Detection of broken wires using a high resolution magnetic test method
Technical Meeting The Non-destructive Testing of Rope – Krakow 1995
Single broken wires can be found very easily with electromagnetic test heads which are equipped with search coils encircling the rope and have been used successfully for many decades. Many experts are working with this method and therefore continuously evaluating their diagnostic skills (Mueller, 1952; Mueller, 1957; Rieger, 1983; Beck, 1998). Other forms of rope damage like corrosion, torsional defects or strand contact can be detected from the recorded charts by an experienced examiner. However, a reliable diagnosis of clusters of broken wires (i.e. single broken wires which are close to each other) is not possible. This is especially true for the LMA-method, which cannot be used in this particularly case for exact measurements of local reductions of metallic cross sections. An exact measurement of the cross section loss is only possible if it extends over a length of about 5 times the rope diameter. These restrictions are the reason for the (practically simultaneous) development of the "High Resolution Magnetic lnduction Wire Rope Test Method" at two different research institute (Haller, 1995; Nussbaum, 1996). The "lmaging Method" or "High Resolution Wire Rope Test Method" is a significant improvement of the well known electromagnetic wire rope inspection. The development of the new test method needs two major elements: first development of the test equipment (hardware) and second knowledge of "how to read" the acquired data.
Author: J-M. Nussbaum