Non-destructive Testing of Wire Ropes

Non-destructive Wire Rope Testing by Means
of Magneto-inductive Measurement

The safety inspection of wire ropes on regular basis is essential. Whether track ropes and traction ropes of lifts and cableways, bridge catenary cables or haulage cables, e.g. in mining: Inspection and testing for possible damage or fractures and the reliable load bearing capability is crucial for the safe operation and use of all kinds of plant, machinery, and buildings. This also applies to high-duty wire ropes used as anchoring ropes for cranes or masts as well as on hangars, and for wire-rope reinforced conveyor belts. 

In order to monitor and inspect all these wire ropes effectively and reliably, our technology is being employed for non-destructive wire rope testing. For more than 50 years now, Dr. Brandt GmbH has been developing and producing magneto-inductive rope testing devices, which are used for the gentle and reliable testing of ropes. This enables plant operators and machine owners to carry out a check of the structural integrity of the ropes in addition to visual monitoring and inspection. In other words, certain signs of wear and tear and weak points such as cracks or fractures deep in the rope, which camera technology or visual inspection are unable to detect because they exclusively allow a coverage of the external or outer surfaces, are reliably detected by magneto-inductive testing of the entire rope body and can subsequently be assessed for their effects and consequences.



Basic Functioning of the Magneto-inductive
Wire Rope Testing

Various testing devices are put to use for the magneto-inductive testing of wire ropes. They are either stationary, in which case the rope moves through the testing arrangement (e.g. in the case of a chairlift), or mobile, i.e. they are placed on the respective rope and moved by means of a guide carriage (e.g. in the case of a track cable of a cableway or a catenary cable of a suspension bridge).

Using two or more direct-current coils or, as is the case with Dr. Brandt's standard, several permanent exciters, depending on the rope type and diameter, the rope is homogeneously magnetized in the longitudinal direction. Discontinuities or defective locations such as wire breaks, corrosion, points of wear or even wire braiding faults lead to the formation of a radial component of the magnetic field in addition to the axial component. The leakage flux of these inhomogeneities induces voltage peaks in the normally centered, two or more thin measuring coils surrounding the rope body, the magnitude and direction of which depend, among other things, on the characteristics of the discontinuity. The voltage pulses are processed in a downstream electronic unit and stored and assessed on a laptop using the Dr. Brandt evaluation software. For the additional, scaled down representation on paper of the inspection results over the length of the rope a plotter is also often used for documentation purposes. Aside from documentation, inspection and auditing purposes, the measuring charts and the digital storage of the inspection results are also used for comparison of the results ascertained over different inspection intervals during the entire service life or period of use of a rope.

Even for wire-reinforced conveyor belts, such as those used in the mining industry, a measuring arrangement that is functionally identical but will be tailored to specific belt shapes has been successfully employed by Dr. Brandt for decades.

In all cases, the magneto-inductive measuring head from Dr. Brandt reliably detects signs of corrosion, wear and breaks in the wire – without being influenced by plastic coatings, lubricants or oil paint coatings on the ropes. 

The complete equipment for reliable non-destructive wire rope testing therefore includes the Dr. Brandt Rope Tester with a test block that can be folded away easily from the rope, with integrated permanent exciter and measuring coils as well as an electronic control and evaluation unit,

a laptop and, if desired, an output device for the presentation of the results on paper or for long-term archiving on various data storage media.

Dr. Brandt Rope Testers are available in two versions: For permanent stationary use, as well as for short-term mobile use in inhospitable weather or environmental conditions. If so requested, the measuring devices are available in intrinsically safe design, i.e. they may also operate in environments endangered by firedamp.

For the inspection of stationary ropes or cables such as catenary ropes on bridges, a winch-operated measuring carriage is often employed. Equipment and systems furnished by Dr. Brandt are exclusively of customized design and execution.