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Pipeline Technology Journal 2-2015

Latest developments and news from the pipeline industry

RESEARCH / DEVELOPMENT / TECHNOLOGY Selecting a suitable leak detection system is not an easy task for pipeline operators. The system must meet the needs of the particular application and comply with [relevant] regulations. In this article, regulatory require- ments will be discussed first. The most important regulations for North America are API RP 1130 and CSA Z662-2011 Annex E. API RP 1130 is published by the American Petroleum Institute, which is the largest trade association in the oil, gas and petrochemical industries in the USA with influence that reaches far beyond America. API RP (Rec- ommended Practice) 1130 is even more detailed with regard to leak de- tection systems. Among other items, it includes a collection of general recommendations for operating leak detection systems, such as clear presentation of the results for the operator and for maintenance. It also includes performance criteria for selecting a leak detection system: these criteria are very de- tailed and explain how leak detection systems work. The criteria are out- lined below, and it is easy to see that they are linked and interdependent. - Sensitivity: the leak detection system should detect even small leaks within a short period. - Precision: the leak detection system should locate leaks precisely. The leakage rate, the quantity of escaped product (leakage rate multiplied by time) and the product that is escaping should all be indicated. - Robustness: the leak detection sys- tem should continue active monitor- ing despite unsteady or non-ideal conditions. This includes conditions such as temperature fluctuations, changes in viscosity and sensor fail- ure. It also includes unsteady operat- ing conditions, also known as tran- sient operation, for example due to effects triggered by pumps or valves. - Reliability: the leak detection system should not generate false alarms, even though it is highly sen- sitive. Canadian Standards Association CSA Z662 Annex E represents recommended practice for liquid hydrocarbon pipeline system leak detection in Canada. It emphasizes the need to establish a procedure for making material balance for the entire product transported: when de- signing, operators should consider all physical and operational factors that can influence the material bal- ance system and establish toleranc- es. Under normal operating condi- tions, the uncertainty in the receipt and delivery values used in the material balance calculation, including uncertainties attributable to processing, transmission, and operational practices, shall not exceed 5% per five minutes, 2% per week, or 1% per month of the sum of the actual receipts or deliveries. To meet these requirements, the uncertainty in the individual receipt and delivery measurements under installed operating conditions shall not exceed 2% of the actual measurements. Hereby, the CSA Z662 An- nex E is the only recommended practice to include precise uncertainties for leak detection systems. When the operator has clarified relevant requirements of the appropri- ate regulatory for his application, other characteristics that affect the choice of leak detection system can be considered. These may include technical and environmental parameters such as the length of the pipe- line, whether it runs above or below ground, and the volume, type and quantity of different products to be transported. The desired type of monitoring may also be considered: internal (using process measure- ments), or external (using special measurements). The next step is to review systems available on the market. Assum- ing an internal system has been specified, the preferred type all over the world, the options are reduced to a handful of systems based on various mathematical and physical principles. The RTTM (“Real-Time Transient Model”) is the leading technology at the moment. RTTM is a mathematical model that compares measurements taken during the actual operation of a pipeline with those of “virtual pipeline”, or a com- puter simulation of the pipeline, in real time. KROHNE, a manufacturer of measuring technology and established supplier of systems to the oil and gas industry for more than 30 years, has expanded its product range to include E-RTTM, a leading technology for continuous internal monitoring of pipelines. E-RTTM stands for Extended RTTM, which com- bines RTTM principle with leak signature analysis using leak pattern detection (see Figure 1: Functional principle of a leak detection system based on E-RTTM). Combining two principles has several advantages. In 2012, the U.S. Department of Transportation Pipelines and Hazardous Materials Safety Administration published a Leak Detection Study, DTPH56- 11-D-000001, which states: “The leak detection system itself should always be redundant, by using multiple techniques that differ from each other and therefore compensate for any inherent weaknesses they do not share.” It also describes the benefits of combined leak detection methods: “There is no reason why several different internal leak detec- tion methods should not be implemented at the same time. In fact, a basic engineering robustness principle calls for at least two methods that rely on entirely separate physical principles. As an example, the Ex- tended-RTTM system trademarked by KROHNE uses an RTTM in con- junction with several other API 1130 techniques”. Figure 1: Functional principle of a leak detection system based on E-RTTM PIPELINE TECHNOLOGY JOURNAL 25

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