690和800合金在高溫高壓水中硫致腐蝕失效研究進展

690和800合金在高溫高壓水中硫致腐蝕失效研究進展RESEARCH PROGRESS ON SULFUR-INDUCED CORROSION OF Alloy 690 AND 800 IN HIGH TEMPERATURE AND HIGH PRESSURE WATER

高溫高壓水中的硫對蒸汽發(fā)生器合金的腐蝕是最復雜的腐蝕過程之一。本文從熱力學計算和實驗方面綜述了高溫高壓水中硫致690和800合金腐蝕的研究進展。熱力學計算主要以E-pH圖、伏特等效圖以及離子分布系數(shù)曲線呈現(xiàn)，計算結果表明S的價態(tài)以及與金屬的相互作用主要受溫度、pH以及電位的影響，但熱力學計算沒有考慮S中間產(chǎn)物的影響作用。腐蝕電化學及表面分析結果表明硫致腐蝕受溫度、pH值、S離子種類、Cl－等其他雜質離子、晶粒取向、合金成分以及應力等多因素影響，多因素之間可能存在復雜的交互作用。合金中Cr、Mo和Cu的加入可在一定程度上抑制硫致腐蝕，而Ni含量的增加則使硫致腐蝕敏感性增加。S更易吸附在材料表面缺陷處引起局部優(yōu)先溶解，晶粒取向按照(111)<(100)<(110)硫致腐蝕敏感性增大。As nuclear power operates at high temperature and high pressure, corrosion is considered as one of the issues that threaten the safe operation, though corrosion rarely occurs. To fully understand the electrochemical behavior of nuclear key materials and manage the corrosion degradation of these materials in a proactive manner, a great deal of work have been undertaken in lab. Some sulfur-related specie can cause corrosion degradation of metal materials, which is well known in Corros. Sci.. Steam generator (SG) is one of the most important components in nuclear power plant, and Alloy 800 and 690 are the most frequently used SG tubing alloys. Sulfur-induced corrosion of SG alloys in high temperature and high pressure water is one of the most complicated processes. In this review, we comprehensively review the research processes regarding to sulfur-induced corrosion of Alloy 690 and 800 from two aspects: thermodynamic calculations and experimental. Thermodynamic calculations are mainly presented by E-pH diagrams, volt Equivalent diagrams and species distribution curves. It is concluded that the valences of sulfur and their interactions with metal is mainly affected by temperature, solution pH and electrode potential. Experimental data indicate that sulfur induced corrosion is determined by temperature, solution pH, sulfur species, other impurities like chloride ions, grain orientation, alloy compositions and stress etc. These factors can interact in a very complicated way. Generally, increasing temperature and decreasing solution pH would increase the corrosion degree of SG tubing alloys. Sulfur at the reduced or intermediate oxidation level are more detrimental than complete oxidation level, to the passivity of SG tubing alloys. Chloride ions have a combined effect with thiosulfate on passive film degradation in the case that chloride’s adsorption is dominant; this combined effect is not remarkable if the chloride’s adsorption is not dominant. Elements like Cr, Mo and Cu in alloys would weak sulfur adsorption to some extent and therefore inhibit sulfur-induced corrosion, but increasing Ni content would enhance sulfur-induced corrosion. Both compressive and tensile stress would increase the reactivity of a passive surface of SG tubing. Sulfur would more easily adsorb on the metal surface where it has more defects, resulting an increased dissolution rate. The crystal orientation can enhance the corrosion rate in the order of (111)<(100)<(110).

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