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首页> 外文会议>NACE International corrosion conference expo >LONG TERM ELECTROCHEMICAL BEHAVIOR OF CREVICED AND NON-CREVICED ALLOY 22 IN CaCl2 + Ca(NO3)2 BRINES AT 155°C
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LONG TERM ELECTROCHEMICAL BEHAVIOR OF CREVICED AND NON-CREVICED ALLOY 22 IN CaCl2 + Ca(NO3)2 BRINES AT 155°C

机译：155°C下CaCl2 + Ca（NO3）2卤水中的长颈和长颈合金22的长期电化学行为

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摘要

Alloy 22 is a nickel base alloy highly resistant to all forms of corrosion. In very aggressive conditions (e.g. hot concentrated chloride containing brines) Alloy 22 could suffer localized attack, namely pitting and crevice corrosion. Chloride ion is known to be the most detrimental aggressive agent for Alloy 22 and is able to promote crevice corrosion when tight crevices exist in hot chloride containing solutions of different concentrations. Nitrate ion is an effective inhibitor of chloride induced crevice corrosion when present in a high enough [NO3 -]/[Cl-] ratio. The occurrence of localized corrosion in a given environment is governed by the values of the critical potential (Ecrit) for crevice corrosion and the corrosion potential (Ecorr) that the alloy may establish in the studied environment. If Ecorr is equal or higher than Ecrit, localized corrosion may be expected. This paper discusses the evolution of Ecorr and corrosion rate (CR) of Alloy 22 specimens in 18 m CaCl2 + 9 m Ca(NO3)2 and 18 m CaCl2 + 0.9 m Ca(NO3)2 brines at 155°C. Two types of specimens were used, polished as-welded (ASW) creviced and non-creviced specimens and as-welded plus solution heat-treated (ASW+SHT) creviced specimens. The latter contained the black annealing oxide film on the surface. Results show that, in a few immersion days Ecorr reached a stable value higher than the open circuit potential of a platinum electrode in 18 m CaCl2 + 9 m Ca(NO3)2 for all specimens tested. Specimens tested in this solution did not suffer any type of localized attack. On the other hand, Ecorr showed oscillations of up to 600 mV in 18 m CaCl2 + 0.9 m Ca(NO3)2 during the entire immersion period. These oscillations were due to pitting corrosion development. Crevice corrosion was not observed in any testing case. Corrosion rates for specimens in the latter solution ([NO3 -]/[Cl-] = 0.05) were one order of magnitude higher than for specimens in the second one ([NO3 -]/[Cl-] = 0.5). Nitrate showed to be able to inhibit localized attack even in hot concentrated chloride brines when present in a ratio of [NO3 -]/[Cl-] = 0.5. Localized corrosion occurred only in condition where Ecorr > Ecrit.
机译：合金22是一种镍基合金，对所有形式的腐蚀都有很高的抵抗力。在非常苛刻的条件下（例如，含有浓盐水的热浓氯化物），合金22可能会遭受局部腐蚀，即点蚀和缝隙腐蚀。已知氯离子是22号合金中最有害的侵蚀剂，当不同浓度的热氯化物溶液中存在紧密的缝隙时，能够促进缝隙腐蚀。当硝酸根离子以足够高的[NO3-] / [Cl-]比例存在时，它是氯化物引起的缝隙腐蚀的有效抑制剂。在给定环境中局部腐蚀的发生取决于缝隙腐蚀的临界电势（Ecrit）和合金在研究环境中可能建立的腐蚀电势（Ecorr）的值。如果Ecorr等于或高于Ecrit，则可能会出现局部腐蚀。 本文讨论了在155°C的18 m CaCl 2 + 9 m Ca（NO 3）2和18 m CaCl 2 + 0.9 m Ca（NO 3）2盐水中的22号合金试样的Ecorr演变和腐蚀速率（CR）。使用了两种类型的标本，即抛光的焊缝（ASW）缝隙和非缝隙的标本，以及焊缝加固溶热处理（ASW + SHT）的缝隙标本。后者在表面上包含黑色退火氧化膜。结果表明，在所有浸入的几天中，对于所有测试的样品，Ecorr在18 m CaCl2 + 9 m Ca（NO3）2中均达到了高于铂电极开路电位的稳定值。在此解决方案中测试的标本没有遭受任何类型的局部攻击。另一方面，在整个浸没期间，Ecorr在18 m CaCl 2 + 0.9 m Ca（NO 3）2中显示出高达600 mV的振荡。这些振荡是由于点蚀的发展所致。在任何测试情况下均未观察到缝隙腐蚀。后一种溶液中的样品（[NO3--] / [Cl-] = 0.05）的腐蚀速率比第二种样品中的[[NO3--] / [Cl-] = 0.5）高。当以[NO3--] / [Cl-] = 0.5的比例存在时，即使在热的浓氯化物盐水中，硝酸盐也能抑制局部侵蚀。局部腐蚀仅在Ecorr> Ecrit的条件下发生。

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