ECA of embedded flaws in pipeline girth welds–a review

Highlights: • The significance, status and future R&D direction for ECA of embedded flaws in pipeline girth welds are reviewed and outlined. • Standard stress-based ECA procedures for embedded flaws employ engineering approximations and are widely considered too conservative. The rules for re-categorization of embedded flaws to surface flaws differ for commonly-used standards without clear scientific justification. -- Abstract: The significance and status of ECA of embedded flaws in pipeline girth welds are reviewed and outlined. Industry experience and the literature show that the majority of weld repairs in field construction is for embedded flaws, either volumetric or planar. Since repair welding of flaws is generally done under less-than-ideal conditions (wide range of temperatures, awkward geometries, time constraints, etc.) that could affect the quality of the welds, there is adequate justification for having the best possible technical approach for evaluating such flaws in standards, e.g. the Canadian pipeline standard (Z662). Stress-based ECA procedures for embedded flaws and re-characterization rules in commonly used standards are reviewed and compared, and progress in recent R&D is reviewed. There have been noticeable research and development (R&D) efforts using finite element modelling (FEM) on embedded flaws subjected to large strains, mainly for strain-based design (SBD) and offshore pipelines. The framework used in recent strain-based ECA studies is reviewed and is found to be useful for future development of stress-based ECA.