical correlations have been produced to relate pressure gradient to other parameters of the flow, such as liquid and gas superficial velocities and the physical properties of the fluids.

of 13

Section 18 IE250-IH



In multiphase metering, pressure drop measurement is most usually required for a Venturi. Two issues relate to these measurements:

Bleeding of the impulse lines between the Venturi and the pressure transmitter

Range required for the pressure transmitter However, this is not always possible in a multiphase flow where

fluctuations in the gas and liquid content of the flow will lead to ingress of gas into the impulse lines. This will be less of an issue the higher the operating pressure, since then the liquid and gas densities are closer than they would be at low operating pressure.

To minimise the impact of errors related to impulse lines it is desirable that the measured pressure difference is large compared to the static head between the Venturi tappings.

In slug flow it is possible that the maximum differential pressure through a Venturi (during a high liquid fraction portion of the flow) is up to 5 times the average pressure drop.

Therefore the Venturi differential pressure transmitter needs to have an operating range at least up to 5 times the expected maximum average pressure for the range of use of the meter. This may limit the rangeability of the meter in terms of maximum and minimum flowrates more strictly than may be the case in a single phase flow.

Mixing and Density Measurement

Measurement of average density in multiphase flow is usually achieved using a gamma densitometer which usually measure the attenuation of a gamma ray along a single cross-sectional chord.

Clearly it is required that this line density is equal to the area-averaged density of the flow, and by suitable time-averaging of line densities equal to the volume-averaged density of the flow. This will only be achieved in practice if the flow is homogenised.

of 13

Section 18 IE250-IH



The gas and liquid are likely to be more evenly distributed across the cross-section in a vertical flow than in a horizontal flow, where gravity tends to separate the liquid to the lower part of the pipe.

In vertical flow, the line fraction density is likely to be more representative of the area-averaged density, and therefore a vertical flow orientation is used in most meters which use gamma densitometers.

The impact of mixing and of flow orientation on density measurement becomes less significant at higher operating pressure, where the gas and liquid densities converge.

Sampling and Random Errors Any individual multiphase flow measurement, e.g. pressure drop, density

etc., is meaningless on its own in a system where there is continuously fluctuating velocity and liquid fraction of the flow. An average measurement is required, and two factors will influence this:

A sufficient length of time to allow a representative sample of flow features (for example liquid slugs);

A sufficient number of individual measurements to reduce the confidence interval in the measured average to an acceptable level.

For laboratory evaluations of multiphase meters a test time of 5 to 10 minutes is usually sufficient to capture a representative sample of the flow.

In a field application, the input flow may not be as steady as in the laboratory; for example slugging in the flowline may be influenced by upstream topography so slug intervals at the meter may be several minutes. In this case a longer interval may be required.

If a measurement such as pressure drop is being made which may fluctuate over a 25:1 range during the test, then to achieve high confidence in the measured average of a few percent it would be necessary to take of the order of S103 measurement samples.

This implies a sampling frequency up to about 5 Hz, well within the capability of most types of sensor and data recording systems.

of 13

Section 18 IE250-IH



Flow Patterns Flow patterns can have a significant effect on multiphase flow measurement. In-line meters which do not mix the flow will need to know what the flow pattern is in order to interpret the measurements. If the flow pattern is different to that of the model the output may be incorrect.

Gamma attenuation methods will be influenced by flow patterns if the distribution of the phases along the gamma ray path through the fluid mixture is not representative of the cross-sectional distribution. This is most significant in horizontal flow, although even the measurement of gas fraction using a single energy gamma beam can be influenced by flow pattern in vertical flow.

A bigger problem with gamma densitometers is the effect of fluctuations in distribution on the measurement.

Performance of Single Phase Flowmeters in Multiphase Flows

Some types of single phase meters can be used quite successfully in multiphase flows; the best example is the Venturi. Providing that the correct density is measured and that the differential pressure is correctly sampled and averaged, the Venturi can be used to give a good mass flow measurement.


Orifice meters are less suitable for use in multiphase conditions, due to a significant effect on differential pressure of liquid build-up on the orifice edges.

Positive displacement meters have been modified for use in multiphase flows. Mechanical devices in multiphase flows may be over-ranged and damaged by fluctuations in flowrate in slug flow. These meters should be avoided in single phase metering situations where there is a possibility of gas entering the liquid. They will always give measurements, until mechanical damage occurs.

of 13

Section 18 IE250-IH



Most other types of single phase meters function badly in multiphase flows with greater than about 6% gas in liquid or liquid in gas.

Turbine or Coriolis meters may tolerate a small percentage. Vortex meters tolerate virtually none. Ultrasonic meters can be used under some circumstances, but may fail

to give readings at all.

of 13

Section 18 IE250-IH


COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 19


of 12

Section 19 IE250-IH


Section 19

Basic Concepts of Multiphase Flow and Multiphase Flowmeters

What is Multiphase Flow?

2 phase:

Oil + Gas

or

Oil + Water

or

Water + Gas

3 phase:

Oil + Water + Gas

What is a Multi Phase Flow Meter (MPFM)?

A device for measuring the individual oil, water and gas flow rates in a

multi-phase flow.

The total package of measurement devices for composition and velocity,

including possible conditioning unit, should be considered as an integral

part of the meter.

of 12

Section 19 IE250-IH


Multiphase Flow Regimes

For vertical upward multiphase flow, the flow regime that is observed under a

specific set of flow condition is dependent on

(i) The liquid superficial velocity

(ii) The gas superficial velocity

(iii) The mean gas void fraction

(iv) The size and shape

(v) The component transport properties including density, viscosity, and

surface tension of the flowing components

Impact of Multiphase Meter on Business

of 12

Section 19 IE250-IH


Two-phase Flowmap

of 12

Section 19 IE250-IH


What is Superficial Gas velocity?

A derived velocity obtained by dividing the gas volume flow rate at actual

conditions by the cross sectional area of the conduit. In other words the

velocity of the gas if the gas was in the conduit without liquid.

What is Superficial Liquid Velocity?

A derived velocity obtained by dividing the liquid volume flow rate at actual

conditions by the cross sectional area of the conduit. In other words the

velocity of the liquid if the liquid was in the conduit without gas.

What is Gas Volume Fraction (GVF)?

The ratio of gas volume flow rate and the total fluid (oil, water and gas) flow

rate, both volume flow rates should be converted to the same pressure and

temperature. Expressed as a fraction or percentage.

What is Water Cut (WC)?

The ratio of the volume flow rate of water and the total liquid

volume flow rate, both volume flow rates should be converted to

the same pressure and temperature (generally at the standard

conditions).

It is generally expressed in a percentage.

of 12

Section 19 IE250-IH


Differential Pressure Devices (Venturi)

of 12

Section 19 IE250-IH


Cross Correlation

A cross-correlation flow meter measures the velocity of disturbances.

Composition Measurement

Single Energy Gamma Ray Absorption

In principle gamma ray absorption measurement works in the

0 - 100% watercut region and in the 0-100% GVF environment.

