The stress corrosion cracking of type 316 stainless steel in oxygenated and chlorinated high temperature water

Abstract

Slow strain rate stress corrosion tests have been performed on Type 316 stainless steel in 265°C water containing from 0 to 45 ppm oxygen and from < 0.1 to 1000 ppm chloride. The main difference between the present data and previously published results, the latter mainly for Type 304 stainless steel, is that as well as cracking occurring in water containing high oxygen and chloride, it is shown that a cracking regime exists at very low oxygen contents for a wide range of chloride contents. The type of cracking varies with the oxygen and chloride content of the water and the most severe cracking was of comparable extent in both the gauge length and the necked region of the specimen. The least severe cracking only caused cracks to occur in the necked region of the specimen and there was a range of oxygen and chloride contents in which no cracking occurred. The rest potential for annealed Type 316 stainless steel has been mapped for a wide range of oxygen and chloride content waters and it is shown that at 265°C the ‘no-cracking’ regime of the oxygen-chloride diagram corresponds to potentials in the range −200 to +150 mV(SHE). It is speculated that at high oxygen contents cracking results from the fracture of the passive film, whereas at low oxygen contents the cracking involves fracture from a thin de-alloyed film. The relevance of the type of cracking that occurs in the slow strain rate test to the use of Type 316 stainless steel in high temperature water is discussed.