Hydrogen Embrittlement of Cathodically Protected High-Strength, Low-Alloy Steels Exposed to Sulfate-Reducing Bacteria

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Abstract
Hydrogen embrittlement (HE) of two high-strength, low-alloy steels was studied in conditions typical of the marine environment. Double-cantilever beam specimens, heat-treated to produce the microstructure in the heat-affected zone of a weld, were tested in seawater containing sulfate-reducing bacteria (SRB) at a range of cathodic protection potentials. The threshold stress intensities (Kth) required to cause subcritical crack propagation were recorded. The concentration of H absorbed by the steel (Co) was measured using a permeation technique and was shown to be higher at more cathodic potentials and significantly increased when SRB were present. An inverse relationship was established between log Kth and Co for sterile and biologically active environments. It was concluded that crack propagation occurred by a single HE mechanism, regardless of whether SRB were present. The bacteria were believed to increase sulfide concentration in the biofilm at the metal surface, which promoted increased Co.

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