IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. IA-12, NO. 4, JULY/AUGUST 1976

Minicomputers Used in Metering and Leak DetectionSystems for Liquid Petroleum Products Pipelines

R. D. PHILLIPS AND CHARLES W. CRIDER, MEMBER, IEEE

Abstract-The use of minicomputers as part of a product meteringsystem is new and relatively expensive. The use of minicomputersis discussed from the following: 1) its advantage, practical limitationsand disadvantages; 2) Colonial Pipeline Company's approach and de-sign of computer aided metering systems for certain locations. Com-puter controlied leak detection is discussed from the following: 1)summary of leak detection systems to date with success and problemsof each; 2) Colonial Pipeline Company's use of a minicomputer to con-trol 10 independent lateral lines using pressure drop, flow rate, meter-in versus mneter-out to automatically shut down the line and close outas required. Design of the system, operating procedures, problems, andevaluation are discussed.

INTRODUCTION

T1HERE are two approaches a company can take whenstudying the use of small computers. One is to use a

"computer-type black box," that will perform specified func-tions in much the same manner that a hard-wired machine cando. This is a valid approach and is commonly used, but itgenerally limits the use of the minicomputer. The costs ofsmall processors are declining enough so that the "plug in"concept of repair can be used.

The second approach is to use the computer as an "on line"process computer and to have it perform as many functions aspossible, limited only by the reliability of sensor informationand the ability of the company computer staff to design, pro-gram, and maintain the computer. An "on line" processcomputer is always custom designed for the location, and eachnew duty assigned to the computer will require more interfacehardware and software. By the time the computer is perform-ing useful work, the computer cost is less than 20 percent ofthe project.

This second approaclh obviously requires that a companyutilize personnel skilled in the design of interfaces andsoftware for a computer since this represents about 80 percentof the job.

The Colonial Pipelinie Company has used both methods.Where many stations are identical in function, many of the oldrelay systems are yieldinig to solid state logic programmablecontrollers, and for large tank farms and input locations, asmall computer is being customized for the job. This discus-sion will cover the customized computer system.

Paper IOD-7547, approved by the Petroleum and Chemical Indus-try Committee of the IEEE Industry Applications Society for presenta-tion at the IEEE Petroleum and Chemical Industry Technical Confer-ence, Milwaukee, WI, September 15-17, 1975. Manuscript released forpublication January 9, 1976.

The authors are with the Colonial Pipeline Company, Atlanta, GA30326.

THE COMPUTER AS AN AID IN METERING PRODUCT

Just what is needed to transfer custody of petroleumproducts from one party to another? Agreement between theparties on price per unit and agreement on the volume. Priceis generally easy enough; the problem is with volume agree-ment. 1) Volume changes with temperature. 2) Temperaturevolume change factors are different for every product density.3) Volume changes with pressure. 4) Pressure volume factorsare different for every product density.

Therefore, it has been decided to set a standard to tradeproduct at 600F, 600API corrected gravity, and 0 pressure.Thus, if product is measured dynamically, the resulting grossvolume must be corrected to the established base. If theColonial Pipeline Company takes custody of 100 000 barrelsgross, at 68.60API gravity, at 950F, and at 120 PSI, a ticket ismade transferring 97 780 barrels at the agreed price. Atemperature error of 1°F on a two hour delivery would causea difference of nearly 60 barrels. At $16 per barrel, this wouldbe $960 advantage for only a two hour period to one of theparties; therefore, metering large volumes justifies the bestavailable method.

There are some areas where a computer can do a betterjob than the present practice.

1) Reading temperature and averaging temperature over adelivery; in manual operation, temperature is normally readonce an hour to the nearest degree Fahrenheit. A computercan read temperatures every 100 barrels to the nearest 0.20Fand give a weighted average.

2) lt can read and average pressure over the delivery.3) It can perform the net barrels-calculations. Computer

accuracy on the ticket removes the necessity for home officeaudit and correction.

4) It can convert temperature and specific gravity to APIgravity at 60°F base. The computer eliminates human error intable look-up. At the present time, gravity measurement byinstrument has not proven accurate enough to feed inautomatically the product density. This will probably bepossible in a few more years.

5) It can save station operators time.Some considerations in using computers to compliment

metering are as follows.

