Quantification of the temperature threshold of hydrogen embrittlement in X90 pipeline steel

In the current research, the dependence of hydrogen embrittlement (HE) on the temperature in X90 steel is studied through experimental tests and molecular dynamics simulations. Slow strain rate tests (SSRT) were applied to X90 specimens in the air and the simulated groundwater solution (called NS4), respectively. The fracture morphologies of the specimens were observed by scanning electron microscope (SEM). The results indicate that the temperature threshold of hydrogen embrittlement (HE) in X90 steel is 313 K, beyond which the HE would be weakened with the rise of temperature, and below which the HE would be enhanced with the rise of temperature. To illustrate the underlying mechanism of this phenomenon, molecular dynamics simulations were applied to quantify the correlation of temperature with hydrogen diffusivity, and the results of Devanathan-Stachurski tests were used to quantify the bulk hydrogen concentration at different temperatures. A theoretical model was thus developed based on hydrogen potential thermodynamics to predict the threshold temperature. The predictive model matches well with experimental results, revealing the promoting effect of hydrogen diffusion and accumulation on the crack growth, which is fundamental for understanding hydrogen-induced damage in structural materials.