N80鋼級(jí)平式油管斷裂原因分析

Analysis of Causes for Fracture of N80 TBG Tubing

摘要: 為找出修井時(shí)Φ73.02 mm×5.51 mm N80鋼級(jí)平式油管工廠端螺紋根部斷裂的原因，分析該油管的斷口形貌、掃描電鏡形貌以及宏觀和微觀組織，檢測(cè)其機(jī)械性能，研究該油管的失效機(jī)理。試驗(yàn)結(jié)果表明：該失效油管材料的理化性能滿足API Spec 5CT—2011標(biāo)準(zhǔn)對(duì)N80鋼的要求；金相組織與油管斷裂之間的關(guān)系很??；過扭矩上扣、油管柱傾斜以及無扶正器扶正的油管受到復(fù)合載荷振動(dòng)和偏置應(yīng)力，對(duì)油管螺紋斷裂有一定的影響。

Abstract: To find out the causes for the fracture at the factory-end thread root of the Φ73.02 mm×5.51 mm N80 TBG tubing as occurred during the well workover, its fracture morphology, SEM morphology, and the macro/micro structures are analyzed, and its mechanical properties are tested so as to identify the mechanism of the said failure.The test results demonstrate that the physiochemical properties of the failed tubing are up to the requirements for N80 steel as specified under API Spec 5CT-2011;the metallographic structure of the tubing has little relevance with the fracture;and that the fracture is to some extent associated with such elements as making-up with over torque, declination of the tubingstring, and thecombined loading and offset stress as imposed upon the tubing that is not supported with a centralizer.