First:
spiral steel pipe end degaussing method
1, with a coil wound outside the steel pipe, to pass on the exchange electric coil, and gradually reducing the current exchange of electricity, until the phase-out to zero. Degaussing effect: do not change the physical properties of spiral steel pipe, however, in the event of an external magnetic field again, spiral steel pipe will be magnetized.
2, through the heat treatment process punishment, can probably complete demagnetization than the force, but, after degaussing, spiral steel hardness and rigidity will be change, and then when the next encounter magnetic field, after the external magnetic field dissipates, steel will fundamentally no residual magnetism.
3, the heat treatment process of punishment, probably is: anaerobic heated to a certain temperature, and then, with 72 hours and gradually cooled to room temperature.
Second: spiral steel pipe produce a magnetic field reasons
In the welding process, welding satisfied within DC welding, internal welding line and large horn positions due to a large current produce a strong magnetic field, the steel tube in the magnetic field, the magnetic moment or tendency to give in and get an external magnetic field similar bias breakdown. When welding then ended, the magnetic field gradually eliminated until dissipated, because of hysteresis phenomenon, otherwise the tubular body residual magnetic flux density exists, which is what we usually refer to the remanence phenomenon.
Third: Hazard spiral steel field
The existence of residual magnetism, image enhancer deflecting an electron beam deflection, X-ray industrial TV system image produce "S" type distortion, affecting the pores, slag and other natural defects, particularly a lack of penetration, cracks and other linear natural defect detection rate. With the progress of pipeline stage and television system to strengthen the X-ray image transducer type, especially the impact of residual magnetism. The existence of residual magnetism when the pipeline butt welding ring, will produce signs of partial arc, affecting the quality of welding.
