The Relationship between Cathodic Current in Rapid Straining Electrode Test and PWSCC Crack Growth Rate of Nickel Based Alloys under Simulated Primary Water Condition

摘要

Rapid straining electrode tests of nickel based alloys have been carried out under simulated primary water at 320°C with and without dissolved hydrogen (DH) for basic study of PWSCC mechanism. The followings are clarified as an electrochemical behavior of bare metal surface appeared just after oxide film failure under simulated primary water. 1) Very rapid repassivation of alloy690(UNS N06690) and relatively slow repassivation of alloy 600(UNS N06600) are observed under the condition without DH, however repassivation could not be observed and only cathodic current is observed under the condition with DH. 2) These cathodic current observed under the condition with DH, reaches some plateau value in a few seconds and the currents have been kept constantly more than 30 seconds. The plateau cathodic current of 690 is about 1/5 of those of alloy 600 and 132(UNS N06132). It is suggested that these cathodic current should have some important role for PWSCC, because relatively high susceptible material such as alloy 600 and 132 have higher cathodic current than alloy 690 which has much lower susceptibility to PWSCC and these results suggest that the hydrogen in metals should play important role for PWSCC.