In a pipe, with inner diameter d, containing two phases the

absorption is described with:

3

1

).d](.exp[).()(i

iivm eeIeI

of 12

Section 19 IE250-IH


Im (e) is the measured count rate, Iv (e) is the count rate when the

pipe is evacuated and mi represents the linear absorption

coefficients for the two phases. Apart from the fractions (ai) also

the absorption coefficients (mi) are initially unknown. However, the

latter can be found in a calibration where the meter is subsequently

filled with the individual fluids or they can be entered in the

software after they have been determined offline.

Note that single energy gamma ray absorption concept as a

stand-alone measurement can only be applied in a two-phase

mixture.


Dual Energy Gamma Ray Absorption

The basics of the measurement are similar to the single

energy gamma ray absorption concept, but now two gamma of

energies e1 and e2 are used.

This measurement is applied in three phase oil, water and gas

mixture.

The use of radioactive sources requires proper licences, safety

procedures, and custodianship and, quite often, psychological

and emotional barriers have to be overcome as well. This

makes their use difficult or even impossible in some parts of

the world.

of 12

Section 19 IE250-IH


Commonly used sources are Am-241, Ba-133, Cs-137 and Gd-

153.


Dielectric (Electrical) Properties

Oil-continuous emulsions (water droplets in a continuous oil medium) are

non-conducting.

Water-continuous emulsions (oil droplets in a continuous water medium)

are conducting.

At the transition point going from oil-continuous to water-continuous the

leakage resistance across a capacitive sensor changes from large to small,

causing the sensor to be short- circuited. The measurement fails.

Cheap

Not full range

Igas(e2)

Ioil(e2)

Iwater(e2)

Iwater(e1) Igas(e1)Ioil(e1)

WATER

OIL

GAS

cou

nt

rate

hig

h

ener

gy

lev

el,

I(e 2)

count rate low

energy level, I(e1)

Triangle contains all

possible combinations of

oil, water and gas fractions

Triangle contains all

possible combinations of

oil, water and gas fractions

of 12

Section 19 IE250-IH


Microwave

Electromagnetic radiation, wavelength from 300 mm to 10 mm (1 GHz to

30 GHz)

The impedance, X, of a capacitor is given by

X = wC + 1/R

Where:

w = Frequency

C = The capacitance

R = Resistance

The capacitive component of this impedance grows in

magnitude with increasing frequency, while the conductive

component is independent of frequency. At high enough

frequency (> 1 GHz), the capacitive component dominate

even in water-continuous emulsions.

• By increasing the frequency even further, the sensitivity to

salinity changes decreases, but at these higher frequencies

and thus lower wavelengths it is only possible to measure over

smaller volumes. Full bore measurements are not possible

anymore and a solution often applied is the use of sampling

lines but this might introduce additional problems with

respect to representative sampling.

of 12

Section 19 IE250-IH


Literature Review

Gasch et al (1999)

A good multiphase flow meters should have the following characteristics:

Should be able to work for all flow regimes

Should not be affected by changes in fluid properties (density and

dielectric properties)

Should be non-intrusive system

Robust design

Works in harsh environments

No preconditioning of the flow (“Sever limitation for most applications)

Loh et al (1999)

• “Tomography provides a means of looking inside the flow region

from which local flow information such as volume fraction and

velocity can be extracted”

• “Provides a more accurate means of calculating flow rate and

eliminates the uncertainty in measurement flow rate due to

inability to predict flow profile with existing measurement

methods”

• You need to measure the distribution of the local volume fraction

of the solids and the distribution of local axial velocity

of 12

Section 19 IE250-IH


Loh et al (1999)

Electrical Resistance Tomography Method

Obtains cross sectional images (as used in x-ray radiography)

Enclose the objects to be measured by a number of non-intrusive sensors

Signals produced depend on the position of the component boundaries

within the sensing zone

A mathematical reconstruction algorithm is used to generate the

respective cross sectional images as obtained from the signals observed

by the peripheral sensors

In a conductive fluid, the local conductivity distribution is measured

which then be converted to local volume fraction distribution using

relation such as that developed by Maxwell (1873)

Literature Review

Toral et al (1998) (ESMER Multiphase Flow Meter)

Describes Experimental setup

In calibration:

Training should be done based on a universal database

of multiphase flow features.

Such database may be found on virtual multiphase flow

meters

Conclusions:

ESMER simple in construction. It consists of a straight

pipe with off the shelf sensors.

Accuracy obtained 10-15%

Suited to low cost/medium accuracy application

of 12

Section 19 IE250-IH


COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 20

OIML Recommendation 117

of 9

Section 20 IE250-IH


Section 20

Current Main Suppliers of Multiphase Flowmeters

Types of Multiphase Meters

Full flow multiphase flow meters:

These require no separation of liquid and gaseous phases for their

operation.

Work well only within specified range.

Multiphase flow meters employing separators:

In these meters, gas and liquid phases are first separated and metered

separately using single phase flow meters for gas and liquid (oil+water)

phases

These meters are more expensive and bulky

of 9

Section 20 IE250-IH


COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 21

Terminal Custody Transfer

of 21

Section 21 IE250-IH


Section 21



An important stage in the selection procedure is to list those factors or

constraints which have to be considered. These factors can be divided

into four groups:

Fluid type

Performance requirements

Installation requirements

Environmental and economic constraints

The fluid to be measured has to be specified

Is it a gas, liquid or mixture which is being measured?

What are the properties at normal and exceptional conditions?

Is the fluid hazardous, corrosive or at high pressure?

What is the temperature range and subsequent viscosity density ranges?

What is its electrical conductivity?

Purpose of Measurement and Uncertainty

Does the measurement need accuracy or repeatability?

Is it to satisfy a third party or to improve control of a process?

The flow range required has to be defined. This will include the

maximum and minimum for the measurement.

of 21

Section 21 IE250-IH


The desired uncertainty across different parts of the range has to be

defined.

Installation

The meter's installation requirements are of paramount importance

since virtually all meter types are affected by the surrounding

pipework.

Questions to be asked include:

What straight pipe can be utilised to locate the meter?

Can the existing pipe be split to install the meter?

What is the access to the meter location?

Environmental Considerations

This does not normally mean the effect of the meter on the

environment but this may have to be considered. This is

especially true if the installation is in a hazardous area where

intrinsic safety rating has to be applied.

What effect does the installation environment have on the

meter (e.g. safety of installation and access) together with

the effect of ambient temperature and humidity (maybe no

influence on the meter).

Economic Issues

of 21

Section 21 IE250-IH


Value of the fluid may have to be considered. The

measurement may be for process control or

safety/environmental accounting purposes. The measurement

may give process efficiency benefits.

Purchase price of flow meter is of importance.

Other considerations include the cost of secondary

instrumentation, pipe installation costs, including space

requirements, operating costs including maintenance and

spares.