Initial Cost

A computer and its associate equipment may cost up to sixtimes that of equipment used in conventional meter stations.However, if six separate meter installations are at one location,the cost is comparable. This cost is decreasing as new elec-

341

3EEE TRANSACTIONS ON INDUSTRY APPLICATIONS, JUlLY/AUGUJST 1976

troniics arle peri'ected. Colonial uses the following lhardware at acoinputer assisted metering station:

I) rrneter--supplies both a one conitact closure per barrelanid higl speed (500-1000) pulse counts per barrelprover signal

2) resistan-ice temperature equipmenit3) pressure transmitter4) prover loop for proving meter5) saimipling tacilities for product gravity and temiperature6) comiputer equipnient

a) Lockheed Mac 16 comlputer with 8K memoryb) ASR 33 teletypewriterc) 2000 character Hazeltine (CRTd) real tinme clock and power fail restarte) relay outputsf) analog to digital converterg) two 6 digit counters for eachi miieterII) valve inputsi) high speed meter inlputs.

System AMainitenzanceThe comlputer systemn's hardware riay not require eniougl

maintenanice to keep an "all purpose" technician proficient.Thius, outside help, when needed, is required. Software main-tenance keeps the system at its optimunm capability.

Wlhile Colonial Pipeline's approach made an effort toperform all the operations automatically, the ability of theoperator to correct information the computer gathered wasretained. A CRT screen and keyboard is used by the operatorto operate the system.

The computer monitors the stations, and when valveposition indicates a delivery is started, the operator is asked onthe CRT "What is batclh no., observed gravity, and observedtenmperature?". This completes the informationi the computerneeds fronm the operator. The comnputer averages temperatureanld pressure. notes tinme beginning and end, deternminesshipper and product froml batclh no., retrieves meter factorfrotim menmory and calculates a net ticket, displays a completedticket for operator approval, anid prints ticket on commiiandneeding only operator signiature.

In designing the miieter system, the first thought isreliability.

Barrel Counlt AccuracySince eaclh barrel equals 16 dollars, a stray pulse or a lost

pulse caninot be tolerated.1) All inputs into the computer and counters are optically

isolated.2) Couniters are rnLll oni a 48 V dc battery system so that

power failure will not interrupt counitinlg.3) Counters are independenit of the computer. Coinputers

read couniters uinder program conitrol.4) There are special fitltering circuits on power supplies.5) The coml-puter was pick-ed foir long terin reliability--

riot price.

Redundlanc'

Meters withi attachled registers, separationi of electroniccount system from comiiputers, glass thermometer, anid

pressure gauges, allow a back uLp to miiake a hlanidwrittenl ticketit the electronic system shlouldlhave a problem.

Colonial Pipeline wanted to use the computer to obtainimllaxiiiauIm benefit. Thus every tfunction-l whlichi could be doneby the comnputer was inicluded. See Fig. I for a custody trans-fer ticket.

We take the items in order arid shtow how th-ie conputerdete-rmines the following.

1) Location_--The software progranm- thie locationi is known.2) Date-The computer is equipped with real time clock

date.3 ) Linie-The computer reads the valve indication and

kniows which line is open.4) Type Transactioni--Determined from the valves.5) Location Code- Through the software program plus

reading the valves.6) Ticket No.-The compuiter stores the last number and

adds onie to the last ticket.7) Shipper-Decoded by the computer froimi tthe batch no.

and stored tables.8) Consignee-Reads thle valves or the batch no. or both.9) Batch No. --Put in by thie operator into the CRT-

coinputer reads and stores.10) Product--Decoded from the batch no. and stored

tables.I 1) Colonial Tank #-- Read ftronm the valves,12) Observed Gravity at 0F-lnput by the operator.13) Gravity API at 600F-Calculated by the computer from

data in 12.14) Mleters Used--The conmputer reads the valves.15) Proving Report No. -Retrieved from the memory by

the comiiputer.16) Mleter Factor-Same as 15).17) Average Pressure-The computer reads the pressure

and averages.18) Pressure Factor---The comiiputer solves equation using

items 13) and 17).19.) Average Temperature-The computer reads the

temnperature at 100 barrel incremenits ai-id averages.20) Temlperature Factor-Calculated by the computer using

items 13) and 19).21 ) Gross Barrels-The conmputer reads the couLnter.'2.2) composite Factor--The computer maultiplies 15 X

