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Specimens from nickel-based clad pipeline girth welds were tested in H 2 S solution. The results of the fatigue crack growth rate curve at higher Δ K values were about 4 times higher than the in-air values. The rate at 180 °C was generally higher than the in-air data for flaw assessments found in the British Standard BS7910 by a factor of up to 3 times. From the analyses of the diffusible hydrogen, the backing steel of such pipelines are predominantly protected from the sour environment by the corrosion-resistant alloy clad layer. The results from this study are relevant for desktop Engineering Critical Assessment of girth welds of such pipelines. [ABSTRACT FROM AUTHOR]

Abstract: Steel pipelines used for oil and gas transportation are joined by girth welding and welds may contain weld imperfections/defects such as lack of fusion, under-cuts, porosity, slag inclusion etc. of certain height and length at certain location along the longitudinal direction of the weld. During the installation and operation, these pipelines are exposed to large plastic deformation. Fracture assessment procedures: BS7910:2005 [1] or R6 [2], are not suitable for such plastic strains (3%). The evolution of crack tip opening displacement (CTOD) of the pipeline with elliptical embedded crack in a girth weld is investigated under biaxial loading conditions using a three dimensional elastic–plastic finite element method. Based on the results, empirical formulas depicting relationship between the CTOD and the global strain are proposed. [Copyright &y& Elsevier]