Mitigation Effect of Alkaline Water Chemistry upon Intergranular Stress Corrosion Cracking of Sensitized 304 Stainless Steel

Abstract

Alkaline water chemistry (AWC) has been studied as a new water chemistry control to mitigate intergranular stress corrosion cracking (IGSCC) of sensitized type 304 stainless steel (SUS304). The AWC was found to be capable of reducing crack growth rates (CGRs) of the IGSCC. At first, the direct effect of AWC upon IGSCC was studied experimentally. The 1/4T compact tension specimen was used for measurement of CGRs of the SUS304 in high temperature and high purity water. Crack length was monitored by a reversing direct current potential drop method. The CGR of SUS304 at 400 ppb O₂ concentration was reduced ten-fold when solution pH was increased to 9. During this time, electrochemical corrosion potential (ECP) of the specimen did not change so much. Second, it was predicted by a radi-olysis calculation that the AWC would reduce H₂O₂ concentration under the hydrogen water chemistry (HWC). Since the H₂O₂ concentration was more effectively suppressed by AWC, the required hydrogen concentration in feedwater to lessen the ECP of the reactor components was lower in AWC than at neutrality. Therefore, an indirect effect, that is moderation of the corrosive environment, could also be expected in addition to the direct moderation effect under HWC condition.

KEYWORDS:

• stress corrosion cracking
• pH control
• pH value
• mitigation effects
• alkali
• hydrogen water chemistry
• hydrogen peroxide
• crack growth rate
• electrochemical corrosion potential
• corrosion current
• radiolysis
• stainless steel-304