某L485MB钢级天然气输送管线试压开裂原因分析

Cause Analysis of Cracking During Pressure Test of a L485MB Natural Gas Pipeline

为了确定某L485MB钢级天然气输送管线试压过程发生开裂泄漏的原因,通过宏观检测、力学试验、X射线衍射分析、扫描电镜分析、能谱分析和承压能力估算等方法,对开裂泄漏管段进行了试验分析。结果表明,失效螺旋埋弧焊管的化学成分、冲击性能、弯曲试验、维氏硬度试验结果均符技术规格书要求,但管体屈服强度低于技术规格书的要求。开裂泄漏钢管3PE防腐层的性能符合GB/T 23257—2017标准的要求。根据X射线衍射和能谱分析结果,发生开裂泄漏的螺旋埋弧焊管管内底部存在泥沙和积水,导致钢管内壁底部位置发生了较为严重的吸氧腐蚀。另外,因输送管线位于临近海水区域,积水中含有浓度较高的氯离子,对管道内壁的腐蚀起到了促进作用,使管道局部壁厚大幅减小,承压能力大幅下降,最终造成该管线在试压过程中发生开裂泄漏失效。

In order to find out the cause of cracking and leakage of a L485MB grade natural gas pipeline during pressure test,the cracked pipe section was tested and analyzed by means of macro inspection,mechanical test,X-ray diffraction analysis,scanning electron microscope analysis,energy dispersive spectrometer analysis and pressure bearing capacity calculation.It is shown that the results of chemical composition,impact performance,bending test and Vickers hardness test of the failed spiral submerged arc welded pipe all meet the requirements of the technical specifications,but the yield strength of the pipe body is lower than the requirement.The properties of the 3PE anti-corrosion layer meet the requirements of GB/T 23257-2017 standard.According to the results of X-ray diffraction and energy spectrum analysis,there was sediment and accumulated water in the bottom of the cracked pipe,which resulting in serious oxygen absorption corrosion in the bottom position of the pipe inner wall.In addition,since the pipeline is located in the coastal area,the accumulated water may contain chloride ions with high concentration,which promotes the corrosion of the inner wall of the pipe,greatly reduces the local wall thickness and pressure bearing capacity of the pipeline,and finally leads to the cracking and leakage failure of the pipeline during the pressure test.