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PIPELINE LEAK DETECTIONEric Penner

Josh Stephens

4/30/09

OverviewIntroduction

WHERE ARE PIPELINES LOCATED?Roughly 500,000 miles of pipeline in US300,000 miles of gas pipeline200,000 miles of oil pipeline

About 1.2 million miles of pipeline in the worldRussia and Canada are next two on list with ~250,000 miles and 100,000 miles of pipeline, respectively

DIFFERENT PIPELINE SYSTEMS

Significant IncidentsSignificant incidents meet any of the following conditions as defined by the PHMSAFatality or injury requiring hospitalization$50,000 or more in total costs, measured in 1984 dollarsHighly volatile liquid releases of 5 bbls or more or other liquid releases of 50 bbls or moreAny liquid releases resulting in an unintentional fire or explosion

SIGNIFICANT INCIDENTS 1988-2008

WHAT ARE THE PRIME CAUSES?Excavation damage is the number one causeMost experts regard corrosion as second leading cause, feeling that a strong portion of those under the All Other Causes heading are corrosion related as well

Methods of Leak Detection

HARDWARE LEAK DETECTIONGenerally good sensitivityAble to detect large and small leaks quicklyLeak location can be estimated via instrumentationPrevious two points help minimize environmental and economic impact in event of leakHigh level of instrumentationInstallation and maintenance costs can be relatively highComplex installationsConsiderable amount of below surface activityProsConsIN BRIEF: ACOUSTIC EMISSIONSMethod relies on escaping fluid giving off a low frequency acoustic signal

Acoustic sensors placed around entire length of pipeline to monitor interior pipeline noiseBaseline or acoustic map createdDeviation from baseline triggers system alarm

IN BRIEF: VAPOR SENSOR METHODVapor sensing tube placed along entire length of pipelineTube is permeable to material being transportedIf leak occurs, some material diffuses into tubeTest gas is pumped through and analyzed for vapors of pipeline fluid

IN BRIEF: ULTRASONIC FLOW METERGenerates an axial sonic wave in pipe wallDifference in time for wave to travel upstream and downstream allows for computation of flow rateRelies on mass flow balance

FIBER OPTIC SENSING: BASICSProbes placed along pipeline every 0.5 metersEscaping hydrocarbons change surrounding temperatureLiquid leaks TGas leaks T (Joule Thompson effect)Scattered light analysisRaman (intensity based)Brillouin (frequency based)

MeasurementPerformanceSensitivity50 ml/minLeak SizeMagnitude estimatedLeak LocationWithin 1 meterDetection Time30 seconds to 5 minutesCost1200 km single pipelineRoughly the distance from Houston to El Paso~$18 million in equipment costs aloneFigure does not include installation Conclusion: fiber optic leak detection requires a sizeable upfront investment

Performance and CostSoftware Leak DetectionInstrumentation is used to measure internal parameters of the pipeline

What methods are available?

Balancing SystemsPressure AnalysisGeneralized Likelihood Ratio

Mention how I will go through each of these and describe how each is utilized. Hardware methods dont have to worry about biases like software does.16Balancing SystemsBasic principle is conservation of mass

Basic line balance does not compensate for changes in line pack due to pressure, temperature, or product compositionVolume balance is an enhanced, automated technique, which does account for line pack correction by assessing changes in volume due to temperature and/or pressure variations using SCADA (Supervisory Control and Data Acquisition)

MIMOSteady State assumedcontrol system: a computer system monitoring and controlling a process17Stream 1 and 2 measuredDiscrepancy in flow measurement

Why pressure measurements?Sensor 1LeakSensor 2Case 10.400Case 200.40Case 300-0.4

18Balancing SystemsExample: 1250 m pipelineCan identify leaks as small as 5% of flowFlow metering at the end of each pipeline segment will not identify location of leakCannot distinguish leak from biasCannot find location of leakCost: ~ $200,000

MIMOPressure AnalysisHow is this implemented?Pressure indicators segmenting pipeline

Changes in flow produce changes in pressure transientsPropagate through the system until steady-state is reached

SCADA values used to calculate theoretical hydraulic profile or baseline

20Pressure AnalysisLimitationsNot only leaks cause disturbances in pressure changes (junctions, nodes, bends)

Presence of a leak can be determined from specific deviation or combinations of several deviationsExample: 1250 m long pipelineLeaks as small as 5% of nominal liquid flowLocated with an error smaller than 5 metersCost: ~ $200,000Cannot distinguish a leak from a bias

Volume balance and pressure deviationGENERALIZED LIKELIHOOD RATIOStatistical method modeled after flow conditions in pipelineMathematical model used that describes effects of leaks and biases on the flow process Detects leaks in pipeline branch, location in the branch, and magnitude of the leak.Identifies various types of gross errors

