00022443THE APPLICATION OF A CONTINUOUS LEAK DETECTION SYSTEM TO PIPELINES AND ASSOCIATED EQUIPMENT

8/18/2019 00022443THE APPLICATION OF A CONTINUOUS LEAK DETECTION SYSTEM TO PIPELINES AND ASSOCIATED EQUIPME…

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THE APPL ICATION O F A C ON T I N U OU S L EAK D ET EC T I ON SYSTEM

TO PIPELINES A ND ASSOCIATED EQ UIPMENT

Copyright Materail

IEEE

Paper

No

PCIC-88-45

Chet Sandberg PE, Jim Holmes, Ken McCoy, Heinrich Koppitsch

Raychem Corporation

300

Consti tution Dr. Menlo Park CA 94025

Abstract

In recent years the problem of leak detection in pipelines,

tanks, and process vessels has been the focus of many man-

hours of effort.

This paper will look some examples of leaks

occurring in pipelines, give a overview of classical eak detec-

tion systems and give the engineering basis of a new type of

detector system. This system is a flexible hydrocarbon sens-

ing cable that can be installed along pipelines, in double con-

tainment tanks and piping or in trenches to detect and locate

leaks of common ndustrial hydrocarbon solvents or fuels while

ignoring the presence of water. The simple electrical circuit is

also described hat locates and detects a leak anywhere along

the length of the sensor.

Introduction

Leaks of hazardqus fluids such as crude oil, gasoline, or

chlorinated solvents can result in very serious environmental

pollution f the leak is not quickly detected and repaired. Even

domestic drinking water may become contaminated with toxic

chemicals f the groundwater supplying aquifers and wells be-

come contaminated with leaking Hydrocarbons. The

U.S

En-

vironmental Protection Agency (EPA) has proposed

regulations designed to prevent contamination of groundwater

from the estimated 1.4 million underground storage tanks in

service. This focus on leak detection is just as serious in the

area of transmission pipelines. In one instance approximate-

ly

30,000

arrels of No. 2 fuel oil was lost as a result of a leak

in a buried pipeline n suburban New Castle County, Delaware.

When the leak was investigated, t was found to be less than 1

gallon per minute. The fuel oil seeped into the water table and

threatened a downgradient stream and irrigation pond. Even

though recovery wells were drilled, only about 10%of the fuel

oil was recovered and significant economic resources were ex-

pended(1). Continuous eak detection of small eaks has been

difficult in the past, but a new technology is available to con-

tinuously monitor pipeline transmission of hydrocarbons.

Types of leaks in pipelines and piping systems

Various types of leaks can occur in pipelines and piping sys-

tems and there are various types of leak detectors to analyze

each. The rupture eak is east common, but very dangerous.

Catastrophic failure can cause significant damage to the en-

vironment, especially in under sea and remote land applica-

tion. These leaks are, however, he easiest to detect since hey

are accompanied by easily measured pressure drops or

volume discrepancies.

A

more difficult and equally dangerous leak is the small, hard

to detect leak. Corrosion, erosion, weld or joint failure and

fatigue can all lead to small leaks. Leaks as small as

1

gallon

per hour can build up large lost volumes before they are

noticed. Up to now, these types of leaks have been almost im-

possible to detect with conventional means described below

in the section Current Leak Detection Methods. The

hydrocarbon sensor described later in this paper is the first

economically feasible distributed system available to monitor

pipelines or small or large leaks.

Current Leak Detection Methods

Leak detection systems are classified nto wo main categories,

static and dynamic. Dynamic systems are preferred since they

can be used while the pipeline is operating. Static leak detec-

tion methods are useful after a leak has been detected n order

to find its location. Continuous monitoring of pipelines gives

rise to a number of leak detection echniques. Meter variance

or compensated volume balance is the predominate method.

This method s limited by the accuracy of the volume measure-

ment and the variations associated with it. Pressure monitor-

ing and rate of flow can detect large leaks and over-and-short

calculations can detect smaller leaks. Differential-pressure

transmitters across sectionalizing valves can continuously

monitor for a negative pressure which indicates a large leak.

Another method was attempted by wrapping an oil soluble

tubing around certain critical sections of pipeline. The internal

pressure of this tubing was then monitored for

loss

of pres-

sure. However, this system was a complete failure and aban-

doned

(2).

