Low-Temperature Stress Corrosion Cracking of Austenitic and Duplex Stainless Steels Under Chloride Deposits

Corrosion performance of austenitic-ferritic (duplex) stainless steels UNS S32101, S32202, S32304, and S32205 and austenitic stainless steels UNS S30403 and S31603 was studied in the presence of chloride deposits simulating non-rinsing atmospheric conditions. The effect of temperature, relative humidity, concentration, and composition of the chloride deposits on the tendency for atmospheric, low-temperature, chloride-induced stress corrosion cracking (SCC), pitting, and selective corrosion was assessed using prestressed samples with a circular weld. In the presence of calcium chloride, SCC was observed at temperatures as low as 20 degrees C and 30 degrees C on the austenitic stainless steels UNS S30403 (Type 304L) and UNS S31603 (Type 316L), respectively. The only cases of SCC of tested duplex stainless steel grades were found at 70 degrees C, which otherwise suffered mainly selective dissolution of the ferrite phase with one order lower depth of attack. The initiation of SCC and selective/pitting corrosion was governed by the equilibrium chloride concentration in a solution formed by contact with chloride-containing deposits and with air at a given relative humidity. Threshold levels of critical chloride concentrations, critical relative humidity in the presence of specific deposits, and maximum temperatures for safe applications of the studied grades were established.