Overview:
Leak detection systems are used by pipeline operators to protect the public and the environment from consequences of a pipeline failure. Leak detection systems do this by automatically alerting the operator when a leak occurs, so that appropriate actions can be taken to minimize spill volume and duration. There are many different leak detection methods. Some simply compare “metered out” product volumes with “metered in” volumes. , Others utilize complex computational monitoring systems that simultaneously monitor numerous operating conditions. Other methods fall somewhere between these two examples in their level of complexity.
In most cases, pipeline operators will employ two or more different types of leak detection systems in order to improve the effectiveness of their leak detection program. It should be noted that in addition to electronic systems, other methods of leak detection, including aerial and land-based surveillance are routinely employed. This fact sheet specifically discusses electronic leak detection systems that work in conjunction with Remote Control Centers to monitor pipelines.
Leak Detection Methods
Leak detection methods vary from the complex instrumentation and computer analysis of computational pipeline monitoring (CPM) systems, to simpler instrumentation and calculations. The method(s) chosen depend on many factors, some of which include the length and complexity of the pipeline, the nature of the pipeline’s operation, the nature of the pipeline’s surroundings and possible exposures, and the product transported in the pipeline.
Electronic leak detection methods include:
- Volume balance “meter out” versus “meter in”. This is a simple inventory balance to compare the volume of product at an originating point on the pipeline with the volume monitored at intermediate or destination points elsewhere on the pipeline. This method works best for products that are relatively incompressible.
- Mass balance “meter out” versus “meter in”. This is a more complex inventory balance to verify that no discrepancy exists between the mass of product measured at an originating point on the pipeline with the mass observed at intermediate or destination points elsewhere on the pipeline. Because this system measures mass, additional instrumentation is used to capture on-line temperatures and pressures. This method works best for products that have some degree of compressibility.
- Simple “Rate-of-Change”. This method monitors key operating parameters at various points along the pipeline and reacts when these variables change at an abnormal rate or in some other unusual way.
- Combination “Rate-of-Change”. This method monitors key operating parameters at various points along the pipeline and reacts when different combinations of these variables change at an abnormal rate, or in some other unusual way.
- Computational pipeline monitoring. This leak detection method employs numerous monitored variables, and a sophisticated computer model to identify upsets or potential leaks. Monitored inputs include operating parameters for temperature, pressure, flow and density, and include equipment inputs such as pump start/stop and valve open/close signals. The data from all sensors is compared against a baseline model for values that differ from the modeled case indicating a potential leak. Operational transients such as pump starts, line fills, valve closures, etc., may be modeled as well, so that this automatic leak detection system can continue to work during operational changes that occur in the normal day-to-day operation of the pipeline system.
Leak Detection Sensitivity
Leak detection sensitivity is a reflection of the systems’ capability to detect a leak of a certain size in a predetermined time. Small leaks are the most difficult to detect, and take the longest time to set off an alarm or actuate some other system component. Some small leaks may fall below the threshold of leak detection systems, due to pipeline hydraulics, accuracy of the detectors, and alarm thresholds. Volume or mass balance systems are typically employed to detect these smaller leaks. Larger leaks are more easily detected, but must be detected quickly. Rate-of-change and computational pipeline monitoring are typically employed to detect these larger leaks.
Leak Detection Location
Identification and isolation are important steps in minimizing the consequences of any leak. Leak detection systems are used in order to do both. In most cases, it is not possible to pinpoint the location of a leak from a remote location, but leak detection systems, utilized by properly trained and qualified controllers or dispatchers, can, in a vast majority of cases, determine an approximate location so that the affected segment can be isolated.
Date of Revision: 110205