The Contribution of In-Line IMU Inspection to Geohazard and Crack Management Strategies

Abstract

Geohazards and external loads are a significant threat to the integrity of pipelines in hilly terrain, at river crossings and where ground subsidence is taking place. Well designed pipelines can tolerate strains that exceed the nominal strain of 0.5% that corresponds specified minimum yield strengths, however the presence of weld defects and stress corrosion cracking can reduce the load capacity dramatically. Welds that are to specification but are under-matched on actual strength to the adjacent parent pipe have also been recognised as potentially vulnerable to low strain failures in high strength pipes. Modern pipelines in terrain susceptible to geohazards normally include design studies to identify and avoid or mitigate the threats. Surveillance of the right-of-way is also routinely carried out for pipelines with good integrity management practices, and particularly for major strategic lines. In-line inspection using an inertial measurement unit (IMU) is a well-known method to detect ground movement loads and contributes to the integrity management of pipelines. In this paper we illustrate : 1. How IMU inspection is an important tool in the management of geohazards and how it compliments other methods of geohazard assessment. 2. How locations of elevated pipe strain are identified and evaluated for external loading threats, and can be aligned with other data sets that indicate the pipeline load capacity. 3. How the locations of bending strain can be prioritised for further action. 4. How the loading profile in the pipeline can be incorporated into crack management strategies in order prioritise locations for further investigation or assessment.