icepim 2015 international conference on pipeline integrity

By:

K.K. Tandon – Director (Technical)

M/s Bhotika Pipeline Services Co. Pvt. Ltd.

Ex. G.M., Engineers India Limited (EIL)

ICEPIM 2015

International Conference on Pipeline Integrity management

Pipeline as a large pressure vessel.

Conventional NDT not feasible.

Hydro-testing limitations:

◦ Only a fail/ no fail test

◦ Interruption in supplies

◦ Availability of large amount of clean water

◦ Disposal of contaminated water

◦ Safety of public at large

Hydro-testing continues to be practised:

◦ For new pipelines

◦ For large scale rehabilitation projects

No provision for Launchers/ Receivers

Reduced bore mainline valves & check valves

Low flow conditions resulting in reduced velocity

Miter bends

Less than 3D bends

Large diameter unbarred Tee

ECDA & ICDA (Ref. NACE Standards RP0502-2002,

SP-0208-2008)

CPL Survey

DCVG Survey/ other Corrosion Control Surveys

Corrosion Probes

Guided Wave Inspection Technique

OISD GDN-233 Guidelines on inspection of on land non-

piggable pipelines.

Longitudinal guided waves

are induced into the pipe

body.

When these waves intersect

any pipe anomaly, mode

conversion takes place into

laminar waves and reflect

back to the tools original

location.

Reflected signals are digitally

captured and processed.

Teletest equipment hardware

and software developed by

TWI, UK on this principle.

The basic TeleTest system based on Long Range

Ultrasonic Testing (LRUT) comprises of the following:

◦ A low frequency flaw detector, the Teletest Focus pulser receiver

unit.

◦ Transducer ring or tool that wraps around the pipe.

◦ A laptop computer that contains the software controlling the

system.

◦ Cable connector between the Teletest Focus unit and tool.

◦ Communication between the Teletest Focus unit and laptop

through ethernet.

Contd…

Figure-2:

The TeleTest Equipment System

To determine the health of the pipeline in quantifiable

terms:

◦ To determine if any defect detected by the online inspection would

fall at the uprated pressure.

◦ To determine if any existing defect can extend and cause failure

at the uprated pressure.

◦ To consider all other factors (e.g. cracks, extensive fracture

propagation) which could conceivably influence the integrity of the

pipeline at the uprated pressure.

Imperfection:

◦ May cause failure above the pressure that causes nominal yield

of the pipe.

Defect:

◦ Will fail at or below the pressure that causes nominal yield of the

pipe.

Critical Defect:

◦ Will fail at or below the maximum allowable operating pressure.

Metal Loss (corrosion and gouges)

Metallurgical (hard spots, inclusions, laminations, and

weld porosity)

Cracks (axial)

Cracks (circumferential)

Dents and buckles with or without metal loss

Figure-3: Imperfection and defect sizes

(36-inch-diameter × 0.375-inch wall thickness X60)

Design & construction of intelligent pig tools

with specific emphasis on Magnetic Flux

Leakage (MFL) technology.

Ideal pipeline would be:

◦ Be perfectly straight from end to end

◦ Have a constant ID with no weld penetration

◦ Be perfectly round

◦ Have an inside surface which was polished or epoxy coated

◦ Have no off-takes

◦ Contain no valves or any other device

◦ Be pumping a light, refined oil at a speed of about 1m/sec.

◦ Should be equipped with suitably designed pig Launchers/

Receivers.

Can be defined as the pigging that generates and

records some data for analysis for establishing the

health of the pipeline segment in quantifiable terms.

Contd…

PIGGING

UTILITY PIGGING INTELLIGENT PIGGING

For Pipeline Cleaning

Hydro-testing

Drying

Internal Coating

Condensate Removal

Product Separation

(Batching)

Decommissioning

Geometry Pigging Corrosion Monitoring

Based on

MFL Principle

Based on

Ultrasonic Principle

Conventional Pig Tool

High Resolution

Pig Tool

Transverse Field

Inspection Pig Tool

The objective is to find the location and size of dents

and ovalities in the cylindrical geometry profile of

pipelines.

