Stress Intensity Factor of Dents With Axial Cracks

Abstract Recent field studies have identified pipeline dents interacting with anomalies, such as axial cracks, that were not captured by in-line inspection (ILI) tools or the dent engineering critical assessment (ECA) methodologies. This study investigates the limitations of the current Level-3 dent ECA approach as specified in API-1183. A key gap in current dent assessments is the lack of guidance addressing scenarios where dents interact with crack-like anomalies. Specifically, this study examines two pressing questions: (1) whether fitness-for-service (FFS) codes such as API 579 and BS 7910 can reliably evaluate the remaining life/strength and failure mechanisms of dented pipelines, and (2) whether a dent exhibiting high plastic strain levels but ductile damage indicator (DFDI) or strain limit damage (SLD) values below unity should trigger further assessment of micro-, meso-, or macro-scale damage using fracture mechanics techniques. Current industry practice applies fatigue and fracture failure assessments based on stress intensity factor (SIF) and reference stress (σref) formulations derived from straight, non-deformed pipe geometries may not provide accurate results for dented pipes. This study critically evaluates whether existing FFS code formulations are suitable for assessing dents, specifically focusing on the accuracy of stress intensity factor (SIF) calculations. The Newman-Raju’s SIF formulations, which underpin the SIF formulations in API 579 and BS 7910, were reviewed and compared with results from the extended finite element method (XFEM) simulations. Significant discrepancies were observed between the two methods, highlighting the potential non-conservatism of current FFS code formulations when applied to the Level-3 dent assessment. To address these gaps, the study recommends refining the Level-3 dent ECA methodology. The findings underscore the need for improved assessment frameworks associated with SIFs to ensure pipeline integrity, particularly where existing standards may not be applicable.