This paper presents an experimental characterisation of fatigue at welded connections for the next-generation high-strength low-alloy offshore riser steel, X100Q. An instrumented girth weld is conducted with a parallel programme of physical-thermal simulation (Gleeble) to develop heat affected zone (HAZ) test specimens. X100Q is shown to exhibit superior fatigue performance to the current state of the art offshore riser steel, X80. Significant differences are demonstrated between the parent material and simulated HAZ in terms of hardness, monotonic strength and cyclic plasticity response, which can be related to the observed microstructural transformations: the refined grain and bainitic block size in the fine-grained HAZ are shown to give a harder and stronger response than parent material, whereas the coarsened bainitic lath structure in the intercritical HAZ gives a softer and weaker response. The simulated HAZ materials exhibit superior fatigue performance to the parent material and weld metal. A significant reduction in life is shown for cross-weld specimens, indicating susceptibility to failure due to HAZ softening for matched or over-matched X100Q welds.

本文介绍了下一代高强度低合金离岸立管X100Q焊接连接处疲劳的实验表征。使用并行的物理热模拟程序（Gleeble）进行仪器化的环焊缝，以开发热影响区（HAZ）测试样本。X100Q表现出比当前最先进的海上立管钢X80更高的疲劳性能。母体材料和模拟热影响区在硬度，单调强度和循环可塑性响应方面显示出显着差异，这可能与观察到的微观结构转变有关：细晶粒热影响区中的细化晶粒和贝氏体块体尺寸显示出比父材料更难更强的响应，临界热影响区中的贝氏体板条结构较粗，响应较弱。模拟的热影响区材料比母材和焊缝金属具有更高的疲劳性能。交叉焊接样品的寿命显着减少，表明由于匹配或过度匹配的X100Q焊缝的热影响区软化而导致的失效敏感性。