Figure-4: Electronic Geometry Pig Tool

Drive-Cup

Locator-Unit

Odometer-Wheel

Digital-Data-Recorder

Pushing-Flange

Sensing-Finger

Transmission-Disc

Figure-5: Basic principle of

Magnetic Flux Leakage (MFL)

Figure-6: Principle of Ultrasonic (UT) Metal Loss

Detection Technique

Table 1: Types of ILI Tools and Inspection Purposes

ILI PURPOSE METAL-LOSS TOOLS CRACK-DETECTION

TOOLS

CALIPER

TOOLS

MAPPING

TOOLS

Magnetic Flux Leakage (MFL) Ultrasonic

(compressi

on wave)

Ultrasonic

(shear

wave)

Transverse

MFL Standard-

resolution

(SR) MFL

High-

resolution

(HR) MFL

METAL LOSS (CORROSION)

External corrosion

Internal corrosion

Detection, (A)

sizing, (B) no

ID/OD (C)

discrimination

Detection, (A)

sizing (B)

Detection, (A)

sizing (B)

Detection, (A)

sizing (B)

Detection, (A)

sizing (B)

No

detection

No

detection

NARROW AXIAL EXTERNAL

CORROSION

No detection (A)

No detection (A)

Detection, (A)

sizing (B)

Detection, (A)

sizing (B)

Detection, (A)

sizing (B)

No

detection

No

detection

CRACK AND CRACK-LIKE

DEFECTS

(Axial)

Stress corrosion cracking

Fatigue cracks

Longitudinal seam weld

imperfections

Incomplete fusion (lack of fusion)

Toe cracks

No detection No detection No detection Detection, (A)

sizing (B)

Detection, (A)

(D) sizing (B)

No

detection

No

detection

CIRCUMFERENTIAL

CRACKING

No detection Detection, (D)

sizing (D)

No detection Detection, (A)

sizing (B) if

modified (E)

No detection No

detection

No

detection

DENTS

SHAP DENTS

WRINKLE BENDS

BUCKLES

GOUGES

Detection (F) Detection (F)

sizing not

reliable

Detection (F)

sizing not

reliable

Detection (F)

sizing not

reliable

Detection (F)

sizing not

reliable

Detection (G)

sizing

Detection,

sizing not

reliable

In case of detection, circumferential position is provided.

LAMINATION OR INCLUSION Limited

detection

Limited

detection

Detection,

sizing (B)

Detection,

sizing (B)

Limited

detection

No

detection

No

detection

PREVIOUS REPAIRS Detection of steel sleeves and

patches, others only with ferrous

markers

Detection

only of steel

sleeves and

patches

welded to

pipe

Detection

only of steel

sleeves and

patches

welded to

pipe

Detection

only of steel

sleeves and

patches,

others only

with ferrous

markers

No

detection

No

detection

MILL-RELATED ANOMALIES Limited

detection

Limited

detection

Detection Detection Limited

detection

No

detection

No

detection

BENDS No detection No detection No detection No detection No detection Detection,

sizing (H)

Detection,

sizing

OVALITIES No detection No detection No detection No detection No detection Detection,

sizing (B)

Detection,

sizing (B)(I)

PIPELINE COORDINATES No detection No detection No detection No detection No detection No

detection

Detection,

sizing

(A)Limited by the minimum detectable depth, length, and width of the defects

(B)Defined by the specified sizing accuracy of the tool

(C)Internal diameter (ID) and outside diameter (OD)

(D)Reduced probability of detection (POD) for tight cracks

(E)Transducers to be rotated by 90°

(F)Reduced reliability depending on the size and shape of the dent

(A)Depending on the configuration of the tool, also

circumferential position

(B)If equipped to bend measurements.

(C)If the tool is equipped for ovality measurement

Shaped area indicates ILI technologies that can be used

only in liquid environments, i.e., liquids pipelines or in gas

pipelines with a liquid couplant.

MFL Technique

Based Tool

Ultrasonic Technique

Based Tool

Can be conveniently used for

liquid and gas transporting

pipelines.

Practically very cumbersome to

use for gas transporting

pipelines.

Indirect method of defect sizing Direct measurement of defects

Conventional MFL tool has relatively less number of

sensors and analog recording.

High resolution system is comprised of a greater number

of sensors and digital recording.

The sensor size and the axial sampling interval which

determines tool resolution and the ability to accurately

characterize the defect.

Contd…

Digital recording mandates that the continuous signals

from the sensors be sampled at discrete intervals. The

signal may be sampled as a function of time or distance

traveled. In the realm of in-line inspection, time based

sampling is undesirable due to the rather large

excursions in tool speeds encountered. The axial

sampling internal is preferred and is the distance along

the pipeline at which the analog waveform is sampled

and stored.

