N80加厚油管过渡区断裂原因分析

Fracture Analysis of Transition Zone of N80 Thickened Tubing

某油田采油井在下Ф73.02 mm×5.51 mm N80加厚油管过程中,发现一根加厚油管过渡区位置出现裂纹,通过对事故油管管体进行力学性能及化学成分试验、断口宏观形貌分析、断口电镜扫描分析,对加厚油管断裂原因进行综合分析。结果表明:该加厚油管的断裂形式为脆断,油管镦粗过程中温度控制不当,造成油管"过烧",形成夹渣物残留在加厚油管过渡区,产生脆性裂纹源,下井过程中油管再次受到拉伸载荷,使裂纹源进一步扩展,最终油管发生断裂。

During the process of lowering the N80 thickened tubing of Ф73.02 mm×5.51 mm in a production well of an oilfield, a crack was found in the transitional zone of the tubing. The fracture causes of the thickened tubing were comprehensively analyzed through the test of the mechanical properties and chemical composition of the tubing body, the macro-morphology observation of the fracture surface and the scanning electron microscopy analysis result of the fracture surface. The results show that the thickened tubing is brittle fracture.The inappropriate temperature control during upsetting process results in 'over-burning' of the tubing, and brittle crack source is generated at the residue formed in the transitional zone of the tubing. During the downhole process of the tubing, it is subjected to tensile load again, which makes the crack source further expand and finally leads to the tubing broken.