Common welding methods for carbon steel elbows in production include: automatic welding of large-diameter, thick-walled (greater than 21mm) pipelines often adopt U-shaped grooves or compound grooves, because U-shaped grooves and compound grooves are time-consuming. Consumption restricts the efficiency of pipeline welding. V-shaped groove processing is simple, time-saving and labor-saving. However, when the large-diameter, thick-walled pipeline V-shaped groove is automatically welded, improper selection of welding process parameters will cause welding defects.
The welding method adopts STT root welding + CRC-P260 automatic welding machine hot welding, filling and covering. Welding equipment: Lincoln STT welding machine, Lincoln DC-400, CRC-P260 automatic welding machine. Shielding gas: STT root welding shielding gas 100% CO2, automatic welding shielding gas 80% Ar+20% CO2. Composite grooves or U-shaped grooves are commonly used for automatic welding of carbon steel elbows. V-shaped grooves can also be used in pipelines with small wall thickness. Their common feature is that the gap between the grooves is small. The wall thickness of the second West-East Gas Pipeline is 21.0mm, and the upper mouth width of the V-shaped groove is about 22mm, which is close to the swing limit of the CRC-P260 welding gun. This type of groove is a huge challenge for automatic welding. Based on past experience, the welding process parameters of the automatic welding test are determined. Using the above parameters to carry out automatic welding test, it is found that automatic welding seam is prone to defects such as non-fusion between layers, non-fusion of side walls, dense pores, and excess height of over-welded parts.
In order to ensure a good cover surface forming effect, the cover surface welding selects a smaller welding speed while reducing the torch swing frequency as much as possible to make the cover surface weld thin and wide, thereby reducing the existence time of the molten pool and achieving a reduction The purpose of overheight of the overhead welding position. According to the test welding results and analysis, the process parameters of STT root welding + CRC automatic welding filling and surface covering of the tie line of the West-East Gas Pipeline 2 were finally determined. According to the welding parameters in Table 3, the carbon steel elbow weld has no pores, cracks, lack of fusion and other defects after inspection, and the weld surface is formed. The mechanical properties of the welds have been tested by the Welding Technology Center of the China Petroleum and Natural Gas Pipeline Science Research Institute, and all indicators are in line with the construction requirements for the tie line connection of the Second West-East Gas Pipeline. The successful application of STT root welding + CRC-P260 automatic welding on large-diameter, thick-walled (V-shaped groove) pipelines fully embodies the high-quality, high-efficiency, and low-labor intensity characteristics of automatic welding technology.
The above information is provided by carbon steel pipe bend supplier.
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