Welding parts have magnetic welding bad how to do

In the production of oilfield construction units, welding of magnetized pipeline is often encountered, because of the large magnetic deflecting blowing during welding of magnetized pipe. Poor weldability. This paper mainly introduces the magnetized tube using dc degaussing electrode arc welding, or ac degaussing electrode arc welding, and by means of electromagnet or permanent magnet degaussing electrode arc welding. Causes of remanence and its influence on welding quality In the production of oil field, magnetic deflecting phenomenon sometimes occurs in the welding of heat pipeline and gas injection pipeline, which affects the whole welding process. The formation of magnetic deflecting phenomenon is the result of the existence of residual magnetism in the tube metal. In general, the remanence is divided into induction magnetism and process magnetism. Induction magnetism is often produced in the process of factory tube. The electromagnetic crane is used for loading and unloading, the steel tube is stopped in the strong magnetic field, the magnetization method is used to complete non-destructive inspection, and the steel tube is placed close to the strong power supply line. Process magnetism often occurs during assembly and welding operations and when magnetic grippers and fixtures are used, and pipes are welded with direct current, long time contact with electrical wires connected to the DC power supply, etc. Degaussing method Most of the oilfield construction is carried out in the field, and the corresponding pipeline demagnetization technology measures are formulated when the pipeline is welded and prefabricated. (1) demagnetization method 1. Arc welding method with dc degaussing electrode; 2. Arc welding with ac degaussing electrode; 3. Electromagnet or permanent magnet degaussing electrode arc welding method. (II) Analyze the remanence parameters and select the demagnetization method based on the specific conditions of the construction site: The remanence grade is weak, and the remanence induction intensity is 100×101. The dc and ac demagnetization is completed by the electromagnetic coil composed of welding wires with a cross-section of 35 ~ 50mm2. The wire is wound on the steel pipe or two butt steel pipes, and the coil with different turns is wound according to the magnetic remanence of the steel pipe. Arc welding rectifier with current of 300 ~ 700A must be used for direct current demagnetization. When using ac degaussing, arc welding transformer with current of 300 ~ 700A is used. With the help of special electromagnet demagnetization, arc welding rectifier or arc welding transformer as a power source to carry out. When the degaussing. The magnetic field should be greater than the remanent magnetic field. HI = H2 (1.2 ~ 1.5) Where H1 — degaussing magnetic field intensity H2 — remanent magnetic field intensity; The intensity of degaussing magnetic field is determined according to the formula: H = I, N/L Where, I – current of the coil A; N – number of turns of degaussing coil; L — Winding length m. To measure magnetism, the HM II-97X magnetometer is recommended. The magnetometer is a portable instrument designed to assess the magnetic induction strength of fluctuating magnetic fields and magnetic leakage fields in the air gap of the magnetic system (the instrument consists of a measuring converter, electronics and charging device, and is powered by a 9V battery pack). 1. Demagnetization with direct current. A. Determine the size and direction of remanent magnetic field of steel pipe by means of magnetometer; B. A coil composed of flexible welding wires with a cross section of 35 ~ 50mm2 is configured on the steel pipe and connected to the arc welding rectifier, so that the direction of action of the magnetic field formed by it is opposite to that of the remaining magnetic field of the steel pipe. C. At the beginning of demagnetization, the current is 80 ~ 100A. D. During the demagnetizing process, the result of the action of the demagnetizing field must be checked periodically on the steel tube with a magnetometer (measured when the power supply is switched on) and, if necessary, the current must be controlled or its direction changed (the method of changing the wire on the arc welding rectifier). E. After the demagnetization, in order to smoothly reduce the flux, the current should be gradually reduced within 1min until zero, and then cut off the power supply. (1) Degaussing a single steel tube. At one end of the steel tube, the coil of 8.12 turns is wound around the outer circle to degausse with the maximum magnetic field; The other end of the tube is then demagnetized in the same way. When a single steel pipe is degaussed to the steel pipe connection, the distance between the two steel pipes is not less than 300mm, and the method of degaussing is completed by winding 18 to 20 turns of coils at 80 ~ 100mm away from the end face of each pipe. (2) When the steel pipe connection is demagnetized, a welding wire with a cross-section of 35 ~ 50mm2 is wound at the butt steel pipe end to form a common coil of two steel pipes. The coils can be overlapped (clockwise or counterclockwise), with a total number of turns ranging from 16 to 22. At this point, the steel pipe with more turns should be on the steel pipe with larger remanence. When the remanence level is less than 20×10-4T, the welding at the root of the weld is completed (this degaussing process is the best). (3) Under special circumstances, the welding clamp with the electrode will be short-circuited for 10s at the other end of the electrode under the current of 300A, and then disconnected. After each short-circuited and disconnected cycle, magnetometer is used to check the magnetism, and the demagnetization process is repeated if necessary. 2. Use alternating current to demagnetize. It is mainly applied to the end of single steel pipe and butt steel pipe with wall thickness up to 25mm. At this point, in addition to the above method of demagnetization, there are the following supplements: A coil composed of a welded wire is used to connect a steel wire with a length of 0.5 ~ 1.0m and a diameter of 1.5 ~ 3.0m in the loop. This steel wire is placed on the insulating and non-combustible material pad (such as asbestos brick). The steel wire can smoothly change the size of the current, thus changing the size of the degaussing magnetic field. When the power is switched on, the wire is heated and burned off in a certain time. The burning time depends on wire diameter, length and current value. After the wire is burned out, magnetometer is used to check the remanence. When the demagnetization effect is insufficient, demagnetization must be repeated. The removal of demagnetization system can be carried out after the root weld is welded, and it is recommended to be removed immediately after demagnetization.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods