连续油管失效分析

Failure Analysis of Coiled Tubing

针对两个油田用连续管失效分析案例,采用金相显微镜对显微组织观察,拉伸试验机进行力学性能测试,采用扫描电镜对试样断口进行观察及夹杂物能谱分析。结果表明:案例一中CT80连续管失效处的裂纹两侧组织为铁素体+珠光体,硬度降低。断口上未见明显的疲劳贝纹线,断口形貌为浅韧窝,能谱分析断口有夹杂物,得出该裂纹是由于硫化物应力腐蚀引起。案例二中CT110连续油管化学成分、力学性能均满足要求,但外壁机械损伤严重;推断连续管外表面机械损伤,引起应力集中,在疲劳弯曲载荷作用下从损伤部位起裂最终造成断裂。

Aiming at two failure analysis cases of coiled tubing used in oil fields,metallographic microscopy was used to observe the microstructure,tensile testing machine was used to test the mechanical properties,and scanning electron microscopy was used to observe the fracture surface of the sample and analyze the inclusion energy spectrum.The results showed that the microstructure on both sides of the crack at the failure of the CT80 continuous tube in Case 1 was ferrite and pearlite,and the hardness decreased.There were no obvious fatigue shellfish lines on the fracture surface,and the fracture surface was characterized by shallow dimples.Energy spectrum analysis showed that the crack was caused by sulfide stress corrosion.In Case 2,the chemical composition and mechanical properties of CT110 coiled tubing met the requirements,but the outer wall was severely damaged by mechanical damage.It was inferred that the mechanical damage on the outer surface of the continuous pipe causes stress concentration,and under the action of fatigue bending load,it cracked from the damaged part and ultimately caused fracture.