The embrittlement of a duplex stainless steel by hydrogen in a variety of environments

The resistance of a duplex stainless steel to hydrogen embrittlement in a variety of environments was investigated and a comparison between different sources of hydrogen attempted. The conditions all involved slow straining to failure: (i) in gaseous hydrogen at pressures up to 0.2 MPa; (ii) in air after thermal charging at 350 degrees C in high pressure hydrogen (32 MPa); (iii) whilst cathodically charging with hydrogen by polarization in various aqueous environments at 70 degrees C and (iv) in an acidified chloride solution saturated with hydrogen sulphide (NACE) at 70 degrees C. All the environments produced a major drop, compared to the 78% reduction in area at fracture observed in air, to values in the region of 20-30% acid the metallography and fractography exhibited common features that indicated that hydrogen embrittlement was involved. The presence of hydrogen sulphide in the environment did however introduce the complication of extensive chemical attack during and after crack propagation. Tests in this solution were further complicated by surface films and localised corrosion in the form of pits. Results obtained in the different environments are compared in terms of the contribution that hydrogen embrittlement makes to the ultimate failure.