Purpose
An Eddy current test identifies damage on the inside and/or outside of pipes in the form of holes, cracks, dents and similar and shows whether a pipe leak is incidental or whether several pipes are in poor condition.
Eddy current testing of pipes
The Eddy current test is a method of inspection. Measurements are performable without the need to remove coatings. Despite its numerous advantages, pipe inspection by means of Eddy current testing is not a widely known method. Eddy current tests are used for such components as condensers, evaporators, generators and concentrators or, in other words. any machine that has pipes.
Performance of test
For the proper functioning of the test there needs to be a calibration pipe with the same specifications as those of the pipes under inspection. Artificial errors will be induced in the calibration pipe at calibrated depths on the inside and outside of the pipe. The instrumentation can be adjusted by means of the calibration pipe. During the test a probe that contains a coil will be inserted into the inspected pipe and then extracted at a constant speed. A small current that runs through the coil generates a magnetic field in the coil. The magnetic field penetrates the material where all kinds of Eddy currents are then generated. This sequence also occurs in the opposite direction in the material. Balancing the instrumentation eliminates the difference between the generating and generated eddy currents. In effect, this produces a difference of 0. If they pass a defect in the pipe during the test, the eddy currents will have to cover a longer distance, creating a difference impedance. This difference (phase shift) is converted to a signal on the computer. The signal can be analysed and, based on the amount of phase shift, it is possible to determine the depth and the type of the phase shift. It is also possible to establish whether the defect occurs on the inside or outside of the pipe. If the pipes of (for example) a condenser are measured in this way, a complete picture can be obtained of the pipes. A printout will be made of the pipe group, showing the error pattern by means of colours. In principle, all changes in the pipes are displayable in the same way.
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