Abstract The remaining strength and the fatigue life of externally pitted corroded metallic pipeline are often assessed using an idealization to model the pit morphology, typically semi-ellipsoidal and cuboidal. Such idealized pit geometries are shown herein to underestimate Stress Concentration Factors (SCFs). By implication this leads to significant overestimates of fatigue life for pitting corroded pipes under sustained cyclic loading which could be the reason behind some of the recent unexpected pipeline failures. Further investigation clarified that this can occur only when there is little or no plastic deformation within the pit which is typical for pipelines constructed from brittle and quasi-brittle materials. Therefore, applying the conventional approach that uses simplistic geometries to model corrosion pits is not reliable for stress/fatigue analysis of pipelines with brittle or quasi-brittle materials such as cast iron or high-grade steel. However, for pipelines made of ductile materials, there is a specific internal pressure, termed critical operating pressure herein, below which there is no plastic flow within the pit and simple idealization of pit morphology results in underestimated SCFs. A semi-empirical equation is developed herein to allow this critical operating pressure to be calculated, based on which a protocol is outlined for correct estimation of the SCFs of pitting corroded pipelines. The conclusions of this study are supported by numerical results validated against novel full-scale burst capacity tests with both simplistic and complex-shaped pits.

中文翻译：

---

点蚀管道应力/疲劳分析传统方法的可靠性——开发更安全的方法

摘要 外部有麻点腐蚀的金属管道的剩余强度和疲劳寿命通常使用理想化方法对凹坑形态进行建模，通常为半椭圆形和立方体形。这种理想化的凹坑几何形状在本文中显示为低估了应力集中系数 (SCF)。这意味着在持续循环载荷下，这会导致严重高估点蚀管道的疲劳寿命，这可能是最近一些意外管道故障的原因。进一步调查表明，只有在坑内塑性变形很小或没有塑性变形时才会发生这种情况，这是由脆性和准脆性材料制成的管道的典型特征。所以，应用使用简单几何形状的传​​统方法来模拟腐蚀坑对于具有脆性或准脆性材料（例如铸铁或高级钢）的管道的应力/疲劳分析是不可靠的。然而，对于由延展性材料制成的管道，存在一个特定的内部压力，这里称为临界操作压力，低于该压力时，坑内没有塑性流动，坑形态的简单理想化会导致低估 SCF。本文开发了一个半经验方程，以允许计算该临界操作压力，根据该方程概述了正确估计点蚀管道 SCF 的协议。