Using Small Punch Test to Investigate the Mechanical Properties of X42 Exposed to Gaseous Hydrogen: Effect of Pressure, Pre-charge Time, Punch Velocity and Oxygen Content

This study investigated the effect of pressure, pre-charge time, punch velocity and oxygen content on the mechanical properties of X42 pipeline steel in gaseous hydrogen environment by using small punch test. When exposed to nitrogen, the fracture mode of X42 pipeline steel undergoes ductile fracture, but in the presence of hydrogen, it shifts to brittle fracture. Moreover, an increase in hydrogen pressure or a decrease in punch velocity is found to enhance the hydrogen embrittlement susceptibility of X42 pipeline steel, as evidenced by the decrease of maximal load, displacement at failure onset and small punch energy. But the effect of pre-charge time on the hydrogen embrittlement susceptibility of X42 pipeline steel is not very obvious. Meanwhile, the presence of oxygen has been found to effectively inhibit hydrogen embrittlement. As the oxygen content in hydrogen increases, the hydrogen embrittlement susceptibility of X42 pipeline steel decreases.