The Stress Corrosion Cracking of Sensitized Stainless Steel in Thiosulfate Solutions

The stress corrosion cracking (SCC) of sensitized Type 304 stainless steel in thiosulfate solutions has been studied using constant extension rate tests. Very low concentrations of about 6.10−7M Na2S2O3 (0.1 ppm) gave cracking. With boric acid added, higher concentrations (1 ppm) were required. The SCC was shown to be electrochemically controlled. Below −0.5 VSCE (−0.75SHE). no SCC took place; above this potential, the rate of SCC increased with potential. Straining was required before SCC continued at 0.5 V if the potential was held at or below −0.5 V for extended times.