Causes of magnetic field in spiral steel pipe
In the welding process, DC welding is used. On the welding line, due to the large current at the position of the welding head, a strong magnetic field occurs. Under the effect of the magnetic field, the magnetic moment of the tube body may tend to obtain a magnetic field consistent with the direction of the external magnetic field. When the welding is over, the magnetic field gradually decreases until it disappears. Due to the hysteresis phenomenon, under the tube body and the residual magnetic field density, this is what we usually call remanence.
Magnetic field damage of spiral steel pipe
Existing residual magnetism, image intensifiers, electron beam deflection, and X-ray industrial television image systems have undergone "S"-shaped distortions, affecting natural defects such as porosity and slag, especially linear natural defects such as incomplete penetration and cracks. The detection rate. With the change and improvement of the pipeline steel grades of the X-ray image intensifier TV system, the remanence is particularly outstanding. If the residual magnetism exists and the ring is connected in the pipeline, some arc phenomenon and welding quality will occur. Even seriously affected the quality of the project.
The spiral tube AC degaussing method is a commonly used method:
1. Wrap the coil on the outside of the steel pipe, make the coil pass the alternating current, and gradually reduce the current of the alternating current until it drops to zero. Demagnetization results: The physical properties of the spiral steel pipe are not changed, but the spiral steel pipe is also magnetized when it encounters an external magnetic field again.
2. Through the heat treatment process, it can be completely demagnetized, but after demagnetization, the hardness and rigidity of the spiral tube will change, and the external magnetic field will be encountered in the future, and the magnetic field will be removed, the steel tube will basically have no remanence.
3. The heat treatment process is roughly: heating to a certain temperature without oxygen, and then gradually cooling to room temperature in 72 hours.
