感生磁场对高速运动钢管磁化的影响机理

Influence Mechanisms of the Induced-magnetic Field on the Magnetization of Steel Pipe at High Speed

当高速运动钢管通过磁化线圈时会产生两种电磁感应现象:一方面,钢管电介质切割磁力线会产生感生涡流;另一方面,磁化线圈内部钢管磁介质总量发生变化而产生感生电流。钢管感生涡流和线圈感生电流产生的感生磁场会改变初始磁化场的强度与分布,进一步改变钢管的磁化状态,最终导致不同位置的同尺寸缺陷产生不同的漏磁场。为获得感生磁场对高速运动钢管磁化的影响机理,以楞次定律为基础,建立感生磁场的作用方程,获得钢管在不同位置处时钢管中感生涡流和磁化线圈中感生电流产生的磁场方向,并发现在钢管管头进入磁化线圈时,感生磁场方向与初始磁化场方向相反,而在管尾处两者方向相同,经磁场叠加后,钢管管尾处的磁化强度增强,管体处基本不变,而管头处减弱。利用钢管高速漏磁检测系统进行试验论证,缺陷检测结果与理论分析结论相同。

Two electromagnetic induction phenomena essentially occur when steel pipe moves through the axial magnetizing coil at high speed in magnetic flux leakage（MFL） nondestructive testing.On one hand,the eddy current is generated in steel pipe which is cutting the magnetic lines.On the other hand,due to the change of the magnetic flux,the induced current is formed in the magnetizing coil.The magnetic field generated by the eddy current and induced current magnetizes the pipe with the magnetizing filed together,affecting the magnetization of steel pipe,eventually resulting in difference of the MFL signals from defects in different locations.To find out the influence mechanisms of the induced-magnetic field on the magnetization of steel pipe,based on the Lenz＇s Law,the descriptions for the eddy current and induced current are established,and moreover the induced-magnetic field distributions were obtained.It was found that the induced-magnetic field in pipe tail and the magnetizing field have the same direction,resulting in the increase of the magnetization intensity,the direction of the induced-magnetic field in the pipe head is opposite to the one of the magnetizing field,which brings about the reduction of magnetization intensity,and the induced-magnetic field current in the pipe body nearly has no affection on the magnetization.The relevant experiments in different speeds are conducted by using the hi-speed MFL testing system for steel pipe to verified the influence of the induce-magnetic field,and the test results agree with the theoretical analysis well.