For he spiral steel pipe often produced “outside folds” such defects, many eddy current probe instrument and often can be found. Often outside off to the naked eye visible, but not the only instrument ET alarm embarrassing phenomenon.

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Since the emergence of sector-type vortex phase alarm device, this situation has been fundamentally changed. But chooseing the right instrument and probe and adjust it correctly, is still an important issue can not be ignored. Aonther important factor affecting reliability is the angle between the surface of the tube with natural defects.

Theoretical and experimental studies have shown: When the orientation of artifical groove along the thickness direction of the outer surface of the tube angle is 30 degrees, that can not be detected by MFL parallel to the surface defects, such as class stratification defect.

In the spiral pipe production test, there had been no detection of spiral steel pipe through the wall with a large hole phenomenon MFL method. Since the detection of high speed through the coil ET method is widely used for many years to detect spiral steel quality, especially its compactness. In use it proved that it is difficult to ferromagnetic apiral pipe stuck in the crack-like defects, so the high standards of ET, using the probe coil ET method.