17X 19.23) Corrected Barrels at 600F-The compuLter multiplies

21 X 22.24) Titme Start-iThe computer reads the valve and fnotes

times of start.25) Timiie Finish-The conmputer reads ending switclh and

-totes the timle.26) By--Signed by th-e operator.27) For--Ticket is sigined by the C'osignee or the operator

tills in as required.The versatility of using a computer can be understood by

looking at how the computer is programmed to solve a pipingmatrix to determine wheni a delivery starts. Look at Fig. 2.1mI th'is in1stanle thle product source is tanrks, a4nd thle delive-rypoinit is linle I out or line 2 out. The piping is divided intofive sources (tanks), six pipe sections, and two delivery lines.

342

PHILLIPS AND CRIDER: DETECTION SYSTEMS FOR LIQUID PETROLEUM PIPELINES

(a)

LOCATION1 DAITE LINE TYPE TRAN LOC COrDE TICKET NO.GBw.,-LO: .G75 0:3 7 22 83483 0521

SHIPPER CODE CONrCIGNEEGULF OIL CORP.

BATCH NO. PRODUC- T C0 L.TArwt-t NO. QESRYV GRA'Y GRAY- AT 60 METER LUK:EDGP -:34-12E. H6: 0:1:E 61 .6 60.f. 6 1 .6 9 0 0 0

PRO'%" PRT NO. METER FAC. AY1E PRESS PPE: "s FACI AYE TEMP TEMP FAC.1 0 0 1 .00-31 0075 1 .011107 1. .01 .9:354

GROSS BARRELS- COrIP CORP FAC7TOR CORP BARRELS:. AT .0- DEG F1 1 122 .9:1 110010

START T:TOP BY: EDD COUIC:H11 05. -TIME- 0:5115

05.01.'?5 -DATrE-- D .A TE-5 FOR:

0 EXEC1 COMPUTE2 H7T. PRINT:3 TTY. PRINT

(b)Fig. 1. (a) Standard Colonial Pipeline Company ticket. (b) Ticket information displayed on CRT.

GASOLINE TANKS

Fig. 2. Typical delivery piping.

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0 00 0 0000 0000000 0 90 00 0 0000 0000000 0 100 00 0 0000 0000000 0 110 00 0 0000 0000000 0 120 00 0 0000 0000000 0 130 00 0 0000 0000000 0 14

0 00 1 0001 0000000 0 510 00 1 0010 0000000 0 52

Fig. 3. Pipe block shown with bit pattern as initialized for pipinglayout Fig. 2.

343

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, JULY/AUGUST 1976

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The piping is divided by 18 valves. Initial conditions assumethat all pipes are empty, except sources (tanks). When a valveopens, the information (product) in one pipe is compared tothe product in the other pipe on the other side of the valve. Ifdifferent, a flag is set to rescan the valves, and the data fromboth pipes is consolidated and stored in the pipe data blocksinvolved. Fig. 3 shows a pipe block index for the piping shownon Fig. 2. You will note that initial conditions shiow producttypes and source (normally tank no.) for the five possiblesources. Intermediate piping blocks are empty. The deliverypipes show a custody delivery and the meter number. As valvesare scanned, if a valve is opened, the source material (type andtank no.) is inserted into an intermediate pipe and transferreduntil the source material shows in the delivery pipe. At thistime, the program states a delivery lhas started, and this pipeinformation along with other data is placed into a ticket block.The valve read computer programn is set up to show what pipesare connected by which valves. For example, refer to Fig. 2and Fig. 3. Valve 1 open conmpares Pipe Index 1 and PipeIndex 9. If different, tile computer sets flag to recycle valveprogram then merges 1 and 9 anid stores in 9. The setting ofthe flag to reread the valves insures that the valves willcontinue to be read until there is no chainge in pipe conditioinaind that the source material will arrive at the delivery if valvesare open.

This type of construction makes it easy to set up a largepipitng layout and allows the computer to solve for a coin-pleted patlh. When, as at Linden, NJ you have 29 tanks, 8headers, 5 delivery pumping systems, and 10 delivery lines, itbecomes apparent that it is easier to read h1ow the operator setup than to list all legitimate rouLtes.

The type of product in the pipe data blocks makes itpractical to compare product and alarm when unlike materialis connected by a valve. Later it will also facilitate addingvolume to eachi pipe sectioni and line fill calculation.

