Four operation methods for bottom welding of argon arc welding stainless steel pipe

The welding stainless steel pipe usually consists of bottom welding, filling welding, and cover welding. Stainless steel pipe bottom welding is the most critical part of stainless steel pipe welding. It is not only related to the quality of the project, but also the progress of the project. At present, stainless steel bottom is divided into two processes: backside argon and non-argon.

The back argon protection is divided into solid core wire + TIG process and solid core wire + TIG + water-soluble paper process; the backside is not filled with argon protection is divided into flux-cored wire bottom welding and welding rod (coated wire) bottoming TIG welding.

Stainless steel backing welding usually adopts the TIG process. According to the actual situation on-site, we can use the following four methods for backing welding.

1. The backside uses a blocking plate to block the ventilation protection method (ie solid-core welding wire + TIG)

When stainless steel pipes are prefabricated, the welds can usually be welded by rotation, which is very easy to ventilate. At this time, the two sides of the stainless steel pipe inner welds are usually blocked and ventilated to protect the bottom welding. At the same time, the outer side is made with adhesive cloth. Blocked.

When welding, the process of ventilating in advance and lagging the gas should be adopted. The outer adhesive cloth is torn off by welding. Since the blocking plate is composed of rubber and white iron, it is not easy to damage, so this welding method can guarantee the inside of the weld. It is filled with argon gas and its purity is ensured, to effectively ensure that the metal inside the weld is not oxidized, and the quality of the bottom weld of the weld is guaranteed.

2. Use only soluble paper or a combination of soluble paper and blocking plate for blocking and ventilation protection (ie solid-core welding wire + TIG + water-soluble paper)

When installing and welding stainless steel pipe fixing ports, it is difficult to ventilate inside, and some sides are easier to plug. In this case, a water-soluble paper + blocking plate can be used for plugging. That is, the side that is easy to ventilate and easy to remove is blocked with a blocking plate, and the side that is not easy to ventilate and difficult to remove the blocking plate is blocked with water-soluble paper, and the outside is sealed with an adhesive cloth to paste the weld seam.

When welding stainless steel fixed ports, in many cases, both sides of the weld cannot be ventilated. At this time, how to ensure the protection of the inner side of the weld becomes a problem. In the actual construction on-site, we use water-soluble on both sides of the weld. The method of dealing with paper, ventilating from the center of the weld and sealing with adhesive cloth on the outside successfully solved the above-mentioned problems.

When using water-soluble paper to seal the ventilation, because the ventilation is from the center of the weld, in the final sealing step, the ventilation tube should be quickly pulled out, and the remaining argon gas inside should be used for protection, and the bottom can be quickly completed and the mouth sealed.

With this method, it should be noted that the water-soluble paper should be double-layered and must be pasted, otherwise, it will easily cause the water-soluble paper to be damaged and fall off, and the inner weld will lose the protection of argon gas, which will cause oxidation, which will cause the weld to be cut again Welding can not guarantee the quality of welding, but also seriously affects the construction period. Therefore, we should strictly inspect before welding and stick water-soluble paper.

In many construction sites, we have adopted this welding method for bottoming. The quality can be effectively guaranteed. At the same time, there are certain construction difficulties. Therefore, careful and skilled welders should be selected for this work.

3. The backside is not protected by argon gas, and flux-cored welding wire + TIG process is adopted

This method has been applied in my country for several years, and flux-cored welding wires such as E308T1-1, E308LT1-1, E309T1-1, E309LT1-1, 347T1-1, E316T1-1, E316LT1-1 have been produced, and they have been applied to the field. The welding has achieved good economic benefits.

Since the back is not filled with argon, its advantages are obvious, mainly in terms of high efficiency, simplicity, and low cost, which are suitable for installation on the construction site. However, due to its structural characteristics, the flux-cored welding wire has higher requirements for the welder during operation. Its wire feeding speed is fast and the wire feeding accuracy is high. It is difficult to master. Welders should be specially trained and skilled in welding before they can participate in welding.

4. The backside is not protected by argon gas, and the coated welding wire (self-protected flux-cored wire) + TIG process is adopted

In recent years, my country has also developed stainless steel primer welding wires (namely, coated welding wires, such as TGF308, TGF308L, TGF309, TGF316L, TGF347, etc.), which have been used in actual construction and achieved good results.

The protection mechanism of the stainless steel bottoming wire + TIG process is that the back weld is protected by the metallurgical reaction of the slag produced by the melting of the wire and its alloy elements, and the front weld is protected by argon, slag, and alloy elements.

With this process, the following operating points should be noted: During the stainless steel pipe welding process, maintain the correct included angle between the welding torch, welding wire, and welding parts. The ideal backward inclination angle of the welding torch nozzle is 70°-80°, and the welding wire is clamped to the surface of the weldment. The angle is 15°-20°; the temperature of the molten pool is correctly controlled, and the temperature of the molten pool is changed by changing the angle between the welding handle and the weldment, changing the welding speed, etc., to ensure the beautiful shape of the weld (the width is consistent, no recession, Defects such as over-convex);

During operation, the current should be slightly larger than when welding solid wire, and the welding handle should be slightly oscillated to accelerate the separation of molten iron and molten coating, which is convenient for observing the molten pool and controlling whether the weld is penetrated; when filling the wire, it is best to send it to 1/2 of the molten pool, and press it inward slightly to ensure penetration of the root and prevent recession;

During the stainless steel pipe welding process, the welding wire should be fed in and taken out regularly, and the welding wire should always be under the protection of argon gas to prevent the end of the welding wire from being oxidized and affecting the welding quality; pay attention to the welding quality at the arc starting and ending points, and the arc starting point The spot weld should be polished to a 45° gentle slope, and attention should be paid to defects such as arc craters and shrinkage holes when closing the arc.

The welding wire is used for bottom welding, and there is no need to pass argon gas inside the weld. The welder is simple and quick to operate, has the characteristics of high efficiency and low cost, and can also guarantee welding quality. (In the Urumqi Petrochemical Expansion Project, we use this method to weld a total of 28 joints and repair ports, and the pass rate of one-time perspective welding is 100%), which is worthy of our promotion.