Experimental and numerical study on the ductile fracture response of X65 girth-welded joint made of Inconel 625 alloy

Abstract

This work presents an experimental/numerical study characterizing the ductile fracture response of a pipeline girth weld of a corrosion-resistant alloy, Inconel 625. The welded joint was prepared with a narrow gap geometry. Thus, a newly designed double-groove bar is used to measure the weld metal’s tensile stress–strain curve. The geometry is extracted directly from the girth weld joint reducing the manufacturing process of tensile weld samples. The tensile result obtained from the bimaterial specimen is used to calibrate the modified Mohr–Coulomb damage model. A critical strain locus is defined for both materials, X65 and Inconel 625, depending on the stress triaxiality and Lode angle. A post-softening law is implemented to model the stable crack extension. The damage model is coded in a VUMAT subroutine in Abaqus software. The post-softening response is calibrated using a fracture toughness test. Then, validations are performed using a bimaterial specimen with a single groove and a bending fracture specimen. Overall, the matching is good between numerical and experimental results. Finally, numerical tests are performed for circumferential defective welded pipes to understand the influences of combined loads and misalignment on the pipe’s strain capacity. For partially undermatched weld joints, a flat double-groove bar is recommend for measuring the tensile mechanical properties of narrow gap welds. The CTOD-R curve measured at the FEM node behind the initial crack tip matches well the experimental CTOD based on the J-integral.