When a delivery is started, a ticket block (section ofmemory) is assigned to the delivery, and all the knowninformation on that delivery is stored. Some of the data isconstantly updated during the delivery. When the operatorswitches meterheads, the delivery ends, time is now added tothe ticket block and the ticket data completed.

When the operator is ready, he calls for the ticket which isdisplayed on the CRT complete as it will be typed. SeeFig. l(b). The operator can now check for errors. The operatoris allowed to change temperature, pressure, or batch no. butcannot change gross barrels, time, location, etc., and the com-puter will recompute the data and redisplay the ticket. It isnow typed on the ASR 33, and the operator can accept orabort the ticket. If the operator accepts the ticket, the ticketblock in memory is cleared and ready for a new ticket.

Meter proving involves most of the same math package andhardware that is used for ticket calculation. Colonial allowsthe computer to operate the prover loop after set up by theoperator. This involves operating a prover dump valve andcycling the prover loop, reading the temperature and pressure,knowing product API gravity, reading proving counts for fiveruns, which must be within preset boundaries, and perform-ing calculations to determine meter factor. This factor iscompared with the last factor to determine if more runs areneeded. The results are displayed on a CRT for acceptance bythe operator, and thein stored and printed, providing proverreport and pertinent data in memory.

See Fig. 4 for an example of prover CRT display ready foracceptance. Proving meters is a time consuming task, and thecomputer frees the operator for other duties. Colonial uses aCRT printer to obtain lhard copies of the meter provinig.

THE COMPUTER USED FOR LEAK DETECTION

When the word leak is used in the same sentence witlh pipe-lines, everyone's ears perk up and people see a raging oil fire.When we examine the safety record of pipeline transportation,we find that pipelines are 28 tirnes safer than marine trans-portation, 227 times safer than rail, and 990 times safer thantruck transportation, per ton mile of product moved [ II . Thisby itself indicates that historically pipelines must have somefairly good methods of leak detection.

A computer used to perform leak detection does not doanything which pipelines have not done for years. It does,however, do some of the thlings faster and more continuouslythan the older methods performed by men and equipment.

344

I

PHILLIPS AND CRIDER: DETECTION SYSTEMS FOR LIQUID PETROLEUM PIPELINES

Let us review the present status of leak detection on liquidproducts pipelines and determine which methods can be incor-porated into a computer for any gain.

Visual Observation

Pipelines are monitored periodically from planes, heli-copters, cars, and by foot, This has always been done at theoptimum "cost benefit" to the pipeline company. What ismeant by "cost benefit"? A company is similar in performanceto a person; a farmer will use an amount of fertilizer whichproduces the most return for his investment. Thus visualchecks on the pipeline are made at a frequency determined bythe pipeline location, population density, pipeline hazardsfrom foreign equipment, and possible liability to the pipeline.If a pipeline company does more inspection than is justified,then they are "robbing" the consumer in the area served, asthese costs must be borne by the ultimate consumer. If a regu-latory agency requires excessive inspection or safetyrequirements, then they are imposing a "tax" on the citizens.This is true for all "utilities" and corporations (such asinterstate pipelines), which have government-regulatedearnings limitations.

Computers do not, at this time, make any contribution tovisual inspection.

Pressure TestingThis is the most valuable tool pipelines have for leak

detection. Pipelines are designed to operate at a pressure of72 percent SMYS and are tested beyond this pressure to 90or 100 percent SMYS. Pipelines are monitored during opera-tion for any unexplained change in pressure. The computercan do this more frequently and more precisely than humanmonitoring.

Over and Short or Meter-In Versus Meter-Out

Pipelines have done this for years. Economics again dictatethat if you do not deliver all you receive, you go out ofbusiness. As pipelines become larger, the corrections forpressure and temperature, which we examined under meter-ing, become essential, and conmputers are efficient in fastover-short calculations.

Flow Rate Monitoring

Basically, pipelines hanidle large volumes, and normally theflow rate is constant over a delivery. Again, the computer cancontinuously monitor and make decisions on rate fluctuationswhich can indicate a leak. A flow rate increase combined withpressure drop have always been indications of a probable leak.

