When welding stainless steel, due to the great affinity between stainless steel and oxygen, if the back is not protected by argon filling, the molten metal is easy to oxidize in the welding process and produce welding defects. Therefore, in the argon arc welding of stainless steel pipeline, in order to ensure the welding quality of the back of the weld, argon filling protection measures are usually adopted.

Argon filling methods are as follows:

1.1 argon filling method for small diameter pipe

For small diameter pipes, the whole pipe inflation method can be adopted. This inflation method is relatively simple, but with the increase of pipeline length, argon is wasted greatly. Generally, sectional assembly welding is adopted, and a small amount of intermediate joints are welded. Both sides of the welded pipe mouth are blocked with soluble paper (generally 200 ~ 300mm away from both sides of the welded mouth). The soluble paper can dissolve by itself in the hydrostatic test.

Specific method for argon filling of the whole pipe: plug one end of the pipe with a cork (a hole with a diameter of 3 ~ 5mm shall be punched in the center of the cork to mainly prevent the difficulty of joint arc closing due to excessive argon pressure in the pipe during arc closing), and fill argon from the other end of the pipe.

1.2 argon filling method for large diameter pipeline

For pipes with a diameter greater than 89mm, local argon filling can be used to save argon. The specific method is to add the blocking plate on both sides near the welded junction in advance before welding to form an isolated inflation chamber (generally place the blocking plate 100 ~ 150mm away from the welded junction), inflate one end to the inflation chamber and vent from the small hole in the center of the other blocking plate. In order to reduce the loss of argon in the pipe from the butt joint interval and reduce the protection effect, the adhesive tape can be pasted along the gap of the weld joint before welding, and the adhesive tape can be removed while welding. In order to supplement the argon leaked from the gas chamber, argon shall be continuously filled into the inflation chamber during the whole welding process, and the argon flow shall be appropriate. The flow is too small, the gas protection is not good, and the back of the weld is easy to oxidize. If the flow rate is too large, eddy current will be generated during welding and brought into the air, and the protection effect will also deteriorate. At the same time, it will cause defects such as concave at the root of the weld and affect the welding quality. Generally, the argon filling flow is controlled at 6 ~ 8L / min. In addition, special attention should be paid to that the welding can be carried out only after the air in the inflation chamber or pipe is exhausted during inflation, otherwise the welding quality will be affected.

For local inflation method, two blocking plates shall be placed on both sides of the pipe before welding, and the rope (or iron wire) shall be fastened. After welding, the two blocking plates shall be pulled out of the pipe~

1.3 argon filling and placement of soluble paper

For large diameter pipes and vessels, as long as people can enter, the sliding form can be used for argon filling, and the back sliding form and front welding can be filled with argon simultaneously. For the pipeline whose reverse side cannot be filled with argon synchronously by sliding mode, soluble paper can be used. Place the soluble paper at the position of the blocking plate and fill argon from the weld buckle gap (paste adhesive tape at the gap, remove the adhesive tape while welding, and weld the whole weld joint. The soluble paper will melt automatically during the hydrostatic test.)

The above argon filling protection methods have long auxiliary time and waste argon, which will bring many difficulties in field welding. Yb132cr19ni10nb stainless steel flux cored wire is used to weld 1Cr18Ni9Ti austenitic stainless steel pipeline, which breaks the traditional argon shielded welding method inside the pipeline, improves work efficiency, saves cost, and brings great convenience to construction. From our application in engineering, it is proved that this is a practical, reliable, simple and feasible new welding process, especially for installation units.

Selection of welding equipment

Special nsa4-300 silicon rectifier argon arc welding machine can be used. Simple tungsten argon arc welding machine can also be used. Ax-320 DC welding machine is selected and equipped with a gas electric combined self cooling welding gun. Argon is controlled by rotameter and refitted into simple argon arc welding equipment. Qualified units can purchase ready-made argon arc welding equipment.

The welding wire adopts the Great Wall brand yb132cr-19ni10nb stainless steel flux cored wire produced by Beijing electrode factory. The welding wire uses carbon steel sheet. The chemical composition of the flux core in the middle matches the quality of the welding material. Through droplet transition, the chemical composition of the weld metal is very uniform. The chemical composition and mechanical properties of flux cored wire are as follows:

C≤0.08? Mn1. 0~2.5? Si≤1.0? Cr18~21? Ni9~11? S≤0.03? P≤0.04? σ b≥515? MPa δ 5≥30%

welding technology

4.1 preparation before welding

4.1.1 the range of 15 ~ 20mm of stainless steel nozzle shall be degreased with acetone.