GLR for Gross Error IdentificationProcess ModelSteady state model without leak

is a measurement vector is the true value of state variables is the vector of random error

= constraint matrix

Measurement Bias Model

b is the bias of unknown magnitude in instrument I = is a vector with unity in position i

S. Narasimhan and R.S.H. Mah. "Generalized Likelihood Ratio Method for Gross Error Identification." AIChe Journal 33, No.9(1987): 1514-1519.Process Leak ModelA mass flow leak in process unit (node) j of unknown magnitude b can be modeled by;

the elements of vector correspond to the total mass flow constraint associated with node j

Procedure for single gross error

When there is no gross error;

23GLR for Gross Error IdentificationIf a gross error due to a bias of magnitude b is present in measurement I, then;

If a gross error due to process leak in magnitude b is present in node j, then;

When a gross error due to a bias or process leak is present;

let be the unknown expected value of r, we can formulate the hypotheses for gross error detection as

Ho: is the null hypothesis that no gross errors are present and H1: is the alternative hypothesis that either a leak or a measurement bias is present.

b and fi are unknown parameters. b can be any real number and fi will be referred to as a gross error vectors from the set F

For a bias in measurement iFor a process leak in node j

24GLR for Gross Error IdentificationWe will use the likelihood ratio test statistics to test the hypothesis by:

The expression on the right hand side is always positive. The calculation can be simplified by the calculation by the test statistics, T as:

The maximum likelihood estimate :

Substituting in the test statistics equation and denoting T by Ti:

Where:

This calculation is performed for every vector fi in set F and the test statistics T is:

supremum or least upper bound of a set S of real numbers is denoted by sup(S) and is defined to be the smallest real number that is greater than or equal to every number in S.25GLRMechanical Energy balance

Without leak

Liquids

Gases

With leak of magnitude b and location lb

Liquids

Gases

Miguel J. Bagajewicz and Emmanuel Cabrera. "Data Reconciliation in Gas Pipeline Systems." Ind. Eng. Chem. Res 42, No.22(2003): 1-11

26GLRProblem formulationWithout Error:

Subject to:

With Error:

Subject to:

So:

27GLR ImplementationLeak detection procedure:Hypothesize leak in every branch and solve data reconciliation problem

Obtain GLR test statistic for each branch objno_leak objwith_leak_k

Determine the maximum test statistic objno_leak - objwith_leak_k

We compare the max test statistic with the chosen threshold value: Max{objno_leak objwith_leak_k}> threshold value: leak is identified and located in the branch corresponding to the maximum test statistic

NOTE: Assuming only one possible error 28Sample Pipeline Network

29Simulation Procedure - Leak in Pipe 1

CalculatorLeak simulated in Pipe 1Optimizer30Simulation Results- Leak in Pipe 1Leak SimulatedPipe 1Location(m)4000Magnitude(kg/s)4.915Measured Flow15.482Measured Pressure (KPa)2420.3Estimated Magnitude(kg/s)4.640Estimated Location(m)4048PipeBest Objective function115.9834218.0199360.4256460.7056521.3695616.8630778.6864881.06509123.202031Simulation Procedure - Leak in Pipe 8

Leak simulated in Pipe 832Simulation Results- Leak in Pipe 8Leak SimulatedPipe 8Location(m)450Magnitude(kg/s)2.611Measured Flow4.946Measured Pressure (kPa)2160.1PipeBest Objective function1126.678297.4383101.8644123.7105126.4476126.447763.29480.1519159.922Estimated Magnitude(kg/s)2.609Estimated Location(m)45033GENERALIZED LIKELIHOOD RATIOResultsMore accurate to do GLR in Pro II as opposed to ExcelFor a system with a single gross error, GLR can distinguish between a bias and a leakProcedure more complex for multiple gross errorsAccuracy of the method increases with increasing magnitude of simulated bias

Cost Comparison Economic ValueWhich method is the most economic?Cost = L + P + M + FWhereL is the value of product lost due to leaksP is the value of lost production (ie, that value of product that would have been shipped if a leak and shut down of the pipeline had not occurred)M is the maintenance and installation cost of detection equipmentF is the value of fines levied for leaks

CALCULATING L (PRODUCT LOST DUE TO LEAK)Average leak sizePHMSA data provided an average leak sizeAdjusted average leak size for sensitivity of detection methodDetecting smaller leaks reduces average leak sizeAccounted for frequency of leaks being differentDetecting smaller leaks results in more detected leaksCALCULATING L (PRODUCT LOST DUE TO LEAK)Price of oil and natural gasDifficult to accurately predict eitherOil price varied between $40-$80 Natural gas price varied between $4-$12Clean up costs due to leak includedRange from $700 to $5,000 per bbl

