L51822 A Limit States and Reliability-Based Girth Weld Assessment Framework for Long Pipeline Segments

This report describes the development of a graphical framework enabling probabilistic assessment of surface-breaking planar defects in pipeline girth welds, in terms of multivariate limit state functions incorporating weld strength mismatch effects. This is part of an ongoing effort by the Welding Research Supervisory Committee to align girth weld fitness-for-service assessment methods with recent advancements in limit states- and reliability-based design for pipelines. A previous three-year program (PR-185-9429) by the same investigators produced a database of partial safety factors (PSFs), calibrated against a broad range of reliability targets, for use with limit state functions based on existing stress intensity (crack driving force) and plastic collapse solutions. Several inherent limitations of these solutions, including their inability to account for strength mismatch in the behavior of weld metal and heat-affected zone (HAZ) flaws, motivated the development of new relationships in the present work. The PSF-based approach to probabilistic assessment also had its limitations, namely that it did not provide all of the necessary tools to address multi-weld pipeline segments, and that it was somewhat cumbersome to apply in practice. A more direct method was therefore desired.