Selection Process

Selection process is rarely straightforward. The five criteria

areas listed above are not exclusive.

Suitable flowmeters for a given application can now be

selected by a process of elimination or by a process of choice.

Often more than one type of flowmeter may appear to be

suitable for a particular application in which case further

deliberation is required.

of 21

Section 21 IE250-IH


An Overview of Different Types of Meter

Differential Pressure Meters

The orifice plate is by far the most widely used type of

flowmeter and can be designed, specified and used within

expectations defined by standards.

It is affected by flow profile and hence needs upstream and

downstream straight installation lengths which can be reduced

by flow conditioners.

The orifice plate will work for liquids and gases and gives

performance in a 1.5 to 2% accuracy class ( at best).


Differential Pressure Meters

Nozzles and Venturis perform in a similar manner but provide

less blockage to the flow.

Regardless of the flow conditions at the flowmeter,

differential pressure devices can use multiple tappings, and

not a pair of single pressure tappings, if high accuracy is

required.

Other Differential Pressure Methods

The variable area meter is cheap for both gas and liquid

applications at the 2% accuracy range.

of 21

Section 21 IE250-IH


For gas the sonic or critical flow nozzle provides a good

calibration reference and also a good measurement device for

mass flow. It has a high pressure drop and is not used for

applications where loss of pressure is important.

Positive Displacement Meters

These provide highly accurate and repeatable measurement of

most clean fluids.

They can be heavy and bulky in larger sizes and hence

expensive. Ideal for batch measurement at high accuracies,

and are generally resistant to pipe installation effects.

Often the only meter to use for high viscosities.

Extensively used for fiscal and custody transfer work.

Turbine Meters

Used for high accuracy applications in both gas and liquid.

Restricted range with viscosities greater than 30 cSt. They are

very repeatable but are viscosity and flow condition sensitive.

Fast response and good repeatability ensures a wide range of

applications from fiscal measurement of hydrocarbon liquids

and gases through to process control.

Can be easily damaged

of 21

Section 21 IE250-IH


Oscillatory Meters

In small size pipes, fluidic meters find some specialist niche

applications.

The most common type is the vortex meter, used at the 1 %

accuracy level and provides a good process control meter.

Used in both liquids and gas applications, they are affected by

flow profile and pulsations.

Electromagnetic Meters

Restricted to conductive fluids, these are used extensively in

pipes above 2 inch.

Their wide rangeability and long life without significant drift

makes them the first choice for water distribution systems.

They are relatively unaffected by flow disturbances and a

straight length of about 10 diameters upstream is sufficient to

keep the error caused by a bend or elbow to less than 1 per

cent.

Ultrasonic Meters

Multipath meters provide fiscal standard gas flow

measurement and for lower accuracy applications in oil.

Single-path clamp-on meters often provide the only solution

to non-intrusive measurement but can not be expected to be

better than a 2-5% accuracy class.

of 21

Section 21 IE250-IH


All meters are susceptible to flow profile effects and require

10-30 upstream diameters of straight pipe or suitable flow

conditioners.

Mass Flowmeters

The Coriolis meter provides direct mass measurement of most

liquids. It also measures gas but performs best when the

pressure (density) is high.

Better than 0.4% accuracy this type of meter competes with

positive displacement for liquid applications and some custody

transfer applications.

Meters are not affected by flow profile effects.

Desirable to avoid the vibration of meter, provide firm

clamping and avoid flow pulsations.

Measures mixture density in two phase flows.

of 21

Section 21 IE250-IH


Thermal Meters

Two types:

– The low flow gas thermal meters

– Insertion type hot wire types

Generally thermal mass flow meters are not affected by

skewed or swirling flows.

In-line thermal mass flow meters are sensitive to both skew

and swirl and the manufacturers recommendations for

minimum distances up and downstream of sources of

disturbance should be observed.

Faults and Failures

The reading from a flowmeter is often only questioned when

something is obviously wrong, e.g. a zero reading when flow is

present.

Common causes of faults and failures are listed next, firstly

for meter primaries (the meter itself) and secondly for meter

secondaries (the associated instrumentation).

Problems may also be caused by surrounding pipe fittings e.g.

a blocked filter or a faulty isolation valve.

of 21

Section 21 IE250-IH



Orifice Plates

Orifice plates are subject to edge rounding by erosion,

buckling by overpressure or thermal stresses, roughening of

the upstream pipe, build-up of dirt, misalignment and partial

blockage of pressure tappings.

Most serious effect is the rounding of the sharp upstream edge

of the plate which causes an increase in discharge coefficient

and hence an underestimation of the flowrate.

Venturi Meters and Nozzles

These devices are subject to roughening and fouling of the

throat with a consequent decrease in the discharge coefficient

leading to an overestimation of the flowrate.

Additionally, like orifice plates, roughening of the upstream

pipe, misalignment and partial blockage of pressure tappings

are problems.

Electromagnetic Meters

These meters are sensitive to fouling of the electrodes (if

wetted). Can use liner.

An order of magnitude change in the conductivity of the

metered fluid can change the calibration factor.

Particular items to check are damage to the insulating liner.

of 21

Section 21 IE250-IH


Also required to establish good electrical earthing between

meter body, the fluid, the pipework and the secondary

electronics to provide a common electrical potential.

Turbine Meters

Progressive wear of the bearings changes the meter factor and

linearity.

Partial blocking of the flow passage or material adhering to

the blades will affect the calibration of the meter.

Damage to the blades may occur particularly during cleaning,

and if debris is in the line.

Over-speeding is a primary cause of bearing failure.

Incorrect pulse generation/counting must also be considered.

Vortex-Shedding Meters

Damage to, or adherence of material to the vortex generator

will cause an alteration to the calibration.

Flow pulsations, poor installation and operating below the

minimum Reynolds number are the most common failures.

Positive Displacement Meters

Wear or damage to the rotors or chambers will cause

increased slip and hence an underestimation of the flowrate.

Debris can destroy the meter and block the flow line.

of 21

Section 21 IE250-IH


Secondary Devices (Pressure and Temperature)

Pressure lines and tappings are often a source of trouble

particularly at joints and junctions. For differential

measurement very small leaks and blockages can lead to large

measurement errors. The calibration of the pressure

transmitter and the associated readout must be assured.

Errors in temperature may give errors in the calculated

flowrate and hence the correct installation and calibration of

thermometers is vital.

Electrical/Electronic, Electromechanical Devices

Pulse counters are affected by other electrical devices nearby

if the counter leads are not adequately screened.

For the magmeter, zero shift is the most common source of

error. This has been minimised by modern circuitry.

Mechanical counters are usually reliable but slip can occur in

a magnetic coupling between the primary and secondary and

mechanical couplings can break.

Unintentional Generation of Two-phase Flows

A further source of error is the unintentional production of a

second phase, e.g. cavitation in a liquid or condensation in a

gas, air entrainment due to low pressure.