The above are four basic leak detection systems.Colonial Pipeline Company lhas installed at Linden, NJ a

leak detectioni system using over and short measuring, whichwill detect leaks as small as 20 BPH out of a flow rate of7500 BPH or 0.27 percent and whichl automatically shutsdown the line. This does not sound like much of an accom-plishment but consider these factors:

I) The lines handle gasoline, kerosene, and fuel oil. Thedifference in meter factor between gasolinoe and kerosene onthe samne meter can be more than 0.3 percent. One meter canbe metering in gasoline while the otlher is metering out oil.

3 isLINE 5 MIR.

4 11

LINE 9 MTR. OUT

Fig. 5. Linden pipelines with check meter.

2) The repeatability of the meter on the same product is0.02 percent. The linearity is 0.15 percent with flow ratechange.

3) Product entering the pipeline and cooling 4°F beforebeing taken out can shrink 0.2 percent in volume.

4) Product is compressible. The compressibility factor caneasily equal 0.5 percent.

5) No two meters have the same meter factor. The differ-ence can be as much as 2.5 percent in normal practice.

6) Meter factor changes with meter wear. Normal changebetween proving may amount to 0.1 percent.

Add to these problems the possibility that any equipment,which consistantly gives false alarms and adds to the operatorworkload, could be bypassed by the operator and one cansee why pipelines have minimized effecting automatic shut-down on over and short measurement.

The Colonial Pipeline Company was required as part of itseasement (street crossing) permit to install an over-shortmeter system with a 20 barrel per hour loss maximum andautomatic shutdown. This was a requirement of the New YorkFire Department. Neither Colonial nor the fire departmentrealized the unforeseen difficulties in obtaining this goal.

Colonial did recogniize this requirement was beyond thecapability of existing leak detection equipment, and when thefire department insisted upon this requirement, Colonial addeda computer to the existing metering equipment at Linden andbegan installing renmote meters.

The five pipelines monitored are all delivery lines from theLinden, NJ, end of the Colonial main line system. The pipe-lines are of three operational types (Fig. 5). 1) A single linewith one pump and one destination. 2) A single line withmultiple pumps and nmultiple destinations. 3) A line jointlyused by Colonial and a nearby pipeline firm for delivery toa Colonial shipper.

Colonial Pipeline Company installed the remote meters,leased dc teleplhone circuits, and installed counters at theLindeni control panel to display the remote meter reading.We first tried to use factor conversion counters to make the

remote counter read step by step with the local counters.Observation would show the differenice. This proved impossi-ble. The accuracy required in the factor between the metersis too great. A 0.02 percent error would represent a 20 barreldifference by the time the batch reached 100 000 barrels.

345

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, JULY/AUGUST 1976

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This type of accuracy is not practical over extendedperiods, and it was determined that periodic updates in meterfactor and counter difference would be required. This was

discussed with the fire department, and Colonial agreed to use

a 30 minute initial period and try for two hour updates on

the remainder of the delivery.This endeavor showed that improvements in the trans-

mission circuit were needed. The dc circuit was plagued with

noise and excessive outages. Voice grade circuits and FSK

equipment for remote transmission were substituted for the

dc circuits and are providing acceptable performance.Since the remote gross counter reading could not be corre-

lated by the operator to the local reading, it was necessary to

allow the cotmputer to modify the remote reading and displaythe niecessary information. Thus, for a calibration period,we assume that all barrels B1 entering the system leave the sys-

temii as barrels B2, times a correction factor MF thus B1MFX B2 .

This MF calculationi was programmed into the computer,aid withl imnproved remlote reading, the system was tried again.It wouLld not work, and the result was numiierous false shut-downs.

It was decided to add a leak detection status display to thelinie information display so that the operator and technicialcould see wlhat was happeniing (Fig. 6). The display aided alldesign plhases by collecting pertinent data in one place.

LOCAL METER CHECK METER

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// CHECK MTN AT TIME 3

1 2 3 4 5TIME TIME

Fig. 7. Local meter versus check meter with method for comparison.

The display consists of the over-short line number and thegross local nmeter reading, operator options, the correctedremote meter reading, the factor (MF)l the current barreldifference, and the time in 10-second increments until thenext periodic factor tlpdate. The display is updated once a

minute.

This pipeline data collected makes it possible to see justwhat is happening anid whlat steps are ncessary to operate an

overslhor-t meter system. (See Fig. 7). It is apparent that theimieter reading at timiie tlhree for the local and remote clheckmeters will not comlpare. The remiiote check meter readinigmust be corrected for the difference in meter factors, tempera-ture factors, anid pressure factors, which are proportional to

total volume.

