A New Electromagnetic Inspection Instrument for Large-Diameter Stationary Wire Ropes

Abstract

An electromagnetic inspection instrument for stationary wire ropes up to 95 mm in diameter has been developed. This instrument utilizes two solenoidal coils coaxial with the rope for magnetizing it longitudinally close to saturation.
Because of the inconvenience of coiling up the conductor around the rope for each test, the solenoid type method of magnetization has not been adopted so widely. However, for large-diameter stationary ropes this method has been recognized to be better than yoke type method, as indicated in the facts which follow:
1) The instrument without iron core weighs 70 kgf and is lighter than that of yoke type.
2) Solenoidal magnetizing coils induce longitudinal magnetic field in the rope more effectively than yoke type electromagnet.
3) The distribution of flux density in the rope due to the coaxial solenoid is relatively uniform, and consequently the difference between the inspection sensitivity of a defect in the surface and that of an inner one is relatively small.
4) Inspection signal is satisfactorily stable with the solenoid type instrument, while the magnetic field in the rope is affected by the motion of the rope with the yoke type instrument, which results in a fluctuation on the inspection signal.
The instrument was applied in the field for inspecting the P.W.S.217 cables installed in a suspension roofing, and localized corrosion in these cables was successfully detected.