Cavitation occurs after a sudden restriction in the pipeline

such as a partially closed valve.

of 21

Section 21 IE250-IH


If there is a sudden expansion in a pipe carrying a gas which is

near to its saturation pressure, there may be condensation of

the gas. Again this can be prevented by maintaining the static

pressure at an adequate level.

of 21

Section 21 IE250-IH


Table 2: Broad Areas of Application

Y = Yes N = No L = Limited

of 21

Section 21 IE250-IH


COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 22

Lease Automatic Custody Transfer

of 1

Section 22 IE250-IH


Section 22



Currently it is estimated that world-wide there is a flowmetering

business worth approximately US $1 billion with expanding sales of the

more sophisticated flowmeters such as electromagnetic, Coriolis and

ultrasonic.

Relatively cheap microprocessors have been embedded into flow

measurement devices to effect operation such as linearisation and

compensation and these devices are commonly referred to as ‘smart’.

Another important feature stems from the fact that the output of the

flowmeter can be assessed and compared with that of the flowmeter

when initially calibrated. This would provide a measure of how far the

performance of the flowmeter was short of its calibrated specification.

In conjunction with the application of, for example, fuzzy logic and the

more recent chromatic methodologies to the interrogation of the output

signals this feature shows great promise for fault diagnosis.

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 23

Truck Custody Transfer

of 7

Section 23 IE250-IH


Section 23

Numerical Exercises

Standards Organisations QUESTION 1

LIQUID FLOWING THROUGH A CONVERGING PIPE SECTION

DATA:

V1 = 4 m /s

D1 = 18 inches

D2 = 6 inches

Density of liquid = 850 kg / m3

QUESTIONS:

Determine:

V2 (m /s)

Volumetric flowrate Q (m3 /s)

Mass flowrate m (kg/s)

QUESTION 2

LIQUID FLOWING THROUGH A CONVERGING PIPE SECTION

DATA:

Mass flowrate m = 4 kg /s

D1 = 18 inches

D2 = 6 inches

Density of liquid = 950 kg / m3

QUESTIONS:

Determine:

V2 (m /s)


of 7

Section 23 IE250-IH


QUESTION 3

METHANE FLOWING THROUGH A PIPE SECTION

DATA:

Line pressure = 4.3 bar

Temperature at some point = 29 C

Gas constant = 518 J /kg K

QUESTIONS:

Determine:

Density of Methane ( kg/ m3 ) at the point

Density of Methane ( kg/ m3 ) at the point if temperature doubled

Density of Methane ( kg/ m3 ) at the point if temperature doubled

and pressure doubled

QUESTION 4

METHANE FLOWING THROUGH A PIPE SECTION

DATA:

D = 20 cm

Length of pipe L = 100 m

Density of Methane = 0.717 kg / m3

Pressure difference across pipe length = 0.1 bar

Friction factor = 0.01

QUESTIONS:

Determine:

V (m /s)


Mass flowrate m (kg /s)

of 7

Section 23 IE250-IH


QUESTION 5

OIL FLOWING THROUGH A PIPE SECTION

DATA:

D = 20 cm

Length of pipe L = 200 m

Density of Oil = 1090 kg / m3

Mean velocity = 3 m/s

Friction factor = 0.05

QUESTIONS:

Determine:

Pressure difference across pipe length

Volumetric flowrate Q ( m3 /s)

Mass flowrate m ( kg /s)

QUESTION 6


WITH INSTALLED ORIFICE PLATE

DATA:

Density of oil = 830 kg / m3

Flowrate = 0.8 m3/s

Discharge coefficient of orifice plate = 0.65

Pipe diameter = 0.6 m

Orifice plate b = 0.5

QUESTIONS:

Determine:

Pressure difference across orifice plate

QUESTION 7


of 7

Section 23 IE250-IH


WITH INSTALLED ORIFICE PLATE

DATA:


Pressure difference across orifice plate = 0.5 bar



Orifice plate b = 0.5

QUESTIONS:

Determine:

Volumetric flowrate

QUESTION 8

OIL FLOWING THROUGH A PIPE SECTION WITH INSTALLED ORIFICE PLATE

DATA:


Pressure difference across orifice plate = 0.5 bar



Orifice plate hole size = 0.31 m

QUESTIONS:

Determine:

Volumetric flowrate

Percentage difference in flowrate compared with Exercise 7

QUESTION 9

PRESSURE CALCULATIONS

Piston in a cylinder

DATA:

Force applied to gas in cylinder = 1000 N

of 7

Section 23 IE250-IH


Internal diameter of cylinder = 10 cms

Ambient pressure = 1 bar

QUESTIONS:

Determine:

1. Absolute gas pressure in Pa

1. Gauge gas pressure in Pa

2. Absolute gas pressure in psi

QUESTION 10

PRESSURE CALCULATIONS- Pressure at base of oil tank

DATA:

Height of oil in tank = 4 m


Acceleration due to gravity = 9.81 m / s2

Ambient pressure = 1 bar

QUESTIONS:

Determine:

1. For open tank: absolute oil pressure at base in Pa

2. For open tank: gauge oil pressure at base in Pa

3. For closed tank with pressure of 2 bar above oil: absolute oil pressure at

base in Pa

4. For closed tank with pressure of 2 bar above oil: gauge oil pressure at

base in Pa

QUESTION 11

WORK, ENERGY, POWER, CALCULATIONS

Metal block moved along ground

DATA:

Force applied to move block = 100 N

of 7

Section 23 IE250-IH


Distance moved by block = 20 m

Time taken to move block = 12 s

QUESTIONS:

Determine:

Work done in moving block

Energy expended in moving block

Power (in HP) used in moving block

QUESTION 12

TWO-PHASE FLOW EXAMPLE CALCULATION

A vortex flowmeter is metering steam with a quality of 95% at a pressure of

140 psia ( 965 kPa ).

If the mean K factor is 64 pulses / ft3 ( 2295 pulses / m3 ), calculate :

1. The total mass flow if the counter registers 100,000

2. The mass of saturated vapour ( steam )?

SOLUTION

For a two-phase flow, the total flow is calculated from the equation:

Q lb = rtp x pulses / K

The effective two-phase density is given by:

rtp = rg / { X 1.53 + ( 1 - X 1.53 ) rg / rl }

i.e.

rtp = 0.31066 / { 0.95 1.53 + ( 1 - 0.95 1.53 ) 0.31066 / 55.476 }

= 0.33587 lbm / ft3

of 7

Section 23 IE250-IH


Hence from standard steam tables at a pressure of 140 psia:

the density of the saturated vapour is rg = 0.31066 lbm / ft3

and the density of the saturated liquid is rl = 55.476 lbm / ft3

1. The total mass flow is then:

Q lb = 0.33587 x 100,000 / 65 = 516.7 lbm

2. The mass of saturated vapour is given by the equation:

( Q lb ) g = X ( Q lb ) T = ( 0.95 ) ( 516.7 ) = 490.9 lbm

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 24

Leak Detection Systems

of 3

Section 24 IE250-IH


Section 24

Standards Organisations, Flow Measurement Standards

and References

Standards Organisations

of 3

Section 26 IE250-IH


Flow Measurement Standards

API RP550 (INSTALLATIONS OF REFINERY INSTRUMENTS AND CONTROL SYSTEMS)

