Hydrogen Diffusion in a Model Molybdenum Containing Steel: A Comparison Between Hydrogen Ingress Promoted By H2S or Cathodic Charging

Hydrogen embrittlement may be responsible for premature failure of steels when exposed to sour service environment. Different mechanisms (HIC, SSC, SOHIC…) have been described in the literature.

Based on specifically designed electrochemical Hydrogen permeation tests, it is possible to determine diffusion coefficient, trapped and diffusible hydrogen concentrations and activation energies, number of trapping sites.

A comparison of the characteristics of Sour and non sour service HSLA steels is detailed, based on permeation tests carried out using either a natural H₂S charging of the membrane or a cathodic charging in H₂SO₄ media.