冷加工强化的耐蚀合金管材成功用于酸性天然气气田已有多年的历史,但是,局部活化的点蚀坑以及蚀坑中的应力集中是冷加工强化的耐蚀合金应力腐蚀开裂的重要机制.在高温高压釜中模拟了镍基合金028在高温高压H_2S/CO_2环境下的腐蚀行为.结果发现,镍基合金028在高温高压H_2S/CO_2环境中的均匀腐蚀很轻微,但试样表面有点蚀现象发生,有析出物的试样点蚀更为显著.XPS结果显示,腐蚀后,硫元素只在镍基合金表面钝化膜的表层富集,钝化膜以氢氧化物及氧化物为主,对基体有保护作用.对点蚀坑截面的EDS分析结果表明,硫元素在点蚀坑内部富集,从而导致点蚀坑内局部酸化,加速点蚀坑的扩大.
Cold worked CRAs (Corrosion Resistance Alloys) have been successfully used for corrosive sour gas wells for many years. However, the locally activated pitting and the consequential stress concentration is one of the main mechanisms of stress corrosion cracking failure of cold worked CRAs. The corrosion behavior of Ni-base alloy 028 was simulated in the environment with high temperatures and high partial pressures of H_2S/CO_2. The results show that the general corrosion of Ni-base alloy 028 was slight, but pitting corrosion happened on the surface of the alloy, and the pitting corrosion of the sample with precipitated phase was more obvious. The XPS results indicate that after corrosion, the element sulfur enriched only in the surface layer of the passive film, and the passive film which can protect the matrix was mainly composed of oxides and hydroxides. But the EDS analysis results of the cross section of pitting corrosion indicate that element sulfur enriched inside of the pitting, resulting in local acidification; consequently, the growth of the pitting was accelerated.
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