BS7118 (MEASUREMENT OF FLUID FLOW: ASSESSMENT OF UNCERTAINTY IN CALIBRATION AND USE OF FLOW MEASURING DEVICES)

BS5844 (METHODS OF MEASUREMENT OF FLUID FLOW: ESTIMATION OF UNCERTAINTY OF A FLOWRATE MEASUREMENT)

BS5728 (FLOW OF COLD WATER IN CLOSED CONDUITS) BS1042 (METHODS FOR MEASUREMENT OF FLUID FLOW IN CLOSED

CONDUITS) ISO5167 ORIFICE PLATE/ NOZZLES/VENTURIS) AGA REP NO 3 (ORIFICE PLATE) BS4161 (TURBINE GAS METERS) BS4331 (METHODS FOR ASSESSING PERFORMANCE CHARACTERISTICS OF

ULTRASONIC FLOW DETECTION EQUIPMENT) ISO9330 (MEASUREMENT OF GAS FLOWS BY MEANS OF CRITICAL FLOW

NOZZLES) BS5579 (STANDARD REFERENCE CONDITIONS FOR MEASUREMNT OF

PETROLEUM LIQUIDS AND GASES) BS5792 (FLOW MEASUREMENT USING ELECTROMAGNETIC FLOWMETERS)

of 3

Section 26 IE250-IH


References

1. R.W Miller: Flow Measurement Engineering Handbook. Mc Graw-Hill 3rd Edn. ISBN 0-07-042366-0.

2. D.W.Spitzer: Flow Measurement. ISA 2nd Edn. ISBN 1-55617-736-4. 3. Instrument Engineer’s Yearbook. Inst MC. ISBN 0-904457-33-8

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 25

API Standards

of 2

Section 25 IE250-IH


Section 25

Cavitation and Flashing

Cavitation occurs in two distinct stages. In the first stage voids or cavities are formed, and in the second stage these collapse or implode back into an all-liquid state. Two types of cavitation may occur, gaseous or vaporous, both types requiring a nucleating agent for inception. These nucleating points enlarge into finite cavities within the liquid.

Most liquids contain solid contaminants so that the necessary nuclei for incipient cavitation are nearly always present. The inception of cavitation may be delayed significantly if the liquid has been carefully degassed, polymers added, or the liquid maintained under high pressure for a period of time for the gas to completely dissolved.

If the cavitation process ceases before the second stage, so that vapour persists downstream of the region where bubble collapse normally takes place, the process is called flashing. Since flashing is directly related to the first stage of cavitation, the theory of cavitation also applies to flashing.

When decreased line pressure approaches the vapour pressure of a liquid in a pipe, cavitation begins. This is essentially local boiling caused by decreasing pressure rather than by increasing temperature. The resulting formation and collapse of the vapour cavities is responsible for the audible noise in the pipeline. Excessive cavitation destroys piping, restricts flows, and ruins turbine blades.

Cavitation occurs whenever pressure has been reduced by, for example, flow separation, valves, vortex elements and differential pressure flowmeters. Imploding pressures can reach 100,000 psi.

Dissolved gases and gas bubbles assist in the onset of cavitation. With gas concentrations of only 30 parts per million, fluids will cavitate at higher static pressures than for the liquid alone.

of 2

Section 25 IE250-IH


Cavitation number is defined as: s = 2 ( p – pv ) / r V2 p is the local static pressure pv is the local vapour pressure r is the fluid mean density V is the fluid mean velocity Usually cavitation begins with very small bubbles isolated in a small section of the flowmeter. As the cavitation number decreases, formation becomes more rapid with bubble size increasing. For cavitation numbers below a certain value (called the incipient cavitation number sI) cavitation becomes increasingly destructive to both piping and flowmeters. The addition of small amounts of polymers has been seen to reduce both sI and the noise.

In a flashing liquid, the volume of vapour is frequently greater than the volume of liquid, so that the liquid droplets tend to achieve the high velocity of the vapour. These high velocity droplets impact on the pipe or flowmeter surface causing deformation of the surface. Damage due to flashing is usually in the section downstream of the flowmeter and piping here is often pitted. For liquids near saturation, flashing sometimes begins upstream and the entire flowmeter body can be affected. So proper choice of flowmeter material is essential.

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 26

Standards Organizations, Flow Measurement

Standards and References

of 7

Section 26 IE250-IH


Section 26

Pipeline Requirements and Installation Notes for Dry-Type

Differential Transmitters

General Requirements

For liquid flows in a horizontal pipe ( Figs. 1 and 2 ), the pressure taps should be located at the sides of the pipe, with no more than a ±45° orientation. For horizontal clean gas flows ( Fig. 3 ), the pressure taps should be vertical; for vapors (steam, ammonia) and dirty or condensable gases ( Fig. 4 ), the taps should be located at the side. For vertical pipe installations, the pressure taps can be at any radial position around the pipe circumference ( Figs. 5 to 8 ). The differential-pressure transmitter should be located as close to the taps as possible. This improves the speed of response and reduces the possibility of resonance or attenuation within the leads. Prefabricated manifolds are available for easy close-coupled installation (Fig. 9). Lead lines should be of the same bore, no less than 0.25 in (6 mm) in diameter for clean liquids. For condensable vapor flows, where gas bubbles may be liberated, the diameter should be no less than 0.4 in (10 mm). For long, liquid-filled lines, a gradient of 1 in/ft (80 mm/m) is recommended to allow gas bubbles to rise back into the flow line. If the fluid is of medium to high viscosity (5 to 100 cP), the slope should be increased to 2 to 4 in/ft (160 to 320 mm/m). The tubing bore should be increased to the ISO-recommended values if long lead lines are necessary.

of 7

Section 26 IE250-IH


of 7

Section 26 IE250-IH


General Requirements

The two lead lines should be close together and lagged, if necessary, to reduce density variations due to temperature differences. Any head difference between leads alters the differential, although zeroing under flowing pressure and temperature usually reduces this error.

For clean liquids and dry gases, lead lines are purged through transmitter vents.

If the flowing gas or liquid must be isolated from the measuring element because of corrosion, dirt, sediment, or condensation, seal fluids are used. Several slack, flush-mounted diaphragm seals are also available for isolation.

A seal fluid serves two purposes:- to isolate the process and to provide protection against freezing. The most common seal liquid for oils is a mixture of 50 percent water and 50 percent ethylene glycol or glycerine, or, for lower-temperature protection, a mixture with 60 percent ethylene glycol.

