Both GB/T9711. 2 and API Spec 5L standards have clear requirements for remanence of seamless steel pipes, so it is necessary to master the method of degaussing seamless steel pipes. The AC degaussing method for seamless steel pipes is currently the most common method.
Seamless steel tube AC degaussing process flow chart
1. Wrap the coil around the outside of the steel pipe, apply AC power to the coil, and slowly reduce the AC current until it is reduced to zero. Degaussing results: The physical properties of the seamless steel pipe are not changed, but the seamless steel pipe is magnetized once the applied magnetic field is again encountered.
2. Through the heat treatment process, can be thoroughly demagnetized, but after degaussing, the hardness and rigidity of the seamless steel pipe will change, in the future when the external magnetic field is encountered, after the applied magnetic field disappears, the steel pipe will have substantially no remanence .
3. The heat treatment process is probably: heating to a certain temperature without oxygen, and then
slowly cooling to room temperature with 72 hours.
The reason why the seamless steel pipe generates a magnetic field
In the welding process, the internal welding adopts the DC welding method, and the internal welding large line and the welding head part generate a strong magnetic field due to the large current, and the magnetic tube body obtains or tends to obtain the same magnetic field under the magnetic field. The arrangement of the directions. When the welding is finished, the magnetic field is gradually reduced until it disappears. Due to the hysteresis, there is residual magnetic flux density on the tube. This is what we usually call remanence.
Seamless steel pipe magnetic field hazard
The existence of residual magnetism causes the electron beam direction of the image intensifier to be deflected. The X-ray industrial television system image produces "S"-type distortion, which affects natural defects such as pores and slag inclusions, especially linear defects such as incomplete penetration and cracks. Detection rate.
With the improvement of pipeline steel grade and the change of image intensifier of X-ray TV system, the influence of residual magnetism is particularly prominent. The existence of residual magnetism, when the pipeline ring welding is butt joint, it will produce a phenomenon of arcing, which will affect the welding quality. The existence of remanence has seriously affected the construction quality.
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