Chronic leak detection for single and multiphase flow: A critical review on onshore and offshore subsea and arctic conditions

Leak detection in pipelines has been a prevalent issue for several decades. Pipeline leaks from sources such as small cracks and pinholes are termed chronic leaks, as they have the potential of going unnoticed for long time periods, causing both economic losses and environmental damage. Literature lacks a comprehensive review of chronic leaks, especially under subsea or arctic conditions. Therefore, a primary objective of this work was the critical analysis of the current state of leak detection technology, especially under these conditions. A summary of critical findings from both experimental and field studies is included. A secondary goal was to determine the leak detection accuracy, resource level requirements, and risk of installation and operation for various techniques. The analysis shows medium to large scale leaks between 3 and 10 mm can be detected using dynamic pressure wave monitoring for single phase flow, whereas sequential probability ratio testing (SPRT) using real time transient monitoring (RTTM) can be used to monitor leaks for multiphase flow even in shallow water conditions and along elevated pipeline networks. Vacuum annulus monitoring arrangements can be utilized in order to detect chronic leaks, but are limited in their application due to weight and difficulty of pipeline installation. Additionally, distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) leak detection using fiber optic cables (FOC) was found to be resource intensive and have higher installation cost and operational risks due to unknown equipment reliability and location or sealing of the FOC on the pipeline structure. SPRT using RTTM have comparable accuracy to DTS or DAS leak detection and can be retrofitted to existing pipeline networks. However, more pilot studies utilizing FOC for subsea and arctic conditions need to be developed and examined. Leak detection using new pipeline construction materials such as reinforced thermoplastics (RTP) also warrant further research due to a current lack of reliable technology for these materials.