Contd…

A study was conducted utilizing the test setup depicted

in Figure-10 to determine the effect of sensor size on the

ability to resolve defects. The defect set was comprised

of three machined defects. The maximum depth of each

defect was 30% of bodywall. The axial separation

between the defects was 1.2 inches. The circumferential

separation between the defects was also 1.2 inches. It

should be noted that according to one of the typical

interaction criteria cited in Figure-1, these defects will not

interact and therefore need to be resolved by the sensor

system.

Contd…

In figures 11-13 the results of this study are shown. An

inspection of the results reveals that resolution in the

circumferential direction is indeed dependent on sensor

size.

Both the .25” wide sensor and the .5” wide sensor were

clearly able to resolve the machined defects both in the

axial and circumferential direction.

The .75” wide sensor and the 1” wide sensor displayed

increasing difficulty in resolving the defects in the

circumferential direction.

Contd…

Figure-7: Test Setup

Figure-8: .25 Inch Wide Sensor

Axial sampling interval affects defect characterization.

Axial sampling interval must be less than or equal to .10”

for accurate peak amplitude measurements.

Contd…

Axial interaction may occur if L3 is less than L1 and L2

Circumferential interaction may occur if W3 is less that W1 and W2

Axial interaction may occur if L3 is less than 1”

Circumferential interaction may occur if W3 is less than 6t, where t is

the wall thickness

Figure-12: Typical criteria for interaction

Figure-13: Axial Sampling Interval Versus Peak Amplitude

Figure-14: Typical High Resolution MFL Tool

Figure-15: Typical Transverse Field Inspection Tool

Drive System

Power System

Magnetization System

Sensor System

Data conditioning and recording system

Tool design parameters

Pipeline design & operating parameters

Magnetization Level

Sensor System

Figure-16: Typical Magnetization Curve

Figure-17: Flux Leakage at Three Magnetization Levels

Sensors between the magnet pole pieces measure the

flux leakage field. The purpose of sensor systems is to

convert the flux leakage field into a signal that can be

stored and analyzed.

Induction Coil System:

◦ The most commonly used type of sensor on MFL tools is an

induction coil. Induction coils incorporate several turns of fine

wire.

◦ A changing magnetic field induces a voltage across the wire.

◦ Therefore, no voltage will be induced when no defect is present.

When a imperfection causes flux to leak into the air, a voltage is

induced because the flux density is changing.

Contd…

Figure-18: Coil Sensor Basics

Hall-Effect Sensors:

◦ A charged particle moving (flow of electrons in a charged

conductor) in a magnetic field (leakage magnetic flux)

experiences a potential difference (voltage). This effect is known

as “Hall-Effect’ and voltage is called Hall Voltage.

◦ A magnetic field sensor directly measures the magnetic field. The

most common type is a Hall-effect sensor, which directly converts

the magnetic field level to an output voltage.

◦ Hall-effect sensors are also temperature sensitive, with a drift in

output voltage on the order of a tenth of a percent per degree

Celsius (-0.06 percent/degree F).

◦ Hall effect sensors require power to operate, of the order of tenth

of a watt.

Figure-19: Hall-Effect Sensor

An MFL tool contains a system that magnetizes a length

of the pipe wall. Typically, sets of magnets are used to

provide coverage around the circumference of a pipe.

Either permanent magnets or electromagnets are used.

Permanent magnets have a constant charge, and they

require no power to operate.q

Figure-20: Magnetizing Systems

The magnetization system in an MFL tool should

produce a magnetic field that is:

◦ Strong enough to cause a measurable amount of flux leakage at

defects,

◦ Uniform from inside to the outside surface of the wall thickness

so that changes in the magnetic field do not skew the results, and

◦ Consistent in magnitude along the length of a pipe so that

measurements can be compared at different locations during an

inspection run.

Permanent magnets Vs Electro-magnets

ALNICO Magnets

Rare earth magnets

Temperature sensitivity of magnets

Data generated is large:

Data points = (number of sensors) x (the number of

samples per unit distance) x (the distance traveled)

Data points = (2*24*pi) x (120 samples per foot) x

(100*5280) = 9,504,000,000 10 Billion data points

Tool designers use data conditioning systems to

compress the data and reduce storage requirements.

Figure-21: Data generating system

The data conditioning and data storage devices that are

used in an MFL tool require power to operate, as well as

some sensors. So, the battery power that is available

limits the mileage that can be inspected at any time.

The force exerted by gas or liquid pushing on a cup or

set of cups at the front of the tool pulls the tool through

the line. Differential pressure acting between the front

and back of the drive cups provides a force along the

pipe axis. This force propels the drive cups, which in turn

pull the rest of the tool

Figure-22: Drive System

The intelligent pigging should be considered as a multi

disciplinary project.

