Problems faced by Industries during

PipelineTransportation

Exposures

Leaks Encroachmens

Fire

Table 1: Causes of pollution expressed in the study area

expressed in percentage (author-Newcastle University, UK,

2012)

• Sources No of respondents Percentage

well leakage 4 13

• Pipeline related sources 20 67

• Reservoir/tankers related 1 3

• Facility failures/ ageing 5 17

Classifying leak detection

technologiesWe distinguish them in three categories:

• automated detection - complete monitoring systems that, can report the detection of a gas leak without the need of a human operator, once they are installed (e.g. infrared sensors, fiber optic or cable sensors).

• semi-automated detection - solutions that need a certain amount of input or help in performing some tasks (e.g. statistical or digital signal processing methods)

• manual detection - systems and devices that can only be directly operated by a person (e.g. thermal imagers ).

Methods currently used and their

problems

• Low Orbit Satellite Imaging->Off line system : Once per month + image processing time ,Not effective if clouds present,Under ground pipeline : Hence nothing visible : Not sure whether we are looking at the images of land above our pipeline.

• Helicopter Surveillance->In worse weather conditions, helicopter surveillance becomes impractical,Possibility of human error

• Sonic vibration sensors->Risk of spurious alarms due to movement of vehicles etc.

• Optical Fibre based monitoring

• Meters are installed at at certain intervals and cumulative is checked that is net accumulation in a control volume should be zero->not a continuos method so will take time to detect where is the leakge

COMPARISON OF VARIOUS

TECHNOLOGIES

Technology Parameter/ Criteria

Monitoring Additional

equipment

requirement

Procesin

g time

Probabilty

of false

alarms

Maintenan

ce

Cost

Online Sonic

sensors/ Threat

scan

Online Yes Continu

ous

High Required Very

High

Satellite

Imaging

Fixed No Fixed

frequen

cy

No No High

Optical Fibre

based

monitoring

Online Yes Continu

ous

High Required Very

High

Helicopter

monitoring

Fixed

frequency

No Fixed

Frequen

cy

NO No Low

The Motivation• The specific goals of pipeline leak detection include desired

sensitivity, leak detection time, leak location capability, accuracy of leak volume estimates, and adaptability of a given technology to routine and non-routine activities.

• The system presently used detects gas leakage but the industrieswant it on ppm and ppb level

• For cost cutting linemen are used who use soap solution at joints to check which is not much reliable.

• As important as detecting a leak is, the controller’s response is equally critical. There have been several cases where the leak detection system detected an actual leak and declared an alarm which was ignored by the controller so shifting to fully automated rather than manual and semiautomated

• The pipeline leak detection system should be able to detect a leak as small as 0.5 percent (%) of the daily throughput.

Solutions that can be used

• There are internally (observing hydraulic behavior) and externally (released fluid detection) based(Pipeline Leak Detection) PLD technologies. Computational pipeline monitoring (CPM) is an internally based PLD technology CPM uses pressure, flow, temperature, and/or acoustic instruments to measure single or multi-phase fluid parameters within a segment of pipeline. A Supervisory Control and Data Acquisition (SCADA) system monitors, processes,transmits, and displays the pipeline data to a controller in a control room. Using computer software programs to analyze the information and issue an alarm when a leak is detected

• External methods include hydrocarbon vapor or liquid-sensing devices such as infrared sensors as well as aerial surveillance along pipeline corridors. chemical sensors, and electrical sensors.

What is a good leak Detection

System

10

Pipeline Configurations

Real Time Transient ModelInternally-Based System

• RTTM means “Real-Time Transient Model”.RTTM LDS(leak Detection System) use mathematical models of the flow within a pipeline using basic physical laws such as conservation of mass, conservation of momentum, and conservation of energy.

• RTTM methods can be seen as an enhancement of balancing methods as they additionally use the conservation principle of momentum and energy. An RTTM makes it possible to calculate mass flow, pressure, density and temperature at every point along the pipeline in real-time with the help of mathematical algorithms.