4.1.2 included angle between welding gun, welding wire and weldment

The included angle between the backward inclination of the welding gun and the surface of the weldment is too small, which will reduce the argon protection effect. The angle is too large, the visibility is small, and the operation is difficult. The ideal backward inclination angle of welding gun nozzle is 75 ~ 85 degrees, and the included angle between welding wire and weldment surface is 15 ~ 20 degrees.

4.2 key points of operation

For the welding of horizontal fixed pipe, start the arc striking welding at the position about 10mm ahead of 6 points. The purpose of advance arc striking is to ensure that the joints do not overlap, and the joints of layer 2 and layer 1 are staggered. In the welding process, the welding gun swings slightly to accelerate the separation of molten iron and molten welding core, which is convenient to observe the molten pool and control the penetration. When filling the welding wire, send it to 1 / 2 of the molten pool and press it inward to increase the root penetration and prevent concave. The welding wire shall be regularly fed into and taken out of the molten pool. The removal distance of the welding wire shall ensure that the end of the welding wire is in the argon protection zone to avoid oxidation of the end and affect the protection effect. When changing welding wire, grinding tungsten rod or weld joint, it is necessary to overlap the weld 5 ~ 10mm for arc striking. After the arc is ignited, it will stay for about 5 ~ 10s. After the weld pool with the same width as the welded weld is formed, the welding distance can move forward. No or less welding wire shall be added at the overlap to ensure the uniform width of the weld and the uniform penetration of the reverse side.

If the arc suppression is improper, it is easy to produce defects such as craters and shrinkage cavities. Therefore, arc suppression is very important during operation. When the above defects are found, the defects shall be removed before welding.

The usual argon arc welding equipment is equipped with "attenuation" device. When the arc is stopped, press the "attenuation button" and increase the wire feed. After the welding current gradually decreases until the arc is extinguished, the welding gun protects the arc stop for a period of time to prevent the weld from oxidation. If a welding machine without "attenuation" device is used, the welding speed shall be appropriately slowed down when the arc is stopped. After the molten pool is filled, the arc shall be moved to the groove surface immediately, and finally the arc shall be extinguished.

To obtain a uniform and beautiful weld, it largely depends on correctly mastering the temperature of the molten pool. When it is found that the molten pool is increased and concave, it indicates that the molten pool temperature is too high. At this time, the included angle between the welding gun and the workpiece should be quickly reduced and the welding speed should be accelerated. When the weld pool is small and the weld is narrow and high, it indicates that the weld pool temperature is low. This is to slightly increase the included angle between the welding gun and the workpiece, slow down the welding speed and reduce the amount of welding wire.

When using a simple argon arc welding machine (ax-320 DC welding machine), the polarity is positive connection method, that is, the welding gun is connected to the negative, the workpiece is connected to the positive, and contact arc striking (short-circuit arc striking) is adopted during arc striking. The action during arc striking should be fast to prevent damage to the tungsten electrode and tungsten inclusion in the weld.

It adopts flux cored welding wire without argon filling on the back, which is simple and convenient to operate, eliminates a series of argon filling protection facilities and auxiliary labor, and has high efficiency and low cost. Especially in high-altitude operation, its superior performance is more remarkable.

Compared with the usual argon filling on the back of solid core welding wire, the first layer of sealing welding can improve the efficiency by 1 ~ 2 times and the cost is low. Compared with the back argon filling, it saves 2 ~ 3 times of argon and all auxiliary argon protection facilities.

Stainless steel argon free welding wire tgf308l flux cored welding wire | composition of tgf308l argon free welding wire

Characteristics and uses:

Back oxidation during stainless steel backing welding has always been a difficult problem in the welding process. The general practice is to fill the back with argon for protection. However, when the container is large, the pipeline is long or there is no argon filling space on the back, a lot of argon will be wasted, but the protection is still poor. In order to solve this problem, a new R & D department specially developed stainless steel flux cored wire for TIG welding for butt groove backing welding. During welding, the coating will penetrate into the back of the molten pool to form a layer of dense protective film, so that the back will not be oxidized, and it will be welded on one side and formed on both sides. After cooling, the welding slag will generally fall off automatically, or it can be easily removed by compressed air and water flushing.

It is suitable for all position welding, can weld a good inner weld bead, and has excellent X-ray performance.

The application of this kind of welding material not only simplifies the welding process, improves the production efficiency, but also reduces the production cost,.

matters needing attention:

(1) The polarity of the power supply must be DC positive connection, i.e. DC -, and the current shall be selected according to the plate thickness.

(2) Machining appropriate groove shape.

(3) In order to supply sufficient slag for the back weld bead and ensure sufficient penetration, the root gap must be reserved.

(4) In order to obtain an appropriate amount of deposited metal, the method of fine classification and fast-paced strip transportation should be adopted.

(5) The welding wire is special for single side welding and double side forming. When welding more than two layers of weld beads, it is easy to produce slag inclusion, so it is not recommended.

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