Effect of Constant Load on Hydrogen Diffusion and Trapping of API X65 Grade Linepipe Steel

The present research aims at investigating the hydrogen diffusion and trapping behavior of API X65 grade linepipe steel under constant load test, which is one of the standard sulfide stress cracking (SSC) evaluation methods. The modified electrochemical hydrogen permeation technique is combined to constant load test. Reproducible hydrogen permeation transients are obtained by carefully controlling the electrochemical surface condition without palladium coating. As the applied load increased, steady state permeability and hydrogen diffusivity decreased, and diffusible hydrogen content increased. These results indicate that more hydrogen has reacted with metallurgical defects in the steel which are sensitive to SSC initiation or propagation.