N80油管接箍腐蚀穿孔失效分析

Failure Analysis of Corrosion on Tubing Coupling of N80 Steel Pipe at Oil Field

中海油南海某油田井下N80油管接箍普遍存在腐蚀穿孔现象。本文利用理化性能分析、失效部位的宏观和微观形貌分析、腐蚀产物的元素及成分分析、重演性实验,对该N80油管接箍处的穿孔失效机理进行了分析研究。结果表明,该N80油管接箍材料的化学成分、力学性能及微观结构均符合要求;管材失效部位为接箍内壁连接缝隙处;构件穿孔失效的主要原因是湍流腐蚀(湍流冲刷+腐蚀),接箍内壁结构变化引起的湍流作用,在较高液体流速下造成流体冲刷严重,而高矿化度介质中的二氧化碳腐蚀是其失效的根本原因。

A serious corrosion occurred at the tubing coupling of N80 steel pipe at an oil well of CNOOC. In this paper, the corrosion perforation mechanism of N80 tubing coupling has been investigated by physic-chemical analysis, macro and micro analysis on failure structure, analysis of elements and composition of corrosion products and simulation experiments. It is shown that the chemical composition, mechanical properties and microstructure of the materials are qualified. The perforation part locates at the inner crevice of the coupling where the upper and lower tubing are connected. The main reason for failure can be ascribed to turbulence corrosion wherein the structural change of inner passage results in the turbulence. Meantime, the corrosion attack of carbon dioxide in high salinity solution is the main contribution to the failure of the tubing coupling.