• RTTM LDS can easily model steady-state and transient flow in a pipeline. Using RTTM technology, leaks can be detected during steady-state and transient conditions.

• With proper functioning instrumentation, leak rates may be functionally estimated using available formulas

12

Software Method - RTTM

AdvantagesIt takes into account the configuration of the pipe as well as the product characteristics.

Very fast in detection and location

Very less probability that it will produce False Alarms.

Involves computer simulation of pipeline conditions using advanced fluid mechanics and hydraulic modeling.

Can be used for anykind of Pipeline whether it is Underground or Overground or small or big.

Measuring purely the flow won’t show up the true leak. RTTM measures the temperature and pressure at outlet and inlet. A robust set of algorithms calculates the flow.

13

Software Method – Gradient Intersection

Xleak

14

Simulation Procedure - Leak in Pipe 8

Calculator

Leak induced in Pipe 8

Optimizer

15

Simulation Results- Leak in Pipe 8

Leak Simulated

Pipe 8

Location(m) 450

Magnitude(kg/s) 2.611

Measured Flow 4.946

Measured Pressure (kPa)

2160.1

PipeFunctional Values

1 126.678

2 97.438

3 101.864

4 123.710

5 126.447

6 126.447

7 63.294

8 0.151

9 159.922

Estimated

Magnitude(kg/s)2.609

Estimated

Location(m)450

Analysis of Pipeline Leak Detection

System

How calculations are done

Balancing SystemsUses the principle of mass conservation

Basic equations used in RTTM are:

Continuity equation:

Momentum Equation:

Energy equation:

dt

dMtMtM L

OI =− )()(..

0=∂

∂+

x

v

dt

dρ

ρ

0.1

=+∂

∂+ Df

x

p

dt

dv

ρ

0.1

=−− Lldt

dp

dt

dh

ρ

Variables invoved in equation

04-Nov-14

In this model Energy Conservation is not of that

significance because it does not help in leak

detection.

It should be mentioned that this model is only for

the pipeline flow in single phase gas or liquid .

Modelling multiphase flow is much more complex

and accuracy is not sufficient to be used in pipeline

leak detection

Practical Test of the Model

DIAGNOSING AND LOCATING OF THE LEAKAGE

04-Nov-14

04-Nov-14

04-Nov-14

04-Nov-14

• An RTTM module calculates estimates M_i,M_o for mass flow at

inlet and outlet, respectively. This can be done using measurements

for pressure and temperature at inlet (P_i, T_i) and outlet (P_o,

T_o). These estimated mass flows are compared with the measured

mass flows m_i,m_o yielding the residuals x=M_i - m_i and y=M_o

- m_o. These residuals are close to zero if there is no leak;

otherwise the residuals show a characteristic signature. In a next

step, the residuals are subject of a leak signature analysis.

Assumptions

• Isothermal pipeline flow

• Newtonian fluid

• Fully Developed Laminar Flow

• Leakage treated as flow through orifice

• Steady State

Solution

Discharge Coefficient

• The discharge coefficient is the ratio of the actual

discharge to the theoretical discharge, i.e., the ratio of

the mass flow rate at the discharge end of the nozzle to

that of an ideal nozzle which expands an identical

working fluid from the same initial conditions to the same

exit pressures.

34

Software Method – Gradient Intersection

Xleak

For a simple horizontal pipeline Pressure drops linearly if friction factor f and pipe diameter D are constant along the pipeline and in absence of a leak. If a leak occurs at leak location x_leak, upstream pressure drop will increased and downstream pressure drop will decreased .Practically the pressure drop can be determined by using double sensor s1 and s2 with known distance between them l_12 at upstream and another pair s3 ,s4with distance l34 at downstream

Disadvantages

– It is a complex way of leak detection requires trained personnels and maintenance

– The RTTM method costs much more than the other methods

– Errors in instrument calibration could raise false alarms

– The accuracy of RTTM is limited by multi-phase flow measurement accuracy

CONCLUSION