At present, the commonly used methods for welding steel pipes
are electrode arc welding (SMAW), submerged arc welding (SAW), gas tungsten arc welding (GTAW), gas melting arc welding (GMAW), flux cored arc welding (FCAW) and the following To welding and so on.
(1) The advantages of electrode arc welding are that the equipment is simple, portable, and flexible in operation. It can be applied to the welding of short seams in maintenance and assembly, especially for the welding of hard-to-reach parts. The disadvantages are high technical requirements for welders, high welder training costs, poor working conditions, low production efficiency, and are not suitable for welding special metals and thin plates. Electrode arc welding is equipped with corresponding electrodes, which can be applied to the welding of 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, a part of the flux melts into slag and undergoes a liquid metallurgical reaction with the liquid metal. The other part of the slag floats on the surface of the molten 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 performance of the weld metal; on the other hand, it can also make the weld metal The seam metal is cooled slowly to prevent defects such as cracks and pores. Compared with electrode arc welding, its advantages are high weld quality, fast welding speed, and good working conditions. Therefore, it is especially suitable for the welding of straight seams and circular seams of large workpieces, and mechanized welding are mostly used. The disadvantage is that it is generally only suitable for the welding of flat seams and corner seams. For welding in other positions, special devices are required to ensure that the flux covers the weld area and prevents the leakage of molten pool metal; the arc and the groove cannot be directly observed during welding. The relative setting of the welding seam needs to use the welding seam automatic tracking system to ensure that the welding torch is aligned with the welding seam without welding deviation; when the current is large, the electric field strength of the arc is high, and when the current is less than 100A, the stability of the arc 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 welded joints, 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 joining thin sheet metal and backing welding because it can well control the heat input. This method can be used for welding almost all metals, especially for dry welding metals such as aluminum and magnesium that can form refractory oxides and active metals such as titanium and berkelium: the welding quality of this welding method is high, but it is different from other arcs. Compared with traditional welding, its welding speed is slower, the production cost is high, and it is greatly affected by the surrounding airflow, so it is not suitable for outdoor operation.
(4) Gases commonly used in MIG welding are argon, helium, carbon dioxide, or a mixture of these gases. When argon and nitrogen are used as the shielding gas, it is called molten inert gas shielded welding (abbreviated as MIG welding internationally); when a mixture of inert gas and oxidizing gas (O2, CO2) is used, or C02 and C02+ When the mixed gas of 02 is shielding gas, it is collectively called melting electrode active gas shielded welding (abbreviated as MAG welding internationally). The main advantage of gas metal shielded welding is that it can be conveniently welded in various positions, and it also has the advantages of faster welding speed and higher deposition rate. Active gas-shielded welding can be applied to the welding of the most important metals, including carbon steel and alloy steel. MIG welding is suitable for stainless steel, aluminum, magnesium, copper, titanium, zirconium, and nickel alloys. Arc spot welding can be performed using this method.
(5) Flux-cored arc welding can be considered a type of gas metal arc welding. The welding wire used is flux-cored, and the core of the welding wire is filled with powders of various components. The protective gas is added during welding, mainly CO2 gas, and the powder is decomposed or melted by heat, which plays the role of gas-making and slag-making to protect the molten pool, infiltrate alloy and stabilize the arc. When flux-cored arc welding does not add additional shielding gas, it is called self-shielded flux-cored arc welding. It uses the gas generated by the decomposition of the powder as the shielding gas. The change of the dry elongation of the welding wire in this welding method will not affect the protection effect, and its change range can be large. Flux-cored arc welding has the following advantages: good welding process performance, beautiful weld bead shape; fast deposition speed, high productivity, continuous automatic and semi-automatic welding; easy adjustment of the alloy system, which can pass through the metal sheath and flux core Ways to adjust the chemical composition of the deposited metal; low energy consumption; low overall cost. The disadvantages are complex manufacturing equipment, high technical requirements for the manufacturing process, high storage requirements for flux-cored welding wire, and welding wire easy to gets damp. 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 steel pipe girth welding. It refers to a process method in which the arc is struck at the top of the steel pipe weld and welded downward. Downward welding has the advantages of high production efficiency and good welding quality.