Investigation of electrolytic hydrogen charging on the welding of a Line Pipe Steel API 5L X52 and its impact on fracture toughness using SENT specimens

Hydrogen is considered a key alternative to fossil fuels in the broader context of ecological transition. Repurposing methane pipelines to hydrogen is one of the challenges facing the ecological transition. However, hydrogen has the ability to diffuse within metallic lattices, causing the well-known phenomenon of hydrogen embrittlement (HE) [1]. For this reason, materials typically ductile can experience unexpected brittle fractures. For this reason, it is necessary to assess the HE propensity of the current pipeline network to ensure its fitness for hydrogen transport. In this work, the influence of the microstructure of the circumferential welded joint of an X52 pipeline steel was correlated with the amount of hydrogen electrolytically introduced into it. Base material (BM), heat affected zone (HAZ) and fused zone (FZ) were subjected to ½, 1, 2 and 4 hours of continuous charging with a current density J = -10 mA/cm2 in a solution composed of [H2SO4 ] = 0.05 and 2 .00 g/L of CSN2H4 . The HAZ used was reproduced from the BM through an appropriate heat treatment and characterized microstructurally and mechanically to verify its similarity to the original one. The electrolytic test revealed that the FZ is the material that can absorb the most hydrogen, followed by BM and HAZ. The BM reaches high concentrations of hydrogen due to the numerous non metallic inclusions that characterize it. Afterward, the materials underwent fracture mechanics tests with single edge notch tension (SENT) specimens. The tests took place both in air and under electrolytic charging to record the change in fracture toughness calculated as the J integral at the maximum force according with BS 8571 standard [2]. BM is the most sensitive material to a hydrogenated environment because it presents the highest drop in toughness between the test in air and in hydrogenated environment.