Hydrogen uptake by structural steels at cathodic protection in sea water inoculated with sulfate reducing bacteria

Abstract

AbstractThe effect of sulfate reducing bacteria (SRB) on the hydrogen permeation rate through ferrite‐pearlite and sorbite steels of quite similar chemical composition was studied using a specially designed facility. Tests were carried out in synthetic sea water, sterile or inoculated with bacteria, at potentials corresponding to cathodic protection (− 800 mV to − 1400 mVNCE). Cathodic polarization within the studied potential range did not stop the metabolism of SRB. Presence of SRB was found to increase the hydrogen permeation rate, to form S2− ions, to increase the polarization current, to modify the impedance spectrum and to change the appearance of cathodic deposits in comparison with sterile conditions. The promoting effect of SRB on the hydrogen uptake was concluded to be the result of the increase in polarization current due to the formation of the less protective layer of cathodic deposits on the steel surface, the presence of S2− ions and the possible decrease in pH. Despite the similar tendencies, the effect of SRB on hydrogen uptake was more pronounced in the case of sorbite steel. The bacteria action can cause hydrogen deterioration of steel at potentials, recognized as safe ones at cathodic protection.