Many eddy current probe instruments can not find such defects as "folding out" which often occur in SSAW steel tubes. Often visible to the naked eye outside, but not the only instrument ET alarm embarrassment. Because of the appearance of sector scroll phase alarm device, this situation has changed fundamentally. However, it is still an important issue not to be neglected to select appropriate instruments and probes and adjust them correctly. Another important factor is the reliability of the natural angle of the tube surface defect. The theoretical and experimental results show that when the orientation angle of the groove along the outer surface thickness direction of the pipe is 30 degrees, it can not be detected by MFL parallel to the surface defects, such as hierarchical defects.


In the production test of SSAW steel pipe, no MFL method was used to detect the large hole phenomenon of spiral steel pipe passing through the wall. High-speed detection by coil ET method has been widely used for many years to detect the quality of spiral steel, especially its compactness. It proves that the ferromagnetic spiral tube is difficult to be stuck in the crack defect in use, so the ET standard is very high. The probe coil ET method is adopted.