Threshold Temperature for Stress Corrosion Cracking of Duplex Stainless Steel Under Evaporative Seawater Conditions Available to Purchase

The susceptibility of 22 Cr and 25 Cr duplex stainless steels to stress corrosion cracking under evaporative seawater conditions has been evaluated using a modified drop evaporation test. At an applied stress of 90% σ_0.2, a threshold temperature for cracking between 70°C and 80°C was identified for both materials. Observation of patchy corrosion and occasional pitting beneath the salt layer was consistent with an aggressive underdeposit chemistry, but the extent of corrosion was dependent also on the applied stress. No cracking was observed below the proportional limit in the stress-strain curve at 100°C, suggesting that a combination of this chemistry and microplastic deformation is responsible for cracking of the steels. The engineering implication is that existing recommendations for the critical temperature for coating of duplex stainless steel to avoid failures in service may need to be revised downward.