Criteria and requirements for
leak detection systems and methods
The following document describes criteria and requirements for the Leak Detection Systems (LDS) and methods.
The provided information is based on public information, relevant industry standards and guidelines, as well as professional experience of our company in the field of LDS.
The field of leak detection is relatively new in comparison with the pipeline transport industry and lacks a solid and complete set of regulatory and technical requirements. Given that pipelines come in different types, sizes, topologies; given that pipelines are operated under different operating conditions of pressure, temperatures, and flow rates; and given that pipelines carry different kinds of fluids and gases; it is important that a comprehensive and adequate set of leak detection requirements and criteria is put in place by standard and quality assurance organizations. At present time there are a limited number of country specific organizations or guideline documents that deal with this topic and among them are American Petroleum Institute (API), Pipeline Research Council International (PRCI), Russian Scientific and Research Institute for Oil and Oil Products Transportation (NII TNN), German ‘Technische Regel für Fernleitungsanlagen’ (TRFL – translated as Technical Rule for Pipeline Systems), Saudi Aramco’s engineering standard for LDS “SAES-Z-003”.
According to the American Petroleum Institute document “RP 1130” LDS are divided into internally based systems and externally based systems. Internally based systems utilize field instrumentation (for example flow, pressure or fluid temperature sensors) to monitor internal pipeline parameters. Externally based systems also utilize field instrumentation (for example vapor sensors, acoustic microphones or fiber-optic cables) to monitor external pipeline parameters.
In documents and guidelines published by Pipeline Research Council International LDS are divided into two types:
- Direct approach based systems – use visual observations, soil sampling and various field instruments to monitor pipeline parameters.
- Indirect approach based systems – analyze changes in measurements and data against mathematical modeling to monitor pipeline parameters.
American Petroleum Institute document “API 1130” defines the following important requirements for LDS:
- Sensitivity: An LDS must ensure that the loss of fluid as a result of a leak is as small as possible. This places two requirements on the system: it must detect small leaks, and it must detect them quickly.
- Reliability: The user must be able to trust the LDS . This means that it must correctly report any real alarms, but it is equally important that it does not generate false alarms.
- Accuracy: Some LDS are able to calculate leak flow and leak location. This must be done accurately.
- Robustness: The LDS should continue to operate in non-ideal circumstances. For example, in case of a sensor failure, the system should detect the failure and continue to operate (possibly with necessary compromises such as reduced sensitivity).
Today, there are a number of LDS provided by various leak detection solution vendors to address the need for an effective and timely detection of pipeline leaks, and it is understood that each technology has its advantages and its limitations. It should be noted that some leak detection solution providers, for clearly commercial reasons, appear to be making unsubstantiated claims about their ability to detect leaks, taking advantage of the lack of clear and solid set of leak detection requirements, and also taking advantage of the lack of a mechanism to verify leak detection claims at the bidding and evaluation phases.
The following requirements and evaluation criteria are based on the professional experience of our company in the field of LDS, analysis of commercially available LDS and their respective methods against publically available guidelines and documents that are produced and endorsed by international organizations. General requirements for LDS:
- 1) Detection of leaks due to corrosion, technical accidents and theft of product.
- 2) Applicability for all types of products – liquids, gases and mix.
- 3) The underlying system’s methods should be practically proven in the industry.
- 4) Applicability for existing pipelines with extended infrastructure that includes parallel pipelines, intersec tions of pipelines, intermediate cut-off and isolation valves, pumping and storage stations, etc.
- 4) Ease of support and adaptation to future changes and expansions of monitored pipeline networks.
Evaluation criteria and technical requirements for LDS:
- 1) Fast response time – usually no more than 5 minutes. It should be noted that there are scenarios (for example slowly developing leaks) for which detection time can be greater. The relationship between leak size and the response time is dependent upon the nature (underlying method) of the LDS. Some systems manifest a strong correlation between leak size and response time, while with others, response time is largely independent of leak size.
- 2) Minimal detectable leak size or leak flow rate – in general, computational methods are able to detect leaks in the range of 1-2% of throughput (flow) in the pipeline. It should be noted that detected leak size or leak flow rate is dependent on the random (background) noise and operational mode of the pipeline. For example, during transient and non-stationary modes the detection characteristics can be worse than those during stationary modes.
- 3) High reliability – proper reporting of real alarms and low rate of false alarms and misses. The current state of leak detection technology allows for the reliable detection of leaks whose sizes are approximately 1-2% of throughput without excessive false alarms (depending on system specific variables).
- 4) High accuracy of localization – the current state of leak detection technology allows for very accurate localization of leaks usually within 1-2% of protected section length (for example for 15 km section the localization error should not exceed 150-300 meters).
- 5) High robustness – this criteria measures error handling capabilities when system components malfunction. It also measures a system’s ability to function in complex pipeline configurations when not all the needed information is available. Pipeline operators should be alerted at the first sign of degradation so that restoration efforts can be initiated, and complete loss of leak detection ability can be avoided.
- 6) High availability – this criterion measures the percentage of time during which systems operate at its full capacity. During steady-state conditions, the flow, pressure and other parameters in the pipeline are more or less constant over time. During transient conditions, these variables may change rapidly. For example the pressure and flow at inlet or outlet will change at start-up or stop of a pump or when batches change and different products are presented in the pipeline. Gas pipelines are almost always in transient conditions, because gases are very compressible. Even in liquid pipelines, transient effects cannot be disregarded most of the time. LDS should allow for detection of leaks for both conditions and provide leak detection during the entire operating time of the pipeline. The percentage of time during which operational transients exist is an important factor in selecting the appropriate computational method.
- 7) Ease of installation and operation – the system should be easy to install and should not require expensive equipment and complicated ground works. It should be also noted that systems should not require continuous presence of professional staff and operators for proper operations. Furthermore, systems should not require prolonged periods of on-line tuning and regular seasonal adjustments.