Dent-Weld Interaction for Strain Assessment

Abstract Dents are an integrity threat to oil and gas pipelines. Due to the higher perceived risk of cracking associated with dents on welds, the acceptability thresholds for dents interacting with welds are more stringent than that for plain dents in the pipe body. Similar to the depth based criteria, when curvature strain assessment is utilized to determine dent acceptability, the acceptability threshold for a plain dent on the pipe body and a dent interacting with a weld is 6% (material specific limits are also available) and 4%, respectively. When applying these screening criteria based on in-line inspection data, one practical challenge is to determine whether a dent is interacting with weld or not. Since weld interaction directly dictates the dent acceptability threshold, it affects repair decisions and hence may have a large impact on a pipeline operators’ budget and potentially pipeline safety. Overly conservative dent-weld interaction rules can cause unnecessary repair or investigation; whereas non-conservative dent-weld interaction rules may lead to injurious and non-compliant dents left in place unrepaired. This paper presents a study of the dent-weld interaction rules from strain assessment perspective. A strain assessment database with greater than 9,000 dents, detected and measured by ILI, was utilized in this study to investigate the potential of applying existing dent-weld interaction criteria for strain assessment purposes. Recommendations are made with respect to applying such criteria for dent screening based on ILI data.