管道斜接环焊缝适用性评价

Fitness-for-Service of Miter Girth Weld in Oil and Gas Pipelines

斜接引起的应力集中效应致使斜接环焊缝比普通环焊缝更加危险,因此需进一步明确在役管道超标(斜接角度≥3°)斜接环焊缝的适用性。总结对比了现行斜接环焊缝(缺陷)评价标准,推荐采用SY/T 6477—2017 《含缺陷油气管道和强度评价方法》标准评价无缺陷斜接环焊缝,分别采用修正的米勒(Miller)方法和BS 7910:2019 《金属结构裂纹验收评定方法指南》标准评价含体积型缺陷和平面型缺陷斜接环焊缝,并将斜接导致的弯曲应力作为附加载荷考虑。通过有限元分析及全尺寸压力爆破试验明确了斜接与缺陷对于环焊缝失效的影响,评估了评价方法适用性及保守性。研究表明:纯内压作用下,内压导致的环向应力主导了无缺陷斜接管的失效,但随着斜接角度的增大,应力集中效应逐渐突显;压力试验数据验证了标准中斜接评价方法适用范围(斜接角度≤10°)的合理性;斜接和缺陷的存在导致钢管抵抗均匀变形能力及承压能力下降,对于含缺陷(尤其平面型缺陷)斜接,当斜接角度较小时,缺陷会成为环焊缝失效的主要致因。

The stress concentration effect caused by miter girth welds makes it more dangerous than general girth welds.Therefore,it is necessary to further clarify the fitness-for-service of miter girth welds of in-service pipelines exceeding standards(miter angle≥3°).The current evaluation standards for miter girth welds(defects) are summarized and compared.It is recommended to use SY/T 6477-2017“Remaining strength evaluation method for oil and gas pipeline with flaws”to evaluate non-defect miter girth welds,and to use the modified Miller method and BS 7910:2019 “Guide to methods for assessing the acceptability of flaws in metallic structures” to evaluate the miter welds with volumetric or planar defects,and the bending stress caused by miter pipe is considered as the additional load.Based on finite element analysis and full-size pressure burst test,the influence of miter weld and defect on the failure of girth weld is identified,and the applicability and conservativeness of the evaluation method are assessed.Research shows that under pure internal pressure,the hoop stress caused by internal pressure dominates the failure of defect-free miter pipes,but as the miter angle increases,the stress concentration effect gradually becomes prominent.The pressure test data verifies the rationality of the application range of the miter weld evaluation method in the standard(miter angle is less than 10°).The existence of miter weld and defect leads to the decline of uniform deformation resistance and pressure capacity of steel pipe.For the miter weld with defects(especially planar defects),when the miter angle is small,the defects become the main cause of girth weld failure.