Prompt Assessment of Wire Ropes Technical Condition Based on Magnetic Testing Data

Abstract

A combined approach to the prompt analysis of technical condition of steel wire ropes of various functions is proposed. It is based on the bearing capacity (strength) criterion and the magnetic testing results. The principals are stated related to the strength assessment of degraded rope with measured local wire breaks and loss of metallic area due to corrosion (abrasion). After processing the received diagnostic charts the strength analysis is performed by means of appropriate mechanical model in terms of weak element hypotheses used in structure mechanics. Stress analysis gives the conservative strength estimates which will be referred to reliability margin. The stress safety factor is evaluated regarding the steady and cyclic loading. Because the measured data are of random nature and do not account for the distribution of faults at cross-section the statistical modeling of wear location over wires is performed. The total strength decrease is determined by superposition of strength reduction due to metallic area loss, and due to the wire breaks. Thus, the stress safety factor is considered as a probabilistic indicator of the state of the rope strength. The rope in service should be discarded if its stress safety factor becomes less than the empirical allowable strength factor which defines the rope margin of survival capability as a partially worn-out structure. Adjusted for regulatory disposal rules, three categories of worn rope condition are considered: serviceable, with a limited service life, and inoperative. These categories are presented by the green-yellow-red ranges at so-called «rope status map» in specified coordinates «Number of wire breaks — Loss of metallic section». The rope bearing capacity is promptly assessed by placing two mentioned testing data in corresponding position at the status map. An example is given related to the assessment of the status map for the load-carrying cable rod of the well pumping unit. Based on the obtained results the recommendations are formulated for application of the rope status maps as the templates for service personnel concerning further operation.