加氫水化學與鉑覆膜對敏化304不銹鋼之應力腐蝕龜裂之影響

The Influence of Hydrogen Water Chemistry and Platinum-coating on Stress Corrosion Cracking of Sensitized Type 304 Stainless Steels

沸水式反應器（Boiling water Reactor, BWR）的結構組件中應用很多不銹鋼材料，其主因在於不銹鋼通常具備良好的抗蝕能力；但在多年運轉後，不少反應器的壓力槽內部組件依然出現沿晶應力腐蝕龜裂（Intergranular Stress Corrosion Cracking, IGSCC）的問題。近年來，加氫水化學（Hydrogen water Chemistry, HWC）搭配貴重金屬化學添加（Noble MetaI Chemical addition, NMCA）覆膜處理技術，逐漸被廣泛用以解決不銹鋼於BWR環境中的IGSCC問題。理論上，從水的再結合反應預測，在加氫水化學環境下當水中氫氧莫爾比（MH/O）大於2時，組件材料表面的電化學腐蝕電位（Electrochemical Corrosion Potential, ECP）值會被降低，不過受到貴重金屬催化作用的影響，即使MH/O小於2仍然有ECP下降效果。本研究在不同MH/O的水化學環境中，進行不同披覆條件試片的慢應變速率拉伸（Slow Strain Rate Tensile, SSRT）試驗，並同時監測ECP值的連續變化。實驗結果顯示，貴重金屬催化作用導致ECP下降的效果必須在高溶氫水化學環境較為明顯，無論有無貴重金屬覆膜的試片在HWC環境均無IGSCC發生。

The reactor internal structural components in boiling water reactors (BWRs) are composed of stainless steel (SS) materials due to their good corrosion resistant properties. However, vessel internal cracking (VIC) problems due to intergranular stress corrosion cracking (IGSCC) were still found. Two technologies, hydrogen water chemistry (HWC) and noble metal chemical addition (NMCA), have been proposed to mitigate VIC problems. In theory, the electrochemical corrosion potential (ECP) on surface of component material is reduced when the molar ratio of hydrogen to oxygen (MH/O) in H2O recombination reactions is greater than 2. It was also found that even ECP would be reduced with the catalysis of noble metals when M H/O is smaller than 2. In this study, the specimens of different coating condition were tested in the water chemistry of various M H/O by slow strain rate tensile (SSRT) and continuous monitoring of ECP. The result came out that ECP reduction was more profound under the condition of higher dissolved hydrogen. In HWC environment, no IGSCC occurred regardless of specimens with or without noble metal coating.