2. Local argon filling method

When the pipe diameter is large and the pipe length is long, if the pipe is filled with argon directly, the welding quality is not easy to be guaranteed, and a large amount of argon gas is wasted, which increases the engineering cost. In order to save argon, a partial argon filling method can be employed.

The partial argon charging can be carried out by a water-soluble paper method. Before the pair is paired, water-soluble paper is applied to each side of the pipe at 150 mm from both sides of the weld to form a set of temporary blocking plates, and then an argon-filled needle is used to fill the tube with argon gas at the gap (see Figure 2). When the piping system is subjected to a hydrostatic test, the water-soluble paper dissolves quickly in the water and is removed with water without adverse effects.

In addition, an argon-filled jig can be fabricated for local argon-filled protection, and the argon-filled fixture is shown in FIG. Before the welding, the argon-filled clamp plate is placed on both sides of the pipe in advance, and the clamp is taken out from the pipe after the welding is completed. This method is suitable for ground prefabrication of stainless steel pipes, which is simple and easy.

3. Reverse protection box method for argon filling

As long as the diameter of the pipe can be entered, the argon can be filled by the tracking protection box method, and the sliding of the protection box is synchronized with the front welding. When argon is filled, the flow rate of argon gas should not be too large, and the gas can not be supplied to the molten pool.

4. Judging the effect of argon protection

The argon protection effect can be judged based on the weld color. During the welding process, the welder can adjust the shielding gas according to the color, so that the weld seam can achieve a good protection effect. The weld color and protection effect are shown in Table 1.

5. Precautions for argon-filled protection

(1) When the argon arc welding is performed, the back side of the weld should be supplied in advance, and the flow rate should be appropriately increased. After the air is discharged, the flow rate is gradually reduced. The tube should be filled with argon without interruption during the welding process. The lag is stopped during the stop welding, so that the weld is fully protected. In addition, it should be noted that the welding can only be carried out after the air is drained, otherwise the protection effect of argon filling will be affected.

(2) The argon flow rate should be appropriate. If the flow rate is too small, the protection is not good, the back side of the weld is easy to be oxidized; if the flow rate is too large, eddy current will be brought into the air during welding, the protection effect will also be deteriorated, and defects such as concave in the root of the weld will be caused, which will affect the welding quality.

(3) The argon inlet should be placed as low as possible in the closed section, and the air outlet should be placed in the closed section. Since argon is heavier than air, it is easier to ensure a higher concentration by charging argon from a lower position, and the argon-filling protection effect is better.

(4) In order to reduce the loss of argon gas in the pipe from the gap of the nozzle, affecting the protection effect and increasing the cost, the tape can be attached along the gap of the weld before welding, leaving only the length of the welder for one continuous welding, and removing the tape while welding.

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