The stress corrosion cracking of heavily sensitized type 316 stainless steel in water in the temperature range 50–100°C

Abstract

The susceptibility to stress corrosion cracking of a Type 316 stainless steel tubing material which had been sensitized in a steam generating rig operated at temperatures from 502 to 533°C was assessed using the slow strain rate technique. The experiments were performed in de-aerated and in oxygenated water with and without chloride additions and in the temperature range 50–100°C. The material was susceptible to stress corrosion cracking and to mechanically induced cracking during dynamic straining. Susceptibility to stress corrosion cracking increased with increasing temperature and with increasing oxygen and chloride contents. Cracking occurred with greater than 200 ppb oxygen present even when the chloride content was less than 5 ppb. The maximum allowable oxygen content decreased further when the chloride content was increased. The maximum chloride content for immunity to stress corrosion cracking was 5 ppm even when less than 5 ppb oxygen was present in the water. The severe susceptibility of the material was caused by the complicated metallurgical state of the inner tube surface, but cracking could be prevented by appropriate potentiostatic control.