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首页> 外文期刊>Metallurgical and Materials Transactions, A. Physical Metallurgy and Materials Science >Environmental Aspects of Near-Neutral pH Stress Corrosion Cracking of Pipeline Steel
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Environmental Aspects of Near-Neutral pH Stress Corrosion Cracking of Pipeline Steel

机译：管线钢近中性pH应力腐蚀开裂的环境因素

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The severity of four different soil environments toward the development of near-neutral pH stress corrosion cracking (SCC) of pipeline steel was evaluated using slow strain-rate testing (SSRT). These soils were collected from pipeline sites where near-neutral pH SCC has been observed. It was demonstrated in this investigation that SSRT can differentiate the severity of various soil electrolytes to near-neutral pH SCC. For different soils, the relative susceptibility was found to be determined by the pH values of the soil electrolytes in equilibrium with a given CO_2/N_2 gas mixture. The higher the pH value up to approx 7, the more conducive the soil electrolyte was to near-neutral pH SCC. The pH value in a soil electrolyte was found to depend on the level of CO_2 in the soil solution and the initial HCO_3~- concentration before the introduction of CO_2. For a given Soil, the susceptibility depends on the actual level of CO_2 in the soil electrolyte. Higher levels of CO_2 lower the pH in the soil electrolyte and tend to increase the susceptibility to SCC. In laboratory tests, cathodic polarization was found to increase the susceptibility to failure, possibly by inhibiting general corrosion, which otherwise removed discrete stress-raising pits and defects from the specimen surface that acted as crack initiation sites or by increasing the extent of hydrogen-induced crack initiation or propagation. In the field, cathodic polarization is likely to prevent near-neutral pH SCC by increasing the pH at the pipe surface to values greater than 7.5. The pH was maintained near-neutral in the lab tests by continuous purging of the test solution with CO_2/N_2. A method is proposed for assessing the relative aggressiveness of various soil extracts to near-neutral pH SCC. Aggressive soil extracts appear to exhibit a narrower variation in pH between solutions purged with N_2 and with CO_2 than that for less-aggressive soil extracts purged with the same gases.
机译：使用慢应变速率测试（SSRT）评估了四种不同土壤环境对管道钢接近中性pH应力腐蚀开裂（SCC）的发展的严重程度。这些土壤是从管道站点收集的，这些站点已观察到接近中性的pH SCC。这项研究表明，SSRT可以将各种土壤电解质的严重程度区分为接近中性的pH SCC。对于不同的土壤，发现相对敏感性是由与给定的CO_2 / N_2混合气体平衡的土壤电解质的pH值确定的。 pH值高达约7时越高，土壤电解质对接近中性pH SCC越有利。发现土壤电解质中的pH值取决于土壤溶液中CO_2的含量和引入CO_2之前的初始HCO_3〜-浓度。对于给定的土壤，磁化率取决于土壤电解质中实际的CO_2水平。较高的CO_2含量会降低土壤电解质的pH值，并倾向于增加对SCC的敏感性。在实验室测试中，发现阴极极化可增加失效的敏感性，这可能是通过抑制一般腐蚀而造成的，否则腐蚀可从试样表面去除离散的应力坑和缺陷，这些缺陷和裂纹起裂纹的作用，或者通过增加氢诱导的程度裂纹萌生或扩展。在现场，阴极极化可能会通过将管道表面的pH值增加到大于7.5来防止接近中性的pH SCC。在实验室测试中，通过用CO_2 / N_2连续吹扫测试溶液，将pH保持在接近中性的水平。提出了一种评估各种土壤提取物对接近中性pH SCC的相对侵略性的方法。侵略性土壤提取物在用N_2和CO_2吹扫的溶液之间的pH值变化似乎比用相同气体吹扫的腐蚀性较弱的土壤提取物的pH值窄。

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