Summary and Analysis of Influencing Factors on the Flaw Detection Results of Eddy Current Flaw Detector

1. Introduction of eddy current flaw detector

Eddy current flaw detector is suitable to test the welding quality of components and parts of pipelines, aircraft, vehicles and bridges in petroleum, transportation and construction industries, as well as the processing workpiece quality of various light metals, steel pipes, and copper pipes and aluminium pipes. Eddy current flaw detector is made of metal parts, because of discontinuity magnetic domain, the magnetic line of force on the surface and near the surface of the workpiece will be partially distorted and absorbed. The magnetic powder attached to the surface of the workpiece will be visible in the form of magnetic traces under appropriate light, so as to show the position, character and size of discontinuity.

2. Application of eddy current flaw detector

Eddy current flaw detector has been widely used in pipe, bar, profile, welding parts, machining parts and forging flaw detection. Especially in the regular inspection of pressure vessels, it plays a unique role. Eddy current flaw detector can detect cracks, hairlines, white spots, folds, inclusions and other defects in ferromagnetic materials. It has high detection sensitivity, and can virtually show the location, shape, size and severity of defects. It has good repeatability in checking defects. In addition, it is an indispensable NDT testing equipment provided by NDT equipment manufacturers.

3. Influencing factors of eddy current flaw detector

Usually, there are many factors that affect the results of eddy current flaw detector, such as the change of material, the size of the workpiece and detection coil, the shape and location of defects and detection conditions. In the eddy current inspection of copper and copper alloy pipes, the drive-through coil method dominates. Various influencing factors are as follows:

① Defects: including the depth, length and width of the defect, the position of the defect (inner surface, outer surface), and the type of defect (hole, groove).

② Material: the influence of copper and copper alloy tube material on eddy current testing is mainly on the conductivity. In the same alloy composed material, segregation and residual stress both will cause the conductivity difference.

③ Pipe size and filling factor: the change of pipe diameter directly affects the filling rate.

④ Pipe wall thickness: noise signal is produced by the change of copper pipe wall thickness.

⑤ Relative position of the tube and the detection coil: when the copper tube passes through the inside of the drive-through coil, it is prone to cause vibrations, which will change the relative position of the tube and the coil.

⑥ Speed fluctuation: eddy current flaw inspection of copper and copper alloy pipes operates at a speed of 100 meters per minute or higher. The change of pipe velocity affects indication of defects. For example, when the transmission speed is 120m / min, the fluctuation of the speed should not be greater than ± 10%.