Integrity Assessment of an In-Service Gas Pipeline Featuring Dent Defect at a Highway Crossing

Abstract

Underground pipelines are susceptible to different types of damage/flaws such as metal loss, buckling, dents, gouges, cracks, etc. during installation and operation. The structural integrity of the pipelines featuring such defects needs to be ensured for safe operation and to avoid serious hazards (fire/explosion/fatality/injury etc.). This paper discusses the integrity assessment of an actual case of an in-service gas pipeline featuring dent damage located at a highway crossing. A routine in-line inspection (ILI) of the considered pipeline showed the presence of a dent type of damage with a maximum depth of 5% spread over an area of 325 mm x 275 mm. Since the pipeline is located approximately 7.5 m below a 10-lane expressway with heavy traffic, dig verification of the dent was found to be not feasible. Level-3 integrity assessment based on API 579-1/ASME-FFS-1 2021 Fitness-For-Service standard has been performed using commercial finite element (FE) software ABAQUS/CAE. The considered pipeline is subjected to overburden pressure of soil embankment and cyclic loads such as vehicular loads (as per IRC: 6-2017) and internal pressure. The dented pipeline segment was assessed for potential failure modes i.e., protection against plastic collapse, local failure, collapse from buckling, and fatigue damage. FE analysis of the pipeline-soil system has been carried out considering the material and geometric nonlinearity, and contact interactions. The study suggests the pipeline is safe for further operation with existing dented defects. The methodology presented in this paper can act as a guide for the integrity assessment of pipelines with dent damage located at highway crossings.