Effect of cathodic potential on hydrogen permeation of API grade steels in modified NS4 solution

The goal of this work was to simulate the effect of H2S produced by SRB (Sulfate reducing bacteria). This H2S effect was evaluated by different electrochemical tests carried out with the API X60 grade steel. Therefore, Polarization curves, Slow Strain Rate Testing (SSRT) and hydrogen permeation test were carried out using a modified synthetic soil solution – NS4+thiosulphate. In addition, the Slow Strain Rate Testing and hydrogen permeation tests were performed at free corrosion potential (Ec) and cathodic potential equal to 300mV below Ec. These results were compared with the NS4 standard. To conclude, the API X60 steel presented decrease in ductility in the modified NS4 solution at more cathodic potential. This behavior occurred probably because of the increment of hydrogen flux detected in modified NS4 solution in relation to NS4 standard. The contribution of hydrogen embrittlement to EAC (environmentally assisted cracking) is consequently confirmed.