Reliability Analysis of Dented Pipelines in the Absence of Deformation Profiles

Dents associated with stress risers contribute to pipeline degradation, as they may increase the likelihood of loss-of-containment incidents. The regulatory-based dent and threat integration integrity management utilizes dent depth and potential interaction with stress risers such as crack, corrosion, and/or welds criteria. However, there have been industry incidents that passed such criteria and still resulted in loss of containment. As part of pushing the boundaries of pipeline integrity assessment towards quantitative risk assessment (QRA), a semi-quantitative analysis of dents (SQuAD) had been recently developed; where a strain-based limit state is used to account for pipe properties, dent geometry, and threat integration uncertainties. SQuAD utilizes deformation surface profile reported by caliper in-line inspection (ILI) tools to estimate the radius of dent curvature. Deformation surface profiles are usually provided by the ILI vendors, but it may not be practical to obtain these profiles on all dent features reported across a pipeline system. In the absence of such data, pipeline operators face a challenge in assessing dent severity using the QRA framework. Herein, a practical surrogate model of dent curvature parameters is proposed to enable the use of SQuAD approach without full knowledge of deformation profiles. The surrogate model is a function of ILI reported dent characteristics (i.e., depth, width, and length) and provides a width and length scaling scheme that makes use of dent shape factors. Based on a set of dent cases, the analysis results obtained from SQuAD approach with the surrogate model using several scaling schemes were compared against those obtained from SQuAD approach with ILI-based deformation surface data. It was concluded that with a proper scaling scheme, SQuAD-based surrogate model approach can produce reasonable results with sufficient conservatism compared to the SQuAD-based ILI deformation approach. The proposed approach is suitable for dent integrity screening decision purpose, which would help pipeline operators to assess, rank, and prioritize resources in dent and threat integration integrity management programs.