Expensive

Pre-inspection activities.

Field activities during intelligent pig run.

Post intelligent pig run activities including data

assessment.

Pull Through Test

Information review

Pipeline cleaning & geometry assessment

Placement of aboveground markers

The proposed intelligent pigging tool shall be calibrated

through pull through test at tool owning agencies works.

Test pipes shall have comparable wall thickness as the

actual pipe to be inspected.

Tool velocity during pull through.

Pull through test data regarding known defects should

coincide within acceptable tolerance limits with the

actual size of the defects including relative position.

TYPICAL PULL THROUGH TEST REPORT

Figure-23: Pull Test — Feature length comparison

Figure-24: Pull Test — Feature width comparison

Figure-25: Pull Test — Feature wall loss comparison

All pipeline features should be known & evaluated.

Presence of non-return/ check valves.

Presence of internal corrosion monitoring probes.

Internal cleaning is a must before launching the

intelligent pig tool.

Special cleaning pigs such as magnetic cleaning pigs

should be deployed.

Electronic geometry pigging is most advisable.

Marking systems are essential to have reference

locations which establish a relationship between the

locations of significant defects on the pipeline & those on

the survey charts.

The following two types of markets systems are currently

in vogue:

◦ Magnet marker system

◦ Aboveground market coils

Permanent magnet markers are placed at approximately

1 km interval.

The system is most effective.

Figure-26: Proper placement of a horseshoe marker magnet

Electro magnetic coils are provided by intelligent pig

manufacturers which can be placed directly over the

ground.

Pipeline Cleaning

Electronic Geometry Pigging

Launching

Pig Tracking

Receiving

Of late, pipeline owners require XYZ mapping data

acquisition preferably to be done concurrently with the

MFL tool run.

XYZ mapping was developed to determine

3-Dimensional graphical pipeline coordinates. Inertial

navigation unit is attached with the MFL tool.

The major advantage of XYZ mapping is that all the

anomalies detected on the pipeline can be located with

XYZ coordinates assigned to these features. This

facilitates defect identification in the field very accurately

without any hassles.

Figure-27: Typical Launcher/Receiver Arrangement

Defect Verification

Data Analysis

Reporting

Flaw selection

Flaw verification procedure

Figure-28: Defect verification

Figure-29: Data analysis

The typical final inspection report shall consist of the

following information:

◦ Tool operational data,

◦ Pipe tally,

◦ List of features,

◦ Summary and statistical data,

◦ Fully assessed feature sheets, and

◦ Defect assessment method.

Data sampling frequency or distance;

Detection threshold;

Reporting threshold, normally taken at 90 percent POD,

if not specified otherwise;

A tool velocity plot over the length of the pipeline;

Optionally, a pressure and/or temperature plot over the

length of the pipeline; and

In case of MFL pigs, the magnetic field strength H in

Am-1.

The pipe tally list shall contain the parameters:

◦ Log distance, in m;

◦ Joint number giving log distance at upstream girth weld;

◦ Joint length, in m; and

◦ Description of installation.

The list of features shall contain the following

parameters:

◦ Log distance;

◦ Joint number;

◦ Nominal pipe wall thickness or reference wall thickness as

measured by the tool;

◦ Feature description adjacent to girth weld;

◦ Distance to upstream girth weld;

◦ Orientation;

◦ Feature length, width and depth;

◦ ERF (Estimated Repair Factor); and

◦ Internal/external/mid-wall indication.

Total number of metal loss features,

Number of internal metal loss features,

Number of external metal loss features,

Number of general metal loss features,

Number of pits,

Number of axial and circumferential grooves,

Number of metal loss features with depth 0-9 percent,


Contd…








Number of metal loss features with 0.6 ≤ ERF ≤ 0.8,

Number of metal loss features with 0.8 ≤ ERF ≤ 0.9,

Number of metal loss features with 0.9 ≤ ERF ≤ 1.0, and

Number of metal loss features with ERF ≥ 1.0.

Fully assessed feature sheets shall contain the following

information to the full sizing specification:

◦ Length of pipe joint and orientation of longitudinal seam (when

present),

◦ Length and longitudinal seam orientation of the 3 upstream and 3

downstream neighbouring pipe joints,

◦ Distance of upstream girth weld to nearest upstream marker,

◦ Distance of upstream girth weld to nearest downstream marker,

◦ Distance of metal loss feature to upstream girth weld,

◦ Distance of metal loss feature to downstream girth weld,

◦ Orientation of metal loss feature,

◦ Feature description and dimensions, and

◦ Internal/external/mid-wall indication.

