NEW ASPECTS OF TESTING SEMI-FINISHED PRODUCTS BY ELECTROMAGNETIC METHODS

In classical non-destructive testing an optimum solution is possible for each individual problem. This is based on the principle that the best technical solutions can only be achieved with highly specialised instruments and systems. Examples of such instruments are the representatives from the large family of eddy current instruments based on the principle of through coils and rotating probes, as well as instruments which operate on the principles of magnetic DC flux leakage and AC flux leakage. When facing complex test situations, one tends of course to combine several individual test methods in a suitable fashion into whole test systems. This is particularly the case when one cannot obtain sufficiently reliable results with only one test method. An example is the desired freedom from surface defects of pipes, rods and wires. Since, for example, longitudinal and circumferential cracks cannot generally be measured with equal sensitivity with through-coils or rotating scanning coils as the items to be tested are passed sequentially through the individual test stations. In cases of especially high requirements for the reliability of detection of diverse defect types, the individual test systems are combined into a so-called multi-test system, which often includes additional possibilities of NDT, such as the examination of material properties using magnetic-inductive methods, of geometries and other parameters. Generally, the amount of testing, as well as the cost for complete NDT increases with the number of applied test methods.