Compensated Volume Balance

The current major method of leak detection is the compen-

sated volume balance method. This method essentially

measures the volume in and subtracts the volume out .

There are meters which are guaranteed repeatable to within

.05 . In a typical system such as one in operation in Alaska

from the Tesoro Nikiski refinery on the Kenai Peninsula to

Anchorage 3), n alarm will sound when there is a significant

difference in volume. The pump station management will

determine

f

the difference in the two measured volumes is the

result of an operational change or

if

the pipe s leaking. Opera-

tional changes can result from a change in product grade,

change of pumps or pumping pressure, or a change in

temperature because of storage tank changes.

If

there has not been a change in operational criteria, the

pipeline will be shut down and sections blocked with valves to

isolate he possible eak. If before shutting down the pipeline,

the discrepant volume should increase by a factor

of

2 the

pumping stations will automatically be shut down. Should a

241

88CH2661-7/88/0000-0241 01.00 988 IEEE


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rupture of the pipeline occur a negative surge will travel back

to a pumping station and will be detected by a suction- pres-

sure switch and the pipeline will be shut down. Vibratory sen-

sors are located at the pumping stations and will detect an

earthquake of 3.0 on the Richter scale and shut down the

pipeline.

The problem in the compensated volume method is there

usually needs to be a large volume before conclusive leak

detection can be made. Leaks of 2% for liquids and 10% for

gasses are needed for detection, accord ing to some

authorities. Smaller leaks can be can be detected with a non-

linear adaptive state basis

on

pressure and flow measure-

ments at the inlet and outlet. 4) However, based on flows of

IO bb/hr., the leaks can be significant before they are

detected.

Acoustic Traveling Pig

A

novel leak detector is the Texaco pig which detects a leak

by sensing the acoustic energy generated by escaping fluid.

The location is recorded by an on-board odometer and this

data correlated to the ultrasonic data thereby detecting the

leak. The leak detector instrument is articulated in four sec-

tions: two for rechargeable batteries, one for a printer, and

one for the hydrophone and circuit cards. The articulated Pig

is used on pipe sizes from

6

in to

10

in. Twelve inch pipe is

checked by a model having all components in a single section.

5)

Leaks were successfully detected and located by the pig

in field pipelines in Canada and Texas.

Thermal and electro-optical methods

An airborne remote sensor can detect leaks from natural gas

pipelines by monitoring he methane and ethane gas in the at-

mosphere above the pipeline. The sensor is a passive electro-

optical system, operating in a downward-looking mode. It is

designed to detect low levels of methane and ethane by look-

ing at their infra-red spectral signatures using a non-dispersive

gas filter correlation technique. This system is experimental

and the results of the field trials are unknown to the authors.

6)

A

similar airborne system using thermal infrared images has

been tested on water distribution systems in South Dakota. A

typical system has from

640

to 2400 KM of pipeline and the

normal line water loss is 10 to 15 per cent. Major leaks,

generally from

10

to 200 cubic meters per day, are easy to

identify because they usually pond. Minor leaks, called

seeper leaks, which generally range from 2 to

10

cubic

meters per day are more common and are difficult to detect

using conventional ground surveys. Fifteen possible leaks

were identified from thermal images. Five of these sites were

eventually confirmed as leaks.

7)

Hydrocarbon distributed sensor cable

The hydrocarbon sensor system

8 )

consist of an alarm

module and sensing cable. This sensing cable provides dis-

tributed coverage by detecting eaks of most uels and solvents

at any point along its length. The cable can be used in engths

of up to

2

Kilometers with a resolution of approximately

1%

of

the length for leak detection. The core of the cable, Figure 1,

is constructed of an alarm signal wire, a continuity wire and

two sensor wires. It is encased in a conductive-polymer ayer

242

signal

sensor

.

--

cbnductive Halar'

polymer layer braid

Figure 1

that swells during exposure to most hydrocarbon-based

sol-

vents and fuels. This material is surrounded with a Halar (9)

braid that restrains outward swelling. When a solvent or fuel

contacts the cable, the conductive- polymer swells inward and

makes electrical contact with the two sensor wires. The cable

must be replaced once it has contacted a solvent or fuel.

