Abstract This study examined the challenges and necessary steps for performing a fitness-for-service (FFS) assessment of cracked clad pressure vessels in sour service through a Level 3 FFS assessment of a degraded Inconel 625–clad A516 Gr 70 pressure vessel containing crack-like flaws, in accordance with API 579-1/ASME FFS-1. The vessel, exposed to well fluids containing H2S, CO2, and chlorides, exhibited cracks due to weld defects in both the clad and the base metal. Advanced nondestructive testing (NDT) inspections identified critical defects, including a 3105-mm-long circumferential crack resulting from the welding process. Advanced elastic–plastic finite element analysis (FEA) was used to derive J-integral and reference stress solutions. Fracture and material properties, such as Master Curve toughness, true stress–strain curves, and residual stress distributions, obtained from FEA, were included. Results from the J-based Failure Assessment Diagram (FAD) indicated that the vessel fails the Level 3 FFS criteria, mainly due to the low fracture toughness of the A516 Grade 70 base metal under sour conditions, the presence of tensile residual stresses, and the presence of a long crack. The study highlights the challenges and the necessary steps for FFS assessment of clad vessels and presents an advanced FEA method for evaluating such vessels.
Amir Yazdanmehr (Tue,) studied this question.