With the rapid development of the petrochemical industry, stainless steel materials have been widely used, and higher requirements have been put forward for pipeline and plate welding. The previous stainless steel arc welding backing method has gradually been phased out, and argon arc welding backing welding has been adopted.

Argon arc welding has a higher cleanliness and faster backing than arc welding, but some problems have also arisen. During the welding process, as the back of stainless steel argon arc welding is prone to oxidation and defects, back protection measures must be taken to ensure the mechanical properties and corrosion resistance of the weld seam. Therefore, effective protection must be taken when welding stainless steel.

Today, we will introduce several commonly used methods for protecting the back of stainless steel welding:

Back argon protection method

Commonly used protective gases can be divided into pure argon gas protection and mixed gas protection. A certain proportion of argon nitrogen mixed gas is more conducive to austenitic stainless steel welding, while some inert gases are not used due to their high cost.

Argon filling method is a relatively traditional back protection method, which has the characteristics of good back protection, easy to master, high cleanliness, and high qualification rate. It is divided into protective cover argon filling protection method, local argon filling protection method, welding seam direct filling, argon connection protection method, etc.

1. Protective cover filled with argon protection method

This method is commonly used in stainless steel welding of plates and large diameter pipes. The protective cover is connected to a metal pipe and an argon hose, and the argon valve is opened to fill the protective cover with argon gas.

Another person needs to hold a metal tube as a handle to synchronize the sliding of the protective cover on the back molten pool with the welding of the plate or tube.

This provides effective protection for the back, characterized by concentrated protection, no need to turn on too much argon gas, and less waste of argon gas.

2. Local argon filling protection

For pipelines with smaller local spaces and shorter sizes, local protection is easy to use.

Method: Seal the welding joint of the pipeline with tape (to prevent air leakage), and seal both ends of the pipeline with sponge, rubber, paper shell, etc. Insert the argon hose from one end to fill with argon gas. It is best to make a small hole (sponge is not required) at the sealing point of the other end of the pipeline, which is conducive to the final backing welding joint and will not cause dents due to high internal pressure.

When welding, in order to prevent a large amount of argon gas from being discharged from the weld seam, the sealing tape for the weld seam should be torn and welded one by one, which can reduce more loss of argon gas and effectively protect the weld seam. Characteristics: Waste, slow argon filling, high cost.

3. Direct argon filling protection method for welded junction

For pipelines that are too long and have a slightly larger diameter, local argon filling is too wasteful, quality cannot be guaranteed, and engineering costs are too high. In order to save costs, the welding seam direct argon filling method can be used.

Method of making plugs on both sides of the weld seam

Process the sponge into a plug with a slightly larger pipe diameter and connect the two sponges with iron wire between them, with a distance of 300-400mm, to form a double plug. Connect one end of the plug to a longer section of steel wire.

When aligning, first plug the plug at 150-200mm on both sides of the weld seam to be welded. The long iron wire at one end should be longer than the length of the pipeline at one end of the weld seam and expose the pipe end. One end of the metal small pipe should be flattened and connected to an argon hose. The flattened end should be inserted into the already aligned weld seam for argon filling, preferably in the top direction. This way, the small pipe should be pulled out before the final joint is bottomed out and welded with residual gas from the pipeline. After welding, use iron wire to pull out the plug.

Water soluble paper protection method

Before assembly, apply water soluble paper at 150-200mm on both sides of the welding joint as a seal. After alignment, perform the same gas filled welding as the sponge plug. When the pipeline undergoes a hydraulic test, the water soluble paper will dissolve and be discharged with water.

4. Argon protection judgment

The argon protection effect can be judged based on the color of the inner weld seam, so that operators can adjust the argon gas according to the color to achieve the best protection effect. Its color is best in white and gold, with gray and black being the worst

5. Precautions for stainless steel back protection

(1) Before argon arc welding, the back of the welding piece should be filled with argon for protection in advance. The flow rate should be appropriately increased, and after the air is discharged, the flow rate gradually decreases. During the welding process, argon should be continuously filled into the pipe. Only after welding is completed can the argon hose be removed to provide good protection for the weld seam.

It should also be noted that welding can only be carried out after the air is completely discharged, otherwise it will affect the protective effect of argon filling.

(2) The argon flow rate should be appropriate. Low flow rate, poor protection, and easy oxidation on the back of the weld seam; Excessive flow can cause defects such as concave grooves at the root of the weld, which can affect the welding quality.

(3) The argon inlet should be placed as low as possible in the closed section, and the air outlet hole should be placed slightly higher in the closed pipe section. Because argon is heavier than air, filling it from a lower position can ensure a higher concentration and better protection effect.

(4) In order to reduce the loss of argon gas from the gap in the pipe, affect the protective effect, and increase costs, adhesive tape can be applied along the gap before welding, leaving only the length of continuous welding for the welder. The tape should be removed while welding.