EFFECT OF CHLORIDE ON ENVIRONMENTALLY ASSISTED CRACKING OF LOW ALLOY STEELS IN OXYGENATED HIGH- TEMPERATURE WATER - GENERAL CORROSION

摘要

Recent investigations at different laboratories have shown a strong effect of chloride contaminations on the crack growth rate of low-alloy steel (LAS) in oxygenated high-temperature water (HTW). Therefore, a research project was launched to systematically investigate the effects of chloride contaminations on the environmental degradation of materials under BWR-relevant water conditions.This project focused on investigations of the general corrosion and crack initiation behavior of LAS (German RPV steel 22NiMoCr3 7) in oxygenated HTW without chloride and at different chloride contamination levels up to 50 ppb. Chloride was added either permanently or temporarily to simulate a chloride transient during plant operation.During these tests, Electrochemical Noise (EN) and Electrochemical Impedance Spectroscopy (EIS) measurements were performed to monitor the electrochemical behavior. After the tests, the specimens were examined macroscopically and microscopically. In addition, the oxide layer thickness was determined using the Focused Ion Beam (FIB) technique and different surface analysis techniques were performed to analyse the composition of the oxide layer.The applied tests clearly revealed a decrease in oxide layer thickness during permanent chloride contamination. Temporary transients, however, did not cause a long-term memory effect.