Leak Detection Performance Pipeline Safety Trust Conference November
Leak Detection Performance Pipeline Safety Trust Conference November 17 & 18, 2011 New Orleans, Louisiana S
Why Leak Detection? S
Why Leak Detection? (Contd) S Minimize the volume of lost fluid S Reduce risk of fire, explosion or other safety hazards S Protect the company S Minimize cleanup costs with an early response to a leak warning S Protect reputation S Demonstrable acceptance of responsibility by executing a proactive leak detection program S Always increasing regulatory interest in pipeline integrity programs; including leak detection November 17 & 18, 2011 3 Pipeline Safety Trust 2011 Pipeline Safety Conference
History S Manual pressure/flow readings and evaluation S Voice communication between the field any center of responsibility that may exist, or with other stations along the line S Familiarity with the pipeline behavior by controllers and technicians was critical S Right-of-way observation including walk-overs and fly- overs were among few leak detection options November 17 & 18, 2011 4 Pipeline Safety Trust 2011 Pipeline Safety Conference
Automated Measurements S Proprietary logging systems and SCADA S Transmitter and meter technology S Automation tools and products that acquire accurate information about hydraulic behavior S Tools to assist in evaluating the relationships among measurements November 17 & 18, 2011 5 Pipeline Safety Trust 2011 Pipeline Safety Conference
Leak Detection Performance S From the former API 1155 (Evaluation Methodology for Software Based Leak Detection Systems): S The system correctly indicates that there is no leak S The system correctly indicates that there is a leak S The system incorrectly indicates that there is a leak (false alarm) S The system incorrectly indicates that there is no leak (failure to detect) S Definitions absorbed into API RP-1130 (Computational Pipeline Monitoring for Liquid Pipelines) November 17 & 18, 2011 6 Pipeline Safety Trust 2011 Pipeline Safety Conference
Performance Metrics S Sensitivity – Combination of the size of a detectable leak and the time required to detect it S Reliability – A measure of the system’s ability to accurately assess whether a leak exists or not S Accuracy – The ability of a system to estimate leak parameters such as leak flow rate, total volume lost, and leak location S Robustness – The ability of a system to continue to function during unusual hydraulic conditions or when data is compromised November 17 & 18, 2011 7 Pipeline Safety Trust 2011 Pipeline Safety Conference
Meter-Based Leak Detection S Most widely used method on long haul pipelines S Requires meters at all entry and exit points S Achievable sensitivity limited by meter accuracy S Some methods can be implemented in SCADA; or are options with SCADA products S Some products are stand-alone and driven by SCADA data S Alarm thresholds must tolerate and expect the imbalance in meter readings as the line packs and unpacks S Leak evaluation algorithms that correlate actual changes in linepack with meter imbalance provide the best performance Pipeline Safety Trust November 17 & 18, 2011 8 2011 Pipeline Safety Conference
API 1149 Performance Predictions S Predicts theoretical best performance possible with configured uncertainties S No margin for false alarm prevention S Temperature uncertainty and related changes in density during transit is largest influence on performance S Not uncertainty in measurement, but uncertainty in temperature profile along the line S One type of leak detection system can more accurately estimate the temperature profile than other systems November 17 & 18, 2011 9 Pipeline Safety Trust 2011 Pipeline Safety Conference
Definitions S Dry Volume – Volume of the pipeline at atmospheric pressure and a reference temperature S Linepack – The incremental quantity of fluid in the line in addition to the dry volume influenced by pressure and fluid temperature S Linepack is heavily influenced by temperature’s effect on fluid density as is pressure, but often to a lesser degree S Profile – Value of a parameter over the length of the pipeline segment November 17 & 18, 2011 10 Pipeline Safety Trust 2011 Pipeline Safety Conference
Definitions (cont) S 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. S 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, 2011 11 Pipeline Safety Trust 2011 Pipeline Safety Conference
Meter Quality vs. Performance November 17 & 18, 2011 12 Pipeline Safety Trust 2011 Pipeline Safety Conference
Meter-Based Leak Basics S Flow/Pressure/Temperature measurements only at segment end-points S Metered flow accuracy important for high sensitivity S Fluid density (molecules/mass per unit volume) varies significantly with temperature S Warm fluid is less dense; Cold fluid is more dense S Temperature/density profile uncertainty is the most limiting factor in leak detection for some pipelines November 17 & 18, 2011 13 Pipeline Safety Trust 2011 Pipeline Safety Conference
Volumetric Flow Measurement S Benefits of volumetric (not corrected for temperature and pressure) flow measurement S Barrel-to-barrel assessment tolerates differences in density at injection and delivery points S Tolerates switching injection sources of different temperatures S Useful on short lines with small changes in temperature/density during transmission S Not useful where temperature/density profiles are significant due to heat loss November 17 & 18, 2011 14 Pipeline Safety Trust 2011 Pipeline Safety Conference
Net barrel Flow Measurement S Benefits of net (corrected for temperature and pressure) flow measurement S Useful for custody transfer S Under steady-state conditions, fluid injected at lower density will balance with delivered fluid at higher density S Injections at slightly higher volumetric flow balances with deliveries at lower volumetric flow S Assumes a stable temperature/density profile November 17 & 18, 2011 15 Pipeline Safety Trust 2011 Pipeline Safety Conference
Net Flow Measurement Issues S Transient conditions thwart many algorithms involving net flow measurements S Line packing and unpacking still result in an apparent net flow imbalance as with basic volume balance methods S 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, 2011 16 Pipeline Safety Trust 2011 Pipeline Safety Conference
