Magneto-Optical Imaging of Arbitrarily Distributed Defects in Welds under Combined Magnetic Field

Abstract

Using the traditional magneto-optical detection methods, micro-weld defects parallel with the magnetic field direction may be overlooked. In order to overcome this, a non-destructive testing method based on magneto-optical imaging under a vertical combined magnetic field (VCMF) is proposed. To demonstrate this, the experimental results of the magneto-optical imaging of weld defects excited by a vertical combined magnetic field (VCMF) or parallel combined magnetic field (PCMF) are compared with those of traditional magnetic fields (constant magnetic field (CMF), alternating magnetic field (AMF), and rotating magnetic field (RMF)). It is found that the magneto-optical imaging under a VCMF can accurately detect weld defects of any shape and distribution. In addition, the center difference method is used to eliminate the influence of noise on the defect contour extraction of magneto-optical images, and the active contour of weld defects in the magneto-optical images is extracted. The results show that many noises can be identifiedby the robustness of the level set method, operating in low-pass filtering, so that much information that is usually lost can be retained.

Quality Assessment of Laser Welding Dual Phase Steels

“…This procedure is a non-destructive testing based on magneto-optical (MO) imaging, which transforms the magnetic leakage field into a light intensity map to visualize defects [77][78][79]. In the study [80], a vertical combined magnetic field (VCNF) and a parallel combined magnetic field (PCMF) were compared to traditional magnetic fields where it was found that magneto-optical imaging under VCMF could detect weld defects of any shape and distribution accurately. This technique was also used in [81], where weld surface and subsurface cracks were detected by an MO sensor.…”

Non-Destructive Testing of Magnetically Impelled Arc Butt Welding of Mild Steel Tubes

“…AC induced magnetic field has a scale effect that produces a concentrated field on the surface [16]. Magnetooptical imaging under a vertical combined magnetic field [17] As per inspection standards, ASME Section-V, Article-7 (magnetic particle examination) and SE709 (standard practice for magnetic particle examination) and ASME Section-VIII, Division 1, the procedure followed for MPT is as follows:…”