This sensor has combined unique radiation chemistry and con-

ductive polymer technologies to develop an industrial system.

The conductive polymer formulation is key to the success of

the device. The formulationmust swell rapidly and remain con-

ductive if the sensor is to detect the fluid of interest. Addition-

ally, the polymer must develop sufficient swelling pressure to

force the conductive formulation through the apertures of the

braided sensing cable to contact the sensor wires. If the

polymer is not crosslinked t will not swell, but simply dissolve.

Therefore, the formulation

is

crosslinked using radiation

chemistry to form a solvent-swellable, three dimensional

polymer network. The expansion pressure generated by this

network is a function of the crosslink density and interaction

between the polymer and solvent. (10 and 11)

Two formulations were developed to cover the range of com-

mon industrial solvents and fuels. One formulation was

developed to swell rapidly in non-polar hydrocarbons such as

diesel fuel and gasoline and was used to prepare a fuel sens-

ing cable. Another formulation was used o fabricate a solvent

sensing cable for the detection of polar fluids such as

chlorinated solvents.

Although the time taken for the sensing cables to respond in

a given fluid is a key property of the sensor, other factors must

also be considered. The cable must be rugged, yet flexible,

so that it can be easily pulled through double containment

enclosures. The formulations must not beso soft that any ac-

cidental oading will cause the conductive polymer formulation

to contact the sensor wires and trigger the circuit. Finally the

conductive polymer layer must be continuous and act as a

water barrier to prevent the sensor from triggering.

Testing was conducted on several thousand feet of sensor

cable with a nominal outside diameter of 0.3 inches. The con-

ductive polymer layer was cross-linked using a high energy

electron beam. The cable was cut into convenient engths. An

initial resistance of greater than 30 megohm was measured

and specified to be equivalent to a sensor in its non-triggered

state. Five cm. of the cable was completely mmersed n a fluid

and the time taken for the resistance o fall below 20 kilo-ohms

was measured. This time represents the response time of


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the sensor since the alarm and locator module register the

presence of a fluid at this resistance value. Response time

after water immersion, bend diameter and pressure triggering

were also measured. The tests showed the resistance be-

tween sensor wires remained greater than 30megohms after

water immersion, a bend radius of less than 5 cm was needed

to trigger the cable and a minimum trigger load of 20 pounds

per linear inch was needed to trigger the alarm.

Fuel sensing cable response times are dependent on the

molecular weight of the target hydrocarbon.

Gasoline takes

15

minutes, while diesel

2

and Toluene take

60

minutes.

Automatic ransmission luid takes 4 to 6 hours. This response

time is based on 2 inches of cable length immersed n the liq-

uid whose temperature is 20 deg C.

Response times are af-

fected by operating temperature.

Electrical Circuitry for Leak Detection

The hydrocarbon sensor makes use of a four wire circuit

shown schematically n Figure2. The sensing electrodes are

represented by the zigzag lines, while the insulated telemetry

pair are indicated by the solid lines on the top and bottom of

the circuit. The key elements of the leak locating circuitry are

High lmpedence Voltmeter

onstant Current Source

Hydrocarbon Sensor Electrical Schematic

Figure

2

the constant current source and the high impedance volt

meter. Also note that the four conductors are joined to form

two loops at the far end of the monitored section.

If

the cable has not been swollen by a hydrocarbon eak, there

is no path between the two electrodes and no current flows

from the constant current source. As shown in Figure3, a leak

that swells the polymer between he two electrodes completes

the loop and the current source can now generate a current

flow in the closed circuit.

Hydrocarbon Sensor Electrical Schematic

Figure

3

The high mpedancevoltmeter s now used o measure the volt-

age drop,

V,

between the leak location and the instrument.

Since the current is known (i. e. a constant current source) and

the voltage is measured, the resistance of the cable between

the leak and the instrument can be calculated using Ohms

R=V/I . Finally, if the resistance per meter of cable is known

(this is controlled by accurate manufacturing olerances) then

the location in terms of distance is a simple scale conversion.

