Stress corrosion cracking of duplex and super duplex stainless steels in sour environments

The resistance of two commercial duplex stainless steels to sulphide stress corrosion cracking in sour environments has been assessed by means of slow straining in a variety of solutions saturated with hydrogen sulphide over the temperature range from 2 to 95 degrees C. The results suggest that, although one is not susceptible to any loss in ductility, the other suffers a significant loss in ductility and a ductility minimum occurs at some temperature between 25 and 80 degrees C that depends upon the environment. The embrittlement at lower temperatures is attributed to absorption of the hydrogen generated at the steel surface, but this is mitigated by the barrier to permeation presented by the passive film also generated. Associated polarisation measurements and appropriate pitting experiments clearly indicate a reduction of the range of potential in which passivation occurs with increasing temperature and severe pitting above a temperature that depends upon the alloy content of the steel. The prevalence of severe pitting corrosion provides an explanation of the attenuation of the hydrogen embrittlement effects at the higher temperatures, and the resultant occurrence of a minimum ductility. (C) 1998 Elsevier Science Ltd. All rights reserved.