The microstructures and passivation behavior of selective laser melted 316L stainless steel (SLM SS316L) after various heat treatments (500 °C, 950 °C, and 1100 °C) were investigated. The electrochemical results showed that the SLM SS316L sample that was heat treated at 950 °C exhibited the lowest passive current density. The microstructural characterization analysis indicated that the subgrain structures transformed from dislocation-rich subgrain boundaries into island-like cellular trace structures after heat treatment at 950 °C. This led to improved corrosion resistance due to the elimination of dislocations and the homogenization of the composition. Compositional analyses of the passive film indicated that there was no notable change in the passive film composition after heat treatment at 500 °C and 950 °C. However, heat treatment at 1100 °C promoted the formation of Cr(OH)₃ in the passive film, resulting in a reduced corrosion resistance. Based on these results, heat treatment at 950 °C appears to be an adequate post-process for SLM SS316L to optimize the microstructure, while also improving corrosion resistance.

The use of hydrogen-blended natural gas presents an efficacious pathway toward the rapid, large-scale implementation of hydrogen energy, with pipeline transportation being the principal method of conveyance. However, pipeline materials are susceptible to hydrogen embrittlement in high-pressure hydrogen environments. Natural gas contains various impurity gases that can either exacerbate or mitigate sensitivity to hydrogen embrittlement. In this study, we analyzed the mechanisms through which multiple impurity gases could affect the hydrogen embrittlement behavior of pipeline steel. We examined the effects of O₂ and CO₂ on the hydrogen embrittlement behavior of L360 pipeline steel through a series of fatigue crack growth tests conducted in various environments. We analyzed the fracture surfaces and assessed the fracture mechanisms involved. We discovered that CO₂ promoted the hydrogen embrittlement of the material, whereas O₂ inhibited it. O₂ mitigated the enhancing effect of CO₂ when both gases were mixed with hydrogen. As the fatigue crack growth rate increased, the influence of impurity gases on the hydrogen embrittlement of the material diminished.

The hydrogen permeation behaviour of X80 pipeline steel exposed to corrosion environments with different H₂S/CO₂ partial pressure ratios at room temperature was investigated through the high-pressure electrochemical hydrogen permeation test. Both CO₂ and H₂S have a hydrogen permeation promoting effect; however, CO₂ hydrogen permeation promoting effect is much weaker than H₂S. The hydrogen permeation curves have the rising, falling then stable stage. When at a total pressure of 1 MPa, as the H₂S partial pressure decreases, the hydrogen permeation promoting effect weakens, but the peak current of hydrogen permeation gradually increases. The main reason is that the role of corrosion products has changed from promoting hydrogen permeation to hindering hydrogen permeation during the reaction.