Long Pipeline Telemetry

Since the effective range of the hydrocarbon sensor is about

2 KM, continuous surveillance of a long pipeline needs some

sort of telemetry o relay leak detection nformation o a central

location. The type of telemetry equipment chosen is common-

ly used in the telephone industry to monitor pressure

transducers attached to pressurized telephone cable. The

variations n air pressure are converted o a variable resistance

by the pressure transducer. The variation in resistance is in

turn used to modulate a signal on the two wire telemetry cir-

cuit

so

that the equipment located at the end of the line is able

to determine the air pressure at each of the transducer loca-

tions. The transducers are each assigned an individual iden-

tity at the time of installation. The multiplexingscheme is based

on a time splice echnique so that only one of the many trans-

mitters on a given line is transmitting ts measured value at any

given time. The master unit at the head of the line starts the

report ing sequence by a voltage step monitored by all units.

For detection of a hydrocarbon leak, the pressure transducer

is replaced by a loop formed from the sensor pair in the

hydrocarbon sensor cable and an end of line resistor.

If

the

cable is in a non-triggered state, then the transducer circuit

sees a predicted resistance value and the signal returned to

the monitoring equipment is within the normal range.

If

the

cable has been soaked by a hydrocarbon, he resistance seen

by the transducer on the monitoring equipment is shifted

downward in frequency and the monitor recognizes the leak

occurrence. If the sensing oop is broken, the transducer sees

a sudden rise in resistance. The signal returned o the monitor

is shifted up n requency and he monitor recognizes an open

in the sensor.

When a leak is detected, maintance personnel must go to the

monitor location and hook up a Portable Test Box (PTB) to

determine he exact location in the 2 KM section of leak detec-

tion cable. Three different situations can occur to trigger an

alarm. There can be a continuity fault, a single contamination

site on the sensing cable or multiple contamination sites on the

sensing cable. The PTB can be used to determine which of

the three possibilities are present.

Conclusion

The hydrocarbon sensor has shown itself to be a significant

advancement in the technology available for leak detection.

Distributed systems have in the past not been economically

feasible for pipelines and other large systems, leaving volume

balance systems o determine eaks.

As

discussed, he volume

systems have limitations on low leak rates, which the sensor

cable system does not have. The hydrocarbon sensor can be

used for tank farms, ponds, and double containment piping

systems(l2). The same electronic systems can be used for

water sensor cables and acid and base sensor cables.

243


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References:

1. McNally, Joseph. et al, Containment and Removalof Fuel

from Groundwater Beneath a Densely Populated Housing

Development, Proceedings API 1985 Oil Spill Conference

(Prevention, Behavior, Control Cleanup), Los Angeles, CA

Feb 25-28 1985

2. Berto, FrankJ., Computer Aids Line-Leak Detection, Oil

and Gas Journal v71 n49 Dec 3 1973 p 41-47

3. Ewing, Robert C.,

Alaska’s Nikishi Product Line Com-

pleted,Oil and Gas Journal, v 74 n 39 Sept 27 1976 p 76-82

4. Billmann, L., et at, Leak Detection Methods or Pipelines,

Conference Title: Bridge Between Control Science and Tech-

nology, Proceedings of the Ninth Triennial World Congress of

IFAC, Volume 4: Process Industries, Power Systems) IFAC

Proceedings Series 1985n 4 p 1813-1818

5. Flournoy, Norman E., et at, Development

of

a Pipeline

Leak Detector, Journal of Canadian Petroleum Technology

vi7 n3 July- Sept 1978 p 33-36

6. Lee, H. S. et al, Gas Pipeline Leak Sensor Gaspils) for

Airborne Use, Internationat Conference on Pipeline Inspec-

tion. Edmonton, Alberta, Can June 1983 p 555-565

7. Eidenshink, J. C., Detection of Leaks in Buried Rural

Water Pipelines Using Thermal Infrared Images,

Photogrammetric Engineering and Remote Sensing v51 n5

May

1985

p 561-564

8. Raychem Corporation,TraceTek Fuel and Solvent Sens-

ing Cables, Literature Number H52858 August 1987

Halar is a registered trademark of Allied Corporation

10. Treloar, L. R. G., The Physics of Rubber Elasticity,Ox-

ford University Press, London, p 123, 1985

11. Gehman, S .

D.,

Rubber Chem. Technology, 40(21), p

632, 1967

12. National Engineer, New Pipe System Stops Leaking

Fluid Lines,v91 n4 April 1987 p 15

13. Williams,

R.