Natural Flow Imbalance S Difference in injected fluid density and delivered fluid density S Gradual change in fluid density during transit S Temperature/density profiles are poorly understood by most simple algorithms S Profile changes shape with changes in flow rate S Water crossings and occasionally wet soil increase thermal conductivity November 17 & 18, 2011 17 Pipeline Safety Trust 2011 Pipeline Safety Conference
Meter-Based Leak Detection Limitations S Accounting for changes or disturbances in linepack S Operational changes causes the line to pack or unpack as a normal occurrence S 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 S 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, 2011 18 Pipeline Safety Trust 2011 Pipeline Safety Conference
Key Concepts S Pressures and temperatures under steady-state conditions provide current linepack characteristics S Divergence of meter readings (greater imbalance) should be reflected in linepack changes as seen in pressures S Transients disturb this information and can lead to significant short -term linepack uncertainty S Over long time intervals any observed variations in linepack become insignificant compared to the quantity of fluid passing through the pipeline system S Long-term sensitivity settings do not require as much tolerance of linepack uncertainty as do short term leak detection thresholds November 17 & 18, 2011 19 Pipeline Safety Trust 2011 Pipeline Safety Conference
Linepack Estimation S Fluid density assumed to be an average of injection and delivery density S Weighted average S Custom algorithms for curve fitting S RTTM thermal models track fluid density along the line S Change in flow rate alters the temperature/density profile as a new quiescent state develops November 17 & 18, 2011 20 Pipeline Safety Trust 2011 Pipeline Safety Conference
Profiles S Temperature S Occurs when injection and delivery temperatures differ S Subject to heat transfer characteristics of environment S Varies with flow rate / transit time S Pressure S Varies as batched fluids of different characteristics travel S Varies as batches of different densities travel over mountains S Profiles are accurately tracked by Real-Time Transient Models November 17 & 18, 2011 21 Pipeline Safety Trust 2011 Pipeline Safety Conference
Real-Time Transient Model S Most sophisticated volume/mass balance tool S Includes a thermal model to increase the accuracy of linepack evaluation, thus allowing a shorter detection time for a detectible leak S Tracks heat transfer along the line and develops accurate temperature/density profiles as step changes in flow rates or injection temperatures occur S Allows thermal model tuning to achieve the best performance by modeling the hydraulic behavior accurately S Automatic tuning capabilities S Instrument sanity checking November 17 & 18, 2011 22 Pipeline Safety Trust 2011 Pipeline Safety Conference
RTTM Myths S Software is expensive S Not significantly more expensive S Software requires special skills S Training and full technical support is offered by vendors S Knowledge of the pipeline physical details is needed S Software requires ongoing maintenance S Not needed, once performance is satisfactory, but further tuning is often performed to continually improve performance S Required if the pipeline network is changed November 17 & 18, 2011 23 Pipeline Safety Trust 2011 Pipeline Safety Conference
Static Pressure Testing S Extremely high sensitivity S Zero (0) flow results in zero (0) uncertainty in flow measurement S Works well in a relatively incompressible liquid environment S Requires pressure control equipment November 17 & 18, 2011 24 Pipeline Safety Trust 2011 Pipeline Safety Conference
Static Pressure Testing (contd) S Shut in under pressure at near operating pressure S Monitor pressure decay for a period of time S Drop pressure by half S Monitor pressure decay for a period of time S A consistent pressure decay rate indicates decreasing density due to heat transfer S A different pressure decay rate indicates a leak whose rate is pressure dependent November 17 & 18, 2011 25 Pipeline Safety Trust 2011 Pipeline Safety Conference
Static Pressure Test Trends November 17 & 18, 2011 26 Pipeline Safety Trust 2011 Pipeline Safety Conference
Conclusion S Simple linepack assessment algorithms have a place where linepack is stable and linepack variations and uncertainty do not adversely affect leak assessment S RTTM technology significantly reduces linepack uncertainty in transient environments and enables leak detection approaching the limits imposed by meter accuracy S Static pressure testing is a useful integrity verification tool S Matching the proper tool to the pipeline’s operation is critical November 17 & 18, 2011 27 Pipeline Safety Trust 2011 Pipeline Safety Conference
Training & Response S A critical component of any pipeline integrity management program S Response protocol should be included in training and be enforced S Controller can shut down the line on any suspicion of a leak S Details regarding actions, reporting, etc. S No internal penalty for reasonable judgment S A culture focused on pipeline integrity management is critical November 17 & 18, 2011 28 Pipeline Safety Trust 2011 Pipeline Safety Conference
References S API 1130 – Computational Pipeline Monitoring for Liquid Pipelines S API 1149 – Pipeline Variable Uncertainties and Their Effects on Leak Detectability S API 1161 – Guidance Document for the Qualification of Pipeline Personnel S 49 CFR Part 192 - TRANSPORTATION OF NATURAL AND OTHER GAS BY PIPELINE: MINIMUM FEDERAL SAFETY STANDARDS S 49 CFR Part 195 - TRANSPORTATION OF HAZARDOUS LIQUIDS BY PIPELINE November 17 & 18, 2011 29 Pipeline Safety Trust 2011 Pipeline Safety Conference
Contact UTSI - U. S. Headquarters 1560 West Bay Area Boulevard Suite 300 Friendswood, 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 November 17 & 18, 2011 UTSI - Europe Raimundo Fernandez Villaverde 43, 6 L 28003 Madrid, Spain Telephone: Fax: Email: WWW: +34 (91) 534 07 49 +34 (91) 535 42 57 info@utsi. com http: //www. utsi. com Catalina Frey (cfrey@utsi. com) Senior Consultant Daniel W. Nagala (dnagala@utsi. com) President & CEO 30 Pipeline Safety Trust 2011 Pipeline Safety Conference
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