油田管道应力腐蚀断裂成因分析

Cause Analysis of Stress Corrosion Fracture of Oilfield Pipeline

油田管道发生断裂失效,运用宏观分析、微观分析、裂纹扩展分析、形貌分析、微区成分分析、X射线衍射分析和力学性能分析,进行管道断裂失效分析,明确了管道断裂成因;测试结果表明,断裂裂纹沿环向开裂,管道轴向受力大于环向受力,并且裂纹断裂方向与最大拉应力方向垂直;同时,套管未发生颈缩和腐蚀减薄,而且断口平整,断裂属于脆性断裂。断裂扩展区具有典型的河流花样微观特征,属于准解理穿晶断口;套管裂纹由套管内表面向外部延伸,并且裂纹扩展呈树枝状,其裂纹特征符合硫化物应力腐蚀断裂特征。综上所述,该油管断裂由硫化物应力腐蚀开裂导致,裂纹起裂于油管上的缺陷处,该处的应力集中萌生腐蚀开裂裂纹。

The fracture failure of oilfield pipeline is analyzed by macro analysis,micro analysis,crack propagation analysis,morphology analysis,micro component analysis,X-ray diffraction analysis and mechanical property analysis,and the causes of pipeline fracture are determined.The test results show that the fracture crack is along the circumferential direction,the axial force of the pipeline is greater than the circumferential force,and the fracture direction of the crack is perpendicular to the direction of the maximum tensile stress.At the same time,the casing has no necking and corrosion thinning,the fracture is smooth,and the fracture belongs to brittle fracture.The fracture extension zone has typical river pattern microscopic characteristics and belongs to quasi cleavage transgranular fracture.The casing crack develops from the inner surface of the casing to the outside,the crack propagation is dendritic,and the crack characteristics conform to the characteristics of sulfide stress corrosion fracture.In conclusion,the fracture of the oil pipe is caused by sulfide stress corrosion cracking.The crack started at the defect of the oil pipe,where the stress concentration initiated corrosion cracking first.