Hydrogen Effect On Fracture Toughness Of X65 Pipeline And Its HFW Welding

X65 pipeline steel plays a major role in China's oil and gas transportation projects,mainly the Bohai Sea oil and gas transportation pipelines currently in use.However,during the installation process,especially during transportation of LPG there is joint damage caused by pipeline or transportation routes failures.Therefore,this article focus on X65 pipeline steel and the high-frequency electric resistance welded seam,using an electrochemical hydrogen charging,hydrogen embrittlement susceptibility macroscopic fracture toughness testing studied by means of the base metal and weld X65,The main contents and conclusions are as follows:(1)The hydrogen content of base metal and welding have the same tendency,first,the content go up to a highest value and then go down to a stable value.No matter the highest value and stable value,the content of welding is higher than that of base metal,that's to say,welding can contain more hydrogen than base metal.(2)Fracture toughness are measured using combined electrochemical method with three-point bending method.The base metal and welding both show good mechanical properties in the air.When testing in the hydrogen environment,the CTOD of welding show huge fall while the base metal only show slight fall.This result indicate that the susceptibility of hydrogen embrittlement of welding is higher than that of base metal.(3)The weld metal show lower permeability and diffusivity in the permeation test,which indicate that hydrogen cannot pass through the base specimen,so the probability of cracking will be very high in this steel.Also,the density of hydrogen traps was calculated from the permeation curve.A higher density of reversible trap sites was observed in the weld metal,which is an indication for higher susceptibility of this metal to HIC.(4)Crystallographic texture measurements showed that there were some resistant and non-resistant textures in both and weld metal,so it is difficult to estimate HIC susceptibility.The fraction of LABs and ?1 type boundaries are higher in the lower in the weld metal which make it prone to HIC.