The abnormal eddy current signal after stress relief heat treatment of U-tube

During the manufacturing process of U-tube, the method of electrode heating heat treatment is often used to conduct stress-relieving heat treatment on the section of U-tube. After the heat treatment, the U-shaped pipe needs to be subjected to eddy current detection in the bend. During the signal analysis, it is found that there is an abnormal signal at the position of electrode clamp, that is, the thermal transition zone. It is verified that the signal is not due to a discontinuous signal, but is produced by an inherent processing signalas confimed by other non-destructive testing methods.