Effect of Water Chemistry on Corrosion Resistance of Alloy 600 SG Tubes Under Acidic Conditions

摘要

The environment of crevices between Alloy 600 (75Ni-15Cr-9Fe) Steam Generator (SG) tubes and tube support plates in secondary side coolant is assumed to be in an acidic condition due to the concentration of SO_4~(2-). Therefore, the influence of the water chemistry in acidic conditions on Stress Corrosion Cracking (SCC) and general corrosion was systematically studied, in addition to the influence of applied stresses and heat treatments of Alloy 600. The results of the C-ring tests were that SCC cracks apparently appeared below pH 3 (measured value at room temperature), which suggested a threshold of SCC susceptibility under the acidic condition. Electrochemical measurements showed that active dissolution of Alloy 600 was observed in acidic. Based on corrosion product analyses at the crack tip, the stability of the chmmium-rich oxide film is important for understanding the effect of the various acidic conditions.