Engineering Critical Assessment of Embedded Flaws in Undermatch Pipeline Girth Welds

There is increasing demand for subsea transport of well-produced fluids that requires the use of bi-metallic pipelines. To optimize project costs, bi-metallic pipelines are often installed subsea by methods inducing cyclic plastic deformation. Engineering critical assessment (ECA) is typically required to derive acceptance criteria for weld flaws, most of which are embedded. As bi-metallic girth welds usually undermatch the parent metal, and ECA normally requires overmatch, this may be problematic. Although plastic deformation does not degrade the fracture toughness of overmatch welds, this may not hold for undermatch welds. Furthermore, in ECAs, the crack driving force (CDF) in embedded flaws is typically approximated by that in surface flaws, which may not always be appropriate. Therefore, this paper establishes a set of new CDF estimation schemes for embedded flaws in even-or overmatch welds and develops an ECA procedure for embedded flaws in undermatch bi-metallic girth welds.