基于偏置磁化的管道内表面裂纹涡流热成像检测方法研究

DC-biased Induction Thermography for Sub-surface Defects of Pipelines

因高频热激励磁场趋肤效应的限制,涡流热成像无法实现生产过程中管道内表面裂纹的在线检测。为突破上述问题,提出了基于偏置磁化的管道涡流热成像检测方法:在偏置磁化场作用下,铁磁性管道内表面裂纹会引起外表面趋肤深度层内磁导率分布发生畸变,进一步形成表面非均匀温度场分布,从而可建立内表面裂纹与外表面温度场的关联关系。以电磁感应加热原理与铁磁性材料非线性磁特性为基础,对新方法检测原理进行了阐述;建立有限元仿真模型,利用数值有限元仿真方法分析并获得不同埋藏深度裂纹缺陷引起的磁力线挤压现象以及磁导率变化规律;建立管道偏置磁化涡流热成像检测系统,对不同埋藏深度内表面裂纹进行自动化检测试验,试验结果证明,在移动速度为150mm/s条件下新方法能够有效检测埋藏深度为5.0mm的内表面裂纹。新方法不仅可以用于管道涡流热成像自动化检测,对其他铁磁构件的热成像无损检测同样具有重要的理论意义与实用价值。

Due to the limitation of skin effect of high frequency electromagnetic field,induction thermography cannot realize the scanning detection of sub-surface defects of pipeline.In order to overcome this problem,a DC-biased induction thermography for pipelines based on DC-biased magnetization is proposed:under direct current(DC)magnetization,the sub-surface defects will cause the distortion of the permeability distribution in the skin depth layer of the outer surface,and further form the non-uniform temperature field distribution on the surface,which will establish the correlation between sub-surface defect and the temperature field on the surface.Firstly,based on the principle of induction heating and the characteristics of non-linear ferromagnetic materials,the detection principle of the proposed method is described;then,the finite element simulation model is established to analyze and obtain the squeezing effect of magnetic lines and the permeability variation law caused by defects in different buried depths;finally,DC-biased induction thermography system for pipelines is developed.The experimental results show that the novel method can effectively detect the sub-surface defects with buried depth up to 5.0 mm at the inspection speed of 150 mm/s.The proposed method can not only be used for the scanning detection of pipelines,but also has important theoretical significance and practical value for induction thermography of other ferromagnetic components.