Improvement of strain-based failure assessment diagram for pipeline girth weld

Strain-based failure assessment diagram(SBFAD) is an important method to assess the crack defects in pipeline when the nominal stress of pipeline exceeds the yield strength of the material. Weld strength matching is an important parameter afecting the fracture behavior of pipeline girth weld, while the traditional SBFAD method does not consider the influence of weld strength matching. In view of this, the finite element model of local circumferential crack driving force on the outer surface of pipeline girth weld was established by numerical simulation method. The efect of crack depth, crack length, weld strength matching coefficient and pipe yield strength on the assessment accuracy of SBFAD for the crack defect of pipeline girth weld was verified based on the reference strain calculation method proposed by Guide to methods for assessing the acceptability of flaws in metallic structures(BS 7910-2019). Then, the improved method and calculation model of reference strain were proposed, with the weld strength matching accurately incorporated into SBFAD. Generally, the improved SBFAD method significantly improves the application scope and assessment accuracy of theassessment method, and could provide reference for the applicability assessment of pipeline girth weld in engineering.