The ethylene glycol mixture has a specific gravity of about 1.07; the glycerine, about 1.13. The 50 percent ethylene glycol mixture freezes at -35°F (-37°C), and the 60 percent mixture at -56°F (-50°C). The 50 percent glycerine mixture freezes at -9.4°F (-23°C) and the 60 percent at -56°F (-49°C).

For water and low-gravity aqueous solutions of salts and acids, dibutyl phthalate has been found highly satisfactory. Dibutyl phthalate has a specific gravity of 1.05, freezes at -31°F (-35°C), and has a boiling point of 612°F (322°C).

For liquids with a specific gravity greater than 1.01 heavier seal fluids must be found. Chloronaphthalene or Halowax oil, various Arochlors, transformer sealing fluids, Kel-F oil (trifluorochloroethylene polymers), fluorolubes, and acetylene tetrabromide have been used, but many are toxic, highly viscous, or have other disadvantages.

No really satisfactory sealing medium for large displacement secondary elements (wet-type meters) has been found for materials such as concentrated sulfuric acid, although lighter oils, such as Nujol or other acid and caustic treated oils, have been used.

Use of oil lighter than the flowing fluid introduces serious maintenance problems.

of 7

Section 26 IE250-IH


of 7

Section 26 IE250-IH


Table 8.3 Recommended Minimum Internal Diameters of Lead Line

of 7

Section 26 IE250-IH


of 7

Section 26 IE250-IH


Pressure Taps For gas and vapor flows a pressure-tap connection is required if a pressure compensation is to be made. The precautions outlined for the differential-pressure connection should be followed. The pressure transmitter is usually connected via a tee to either the upstream or downstream pressure lead line. The tap selected depends on whether an upstream or downstream gas expansion factor is to be calculated. A second pressure tap is recommended when using meters that have a sizable change in volume as the differential increases (bellows, manometer type, etc.). The presence of pulsations, or severe line noise, may result in cross talk between the differential-pressure and pressure meters that can result in errors in both measurements.

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 27

Contoured Devices

of 7

Section 27 IE250-IH


Section 27

Contoured Devices

These have the advantage of sweeping solids through the throat and of

reducing permanent pressure loss. They are normally more rugged than orifice

meters and usually better therefore for metering steam or other high velocity

applications.

Flow Nozzles

Several flow-nozzle contours are available. The ASME wall-tap flow nozzle

(either low- or high-b series) is preferred in the United States, while in Europe

the ISA 1932 design is widely used.

In the United States, the ASME low-b-series nozzle is sometimes modified to

have throat taps, and this has become the accepted standard for testing steam-

turbine performance.

of 7

Section 27 IE250-IH


of 7

Section 27 IE250-IH


ASME Long-Radius Wall-Tap Nozzle. The ASME flow nozzle has a contoured

elliptical inlet in which the curvature is the quadrant of an ellipse. For beta

ratios from 0.2 to 0.5 (the low b series), the design is as shown in Fig. 9. For

beta ratios between 0.45 and 0.8 (the high b series), the design is as shown in

Fig. 10.

The nozzle wall and flange thickness should be sufficient to prevent distortion

caused by pipeline pressure, temperature, or bolting strains. The nozzle should

be well centered in the pipe, and the installation requirements relative to

upstream piping conditions, thermal wells, etc., should be followed for good

measurements.

It is important that the downstream pressure tap be inside the exit. Also,

outward widening of the cylindrical throat should be avoided, since this causes

a rising discharge coefficient at high Reynolds numbers.

The throat taper, if any, should always decrease the throat diameter toward

the exit, with no bell mouth or diameter increase.

Discharge-coefficient data has been reduced to an empirical equation for pipe

Reynolds numbers greater than 10,000. Teyssandier (1986) has presented data

that indicates that these equations are valid for line sizes of 1.5 to 3.4 in (38 to

87 mm) within the stated tolerance. This equation is graphed in Fig. 11. For

low Reynolds numbers, Benedict's (1966) equation, which was empirically fitted

to the ASME low-Reynolds-number data, may be used.

This equation is:

C = 0.19436 + 0.152884 ln Rd - 0.0097785 (ln Rd)2 + 0.00020903 (ln Rd)3

Figure 13 is a plot of this equation.

of 7

Section 27 IE250-IH


Classical Venturi Tube

Classical venturis are shown in Fig. 15. They are grouped as:

1. Classical venturi with rough-cast inlet, recommended for line sizes of 4

to 32 in (100 to 800 mm)

2. Classical venturi with machined inlet, recommended for line sizes of 2 to

10 in (50 to 250 mm)

3. Classical venturi with rough-welded sheet-iron inlet, for line sizes of 8 to

48 in (200 to 1200 mm)

of 7

Section 27 IE250-IH


Venturis in the first two groups are cast in a sand mold, and the inlet

may be left as cast (group 1) or machined (group 2).

• Although standards limit the maximum line size to 48 in (1200

mm), classical Venturis have been fabricated for use in 120 in

(3000 mm) lines.

• In the United States, the rough-cast inlet is almost always used

while in Europe all three groups are commonly used.

• The exit cone (recovery cone) may have an included angle

between 7° and 15° with 7° being preferred for minimum

permanent pressure loss.

• The 7° cone may be shortened to reduce lay-in length without

significantly altering recovery.

of 7

Section 27 IE250-IH


COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



Section 28

a. Computer System Control A b. Computer System Control B

of 6

Section 28a IE250-IH


Section 28a

Computer System Control A

Control Systems

• Control System is a device or set of devices which are used to command or regulate the behavior of other devices or systems.

• Earlier Control Systems are Manually controlled, now they are independent of human involvement.

Ex: 1. Flowmeter control system 2. A motor driving the load 3. Washing machine

Typical Control System

Signal

Conditioning

Analog

Control

Hardware

Actuator Plant

Analog Sensors

TransducersSignal

Conditioning

outputR Error

PV

of 6



Elements of Control System

Signal Conditioning: Amplification, filtering, attenuation and multiplexing.

Controller: A device that carries out the computation of the control signal.

Actuator: Object such as motor that provides the power to control a process.

Sensor: Device such as thermostat that computes a signal proportional to a physical variable such as temperature.

Transducer: an electronic device that converts energy from one form to another.

Generic Block Diagram of Digital Control System

Pre-

FilterA / D Computer D / A

Smooth

Filter Plant

Sensor

Anti-

Alias

Filter

A / D

Clock

outputR

of 6



Elements of Digital Control System

Pre-filter: Filter that precedes the control loop. A/D: It converts continuous signal to digital signal. Digital Computer: It carries out computation, and consists of a processor,

a memory, and I/O devices. D/A: It converts digital signal to continuous signal. Smooth Filter: used to remove noise or other high frequency components

of a signal. Sensor: Device that outputs a signal proportional to a physical variable. Anti Alias Filter: Filter designed to remove signals that might cause

aliases before they are sampled.

Simplified Digital Control System

Digital

ComputerDAC

Smooth

FilterPlant

Digital

Sensors

Digital

Multiplexer

Clock

R OUTPUTFCE

Modes of Closed Loop Control

Closed loop control can be:

Manual

On-Off

PID

Advanced PID (ratio, feedforward, etc….)

