leak detection performance
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Leak Detection Performance
Pipeline Safety Trust Conference
November 17 & 18, 2011
New Orleans, Louisiana
Why Leak Detection?
Why Leak Detection? (Contd)
Minimize the volume of lost fluid Reduce risk of fire, explosion or other safety hazards Protect the company
Minimize cleanup costs with an early response to a leak warning
Protect reputation Demonstrable acceptance of responsibility by
executing a proactive leak detection program
Always increasing regulatory interest in pipeline integrity programs; including leak detection
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference3
History
Manual pressure/flow readings and evaluation
Voice communication between the field and any center of responsibility that may exist, or with other stations along the line
Familiarity with the pipeline behavior by controllers and technicians was critical
Right-of-way observation including walk-overs and fly-overs were among few leak detection options
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference4
Automated Measurements
Proprietary logging systems and SCADA
Transmitter and meter technology
Automation tools and products that acquire accurate information about hydraulic behavior
Tools to assist in evaluating the relationships among measurements
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference5
Leak Detection Performance
From the former API 1155 (Evaluation Methodology for Software Based Leak Detection Systems): The system correctly indicates that there is no leak The system correctly indicates that there is a leak The system incorrectly indicates that there is a leak
(false alarm) The system incorrectly indicates that there is no leak
(failure to detect)
Definitions absorbed into API RP-1130 (Computational Pipeline Monitoring for Liquid Pipelines)
November 17 & 18, 2011Pipeline Safety Trust 2011 Pipeline
Safety Conference6
Performance Metrics
Sensitivity – Combination of the size of a detectable leak and the time required to detect it
Reliability – A measure of the system’s ability to accurately assess whether a leak exists or not
Accuracy – The ability of a system to estimate leak parameters such as leak flow rate, total volume lost, and leak location
Robustness – The ability of a system to continue to function during unusual hydraulic conditions or when data is compromised
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference7
Meter-Based Leak Detection
Most widely used method on long haul pipelines Requires meters at all entry and exit points Achievable sensitivity limited by meter accuracy Some methods can be implemented in SCADA; or are
options with SCADA products Some products are stand-alone and driven by SCADA data Alarm thresholds must tolerate and expect the imbalance
in meter readings as the line packs and unpacks Leak evaluation algorithms that correlate actual changes
in linepack with meter imbalance provide the best performance
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference8
API 1149 Performance Predictions
Predicts the theoretical best performance possible with configured uncertainties No margin for false alarm prevention Temperature uncertainty and related changes in
density during transit is largest influence on performance Not uncertainty in measurement, but uncertainty in
temperature profile along the line One type of leak detection system can more accurately
estimate the temperature profile than other systems
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference9
Definitions
Dry Volume – Volume of the pipeline at atmospheric pressure and a reference temperature
Linepack – The incremental quantity of fluid in the line in addition to the dry volume influenced by pressure and fluid temperature Linepack is heavily influenced by temperature’s effect
on fluid density as is pressure, but often to a lesser degree
Profile – Value of a parameter over the length of the pipeline segment
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference10
Definitions (cont)
Uncertainty – Potential error in measurements that must be expected and accounted for; also the degree to which something is unknown and must be estimated or assumed based on somewhat related measurements.
Real-Time Transient Model (RTTM) – Accurately tracks fluid temperature/density profiles with consideration of pressure in order to reduce uncertainty in the linepack
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference11
Meter Quality vs. Performance
Influence of Meter Quality on Performance
4.2
2.1
1.4
1.0
0.8
0.60.4 0.4 0.3 0.3 0.2 0.2 0.2 0.1
4.1
2.1
1.4
1.1
0.9
0.60.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4
4.1
2.1
1.5
1.21.1
0.9 0.8 0.8 0.8 0.7 0.7 0.7 0.7 0.7
4.1
2.0
1.4
1.0
0.9
0.60.5 0.4 0.4 0.3 0.3 0.3 0.3 0.3
4.1
2.1
1.4
1.11.0
0.70.7 0.6 0.6 0.5 0.5 0.5 0.5 0.5
4.16
2.26
1.68
1.431.29
1.141.081.061.04 1.03 1.02 1.01 1.01 1.01
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 10 20 30 40 50 60 70 80 90
Detection Time
% N
om
ina
l Flo
w (
74
kb
ph
)
.1, .1 % Meters
.25, .25 % Meters
.5, .5% Meters
.1, .25 Meters
.1, .5 % Meters
.1, 1% Meters
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference12
Meter-Based Leak Basics
Flow/Pressure/Temperature measurements only at segment end-points
Metered flow accuracy important for high sensitivity
Fluid density (molecules/mass per unit volume) varies significantly with temperature Warm fluid is less dense; Cold fluid is more dense Temperature/density profile uncertainty is the most
limiting factor in leak detection for some pipelines
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference13
Volumetric Flow Measurement
Benefits of volumetric (not corrected for temperature and pressure) flow measurement Barrel-to-barrel assessment tolerates differences in
density at injection and delivery points Tolerates switching injection sources of different
temperatures Useful on short lines with small changes in
temperature/density during transmission Not useful where temperature/density profiles are
significant due to heat loss
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference14
Net barrel Flow Measurement
Benefits of net (corrected for temperature and pressure) flow measurement Useful for custody transfer Under steady-state conditions, fluid injected at lower
density will balance with delivered fluid at higher density Injections at slightly higher volumetric flow balances
with deliveries at lower volumetric flow Assumes a stable temperature/density profile
November 17 & 18, 2011Pipeline Safety Trust
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Net Flow Measurement Issues
Transient conditions thwart many algorithms involving net flow measurements Line packing and unpacking still result in an
