Degaussing process of carbon steel pipe

Posted by zora li on February 16th, 2023

When welding pipes, sometimes magnetic deflection can affect the welding process. When welding magnetic carbon steel pipes, problems such as difficulty in arc ignition, destruction of arc combustion stability, deviation of the arc in the magnetic field, splashing of liquid metal and molten metal pool slag often occur, making the weld unable to pass the film inspection. After magnetization High-quality carbon steel pipes must be demagnetized before welding.

The methods of pipeline degaussing usually include high temperature degaussing method, DC degaussing method, AC degaussing method and exponential decay degaussing method.

The high-temperature degaussing method has extremely high requirements on equipment and requires vacuum conditions, so it is basically unusable. Pipeline degaussing can use DC degaussing method, but the power consumption is relatively large (generally several kilowatts, even tens of kilowatts), and the heat generation is relatively severe, so the cooperation of magnetometer is required, and the operation is more troublesome (but the effect is better), and it is difficult to demagnetize large pipes. big. Although the AC degaussing method is simple and effective, it consumes a lot of power (generally tens of kilowatts), generates serious heat, and requires the cooperation of power transmission equipment. For the disadvantages of difficult degaussing of large pipelines, the exponential decay flux linkage degaussing method is an ideal degaussing method, which has the advantages of low power consumption (only hundreds of watts), no heat generation, high efficiency, good effect, and simple operation.

Degaussing is especially necessary when welding and repairing pipes in field conditions or in semi-finished foundations.

1. Degaussing process
For degaussing before welding, the degaussing process for single carbon steel pipe and steel pipe joints has been formulated, including the following contents: ① Determine the size and direction of the residual magnetic field of the steel pipe; ④ After degaussing, check whether the residual magnetism meets the requirements.

2. Degaussing method
In the established process documents, the following degaussing methods are stipulated: using direct current or alternating current, and using electromagnets or permanent magnets to establish a magnetic field.

The electromagnetic coil composed of welding wire with a section of 35~50mm is used to complete the degaussing of DC and AC. The wire is wound on a carbon steel pipe or two butted steel pipes, and coils with different turns are wound according to the residual magnetism of the steel pipes. When using direct current demagnetization, welding rectifiers or converters with a current of 500~1000A must be used, including multi-station ones. When degaussing with alternating current, use a welding transformer with a current of 500-1000A. All power sources used shall have remote control and current regulation, allowing the use of ballast rheostats. When the welding transformer is used for degaussing, it is recommended to use the portable current measuring card meter LI-4505, LI-4501, etc. to measure the degaussing current. With the help of special electromagnet degaussing, welding rectifier or transformer should be used as power supply.