Accidents appear to fall into three main areas of

handling pressurized equipment, loading and unloading

of pigs and defective equipment such as pressure

gauges.

Pyrophoric materials

Hydrate precautions

Slug collection

Notwithstanding, the best of preparation and planning,

the occurrence of contingency situations cannot be

completely ruled out.

Contingency arising out of stuck pig

Contingency due to sudden stoppage of flow

Sudden failure of pipeline

Contingency arising due to excess amount of

condensate/water mixtures and/or black dust/iron oxide

coming out along with cleaning pig or Intelligent tool

shall be taken care.

Figure-30: Typical Line

Preparation/ Inspection

Programme

A changing magnetic field passing by an electrical

conductor will produce a current in the conductor. An

MFL magnetization system traveling down a pipeline

represents a changing magnetic field. The pipe is an

electrical conductor. Therefore, current will be induced in

the pipe.

Increasing the velocity of a tool reduces the applied field

strength by inducing eddy currents.

For the 10-mph case, the magnetic field in the pipe

drops 10 percent. So, the applied field is reduced, which

affects detection and characterization.

Figure-31: Calculated applied fields as a function of velocity

Stress in a pipeline arises due to gas pressure in the

pipe, residual stresses from the fabrication process, field

bends, ground shifts, etc. Metal-loss regions act as

stress risers that increase the effects of stress even

further.

Stress effects are complicated because stress affects

the overall (bulk) permeability of a steel, and it affects

the local permeability at a metal-loss region.

A change in the local permeability at a metal-loss region

can produce significant changes in the amplitude and

shape of the leakage field.

Contd…

As stress increases, the signal amplitude initially

decreases up to 25 percent, then increases passing the

initial amplitude, and continues to rise for practical

operating stresses.

Stress affects detection and characterization because it

affects applied flux densities and leakage fields.

Additional research is needed to better define the effects

of stress.

Remanent magnetization also affects the applied

magnetization level. Remanent magnetization is the

magnetization level left after a tool passes.

Pipeline steels exhibit a hysteresis effect when

magnetized; specially, when the applied field is removed,

a flux density is left in the pipe.

Complete data on pipeline.

Anticipate tool anomalies.

ILI is not the panacea of all the troubles.

Select appropriate (Fitness-for-Purpose) tool.

ILI is expensive & resource consuming activity.

Detection, Identification and sizing of the metal loss

features with a confidence level and probability of

detection are called Defect characterization. All the metal

loss features need to be characterized with at least 80

percent confidence level and 90 percent probability of

detection.

Pin Hole

Pitting

General Corrosion

Axial Grooving

Circumferential Grooving

Slotting

Figure-32: Geometrical representation of

metal loss feature definitions

Figure-33: Location and dimension of metal loss features

As per ASME B31G

There are four levels of evaluation mentioned in ASME

B31G – 2009 i.e. Level 0, Level 1, Level 2 and Level 3.

Contd…

Nomenclature:

Contd…

As per original B31G:

Contd…

As per modified B31G:

Contd…

Level 0 Evaluation:

◦ ASME B31G provides tables of acceptable lengths of corrosion.

◦ The maximum depth of corroded area & longitudinal length is

measured corresponding to the size of pipe.

◦ It can be directly located in the tables corresponding to various

dia of pipelines

◦ Metal loss is acceptable if its measured length does not exceed

the value of L given in the corresponding table.

Contd…

Level 1 Evaluation:

◦ Measure the maximum depth of the corroded area & longitudinal

extent of corroded area.

◦ Define an acceptable safety factor, SF.

◦ The flaw is acceptable where SF is equal to or greater than

SF × So, or where PF is equal to or greater than SF x Po.

Contd…

Level 2 Evaluation:

◦ Level 2 evaluations are performed using what is known as the

Effective Area Method.

◦ The Effective Area Method is expressed as follows:

Contd…

Level 3 Evaluation:

◦ A Level 3 evaluation typically involves a detailed analysis, such as

a finite element analysis of the corroded region.

Contd…

Figure-34: Parameters of metal loss used in

analysis of remaining strength

Contd…

Axial interaction may occur if L3 is less than L1 and L2

Circumferential interaction may occur if W3 is less that W1 and W2

Axial interaction may occur if L3 is less than 1”

Circumferential interaction may occur if W3 is less than 6t, where t is

the wall thickness

Figure-35: Typical criteria for interaction

icepim 2015 international conference on pipeline integrity

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