Design of modified electromagnetic main-flux for steel wire rope inspection

This paper presents the design and construction of modified main-flux equipment for wire rope inspection which has advantages over the in-service inspection and indirect axial-flux measurement used by ordinary main-flux and return-flux methods. The equipment can be adjusted high electromagnetic field strength to produce leakage filed from flaws of various large-diameter ropes. Unique coil sensors connected in series were employed and performed well when sensing leakage fields of the radial, axial and tangential directions. In addition, a standalone system has a simple setup for service inspection. Due to the complicated structure of the wire rope, electromagnetic field theory for anisotropic structures with high electromagnetization was used to design the equipment. The characteristics of the leakage field, in terms of localized fault and loss of metallic cross-sectional area, were distinguished mathematically. The sensor orientation to detect leakage fields was also determined. Performance of the system was then verified experimentally and shown good resolution and repeatability. Furthermore, the equipment is sufficiently sensitive to detect a smallest surface flaw of 1×2 mm at 5 mm equipment lift off. The inspection signals were processed and shown locations, levels and deterioration quantities.