The algorithm determines the controller output.

of 6



Basic Elements of Process Control

Controlling a process requires knowledge of four basic elements, the process itself, the sensor that measures the process value, the final control element that changes the manipulated variable, and the controller.

of 6



Control Elements These are the devices the controller operates:

Pneumatic valves, solenoid valves, rotary valves, motors, switches, relays, variable frequency drives.

Controllers These are the devices that do the controlling:

• Programmable Logic Controllers (PLCs) • Programmable Automation Controllers (PAC) • Distributed Control Systems (DCS) • Proportional, Integral, Derivative (PID) Controllers • Supervisory Control and Data Acquisition (SCADA) • Energy Management Systems (EMS)

Operation of Closed Loop Digital Control System

• Basic operation is described by an a Flowmeter Control System.

• Please provide block diagram and brief description of the operation (see

preliminary example below.

of 6



of 27

Section 28b IE250-IH


Section 28b

Computer System Control B

Basic Control Concepts

TOPICS

Introduction Variables Basic Elements Manual Control Feedback Control System Responses ON – OFF Control Three Term Control

Introduction

This chapter introduces the basic concepts encountered in Process Control.

Some of the standard terminology is also presented

of 27



Control History

Early development of feedback control by James Watt in Scotland using a governor on a steam engine in about 1775. (Flywheel principle)

Broader use of automatic control began to be made in the late 1920’s and the first general, theoretical, treatment of automatic control was published in 1932.

New technologies have created a transformation in control engineering with the advent of DCS and PLC systems.

The theory of automatic control has also developed in parallel with these new technologies.

of 27



Variables

The operations which are associated with process control have always existed in nature, examples are blood pressure, temperature & heart rate etc.

Early forms of process control included some person monitoring a fire to keep up a temperature. This could be considered a version of Manual Control.

The development of automatic control only become a reality when people learned to adapt automatic regulatory procedures to manufacture products or process materials more efficiently.

Automatic control assumes no human intervention.

Variables Involved There are three main terms to consider 1. Controlled Quantities/Variables 2. Manipulated Quantities/Variables 3. Disturbances

Controlled Quantities

Also referred to as Controlled Variables. These are the streams or conditions which the operator wishes to control

or maintain at some level. Controlled variables include such parameters as temperature, pH,

moisture, level, position, flow weight and speed etc. For each controlled there must be a desired value known as a SET-POINT

or reference value.

of 27



Manipulated Quantities

For each controlled variable there is a manipulated variable such as a flow rate.

This manipulated variable is usually controlled through the use of a control valve.

Disturbances

Disturbances enter the process and cause change away from the set-point.

Typical disturbances include change in temperature or pressure or feed-stock.

The automatic control system must therefore alter the manipulated variable so that the set point is maintained in spite of these disturbances.

Also, the set point may be moved, in which case the manipulated variable will need to be changed to adjust the process to the new value.

Manipulated Variable

For each controlled variable the control system operator selects a

manipulated variable which can be paired with a controlled variable. Often the choice is obvious, such as manipulating the flow of fuel to a

home furnace to control the temperature of a house. Sometimes the choice is not so obvious and can only be determined by

someone who understands the process under control. The pairing of manipulated and controlled variables is performed as part

of the process.

Basic Elements

Elements of a Process Control System

A control loop is a self-contained system. Purpose is to maintain a process at a given value. Usually consists of a transmitter for measurement. A controller to evaluate. A control valve which can be changed by the controller.

of 27




Basic Elements There are four essential elements in any process control system. 1. Process 2. Measurement 3. Evaluation 4. Control

Process

In general, a process is an assembly of equipment and material and is related to some manufacturing operation or sequence.

In the case of a tank with a liquid, the level of this liquid is influenced by the flow into and out of the tank.

Any given process can involve dynamic variables and it may be desirable to control all of them.

In most cases, controlling one variable would be sufficient to control the process within acceptable limits.

of 27



Measurement TO CONTROL ANY PROCESS IT FIRST HAS TO BE MEASURED

Measurement means the conversion of a process variable into an analogue or digital signal by means of a sensor or transmitter or both.

The result of any measurement is the conversion of a dynamic variable into some proportional information which is required by some other elements in the process control loop or sequence.

Evaluation

In the evaluation step of a process control sequence, the measurement is examined and compared with the desired value or set-point.

The amount of corrective action required to maintain proper control is determined.

A controller is used for this evaluation. This controller can be pneumatic, mechanical or electronic and would be mounted in a panel.

It can also be part of a computer control system, in which case the control function is performed by software.

Control Element

The control element in a control loop has the most direct effect on the process.

Receives a signal from the controller and transforms this to a proportional operation which is performed on the process.

In most cases, the final element is a control valve which adjusts a flow in a pipeline, for example.

Other final elements include: electrical motors, pumps and dampers. In a typical home heating system, the controlled variable is the room

temperature. A number of disturbances cause the room temperature to vary, e.g.,

outside ambient temp., the number of people in the room or the activity taking place inside the room.

The automatic control system is designed to manipulate the fuel flow to the furnace in order to maintain room temperature at the desired set-point.

Note: Temperature is being controlled and flow rate is being varied.

of 27




Manual Control

Typical Manual Control IT IS CONSIDERED USEFUL TO REVIEW THE MANUAL CONTROL OF A PROCESS AT THIS STAGE.

There must be an indication of the process which can be used as a measurement.

The operator uses this indication to decide what change is required. The set-point is in the mind of the operator.

of 27



Manual Control

The operator compares these two values and changes the final element

accordingly. There are many problems associated with this form of control.

Basic Elements

of 27



Feedback Control

THE SIMPLEST WAY TO AUTOMATE THE CONTROL OF A PROCESS IS THROUGH FEEDBACK CONTROL.

Sensors are used to measure the actual value of the controlled variable. This value is transmitted to the feedback controller. The controller makes a comparison between this measurement and the

desired value which has already been established. Based on the difference (error) between these two values, the controller

sends a proportional output to the control value.

of 27



Feedback Control

ADVANTAGES OF FEEDBACK CONTROL

It is not essential to know what disturbances will affect the process. Also, the relationship between the final control element and the process

is not an issue. Standard hardware can be used for almost any application. The principles of feedback control apply to all types of process control

instrumentation. Traditional, stand-alone feedback controllers offer the simplest

approach to automatic control.

of 27



Feedback Control

System Responses

General Requirements of a Control System

The primary requirement of a control system is that it must be reasonably stable.

The speed of response must therefore be fast. The response must also show reasonable damping. A control system must also be capable of reducing a system error to zero

or to a value close to zero. System Error The system error (e) is the difference between the value of the

controlled variable set-point (SP) and the value of the process variable (PV).

