Hydrogen trapping and hydrogen embrittlement (HE) susceptibility of X70 grade high-strength, acid-resistant, submarine pipeline steel with Mg treatment

The hydrogen embrittlement (HE) susceptibility of X70 grade, Acid-resistant, submarine pipeline steel with Mg treatment was studied via constant loading and slow strain rate tension (SSRT). The hydrogen diffusion and trapping behaviour in the tested steels treated with different Mg content was analysed by electrochemical hydrogen permeation testing and thermal desorption spectroscopy (TDS). The results suggested that micro/nanocomposite inclusions with "core-shell" structures obtained via Mg treatment have a greater activation energy of hydrogen desorption. On the one hand, this kind of inclusions can trap more hydrogen and reduce the diffusion coefficient of hydrogen in steel; on the other hand, the internal rigid core of Al–Mg–Ti–O and external soft shell of MnS not only play a role in stress shielding but also hinder the initiation and expansion of stress cracks. For the X70 grade high-strength, acid-resistant submarine pipeline steel, an optimal Mg addition amount is 0.003% (mass fraction).