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PHILLIPS AND CRIDER: DETECTION SYSTEMS FOR LIQUID PETROLEUM PIPELINES

The remote meter reading must also have a correction madefor line pack for this delivery. Both of these corrections arenormally larger than the allowable shortage allowed for leakdetection.

The computer can determine the value of MF as a deliveryis made. Then, it uses that factor for the delivery. When theprogram is first loaded, a relatively large factor is assumed,such as 1.500.

When a delivery is started, the previously determined factoris increased by 0.0030 to account for product changes. Thebarrel shortage allowed is set to 40, and the local line meterand check meter current readings are saved as a reference.

While the first few barrels are pumped into the pipeline,the computer monitors the counters to detemine the linepack. Several barrels will be pumped in before any barrelscome out. When the remote check meter is less than 25BBL, but more than zero, line pack is set to the differenceof line meter minus check meter.

For these small values, the check meter is about equal tothe check meter times MF and no factor is used. The linepack. value may not exceed a predetermined constant foreach pipeline.

From observations of the line pack process, these limitswere determined. The value of the observed line pack is thenadded to the converted check counter before any calculationsare made. lt should be noted that the line pack will vary asmuch as three times the errors allowable for different deliveryconditions.

The computer scans all inputs every 10 seconds and checksfor a difference between the local meter counter and the cor-rected remote meter counter. A satisfactory difference is -40BBL in the first half hour and -20 BBL subsequently.

As delivery progresses, the factor MF may be changed inthe following ways: 1) a periodic recomputation; 2) a recom-putation due to a positive difference; 3) a recomputation re-quested by an operator after an alarm.

The first periodic recomputation occurs half an hour intothe delivery. At that time, the over-short barrel allowance isreduced to 20. Subsequent recomputations occur every twohours. This recomputation is only done if the flow rate isabove 8 BBL/10 s-2880 BBL/hr.

This allows for the line pack run out at the remote end,which would create a false factor if a recomputation occurredwith the line shut down. A recomputation may occur any timethat the difference is greater than plus 20 BBL, and the flowrate is also above 2880 BBL/hr for four minutes.

This recomputation normally keeps the difference between0 and 20 BBL enabling quick detection of a negative 20 BBL.A recomputation may also be requested by an operator afteran alarm at -20 has occurred. This allows him to restart theline after determining the cause of the shutdown.

Once a line is started and is into a two hour period of de-tecting a 20 BBL leak, the detectable product loss is small.For a delivery rate of 7500 BBL/hr, a loss of 10 BBL in7500 could be detected.

The flow chart for this operation is shown on Fig. 8.A separate method of line monitoring is also combined into

the leak detection system. This is a pressure drop monitor.Once a line is started and the pressure is above 150 psi, the

Fig. 8. Linden leak detection.

new line pressure is compared with the previous line pressureevery 10 s.

If a negative difference of at least 14 or 20 psi, dependingon a line size, is measured, an alarm bell sounds. A CRTalarm display is also generated showing the previous and cur-rent pressures and the difference (Fig. 6(b).) This mode ofalarm can quickly detect a large pipeline break.

This system is used on all 10 delivery lines at Linden. Oper-ator options are the following: 1) release, which resumes thepressure check; 2) release with time delay.

The latter suspends -pressure checks on that line for 10min and then resumes. The delay feature can be used to elimi-nate unnecessary alarms during normal pipeline operations,which would cause pressure fluctuations.

Hardware used at Linden in leak detection includes thematerial listed for computer metering plus: 1) 6 Rockwellmeters (remote); 2) 18 shutdown functions (7 pumpingsystems, 1 remote valve, 10 local valves); 3) 12 alarm func-tions; 4) 5 leased telephone circuits and associated FSKtone equipment; 5) 30 six-digit counters; 6) 256 valve indi-cations.

The computer has a unique interrupt structure. This allowsthe hardware to respond to peripheral devices and processnumerous software routines concurrently without a real timemonitor software system.

EVALUATIONThe cost of this equipment, over and above the normal re-

quirement for metering, is over $300 000 plus an annual tele-

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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, JULY/AUGUST 1976

phone bill of $3200 and a half serviceman year, or a total ofapproximately $13 000 a year to maintain.

