Nondestructive Testing for Shallow Defect of Ferromagnetic Objects Based on Magnetic Probe Structure

The Electromagnetic inspection technique plays an important role in the nondestructive testing (NDT) for many decades. Today, this NDT area is rather wide and significant. The magnetic flux leakage (MFL) technology is one of the most widely used electromagnetic nondestructive testing (NDT) techniques. MFL tools use permanent magnets to magnetize the detected object near to saturation flux density [1], [2]. Generally, the magnetizer mechanism of MFL are bulky and heavy. Although the shape of the opening and the depth profile of an arbitrary three-dimensional (3-D) defect from MFL measurements can be estimated [3], the inversion method is complicated and susceptible by the magnetization factors. For different shapes and different sizes of detected object, the magnetizer mechanism of MFL should be designed individually, and this requires a lot of time and experimentation. In this paper, a simple and portable magnetic detection device is designed with permanent magnets, magnetic probe structure and the Hall sensors. Compared with the magnetizer mechanism of MFL, the magnetic detection device is very light, low cost and easy to design and manufacture. The magnetic detection device can make qualitative, and quantitative evaluation for shallow defect of ferromagnetic objects.