When welding pipes, sometimes magnetic deflection affects the welding process. When welding magnetic
carbon steel pipes (cs pipe), it often occurs that arc ignition is difficult, arc combustion stability is destroyed, arc deviation in the magnetic field, liquid metal and molten metal Problems such as slag splashing from the welding pool make the weld joint unable to pass the film inspection, and the magnetized carbon steel pipe must be demagnetized before welding.
Pipeline degaussing methods 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. The DC degaussing method can be used for pipeline degaussing, but the power consumption is relatively high (usually thousands of watts, or even tens of kilowatts), and the heat generation is relatively severe, so it needs the cooperation of a magnetometer , the operation is cumbersome (but the effect is better), and it is difficult to demagnetize large pipelines. Although the AC degaussing method is simple and the effect is good, it also has huge power consumption (usually tens of kilowatts) and severe heat generation, which requires the cooperation of transmission equipment. For the shortcomings of large pipelines such as difficult degaussing, the exponential decay and magnetic link 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 bases.
1. Degaussing process
Aiming at the degaussing before welding, the degaussing process of a single carbon steel pipe and the joint of the steel pipe is formulated, including the following contents: ① Determine the size and direction of the residual magnetic field of the steel pipe; ② Select the degaussing method, system diagram and technical means; The degaussing method of the steel pipe or the welded joint is degaussed: ④ Check the residual magnetism after degaussing to see if it meets the requirements.
2. Degaussing method
In the established process documents, the following degaussing methods are specified: using direct current or alternating current, and the magnetic field method established by means of electromagnets or permanent magnets.
The electromagnetic coil composed of welding wires with a section of 35~50mm is used to complete the degaussing of direct current and alternating current. The wire is wound on a carbon steel pipe or two butt-connected steel pipes, and coils with different turns are wound according to the residual magnetism of the steel pipes. When using direct current to demagnetize, welding rectifiers or converters with a current of 500~1000A must be used, including multi-station ones. When degaussing with alternating current, a welding transformer with a current of 500~1000A is used. All power sources used shall have remote control and current regulation devices, 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.
