One of the main concerns in the structural integrity of offshore pipelines is mechanical damage from external loads. Pipelines are exposed to fatigue failure in welded joints due to geometric discontinuity. In addition, fatigue loads such as currents, waves, and platform motions may cause significant plastic deformation and fracture or leakage within a relatively low-cycle regime. The 2007 ASME Div. 2 Code adopts the master S–N curve for the fatigue evaluation of welded joints based on the mesh-insensitive structural stress. An extension to the master S–N curve was introduced to evaluate the low-cycle fatigue strength. This structural strain method uses the tensile properties of the material. However, the monotonic tensile properties have limitations in describing the material behavior above the elastic range because most engineering materials exhibit hardening or softening behavior under cyclic loads. The goal of this study is to extend the cyclic stress-strain behavior to the structural strain method. To this end, structural strain-based procedure was established while considering the cyclic stress-strain behavior and compared to the structural strain method with monotonic tensile properties. Finally, the improved prediction method was validated using fatigue test data from full-scale girth-welded pipes.

海上管道结构完整性的主要问题之一是外部载荷造成的机械损坏。由于几何形状不连续，管道在焊接接头中会遭受疲劳破坏。此外，诸如电流，波浪和平台运动之类的疲劳载荷可能会在相对较低的周期范围内引起明显的塑性变形，破裂或泄漏。2007年ASME Div。2 Code采用主S–N曲线基于对网格不敏感的结构应力进行焊接接头的疲劳评估。引入了对主SN曲线的扩展以评估低周疲劳强度。这种结构应变方法利用了材料的拉伸特性。然而，单调拉伸性能在描述高于弹性范围的材料性能方面存在局限性，因为大多数工程材料在循环载荷下会表现出硬化或软化行为。这项研究的目的是将循环应力-应变行为扩展到结构应变方法。为此，建立了基于结构应变的程序，同时考虑了循环应力-应变行为，并与具有单调拉伸特性的结构应变方法进行了比较。最后，使用全尺寸环缝焊管的疲劳测试数据验证了改进的预测方法。建立了基于结构应变的程序，同时考虑了循环应力-应变行为，并与具有单调拉伸特性的结构应变方法进行了比较。最后，使用全尺寸环缝焊管的疲劳测试数据验证了改进的预测方法。建立了基于结构应变的程序，同时考虑了循环应力-应变行为，并与具有单调拉伸特性的结构应变方法进行了比较。最后，使用全尺寸环缝焊管的疲劳测试数据验证了改进的预测方法。