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Predicting the mechanisms and crack growth rates of pipelines undergoing stress corrosion cracking at high pH

机译：预测高pH应力腐蚀管道的机理和裂纹扩展率

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摘要

A fundamentally based mathematical model was developed with the goal to predict, as a first step, the crack growth rate (CGR) of high pH stress corrosion cracking (SCC) of buried steel pipelines. Two methods were used to predict CGRs and for both methods the model has included the film rupture and repassiva-tion mechanism. The two methods are distinguished by the expression used to determine the active anodic current density at the crack tip. In the first method, this current density is expressed by the anodic polarization curve with a large peak current density and the prediction tends to yield a larger CGR and a lower pH at the crack tip. By contrast, when the Butler-Volmer equation is used to express the crack tip anodic current density, with a predicted low CGR the chemistry at the tip does not appear to have any significant change due to the high buffer of the solution.rnThe predicted mechanism responsible for the steady-state crack growth is shown to be the balance between the increasing stress intensity factor as the crack grows, which tends to increase the crack tip strain rate and thus the CGR, and the change of the crack tip condition, which, for large CGRs, is the significant shift in the more negative direction of the crack tip potential, and for low CGRs, the increase of ferrous ion concentration, and either tends to decrease CGR.rnLimitations currently existing in the model and proposal for further development of the model are discussed.
机译：建立了基于基础的数学模型，其目的是作为第一步，预测埋入式钢管的高pH应力腐蚀开裂（SCC）的裂纹扩展速率（CGR）。两种方法用于预测CGR，两种方法的模型都包括薄膜破裂和再钝化机制。两种方法的区别在于用来确定裂纹尖端的有源阳极电流密度的表达式。在第一种方法中，该电流密度由峰值电流密度大的阳极极化曲线表示，并且预测趋于在裂纹尖端产生更大的CGR和更低的pH。相比之下，当使用Butler-Volmer方程来表示裂纹尖端的阳极电流密度时，由于CGR的预测值较低，由于溶液的高缓冲液，尖端的化学成分似乎没有任何重大变化。导致稳态裂纹扩展的原因是裂纹扩展时应力强度因子的增加与裂纹尖端条件的变化之间的平衡，该应力强度因子随裂纹的增长而增加，裂纹尖端的应变率和CGR均增大。对于大的CGR，是裂纹尖端电势向负方向的显着变化；对于低的CGR，是亚铁离子浓度的增加，并且两者都倾向于降低CGR。该模型进行了讨论。

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