Pipelines are the most used and safest equipment to transport oil and its liquid or gaseous derivatives. Steel pipes are usually manufactured of API 5L X60, X65, X70 or X80 grade steels. x-ray diffraction technique was used to evaluate the microstructural behavior of API X65 steel samples through the analysis of the full width at half maximum (FWHM) values of the diffraction peak during the fatigue damage process. Based on the obtained results, it was possible to identify three stages of fatigue damage. Stage I is associated with crack nucleation, and a deeper understanding of this stage is one of the most relevant goals of this study. Stage II of microcracking is the longest stage, representing most of the fatigue life of the material. Stage III is related to macrocracking, when the material is already structurally harmed and driven to abrupt failure, leaving the operator with little time to act and prevent it. Another important result observed was that the major changes in the FWHM values occurred around 21% of the fatigue life of the material. This point was taken as a critical point and used as a reference to calculate the number of cycles up to the failure of the material. The results obtained show that the x-ray technique can be used to study the beginning of the fatigue life of metallic material with reliably once the FWHM results were compared with earlier indentation results that showed the same trend.

管道是运输石油及其液体或气体衍生物最常用和最安全的设备。钢管通常由 API 5L X60、X65、X70 或 X80 级钢制造。X射线衍射技术用于通过分析疲劳损伤过程中衍射峰的半峰全宽（FWHM）值来评估API X65钢样品的显微组织行为。根据获得的结果，可以确定疲劳损伤的三个阶段。阶段 I 与裂纹成核有关，对这一阶段的更深入了解是本研究最相关的目标之一。微裂纹的阶段 II 是最长的阶段，代表材料的大部分疲劳寿命。第三阶段与宏观裂纹有关，当材料已经在结构上受到损坏并导致突然故障时，操作员几乎没有时间采取行动并防止它发生。观察到的另一个重要结果是 FWHM 值的主要变化发生在材料疲劳寿命的 21% 左右。将该点作为临界点并用作计算直至材料失效的循环数的参考。获得的结果表明，一旦将 FWHM 结果与显示相同趋势的早期压痕结果进行比较，X 射线技术就可以可靠地研究金属材料疲劳寿命的开始。将该点作为临界点并用作计算直至材料失效的循环数的参考。获得的结果表明，一旦将 FWHM 结果与显示相同趋势的早期压痕结果进行比较，X 射线技术就可以可靠地研究金属材料疲劳寿命的开始。将该点作为临界点并用作计算直至材料失效的循环数的参考。获得的结果表明，一旦将 FWHM 结果与显示相同趋势的早期压痕结果进行比较，X 射线技术就可以可靠地研究金属材料疲劳寿命的开始。