At present, the commonly used methods of pipe welding include electrode arc welding (SMAW), submerged arc welding (SAW), tungsten gas shielded arc welding (GTAW), GMAW, FCAW and down-welding.

(1) the advantages of electrode arc welding are simple, light, flexible operation, can be applied to the maintenance and assembly of short seam welding, especially can be used to dry difficult to reach the position of welding. The disadvantages are high requirements on welder operation technology, high cost of welder training, poor labor conditions, low production efficiency, not suitable for the welding of special metal and sheet metal. Welding rod arc welding with the corresponding electrode can be used for most industrial carbon steel, stainless steel, cast iron, copper, aluminum, nickel and their alloys welding.

(2) Submerged arc welding can use a large current, under the action of arc heat, part of the flux into slag and liquid metal reaction. On the one hand, it can protect weld metal, prevent air pollution, and produce physical and chemical reactions with melted metal, so as to improve the composition and performance of weld metal. On the other hand, the weld metal can be cooled slowly to prevent cracks, pores and other defects. Compared with the electrode arc welding, its biggest advantages are high weld quality, fast welding speed and good labor conditions. Therefore, it is especially suitable for large work piece straight seam and ring seam welding, and more mechanized welding. The disadvantage is that it is generally only suitable for the welding of flat seam and corner seam, the welding of other positions need to use a special device to ensure that the flux covers the weld area and prevent the leakage of weld pool metal; During welding, it is not possible to observe the relative tuo of arc and groove directly. Automatic welding seam tracking system is needed to ensure that the welding torch is aligned with the welding seam without deviation. When the current is larger, the electric field intensity of the arc is higher. When the current is less than 100A, the stability of the arc is poor, which is not suitable for welding thin parts with thickness less than 1mm.Submerged arc welding has been widely used in the welding of carbon steel, low alloy structural steel and stainless steel. Because slag can reduce the cooling speed of welded joint, some high strength structural steels and high carbon steels can also be welded by submerged arc welding.

(3) Tungsten gas shielded welding is an excellent way to connect sheet metal and underlay welding due to its good control of heat input. This method can be used in almost all the metal welding, especially for dry welding of aluminum, magnesium, these can form refractory metal oxide and lively metal such as titanium, berkelium: this kind of welding method of welding quality is high, but compared with other electric arc welding, the welding speed is slow, production cost is high, is strongly influenced by the surrounding air, not suitable for outdoor operation.

(4) The gases commonly used in FGDS are argon, helium, carbon dioxide or a mixture of these gases. When argon and nitrogen are used as shielding gas, it is called melting inert gas shielded welding (internationally referred to as MIG welding).When the mixture of inert gas and oxidizing gas (O2, CO2) is used, or when the mixture of C02 and C02+02 is used as protective gas, it is collectively referred to as the fusion electrode active gas shielded welding (internationally referred to as MAG welding).The main advantages of GMAW are that it is convenient to weld at various positions, and it also has the advantages of faster welding speed and higher deposition rate. FGDS can be applied to most important metals, including carbon steel and alloy steel. It is suitable for stainless steel, aluminum, magnesium, copper, titanium, zirconium and nickel alloy. Arc spot welding can be carried out by this method.

(5) Flux-cored arc welding can be considered as a type of gas arc welding. The wire used is a flux-cored wire, the core of the wire with various components of powder. When welding additional protective gas, mainly CO2 gas, powder thermal decomposition or melting, play a role in making gas and slag to protect the melting pool, infiltration alloy and arc stability. 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 powder as the protective gas. The dry extension length of the welding wire in this welding method will not affect the protective effect. Flux cored arc welding has the following advantages: good welding process performance, weld bead forming beautiful; Rapid deposition speed, high productivity, can be carried out continuous automatic and semi-automatic welding; The alloy system is easy to adjust. The chemical composition of deposited metal can be adjusted by two ways: metal skin and core. Low energy consumption. Low overall cost. The disadvantages are complicated manufacturing equipment, high technical requirements of manufacturing process, high requirements for flux-cored wire storage and easy damp wire. Flux cored arc welding can be used for welding most ferrous metals of various thicknesses and joints.

(6) Downward welding is a kind of technology introduced from abroad, which is suitable for circular seam welding of pipeline. It refers to the top of the pipe welding arc, welding down a process. Downward welding has the advantages of high production efficiency and good welding quality.