|NDT.net June 2006 Vol. 11 No.6|
Periodic Non-destructive Evaluation of Steel Wire Ropes: Its Importance and Practical RelevanceDebasish Basak (email@example.com)
Scientist, Central Mining Research Institute,
Barwa Road, Dhanbad-826001, Jharkhand, INDIA
ABSTRACTThe most effective way in which non-destructive evaluation of rope is currently used is as a means of improving the reliability of the initial identification of the location of significant degradation along a rope. Magnetic flaw detectors are used to determine rope wearing. The detectors can measure loss of metallic area (LMA) and detect the local faults (LF) like broken wires and other faults of the rope. Deterioration of a rope during its lifetime leads to a reduction of the rope safety and to its possible destruction. Magnetic non-destructive testing allows an increase in the safe and use of steel ropes due to objective, reliable and documented evaluation of the real rope condition and by ensuring timely rope replacement.
Keywords: Non-destructive evaluation, magnetic method, flaws
INTRODUCTIONSteel winding ropes which are subjected to severe working conditions in hazardous areas such as in mines and on aerial ropeway installations, deteriorate with use. Assessment of rope condition either by visual examination or drawing a specimen rope length and subjecting it to destructive evaluation seldom speaks about integrity of the entire rope length in the installation. Further, ropes which are used on friction winders and aerial ropeway passenger cable car installations, cannot be assessed at any cost, due to non-availability of rope length for destructive investigation. Under these situations, non-destructive investigation is the only means for its evaluation to study the behaviour.
AVAILABLE METHODS AND SCOPESThe most conventional inspection method for wire ropes is the visual inspection in which the experts observe the surface and assess the rope condition empirically. The experts of visual inspection for wire ropes have decreased and cannot evaluate the inner failure such as corrosion. However, the visual method produces a possibility for inadequate inspection due to its subjectivity. Practically, it is hard and nearly impossible to review thoroughly a rope covered by lubricant and grime when a rope length is up to a hundred meters. Additionally, only surface faults of the rope can be detected and this is insufficient to define its condition correctly.
Visual inspection alone is inadequate to provide a real definition of the rope degradation level, even if the inspection is fulfilled conscientiously. Many of the surface defects like broken wires are not detected by inspectors. Using magnetic method, a rope expert has a possibility to estimate the rope condition.
Magnetic non-destructive evaluation of wire ropes has been in regular use in a number of countries for inspection of hoisting ropes in deep mines and inspection of ropeways. Recently used method is based on magnetization of the rope with permanent magnets and detection of the changes of magnetic field around the rope and total magnetic flux.
Equipment recently used for non-destructive testing of steel wire ropes generally uses "permanent magnetic method" to evaluate the rope condition.
OBJECTIVESFollowings are the main objectives for non-destructive evaluation of steel wire ropes:
PRACTICAL RELEVANCE, ASSESSMENT AND EVALUATION OF ROPE BY NON-DESTRUCTIVE METHODFollowings are the practical relevance/utility of the study:
This technique which would provide great insight on the condition of a rope on installation, would alert the operator in respect to hidden problems such as internal corrosion, internal and external broken/defective wires. A complete documentation of gradual rope deterioration throughout its entire service life by periodic inspection, right since the rope installation, would enable the operator to arrive at a decision for preventing premature rope failure under adverse conditions or extensions of rope life in deserving cases.
CONCLUSIONApplication of non-destructive evaluation procedures makes it possible to improve the reliability of detecting broken wires over the whole rope length. It also emphasizes the priorities of wire break discard criteria supported theoretically and experimentally. It is of primary importance to come to an agreement on the method of assessing a rope strength by non-destructive evaluation readings and focus on investigations free from uncertainties and ambiguous judgments.
With this in view, Electrical Laboratory of Central Mining Research Institute (CMRI), Dhanbad, India has been engaged over a considerable period of time in performing non-destructive evaluation on winding ropes in coal and metal mines at BCCL, TISCO, HZL, HCL, UCIL, material handling ropeway at NALCO, and aerial ropeway installations at Parwanoo (HP), Jabli (HP), Joshimath (Uttaranchal), Nainital (Uttaranchal), Science City (West Bengal), Gangtok (Sikkim), Manakamana Darshan (NEPAL).
ACKNOWLEDGEMENTSThe author is grateful to Director CMRI for his kind permission to publish the paper. The views expressed in the paper are of the author's and not of the organization he serves.