Introduction To Common Methods of Steel Pipes Welding

At present, the commonly used methods for welding steel pipelines include electrode arc welding (SMAW), submerged arc welding (SAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and flux cored arc welding (FCAW). and downward welding, etc.

(1) The advantages of electrode arc welding are that the equipment is simple, lightweight, and flexible to operate. It can be suitable for welding short seams in maintenance and assembly, especially for welding hard-to-reach parts. The disadvantages are that it requires high technical requirements for welder operation, high welder training costs, poor working conditions, low production efficiency, and is not suitable for welding special metals and thin plates. Welding rod arc welding with corresponding welding rods can be suitable for 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, part of the flux melts into slag and undergoes a liquid metallurgical reaction with the liquid metal. Another part of the slag floats on the surface of the metal molten pool. On the one hand, it can protect the weld metal, prevent air pollution, and produce physical and chemical reactions with the molten metal, improving the composition and performance of the weld metal; on the other hand, it can also make the weld The seamed metal cools 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 welding straight seams and circumferential seams of large workpieces, and mechanized welding is often used. The disadvantage is that it is generally only suitable for welding flat seams and corner seams. Welding in other positions requires special devices to ensure that the flux covers the weld area and prevents the leakage of the molten pool metal; the arc and groove cannot be directly observed during welding. The relative position of the welding seam requires an automatic welding seam tracking system to ensure that the welding torch is aligned with the welding seam without welding deviation; when the current is larger, the electric field intensity of the arc is higher. When the current is less than 100A, the arc stability is poor and is not suitable for welding. Thin parts less than 1mm thick. Submerged arc welding has been widely used for welding carbon steel, low alloy structural steel, and stainless steel. Because slag can reduce the cooling rate of the welded joint, some high-strength structural steel and high-carbon steel can also be welded by submerged arc welding.

(3) Gas tungsten arc welding can control heat input very well, so it is an excellent method for joining thin sheet metal and primer welding. 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, as well as active metals such as titanium and berkelium. This welding method has high welding quality but is different from other arc welding methods. Compared with welding, its welding speed is slower, the production cost is high, it is greatly affected by the surrounding airflow, and it is not suitable for outdoor operation.

(4) Gases commonly used in gas metal arc welding include argon, helium, carbon dioxide, or mixtures of these gases. When argon and nitrogen are used as shielding gas, it is called molten inert gas shielded welding (referred to 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 a shielding gas, it is collectively called melting extremely active gas shielded welding (referred to as MAG welding internationally). The main advantage of gas metal arc welding is that it can easily weld in various positions, and it also has the advantages of faster welding speed and higher deposition rate. MAG welding can be applied to the welding of 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 compositions. During welding, a protective gas is added, mainly CO2 gas, and the powder is decomposed or melted by heat, which plays the role of generating gas and slag to protect the molten pool, infiltrating the alloy, and stabilizing the arc. When flux-cored wire arc welding is performed without additional shielding gas, it is called self-shielded flux-cored wire arc welding. It uses the gas generated by the decomposition of powder as a protective gas. The change in the dry extension length of the welding wire in this welding method will not affect the protective effect, and the range of change can be larger. Flux-cored wire arc welding has the following advantages: good welding process performance and beautiful weld bead formation; fast deposition speed and high productivity, and can carry out continuous automatic and semi-automatic welding; the alloy system is easy to adjust and can be made of both metal sheath and flux core The method adjusts the chemical composition of the deposited metal; low energy consumption; low overall cost. The disadvantages are complex manufacturing equipment, high technical requirements for manufacturing processes, high storage requirements for flux-cored welding wires, and the welding wires are easily affected by moisture. Flux-cored arc welding can be used to weld most ferrous metals of various thicknesses and joints.

(6) Downward welding is a process introduced from abroad that is suitable for circumferential seam welding of steel pipelines. It refers to a process method that strikes the arc at the top of the steel pipe weld and welds downward. Downward welding has the advantages of high production efficiency and good welding quality.