Effect of Hydrogen on Mechanical Properties of Pipeline Steel Weld Metal

In this study, the effect of hydrogen on the mechanical properties of pipeline steel weld metal was investigated. In pipelines, weld metal is a significant part, and this part especially has been evaluated because of the presence of sour gas containing hydrogen atoms and other hazardous solutes which can harm base metal and weld metal. In this research, hydrogen charging was carried out due to the diffusion of hydrogen atoms into the sample through electrochemical pre-charging and immersion in the solution method. According to the results obtained in this study, in the presence of hydrogen, the yield stress of weld metal in Shielded Metal Arc Welding (SMAW) increased by 16%, and hardness in both direct and indirect charging method increased by an average of 10%. In the presence of hydrogen, elongation was reduced by 28%, and the percentage of ductile fracture decreased by 60% which indicate the brittle fracture. The content of diffused hydrogen was 1.5E-06 mol/cm3 using the Electrochemical Oxidation of hydrogen method. This amount was higher than that of other microstructures. According to microstructures observation (which provided from Optical Microscope (OM), Scanning Electron Microscope (SEM) photos), previous information, and recent reports in this field, it can be inferred that hydrogen diffuses into weld metal microstructure, which most of this is acicular ferrite by residing in dislocation tangles, grain boundaries, precipitations, and inclusions, causes hardening and decreases properties of weld metal. Overlay, the results of this study indicate that hydrogen degrades mechanical properties of weld metals and causes hydrogen defects. Also, weld metal microstructure has a significant effect on materials degradation in the presence of hydrogen.