Talking about the back protection method of weld seam of argon arc welding of stainless steel pipe (3)

Second, the back self-protection stainless steel TGF series welding wire welding

The back self-protecting stainless steel TGF series wire is a special coated wire. When welding, the protective coating will penetrate into the back of the molten pool to form a dense protective layer, so that the back of the weld bead will not be oxidized. After cooling, the slag shell will automatically fall off and be easily removed by compressed air or water. . The welding wire is basically used in the same way as a normal argon-arc welded solid wire, and the coating does not affect the arc and molten pool form on the front side, and the weld metal can meet the requirements in performance. The commonly used self-shielded welding wire is shown in Table 2.

The use of self-shielded welding wire is not limited by factors such as pipe size and welding position, and it is flexible in operation and reduces preparation for argon filling. However, due to the thin coating on the surface of the wire, some inconsistencies in the welding operation occur, and defects such as concaves often appear, so the welder's operation level is required to be high. The self-shielding welding wire is suitable for the bottom of the weld, and should not be used for the bead of the second layer or above, otherwise it will easily cause slag inclusion and the weld bead is not beautiful. When using multi-channel welding with full argon arc welding, it should be used together with solid wire. In addition, there is basically no domestically-made self-protecting stainless steel welding wire with stable performance on the market. Imported self-shielded welding wire is expensive and costly, so it has been limited in application.

Third, the application of argon-free soldering protection agent

In recent years, an argon-free soldering protection agent has been used in the welding of stainless steel pipes (furnace pipes) for petrochemical, thermal power construction and other projects. The protective agent is in the form of a powder in the state of supply and needs to be mixed with methanol or a special binder when used. As a back surface protective agent, a protective coating is formed on the back side of the solder during the soldering process, which can effectively prevent oxidation of the back side of the solder joint.

How to use protective agent:

(1) First remove the oil stains on the back side of the weld.

(2) Take out an appropriate amount of protective agent and mix it in a vessel containing an appropriate amount of methanol (or special binder). Stir them evenly and apply them to the weld surface of the inner wall of the pipe (width 5 to 10 mm). . It should be noted that after the application, a continuous adhesive film will be formed on the surface of the coating, and the powder will be applied to the underside of the film, so the coating cannot be scratched to prevent the adhesive film from being damaged and causing the powder to be damaged. Vent, thus affecting the protection effect.

(3) After being applied for 5 minutes, it can be welded after drying. After welding, a poorly soluble chemically inert film is formed on the back side of the weld, which adheres tightly to the weld surface and has no effect on the radiation detection.

The protective agent has good applicability and can be welded using a normal welding current, or it can be welded with a current 10% larger than normal welding. The protective agent has no effect on the welding operation, not only can prevent the back side oxidation, but also support the molten metal on the back side of the weld, obtain an excellent bottoming weld bead, and there is no weld bead, undercut or deep depression. The pass rate of welding is high.

The argon-free soldering protection agent is easy to operate, that is, coating and soldering, saving time and improving efficiency. When applied to small-diameter welding, the cost is slightly higher than that of argon-filled welding; however, it is worthy of popularization and application when fixed-mouth welding or large-diameter welding. At present, the application of argon-free protective agent is in its infancy in China.

Fourth, the conclusion

For the argon arc welding of stainless steel pipelines, the method of in-pipe argon filling, self-protecting welding wire and argon-free welding protection agent can prevent oxidation of the back side of the weld and effectively improve the mechanical properties and corrosion resistance of the weld. Guarantee.

In actual work, the protection method on the back side of the weld should be flexibly selected according to the factors such as the amount of welding work, the specifications of the pipe and the suitability of the operation, so as to ensure the welding quality and reduce the engineering cost to a large extent.

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