Abstract: The internal wall corrosion of drill pipes after long-term service is the main reason for the fracture of the drill pipes. For the detection of the inner wall corrosion of the drill pipes, a magnetic flux leakage detection method was proposed based on the composite magnetization. The induction coil array was applied to pick up the changes of the AC magnetic fields on the outer wall of the drill pipes. The wall thickness reduction caused by the corrosion of the inner walls might be evaluated. The insufficient range and insufficient sensitivity of hall sensors might be avoided when they were used to measure magnetic fields under strong background magnetic field. The relative magnetic permeability distribution above the wall thickness reduction was analyzed by the finite element simulation software, and the magnetic flux density change rates with and without wall thinning were compared. Simulation and experimental results show that the detection of wall thickness reduction of the drill pipes may be achieved by this method.

Key words: drill pipe, internal wall corrosion, wall thinning, composite magnetization, magnetic flux leakage (MFL) testing

摘要： 钻杆长期服役后内壁出现的腐蚀是造成钻杆断裂的主要原因，针对钻杆内壁腐蚀的检测，提出了一种基于复合磁化的漏磁检测方法。该方法通过阵列感应线圈拾取钻杆外壁交流磁场的变化，进而评价内壁腐蚀产生的壁厚减薄状态，规避了强背景磁场下用霍尔元件测量磁场时量程范围不足、灵敏度不够等问题。利用有限元仿真软件分析壁厚减薄上方的相对磁导率分布，对比了有、无壁厚减薄的磁感应强度变化率，仿真与实验结果表明该方法可以实现钻杆内壁壁厚减薄的检测。

关键词: 钻杆, 内壁腐蚀, 壁厚减薄, 复合磁化, 漏磁检测