Why can argon arc welding as a base for groove welds, especially pipe joints, ensure both welding quality and efficiency?

I. Advantages of argon arc welding as a base

(1) Good quality

As long as the appropriate welding wire, welding process parameters, and good gas protection are selected, the root can achieve good penetration, uniform penetration, smooth and neat surface. There are no defects such as weld bead, incomplete penetration, indentation, porosity, and slag inclusion that are prone to occur during general electrode arc welding.

(2) High efficiency

In the first layer of pipeline welding, manual argon arc welding is called continuous arc welding. And electrode arc welding is a discontinuous arc welding, so manual argon arc welding can improve efficiency by 2-4 times. Since argon arc welding does not produce welding slag, there is no need to clean the slag and repair the weld bead, resulting in a faster speed increase. When welding the second layer of arc welding cover, a smooth and neat argon arc welding bottom layer is very beneficial for arc welding cover, which can ensure good fusion between layers, especially in the welding of small diameter pipes, with more significant efficiency.

(3) Easy to master

The welding of the root seam of manual arc welding must be carried out by experienced and highly skilled welders. Using manual argon arc welding as a base, workers engaged in welding work can generally master it after a short period of practice.

(4) Small deformation

The heat affected zone during argon arc welding is much smaller, resulting in less deformation and residual stress in the welded joint.

II. Process Introduction

(1) Welding Example

The economizer, evaporator tube bundle, water-cooled wall, and low-temperature superheater are made of 20 # steel, while the high-temperature superheater tubes are made of 12Cr1MoV.

(2) Preparation before welding

Before welding, a 30 ° groove should be made on the pipe mouth, and the metal color should be polished within a range of 15mm inside and outside the pipe end. The clearance between pipeline joints is 1-3mm. When the actual gap between the joints is too large, a transition layer needs to be welded on one side of the pipeline groove first. Build temporary shelter facilities and strictly control the wind speed at the welding operation site. If the wind speed exceeds a certain range, air holes are easily generated.

(3) Operation

Using a manual tungsten inert gas arc welding machine, the welding machine itself is equipped with a high-frequency arc starting device, which can be used for high-frequency arc starting. Arc extinguishing is different from shielded metal arc welding. If the arc extinguishing is too fast, it is easy to produce arc pits and cracks. Therefore, during operation, the molten pool should be directed towards the edge or thicker base material, gradually narrowing the molten pool and extinguishing the arc, and finally turning off the protective gas.

For 20 # steel pipes with a wall thickness of 3-4mm, TIGJ50 (or 08CrMoV for 12Cr1 MoV) can be used as the filling material, with a tungsten rod diameter of 2mm, a welding current of 75-100A, an arc voltage of 12-14V, a protective gas flow rate of 8-10L/min, and a DC positive power supply

III. Wide application of argon arc welding

• Advantages:

1. Argon protection can isolate the adverse effects of oxygen, nitrogen, hydrogen and other gases in the air on the arc and molten pool, reduce the burning loss of alloy elements, and obtain dense, splash free and high-quality welding joints;
2. The arc combustion of argon arc welding is stable, the heat is concentrated, the arc column temperature is high, the welding production efficiency is high, the heat affected zone is narrow, and the stress, deformation, and crack tendency of the welded parts are small;
3. Argon arc welding is open arc welding, which is easy to operate and observe;
4. The electrode loss is small, the arc length is easy to maintain, and there is no flux or coating layer during welding, making it easy to achieve mechanization and automation;
5. Argon arc welding can weld almost all metals, especially some refractory and easily oxidizable metals such as magnesium, titanium, molybdenum, zirconium, aluminum, and their alloys;
6. Unrestricted by the position of the weldment, full position welding can be performed.

• Disadvantages:

1. Due to the large heat affected area, argon arc welding often causes deformation, high hardness, sand holes, local annealing, cracking, pinholes, wear, scratches, undercutting, or insufficient bonding force and internal stress damage to the workpiece after repair. Especially during the repair process of small defects in precision castings, they protrude on the surface. In the field of repairing defects in precision castings, cold welding machines can be used instead of argon arc welding. Due to their low heat release, cold welding machines effectively overcome the shortcomings of argon arc welding and make up for the difficulty of repairing precision castings.
2. Compared with electrode arc welding, argon arc welding has a higher degree of harm to the human body. The current density of argon arc welding is higher, and the emitted light is stronger. The ultraviolet radiation generated by its arc is about 5-30 times that of ordinary electrode arc welding, and the infrared radiation is about 1-1.5 times that of electrode arc welding. The ozone content generated during welding is higher. Therefore, it is recommended to choose a place with good air circulation for construction, otherwise it will cause great harm to the body.
3. For metals with low melting points and easy evaporation (such as lead, tin, zinc), welding is more difficult.