Paper deals in-depth with the topic of sustained stress indices applicable to 90° elbows based on non-linear finite element analysis models. A comprehensive overview of the existing literature sources is given in the first part of the paper, showing that there are little sources which deal specifically with this topic and that the ones that do exist result in important scatter of the results. As a result, more than few of the existing sources are non-conservative in their nature. Dedicated non-linear finite element studies have been performed on shell and solid models which are used in conjunction with the regression analysis in order to obtain explicit equations which can be used to calculate both in- and out-plane sustained stress indices in 90° pipe elbows, which can then be used in the typical pipe stress analysis. Newly proposed equations prove to be a good fit for the numerical data, showing little deviation as shown by the correlation parameters presented in the paper. Final part of the paper presents a dedicated section on the high wall thickness elbows and shows the relationship between elbow wall thickness and maximum stress location. It is shown that beyond certain thickness, the maximum stress location shifts from the typical failure location (i.e., side wall) to the locations which are not typically expected (i.e., intrados or even away from elbow). This shifting may have an important effect on the theoretical models which assume failure location.

本文基于非线性有限元分析模型，深入探讨了适用于90°弯头的持续应力指数主题。本文的第一部分对现有文献资源进行了全面概述，表明很少有专门针对该主题的资源，而确实存在的资源导致结果的重要分散。结果，在现有的来源中，有不少于本质上是非保守的。已对壳模型和实体模型进行了专门的非线性有限元研究，将其与回归分析结合使用，以获得可用于计算90°管道内面和面外持续应力指标的显式方程式弯头，然后可用于典型的管道应力分析。事实证明，新提出的方程式非常适合数值数据，如本文中提供的相关参数所示，显示出很小的偏差。本文的最后一部分介绍了高壁厚弯头的专用部分，并显示了弯头壁厚与最大应力位置之间的关系。结果表明，超过一定的厚度，最大应力位置会从典型的破坏位置（即侧壁）转移到通常不会发生的位置（即，内齿甚至远离肘部）。这种移动可能会对假设故障位置的理论模型产生重要影响。本文的最后一部分介绍了高壁厚弯头的专用部分，并显示了弯头壁厚与最大应力位置之间的关系。结果表明，超过一定的厚度，最大应力位置会从典型的破坏位置（即侧壁）转移到通常不会发生的位置（即，内齿甚至远离肘部）。这种移动可能会对假设故障位置的理论模型产生重要影响。本文的最后一部分介绍了高壁厚弯头的专用部分，并显示了弯头壁厚与最大应力位置之间的关系。结果表明，超过一定的厚度，最大应力位置会从典型的破坏位置（即侧壁）转移到通常不会发生的位置（即，内齿甚至远离肘部）。这种移动可能会对假设故障位置的理论模型产生重要影响。