油气管道环焊缝缺陷适用性评价现状与展望

油气管道的环焊缝质量好坏与管道能否安全运行密切相关,近年来管道环焊缝问题日益突显,因此准确评价管道环焊缝缺陷的适用性对于保障管道安全运行具有重要的意义。为了给环焊缝缺陷安全评定提供参考,系统总结了现行的环焊缝缺陷适用性评价方法并归纳为6种类型,剖析了各类方法的原理、特点及适用性,从焊接缺陷、内外部载荷及材料性能等3个方面分析了目前环焊缝缺陷适用性评价过程中遇到的瓶颈问题,并针对高钢级管道环焊缝所暴露出的新问题,提出了环焊缝缺陷适用性评价的未来展望。研究结果表明:①环焊缝缺陷可分为体积型缺陷和平面型缺陷两大类;②对于体积型缺陷,主要考虑塑性失效模式,推荐采用修正的Miller方法 ;③对平面型缺陷,应同时考虑塑性失效和断裂失效模式,推荐采用BS 7910:2015标准中基于失效评估图(FAD)的方法,并根据可用材料参数及保守性选用通用失效评估曲线(FAC)或特定FAC。结论认为,该研究成果有助于保障管道的安全运行。

Current status and prospect of fitness-for-service evaluation on the girth weld defects in oil and gas line pipes

The quality of girth weld in oil and gas line pipes is in close relationship with the safe operation of pipelines. And in recent years, the problem of girth weld has become more and more prominent. Therefore, accurate evaluation on the fitness-for-service of girth weld defects is of great significance to ensuring the safe operation of pipelines. In order to provide reference for the safety assessment of girth weld, this paper systematically summarized current methods for evaluating the fitness-for-service of girth weld defects and classified them into six categories. Then, their principles, characteristics and applicability were analyzed, and the bottleneck problems in the current process of evaluating the fitness-for-service of girth weld defects were analyzed from three aspects, i.e., weld defect, internal and external load and material property. Finally, in view of the new problems exposed in the girth welds of high-grade pipes, the future prospect of the fitness-for service evaluation of girth weld defects was put forward. And the following research results were obtained. First, girth weld defects can be classified into two types, i.e., volumetric defect and planar defect. Second, for volumetric defects, the plastic failure mode is mainly considered, and the modified Miller method is recommended. Third, for planar defects, both plastic failure and fracture failure modes shall be taken into account; the method based on failure assessment diagram (FAD) in BS 7910: 2015 is recommended; and general failure assessment curve (FAC) or specific FAC can be selected according to available material parameters and conservatism. In conclusion, the research results are conducive to guaranteeing the safe operation of pipelines.