Colonial Pipeline Company has had two leaks on theselines in the last 11 years that this equipment would locate.Without this equipment, the leaks were located in less thanthree minutes.

Assuming the equipment lasts 11 years, the cost of thisleak detection system will be $300 000 + (11 X 13000) orapproximately $440 000. Thus while Colonial is proud to havebuilt a leak detection system which is better than any weknow of, the frequency of leaks on pipelines does not justifysubstantial costs for over and short metering with computercontrol. Leak detection systems do not prevent leaks.

Colonial Pipeline Company will continue its efforts to im-prove pipeline operating procedures and equipment to main-tain and improve safe operations protecting both the publicand Colonial. One of these efforts will be to find enough otheruses for the minicomputer so that its excellent performancein leak detection becomes economical. Some projects now inuse are

1) meteringa) meter provingb) net barrels back to supervisory

2) tank gauginga) high level tank alarmsb) tank inventory

3) net barrel alarms (set point alarms)4) station event logging5) product mixing alarm6) flow rate display and alarm.

Thus the use of minicomputers in pipeline operationappears bright. The challenge is to provide such superior appli-cations and equipment that there is no choice but to changefrom the existing dependable applications. The old champ isnot replaced by an equal.

REFERENCES

[1] Special Study, Fatalities 1963 to 1968 by National TransportationSafety Board.

note that the system performance is limited only by the relia-bility of the sensor information. They have done an excellentjob in solving the design problems of hardware and software.I would like to comment on why they can achieve optimumcapability with this system while the former design typescould not achieve this level of reliability.

Computer memory not only allows testing for unreasonablesensor readings but provides a method to detect when a sensorreading begins to-drift. Error from one meter out of a batteryof meters can be isolated while, with the older combinatorconcept, recovery from a missed measurement was not possi-ble. The Linden, NJ, system could not have been assembledwithout memory. Computer memory permits manual entry tobe mixed with automatic entry of system variables. Thehuman operator can interact in a more effective way than hecould with a hard-wired measuring and compensating system.The authors have discussed manual entry of gravity, however,any variable could be entered manually if a satisfactory sensorwas not available.

Leak detection is discussed in a very practical manner,however, the references to percentages of accuracy might bedifficult for the nonmathematician to understand. The manwho wanted to find a 20 barrel difference in 100 000 barrelsis like the Texas Aggie who reported the fossil in the museumwas 100 020 years old. He knew that was accurate because 20years ago the Professor had dated the fossil as being 100 000years old. Extreme care must be used in the selection of al-gorithms to compare volumetric measurement. When takingthe difference between two numbers which have almost thesame value, the percentage error in the difference can be hugeeven though the percentage error in the original twQ numbersis very small.

This paper would be excellent reference material for anyperson interested in installing a small computer in a processenvironment. It shows how the problems of unreliable sen-sors, inaccurate data, and marginal economic justification havebeen solved to a degree sufficient to make a workable system.

;:m | R. D. Philips received the B.S.M.E. degreefrom the University of Oklahoma.He spent four years in the Navy Construction

Batalion, and twenty-four years in the con-struction and instrumentation of oil and pipe-lines. He holds two patents and has paperspublished on surge control, pipeline tempera-ture, and hydraulic systems. He is with theColonial Pipeline Company, Atlanta, GA.

DISCUSSION

W. H. Osborne (Shell Pipe Line Corporation, Houston, TX):The authors are to be congratulated on a fine paper and avery innovative engineering accomplishment. My interest inthe paper is enhanced because I have seen the system in opera-tion. The paper contains considerable detail which is essentialto the designer of such a system. To a casual reader some im-protant concepts might get lost in detail.

Messrs. Phillips and Crider point out that software main-tenance keeps the system at its optimum capability and also

Manuscript released January 9, 1976.

Charles W. Crider (S'62-M'65) received theB.S.E.E. degree from Bucknell University,Lewisburg, PA, in 1964, and the M.S.E.E.degree from the Georgia Institute of Tech-nology, Atlanta, GA, in 1971.

In 1964 he joined the North Electric Com-pany, Galion, OH, where he worked in super-visory control and telemetry systems. He isnow with the Colonial Pipeline Company,Atlanta, GA, where he is presently Super-visor of the Process Computer Applications

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