At present, the commonly used methods for steel pipe welding include metal arc welding (SMAW), submerged arc welding (SAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), flux-cored arc welding (FCAW) and downward welding.
(1) The advantages of metal arc welding are simple equipment, lightweight and flexible operation. It can be used for welding short seams in maintenance and assembly, especially for welding in difficult-to-reach areas. The disadvantages are high technical requirements for welders, high welder training costs, poor working conditions, low production efficiency, and unsuitable for welding special metals and thin plates. Metal arc welding with corresponding electrodes can be used for welding most industrial carbon steel, stainless steel, cast iron, copper, aluminum, nickel, and their alloys.
(2) Submerged arc welding can use a larger current. Under the action of arc heat, part of the flux melts into slag and reacts with liquid metal in liquid metallurgy. The other part of the slag floats on the surface of the metal pool. On the one hand, it can protect the weld metal, prevent air pollution, and produce physical and chemical reactions with the molten metal to improve the composition and properties of the weld metal; on the other hand, it can also slowly cool the weld metal to prevent defects such as cracks and pores. Compared with arc welding, its advantages are high weld quality, fast welding speed, and good working conditions. Therefore, it is particularly suitable for welding straight seams and circumferential seams of large workpieces, and mechanized welding is mostly used. The disadvantage is that it is generally only suitable for welding flat seams and angle seams. Welding in other positions requires special devices to ensure that the flux covers the weld area and prevents the molten pool metal from leaking out; the relative position of the arc and the groove cannot be directly observed during welding, and an automatic weld tracking system is required to ensure that the welding torch is aligned with the weld without welding deviation; the current is large, the electric field strength of the arc is high, and when the current is less than 100A, the arc stability is poor, and it is not suitable for welding thin parts with a thickness of less than 1mm. Submerged arc welding has been widely used in the welding of carbon steel, low-alloy structural steel, and stainless steel. Since slag can reduce the cooling rate of the weld joint, some high-strength structural steels and high-carbon steels can also be welded by submerged arc welding.
(3) Gas tungsten arc welding is an excellent method for connecting thin sheet metal and base welding because it can well control heat input. This method can be used for welding almost all metals, especially for dry welding of metals that can form refractory oxides such as aluminum and magnesium, as well as active metals such as titanium and berkelium: this welding method has high welding quality, but compared with other arc welding, its welding speed is slower, the production cost is higher, and it is more affected by the surrounding airflow, making it unsuitable for outdoor operation.
(4) Gas tungsten arc welding usually uses argon, helium, carbon dioxide, or a mixture of these gases. When argon or nitrogen is used as the shielding gas, it is called metal inert gas shielded welding (internationally referred to as MIG welding); when a mixture of inert gas and oxidizing gas (O2, CO2) is used as the shielding gas, or a mixture of C02 and C02+02 is used as the shielding gas, it is collectively referred to as metal active gas shielded welding (internationally referred to as MAG welding). The main advantage of metal active gas shielded welding is that it can be easily welded in various positions, and it also has the advantages of fast welding speed and high deposition rate. Metal active gas shielded welding can be applied to the welding of most major metals, including carbon steel and alloy steel. Metal inert gas-shielded welding is suitable for stainless steel, aluminum, magnesium, copper, titanium, zirconium, and nickel alloys. This method can be used for arc spot welding.
(5) Flux-cored arc welding can be considered as a type of metal active gas shielded welding. The welding wire used is flux-cored, and the core of the welding wire is filled with flux powder of various components. During welding, an external shielding gas, mainly CO2 gas, is added. The powder decomposes or melts under heat, playing the role of gasification and slag formation to protect the molten pool, alloy infiltration, and arc stabilization. When flux-cored arc welding is performed without additional shielding gas, it is called self-shielded flux-cored arc welding. It uses the gas generated by the decomposition of powder as the shielding gas. The change in the dry extension length of the welding wire in this welding method will not affect the protection effect, and its range of variation can be relatively large. Flux-cored arc welding has the following advantages: good welding process performance and beautiful weld bead shape; fast deposition speed and high productivity, and continuous automatic and semi-automatic welding can be performed; the alloy system is easy to adjust, and the chemical composition of the deposited metal can be adjusted through two ways: the metal sheath and the flux core; low energy consumption; and low overall cost. The disadvantages are complex manufacturing equipment, high requirements for manufacturing process technology, high requirements for the storage of flux-cored wire, and the wire is easily affected by moisture. Flux-cored arc welding can be applied to the welding of most ferrous metals of various thicknesses and various joints.
(6) Downward welding is a process method introduced from abroad that is suitable for circumferential seam welding of steel pipes. It refers to a process of striking an arc at the top of the steel pipe weld and welding downwards. Downward welding has the advantages of high production efficiency and good welding quality.
Post time: May-29-2024