An Automatic Dent Assessment Tool Using Finite Element Method

Abstract

Dents are permanent plastic deformations of the pipeline that occur during pipeline construction and operations. Stress and strain concentration at dents may initiate cracks, which pose a threat to the integrity of the pipeline. Since formation of dents involves plastic deformation, a traditional depth-based assessment method cannot accurately capture the strain concentration, e.g. a sharp dent. Dent assessment methods have shifted to strain-based approach in recent years. Engineering Critical Assessment (ECA) procedures are evolving with the development of new methods to calculate the strains associated with a dent. It has been well established that three-dimensional (3D) elastic-plastic Finite Element Analysis (FEA) is the most accurate in the denting process simulation and dent strain calculation. However, FEA modelling of dents interacting with other threats can be extremely laborious and requires high level of FEA expertise. Moreover, continuum FEA is usually computationally expensive and imposes onerous demands for analysis efforts. This paper describes the process that was used to develop an automatic dent assessment tool via FEA. The tool is capable of simulating the denting process of a plain dent and a dent interacting with other threats (e.g., metal loss or gouge). The dent geometry and curvature in FEA are shown to agree well with captured In-line Inspection (ILI) caliper data. The tool also supports batch processing of numerous dents with a highly intelligent post-processing engine that automatically calculates von Mises equivalent strain, ductile failure damage indicator (DFDI) and strain limit damage (SLD) and outputs the results with visual contour plots. The Rainflow pressure cycling counting algorithm and Miner’s rule are incorporated in the tool to predict the fatigue life of the dent utilizing historical pressure data. Case studies are provided to demonstrate the effectiveness of the tool. The development of the tool greatly facilitates the ECA of dents allowing for accurate and efficient management of dents impacting TC Energy’s pipeline system.