Simulated service test for hydrogen embrittlement of cathodically protected subsea bolting materials

Abstract

A laboratory test is described for hydrogen embrittlement of subsea bolting materials in the form of 12·5 mm² test bars exposed stressed or unstressed to sea water with a small H₂S addition and under potentiostatically controlled cathodic protection. Tensile tests on specimens of alloy· K500 subjected to this treatment showed fracture surfaces similar to those of bolts of the same alloy which failed in service. Analysis revealed hydrogen absorption in both cases. Further experiments established the effects of test duration, stress level, cold work, controlled potential level, and presence of H₂S on embrittlement of this alloy. Embrittlement was indicated by low elongation and reduction of area values and by the presence of an outer zone of intergranular failure, shown in scanning electron microscope examination of the tensile test fracture surface. Recommendations are made for test conditions for general application.