Analysis on Influencing Factors of Eddy Current Flaw Detector

Eddy current flaw detector is a conventional non-destructive flaw detector for non-destructive testing. Eddy current flaw detector is suitable for processing and welding quality of materials and parts such as pipelines, aircraft, vehicles, and bridges in industries such as petroleum, aerospace, transportation, and construction, as well as various light metals, steel pipes, copper quality of processed parts such as pipes and aluminum pipes.

Ⅰ. The general application of eddy current flaw detector

Eddy current flaw detectors use metal parts, and because of their non-continuous existence, the magnetic lines of force on the surface and near the surface of the workpiece are partially distorted and adsorbed. The magnetic powder applied to the surface of the workpiece forms magnetic marks that are visually visible under suitable illumination, and then show the position, shape, and size of the discontinuity.

It has been widely used in the flaw detection of pipes, bars, profiles, welded parts, machined parts, and forgings, especially in the regular inspection of pressure vessels: eddy current flaw detectors can detect ferromagnetic data Defects such as medium cracks, hair lines, white spots, folds, and impurities have high detection activity, and can intuitively display the position, shape, thickness, and severity of defects, reflecting good repeatability of defects.

There are usually many factors that affect the results of an eddy current flaw detector. Material changes, the size of the workpiece and the detection coil, the shape and location of the defect, the flaw detection conditions, etc., all affect the correct evaluation of the flaw detection results.

Ⅱ. Factors affecting the detection of eddy current flaw detectors

In the eddy current inspection of copper and copper alloy pipes, the through-coil method is the main method. The various influencing factors are briefly described as follows:

1. Defects: including the depth, length, and width of the defect, the location of the defect (inner surface, outer surface), the type of defect (holes, grooves), etc.

2. Material: The influence of the material of copper and copper alloy tubes on the eddy current flaw detector is mainly reflected in the conductivity. In the material of the same alloy composition, segregation and residual stress will cause differences in conductivity.

3. Tube size and filling factor: The change in tube diameter directly affects the filling rate.

4. Pipe wall thickness: the noise signal caused by the change in copper pipe wall thickness.

5. The relative position of the tube and the detection coil: When the copper tube passes through the through-type coil, vibration will inevitably occur, and this vibration will change the relative position between the tube and the coil.

6. Speed fluctuation: Eddy current inspection of copper and copper alloy pipes is carried out at a speed of 100 meters per minute or higher. When the speed of the tube movement changes, it also affects the indication of defects. For example, when the conveying speed is 120m/min, the fluctuation of the speed should be no more than ±10%.