apparent net flow imbalance as with basic volume balance methods
Net barrel flow measurements aggravate simple balance algorithms where a difference in density exists at injection and delivery points except under steady-state stable conditions
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference16
Natural Flow Imbalance
Difference in injected fluid density and delivered fluid density Gradual change in fluid density during transit
Temperature/density profiles are poorly understood by most simple algorithms Profile changes shape with changes in flow rate Water crossings and occasionally wet soil increase
thermal conductivity
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference17
Meter-Based Leak Detection Limitations
Accounting for changes or disturbances in linepack Operational changes causes the line to pack or unpack
as a normal occurrence Short-term hydraulic disturbances (transients),
including changes in injection temperatures, and their effect on linepack must be tolerated or understood in short-term evaluation algorithms used in rapid assessments
Over extended periods any effects of transients are diluted; thus allowing good sensitivity by most meter-based solutions over long observation intervals
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference18
Key Concepts
Pressures and temperatures under steady-state conditions provide current linepack characteristics Divergence of meter readings (greater imbalance) should
be reflected in linepack changes as seen in pressures Transients disturb this information and can lead to
significant short-term linepack uncertainty Over long time intervals any observed variations in
linepack become insignificant compared to the quantity of fluid passing through the pipeline system
Long-term sensitivity settings do not require as much tolerance of linepack uncertainty as do short term leak detection thresholds
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference19
Linepack Estimation
Fluid density assumed to be an average of injection and delivery density Weighted average Custom algorithms for curve fitting
RTTM thermal models track fluid density along the line
Change in flow rate alters the temperature/density profile as a new quiescent state develops
November 17 & 18, 2011Pipeline Safety Trust
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Profiles
Temperature Occurs when injection and delivery temperatures differ Subject to heat transfer characteristics of environment Varies with flow rate / transit time
Pressure Varies as batched fluids of different characteristics travel
Varies as batches of different densities travel over mountains
Profiles are accurately tracked by Real-Time Transient Models
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Safety Conference21
Real-Time Transient Model
Most sophisticated volume/mass balance tool Includes a thermal model to increase the accuracy of
linepack evaluation, thus allowing a shorter detection time for a detectible leak
Tracks heat transfer along the line and develops accurate temperature/density profiles as step changes in flow rates or injection temperatures occur
Allows thermal model tuning to achieve the best performance by modeling the hydraulic behavior accurately
Automatic tuning capabilities Instrument sanity checking
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2011 Pipeline Safety Conference22
RTTM Myths
Software is expensive Not significantly more expensive
Software requires special skills Training and full technical support is offered by vendors Knowledge of the pipeline physical details is needed
Software requires ongoing maintenance Not needed, once performance is satisfactory, but
further tuning is often performed to continually improve performance
Required if the pipeline network is changed
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference23
Static Pressure Testing
Extremely high sensitivity
Zero (0) flow results in zero (0) uncertainty in flow measurement
Works well in a relatively incompressible liquid environment
Requires pressure control equipment
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference24
Static Pressure Testing (contd)
Shut in under pressure at near operating pressure Monitor pressure decay for a period of time Drop pressure by half Monitor pressure decay for a period of time A consistent pressure decay rate indicates
decreasing density due to heat transfer A different pressure decay rate indicates a leak
whose rate is pressure dependent
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference25
Static Pressure Test Trends
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Conclusion
Simple linepack assessment algorithms have a place where linepack is stable and linepack variations and uncertainty do not adversely affect leak assessment
RTTM technology significantly reduces linepack uncertainty in transient environments and enables leak detection approaching the limits imposed by meter accuracy
Static pressure testing is a useful integrity verification tool
Matching the proper tool to the pipeline’s operation is critical
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference27
Training & Response
A critical component of any pipeline integrity management program
Response protocol should be included in training and be enforced Controller can shut down the line on any suspicion of
a leak Details regarding actions, reporting, etc. No internal penalty for reasonable judgment
A culture focused on pipeline integrity management is critical
November 17 & 18, 2011Pipeline Safety Trust
2011 Pipeline Safety Conference28
References
API 1130 – Computational Pipeline Monitoring for Liquid Pipelines
API 1149 – Pipeline Variable Uncertainties and Their Effects on Leak Detectability
API 1161 – Guidance Document for the Qualification of Pipeline Personnel
49 CFR Part 192 - TRANSPORTATION OF NATURAL AND OTHER GAS BY PIPELINE: MINIMUM FEDERAL SAFETY STANDARDS
49 CFR Part 195 - TRANSPORTATION OF HAZARDOUS LIQUIDS BY PIPELINE
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2011 Pipeline Safety Conference29
Contact UTSI
UTSI - U.S. Headquarters
1560 West Bay Area BoulevardSuite 300Friendswood, Texas USA 77546
Telephone: +1 281 480 8786
Fax: +1 281 480 8008
Email: info@utsi.com
WWW: http://www.utsi.com
Daniel W. Nagala (dnagala@utsi.com)
President & CEO
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UTSI - EuropeRaimundo Fernandez Villaverde
43, 6L
28003 Madrid, Spain
Telephone: +34 (91) 534 07 49
Fax: +34 (91) 535 42 57
Email: info@utsi.com WWW:
http://www.utsi.com
Catalina Frey (cfrey@utsi.com) Senior Consultant
Daniel W. Nagala (dnagala@utsi.com)
President & CEO
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