Effect of nitrogen content in sensitised austenitic stainless steel on the crack growth rate in simulated BWR environment

The focus of the study is to establish the role of nitrogen addition to type 304L stainless steel, in sensitised condition, on the crack growth rate (CGR) by intergranular stress corrosion cracking (IGSCC) in the simulated boiling water reactor (BWR) environment. The CGR studies were carried out for two heats of type 304L stainless steel with 0.10 and 0.16 wt.% nitrogen and at different dissolved oxygen (DO) levels in high temperature demineralised water whose chemistry was maintained in a recirculating loop. The degree of sensitisation (DOS) was characterised quantitatively by double loop electrochemical potentiodynamic reactivation (DL-EPR) technique. The results clearly show that the susceptibility to IGSCC was substantially lower in the stainless steel with a higher level of nitrogen as reflected by the CGR values. This was attributed to the beneficial role of nitrogen addition against sensitization i.e. lesser coverage of the chromium depleted regions and higher level of chromium in the depleted regions in the stainless steels with higher nitrogen content.