CALCULATING P (LOST VALUE PRODUCT TRANSPORTED)Not the same as leak lossCalculated the value lost via shut down of pipeline to fix leaksThe value of what could have been transported during that down timeAmount flowing through pipeline: API Recommended best practices

CALCULATING M (MAINTENANCE) AND F (FINES)Maintenance assumed to be 5% of Base Cost for each methodFinesEPA fines the costliestCost per bbl estimateClean Air ActClean Water ActIndustry examplesThis estimate multiplied by leak size under each method to calculate the corresponding fine

MethodologyGLR compared with Ultrasonic, Volume Balance, and Pressure Analysis MethodsPressure analysis methods grouped together since there is no significant change in base cost or implementation among them

Excel database created to compare methodsCost of crew, instrumentation, and different levels of tuning required were taken into account for each modelVarious companies were contacted to estimate cost of different detection schemes

MethodologySimulations were run for varying nominal pipe diameters2 to 8 inches for gathering/distribution networks12 to 24 inches for single pipeline

Multiple scenarios tested for eachRange of values used for price of oil, natural gas, and for leak clean up Pipeline length varied from 0.1 to 10,000 milesTime for repair of leak assumed to be the same for all methods6 Nominal Diameter: Oil

20 Nominal Diameter: Oil

20 Nominal Diameter: Natural Gas

Example8000 mi pipeline~ $1 million in cost difference between Ultrasonic and GLR

ConclusionGLR showed to be the most economic for both single pipelines and gathering/distribution networksThis held true for oil as well as natural gasGLR shows more separation from the other methods in the case of oil, due to the higher product value

Implementing GLR results in less fines and less lost production

QuestionsHardware ComparisonMethodPowerSize Estimate of LeakLocationSmallest Leak (gas)Smallest Leak (liquid)Response TimeAcoustic Emissions1 false alarm / yearNot provided+/- 30 mHole 2-10% of pipeline dia.1-3% nominal flow of pipeline15 seconds to 1 minuteFiber Optic SensingReportedly no false alarmsIndicates whether leak is large, medium, or small1 m50 ml/min30 seconds to 5 minutesVapor SensingReportedly no false alarmsIndicates whether leak is large, medium, or small0.5% of monitored area100 l/hr1 l/hr2-24 hoursUltrasonic Flow MetersReportedly no false alarms

Indicated by difference in mass flow measurements (0.15% nominal flow smallest)Known to be between two ultrasonic meters0.15% of nominal flowNear real timeCorrosion PreventionCorrosion-related cost to the pipeline industry is approximately $5.4 to $8.6 billion annuallyCathodic protection is required on all interstate pipelines and has been for decadesTechnique uses a constant low voltage electrical current run through the pipeline to counteract corrosion corrosion can create a galvanic cellPipeline coating is the other common corrosion prevention

This can be divided into the cost of failures, capital, and operations and maintenance (O&M) at 10, 38, and 52 percent, respectively49Pigs and Smart PigsPigs are cylinder shaped plugs of the same diameter as the pipe

Smart pigs are fitted with electronic sensors that can help locate pipeline wall weaknesses prior to a leak appearing

Both scrape build-up off the interior wall of the pipeline, which also helps prevent corrosion

TRANSIENT FLOWAdvanced fluid mechanics and hydraulic modeling are used to simulate pipeline internal conditionsHow is this implemented?Pressure and flow measurements input to simulationPressure-flow profiles createdPredicts size and location of leaks by comparing measured data to predicted dataDetectable leaks were greater than 2% for liquid and 10% for gas

Most complex and costlyGLR for Gross Error IdentificationResults & DiscussionFor the Recycle process network

123456752GLR for Gross Error Identification Sensors1234567Tb^bOverall power = 0.6Bias in sensor 1 Simulations (Ti)123456789102110719119043114962457139423861404105661729160.181819301341894918263122714149171252110535437151591969919751101145281144379270862831008217322139317550295837292612710332619193915380.189755237552659105233621107291538583149624571394265914041056-5834-50-3549-63476648-41-50-3535-3332-6045-5540-5053GLR for Gross Error Identification

Overall power= 0.8Leaks in node B and C54GLR Excel Macro

Pro II vs. Use OF Gas Equations in ExcelNPS = nominal pipe size56Pro II vs. Use OF Gas Equations in ExcelShows 5-10% error for Colebrook57GLR Excel Macro ResultsFig. __. The overall power vs. simulated magnitude. ( ) True 1%, ( )False 1%, ( ) True 3%, ( ) False 3%, ( ) True 5%, ( ) False 5%.Fig. __. Error vs. simulated magnitude. ( ) True 1%, ( )False 1%, ( ) True 3%, ( ) False 3%, ( ) True 5%, ( ) False 5%.