I. Fundamentals of Pipeline Instrumenta-

tion, Automation, and Supervisory Control, ISA Transactions

v 21 n l 1982 p 45-54

14. Fannelop, Torstein K. Flow Processes and Leak Rates

Associated with Broken Underwater Oil Pipelines, Nor-

wegian Maritime Research v5 n l 1977 p 6 13

15. Nicholas, R. E., Leak Detection by Model Compensated

Volume Balance, Pipeline Engineering Symposium 1987 Dal-

las Texas Feb 15- 18, 1987, p 13-20

16. Pipes and Pipelines International,

New Pipeline Leak

Detection Pig, v21 n4 Aug 1976 p 26-28

18. Fukuda, T., et al, Leak Detection and Localization in a

Pipeline System Based on Time Series Analysis Techni-

ques, Journalof Fluid ControlVIn4 Dec 1983 p 5-17

19. Lippitt, T.,

Williams Pipe Leak Detection System,

Pipeline Engineering Symposium 1987 Dallas Texas ASME

PD v6 p 35-41

20

Atherton, David, Magnetic Detection

of

Pipeline Cor-

rosion, Proceedings lnternation Congress on Metallic Cor-

rosion, Toronto Ont Canada, v4 p 151-156

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Leak Detection, Oil and Gas Journal v85 n29 July 20, 1987 p

42-47

Chet

Sandberg,PE,

received his

BS

degree from MIT

in

1967 and his

MS

from Stanford University n 1972. In 1972 he oined the Raychem Corpora-

tion in the Chemelex Heating Systems Division. He has held various posi -

tions at Raychem including Technical Strategy Manager, Electrical

Engineering Manager of the Chemelex Division and Consumer Products

Division Manager. He has managed and participated in research and

development of fiber optic sensors, conductive polymer heating elements

and process instrumentation systems. Chet is a Professional Electrical En-

gineer

in

he State of California, hdds

5

patents and has published Over

I5

technical papers on fiber optics, sensor technology, and electric heat trac-

ing. Chet is a member of IEEE, ASME and ISA. and is chairman of the IEEE

622 Working Group on Heat Tracing. He s a founder of several small star-

tup companies in the Palo Alto area where he l i e s with his wife and

daughter. When not inventing, he loves to ski, sail and keep his 80286 PC

humming.

Jim Holmes

is

the Technical Director

of

Raychem’s TraceTek Products

Group. He started with Raychem n 1977 and

has

worked in development

and technical positions with Raychem’s elecommunications products and

pipeline corrosion protect ionproducts prior o his current position. He has

a B.

S. in

Product Design rom Stanford University and anM

S.

n Engineer-

ing Management rom Stanford University.

Ken McCoyreceivedhis BSEEdegreefrom NorthwesternUniversity n 1971

and an MBA from the University of Santa Clara in 1976. After serving with

the United States Navy and a period of consulting work with SRI Internation-

al, he joined Raychem in 1977. Ken held various positions with the

PetrdeumTechndogy Divisionand was involvedwitha number of corrosion

control products used as pipeline coatings and for cathodic protection. In

1984, Ken was part of a small start-up group that formed the TraceTek

Division. He is now the operations manager or TraceTek and combines his

manufacturing responsibilities with sales support and marketing in the

Pacific Rim countries. Ken spends his free time on the ski slopes or sailing

on San Francisco Bay.

HeinrichKoppRsch received his Dipl. Ing. degree from Technical Univer-

sity, Graz, Austria in 1974. He then worked at Waagner- Biro in technical

sales of turnkey power plants. Heinrich received his MBA at h e a d , France

in 1980. He oined Raychem n 1980 and has held various sales and market-

ing positions with the Chemelex Division n Germany, France and he United

States. He is currently Marketing Manager for the TraceTek Products

Group.

17.

Butts,

E. O., Detecting Leaks in Pipelines and Storage

Tanks, Engineering Journal (Montreal)v6 n3 May-Jun 1977

p45-47

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00022443THE APPLICATION OF A CONTINUOUS LEAK DETECTION SYSTEM TO PIPELINES AND ASSOCIATED EQUIPMENT