The system error is expressed as: e(t) = PV(t) – SP(t) where (t) is a function of time.

of 27



System Error

System Response

The main purpose of a control loop is to maintain some dynamic process variable at a prescribed operating point or set-point.

System response is the ability of a control loop to recover from a disturbance which causes a change in the controlled variable.

There two categories of good response: 1. Under-damped (cyclic response) 2. Damped

of 27



System Responses

of 27



Control Loop Design Criteria

Many criteria are employed to evaluate the response of a process control loop to an input change.

The most common of these include: Settling time Maximum error Offset error Error area The settling time is defined as the time the process control loop needs to bring the PV back to within an allowable error.

The maximum error is simply the maximum allowable deviation of the dynamic variable.

Most control loops have inherent linear and non-linear characteristics which prevent the system from returning the PV to the SP after a system change. This is called offset error.

The area error is the area between the response curve and the set-point line.

System Responses

of 27



ON – OFF Control

Discrete controllers are the most basic form of control and have only two modes or positions, ON and OFF.

A common example is a typical electric iron. When the temperature of the iron falls below the manual setting, the

iron switches ON. When the temperature reaches the desired value (or SET POINT), the

iron switches OFF. This type of control does not actually hold the temperature at the

required value, but keeps the variable within proximity of the SET POINT in what is known as a DEAD ZONE.

System Responses

of 27



ON – OFF Control

The expression for ON - OFF control can be stated as

e = SP - PV where: e = Error SP = Set Point PV = Process Variable In the ON – OFF control mode, the valve is open when the error (e) is positive and the valve is closed when e is negative.

of 27



Three Term Control

Proportional Only Control

A better system is required to overcome the sudden changes of ON – OFF

control. The lack of precise control suggests that an alternative approach is

required. Proportional Control initiates a corrective action which is proportional to

the change in error or deviation of the process from the set-point.

of 27



Proportional Only Control

of 27



Three Term Control

Proportional Control

Proportional Gain

In electronic controllers, the proportional action is typically expressed as proportional GAIN.

Proportional Gain answers the question “What is the percentage change of the controller output, relative to the percentage change in controller input?”

Proportional Gain is expressed as Gain (Kc) = ∆ Output % / ∆ Input %

Proportional Band

Proportional Band (PB) is another way of representing the same information and answers the question “What percentage of change of the controller input span will cause a 100% change in controller output?”

PB is expressed as ∆ Input (% span) for 100% ∆ Output

of 27



Three Term Control Proportional Control

Proportional action is limited in the sense that the control action only responds to a change in the magnitude of the error.

Proportional action will not return the PV to the SP. It will however, return the PV to a value which is within a defined span (PB) around the PV.

of 27



Three Term Control Proportional Control

Proportional Plus Integral Control

It would be an improvement if the controller adjusts the controller to eliminate off-set.

It would also be an advantage to have the controller respond at a speed proportional to the size of the error.

This added control function is called reset or integral (reset is the older term).

This function also eliminates the offset. Shortened to P + I If we assume a step change in set- point at some point in time. Initially there is a sudden change in in valve due to proportional action

(equal to Kc x e). At the same time, the integral portion of the controller, sensing an error,

begins to move the valve at a rate, proportional to the error, over time. If the error is constant, the correction rate will also be constant.

of 27



Proportional Plus Integral Control

When time is used to express integral or reset action, it is called ”reset time”.

Quite commonly, the reciprocal is used in which case it is called “reset rate” in “repeats per minute”.

This term refers to the number of times per minute that the reset action is repeating the valve change produced by proportional action alone.

Process control systems personnel refer to reset time as integral time and denote it by the symbol “Ti”.

The P + I controller includes the characteristic of the I controller. This allows the advantages of both controller types to be combined, fast

reaction and compensation of the remaining system deviation. For this reason, the P + I controller can be used for a large number of

control applications. I addition to proportional gain, the P + I controller has a further

recognisable value which indicates the behaviour of the I component – the reset time (integral action time)

of 27



Proportional Plus Derivative Control

A further function can be added in the form of rate or derivative control. This control function produces a corrective action which is proportional

to the rate of change of error. It should be noted that this correction only exists while the error is

changing, it disappears when the error stops changing, even though there may still be a large error.

Commonly referred to as P + D control. Some large and / or slow processes do not respond well to small changes

in controller output. For example, a large thermal process, such as a heat exchanger, may

react very slowly to a small change in controller output. To improve response, a large initial change in controller output may be

applied. This is the function of the derivative mode. If we assume, the set point is changing at a constant rate. Derivative action contributes an immediate valve change which is

proportional to the rate of change of the error. This would be equal to the slope of the set-point line (the error). As the error increases, the proportional function contributes additional

control valve movement. At a later stage, the contribution of proportional action will have

equaled the initial contribution of the rate action. This is called derivative time td.

of 27



Proportional plus Derivative Control Summary

Derivative (Rate) action is a function of the speed of change of the error. The units are expressed in minutes. The action is to apply an immediate response which is equal to the

proportional plus reset action that would have occurred some number of minutes in the future.

The advantage of a rapid output is that it reduces the time which is required to return the PV to the SP in a slow process.

Proportional Plus Integral Plus Derivative Control

Deciding which control action is required for a particular application depends on the characteristics of the process being controlled.

PID control should NOT be used for “noisy” processes or on one which has stepwise changes because the derivative action is based on the measurement of rate of change. This could lead to unstable control.

PID control is used on processes which respond slowly. Temperature control is a common example of PID control. The derivative

action shortens the time taken for the process to respond. In addition to the properties of the P + I controller, the PID controller is

complemented by the D component. This takes the rate of change of the system into account. If the system deviation is large, the D component ensures a momentary

high change in the manipulated variable. While the influence of the D component falls off immediately, the

influence of the I component increases slowly. If the change in system deviation is slight, the response of the D

component is negligible. This behaviour has the advantage of faster and more accurate

compensation of system deviation in the event of changes or disturbance variables.

The disadvantage is that the control loop is much more prone to oscillation and that optimum tuning is therefore more difficult.

of 27



Three Term Control

of 27



Three Term Control

Summary

of 27



Summary

COURSE RECAP Day 1



0815 – 0830 PRE-TEST


0930 - 0945 Break



1230 - 1245 Break



1420 – 1430



Day 2

0730 - 0915




0915 - 0930 Break

0930 - 1045




1045 – 1230





1230 - 1245 Break


1420 – 1430



Day 3

0730 - 0830






0930 - 0945 Break

0945 - 1130





1230 - 1245 Break



1330 - 1420




1420 – 1430



Day 4


0830 – 0930





0930 - 0945 Break

0945 - 1030






1130 - 1230




1230 - 1245 Break



1420 – 1430



Day 5



0930 - 0945 Break

0945 - 1230




1230 - 1245 Break

1245 - 1345





1400 - 1415 POST-TEST



ie250 ih r

Automotive

references section

ultrasonic flowmeters

multiphase flowmeter

process measurement

level measurement section

flowmeter selection

table of contents section

api standards section