管道是石油和天然气工业的重要组成部分,而轴向裂纹是管道安全运营的重要隐患。传统的漏磁检测技术(MFL)对管道中轴向裂纹的检测灵敏度不高,从而形成检测盲区。本文提出了一种利用复合激励的MFL检测新方法,可实现对轴向和周向缺陷的同步检测。首先,利用U型磁轭对管壁进行交直流复合磁化;直流磁化场直接作用于周向裂纹并形成有效的MFL检测信号,而交流磁化场则在管壁内形成垂直于磁化方向的均匀涡流场;当该涡流场受到轴向裂纹干扰时,将形成二次感生磁场的扰动,因此,新方法通过对管壁表面的漏磁场及二次感生磁场检测,同时获得周向和轴向两个方向的探测能力;最后开展仿真和实验,并分析了新方法中作用于轴向和周向裂纹的磁化场、涡流场和二次感生磁场的分布。结果表明,新方法只需通过一次扫描,即可以获得缺陷的轴向和周向特征,实现了对裂纹的无盲点检测。Pipelines are the critical components in oil and gas industry,axial cracks caused by stress corrosion and fatigue damage are the hidden danger of pipeline safe operation. The conventional magnetic flux leakage( MFL) detection technique is inadequate for accurately detecting the narrow axial crack in pipeline and forms detection blind region. In this paper,a new MFL detection method capable of simultaneously detecting both axial and circumferential defects is proposed utilizing DC-AC composite excitation. Firstly,the measured pipe wall is magnetized by DC-AC compound magnetic field using a U-shaped yoke. The DC magnetic field is directly acted on the circumferential crack and generates effective MFL detection signal. The AC magnetic field generates a uniform eddy current field perpendicular to the magnetization direction inside the pipe wall. When the eddy current field is disturbed by the axial crack,a secondary induced magnetic field is generated. Through detecting the surface magnetic flux leakage and secondary induced magnetic field,the new method can obtain the axial and circumferential crack detection capability simultaneously. Both simulations and experiments were conducted,the distributions of the magnetizing field,eddy current field and secondary induced magnetic field acting on the axial and circumferential cracks were analyzed. The results show that the proposed new method can detect both axial and circumferential cracks effectively with one pass scanning,the pipeline crack no blind spot detection is achieved.国家自然科学基金(51177141,51677158);; 航空基金(2012ZD68003)项目资
