P.W.S.ロープ用電磁探傷装置について

Abstract

Parallel Wire Strand (P. W. S.) ropes are used as major elements in suspension roofings and bridges. Long-term exposure to weather conditions deteriorate them by corrosion internally rather than on the surface. There has been a great need to evaluate this deterioration to decide whether or not they require replacement.Some electromagnetic inspection instruments are available mainly for wire strand ropes which move, such as mine hoisting ropes. However, for stationary ropes, such as suspension cables and mooring cables, there is no equipment available for inspection work, and no prior experience in this area outside of visual examination.A new electromagnetic inspection device for P. W. S. ropes up to 50mm in diameter was developed. This device consists of a exciting coil with two annular poles which magnetizes the rope longitudinally to saturation, and a detector unit which has twin annular arrays of Hall effect elements to sense the radial leakage flux produced by defects. This detector unit has two new features which follow:(1) The inspection sensitivity is independent of the relative rope speed, as required for inspecting stationary ropes.(2) The annular arrays are divided into 6 segments, and each segment can deliver the individual output, enabling us to detect the cross sectional location of defects.This newly implemented instrument was used to inspect P. W. S. 75 suspension ropes. Evaluated degradation of those ropes in terms of loss in the cross sectional area was proved accurate by results of disassembling inspection.