Inhibitive Effect of Oxyanions on the Stress Corrosion Cracking of Type 304 Stainless Steel in Boiling 20 N NaOH Solution

Stress corrosion cracking (SCC) of Type 304 stainless steel readily occurs in concentrated caustic solutions (35 to 65% NaOH) at temperatures near or above their boiling point. Several investigators including Pickett, Pearl, and Rowland ⁽¹⁾; Mcllree and Michels ⁽²⁾; Wilson and Aspden ⁽³⁾; Wilson, Aspden, and Pement ⁽⁴⁾; and Theus ⁽⁵⁾ have reported SCC in dilute caustic solutions also, but in pressurized systems at temperatures considerably higher than the boiling point of the solutions. Subrahmanyan et al, ⁽⁶⁾ have studied in detail the effects of caustic concentration, temperature, stress, and applied potential on the SCC of Type 304 in concentrated caustic solutions up to their boiling point. According to these authors ⁽⁶⁾ the propensity to SCC increased with an increase in the caustic concentration, temperature, and the stress. The failure mode and the fialure time changed with the applied potential. The mode was predominantly transgranular fissuring near the corrosion potential, transgranular plus general corrosion near the active peak, general corrosion in the active to passive transition region, pitting occurred in the transpassive region, and the mode was predominantly intergranular in the pseudo-passive region. There was relatively little corrosion attack in the passive region.