Views:127 Author:Site Editor Publish Time: 2020-08-26 Origin:Site
Eddy current flaw detection is a non-destructive flaw detection technology that uses AC electromagnetic coils to induce eddy current on the surface of metal components. It is suitable for defect detection of conductive materials, including ferromagnetic and non-ferromagnetic metal materials. Due to the eddy current flaw detector, the coil and the component are not required to be in close contact during the detection, and there is no need to fill the lotus between the coil and the component, and it is easy to realize the inspection automation. However, eddy current testing is only suitable for conductive materials, and can only detect defects on the surface or near the surface layer, which is inconvenient to use for components with complex shapes. In thermal power plants, eddy current testing machine is mainly used to inspect condenser tubes, steam turbine blades, steam turbine rotor center holes and welds, etc.
There are usually many factors that affect the inspection results of eddy current flaw detectors, such as material changes, the size of the workpiece and the detection coil, the shape and location of the flaw, and the flaw detection conditions. These all affect the correct evaluation of the inspection results. In the eddy current flaw detection of copper and copper alloy pipes, most of them are mainly through the coil method, and 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 (a hole, groove), etc.
②Material: The influence of the material of copper and copper alloy pipes on eddy current testing is mainly reflected in the conductivity. In the material of the same alloy composition, segregation and residual stress will cause the difference in conductivity.
③Tube size and filling factor: the change of pipe diameter directly affects the filling rate.
④Tube wall thickness: the noise signal caused by the change of copper pipe wall thickness.
⑤The relative position of the tube and the detection coil: when the copper tube passes through the through-type coil, it is inevitable that vibration will occur, and this vibration will change the relative position between the tube and the coil.
⑥Speed fluctuation: The 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 pipe movement changes, it also affects the indication of defects. For example, when the transmission speed is 120m/min, the fluctuation of the speed should not exceed ±10%.
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