Effect of Hydrogen on the Fracture Toughness of X70 Pipeline Girth Welds Fabricated by Different Welding Processes

Girth welds in pipelines are more susceptible to hydrogen-induced damage under hydrogen-containing environments due to defects such as compositional segregation and stress concentration, posing a threat to the safe operation of pipelines. X70 pipeline steel girth welds were investigated in this study. Two types of welded joints were prepared using shielded metal arc welding combined with flux-cored arc welding(defined as Weld 1), and gas metal arc welding(defined as Weld 2), respectively. In-situ gas-phase hydrogen charging was employed, and fracture toughness characteristic values of the welded joints were tested under three environments: air, 1 MPa hydrogen, and 2 MPa hydrogen. The changes in fracture toughness and the micromorphology of crack propagation were investigated. Results showed that Weld 1 exhibited low-strength matching, while Weld 2 exhibited high-strength matching. Under the same environmental conditions, the fracture toughness of Weld 1 was superior to that of Weld 2. The hydrogen pressure in the testing environment had a limited effect on the fracture toughness values of both welds, whereas the mechanical properties of the welds had a more significant influence than the hydrogen environment. In hydrogen-containing conditions, both welds exhibited brittle fracture initiation behavior. Weld 2 showed a larger area of cleavage fracture morphology during crack propagation, indicating a higher sensitivity to hydrogen embrittlement compared to Weld 1. Results indicated that welded joints with higher strength produced by different welding processes were more sensitive to hydrogen embrittlement in hydrogen-containing environments.