Introduction of common methods of steel pipe welding

At present, the commonly used methods of steel pipe pipeline welding include electrode 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, etc.

(1) The advantages of electrode arc welding are that the equipment is simple, light, and flexible, and it can be applied to the welding of short seams in maintenance and assembly, especially the welding of hard-to-reach parts. The disadvantage is that it has high technical requirements for welders, high training costs for welders, poor labor conditions, low production efficiency, and is not suitable for welding special metals and thin plates. Electrode arc welding with corresponding electrodes can be applied to most industrial carbon steel, stainless steel, cast iron, copper, aluminum, nickel, and its alloys.

(2) Submerged arc welding can use a large current. Under the action of arc heat, a part of the flux is melted into slag and undergoes a liquid metallurgical reaction with the liquid metal. Another part of the molten slag floats on the surface of the molten metal pool. On the one hand, it can protect the weld metal, prevent air pollution, and have a physical and chemical reaction with the molten metal to improve the composition and performance of the weld metal; The seam metal is cooled slowly to prevent the occurrence of defects such as cracks and pores. Compared with electrode arc welding, its advantages are high welding seam 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 is mostly used. The disadvantage is that it is generally only suitable for the welding of flat seams and corner seams, and the welding of other positions requires special devices to ensure the coverage of the flux on the weld area and prevent the leakage of the molten pool metal; the arc and groove cannot be directly observed during welding. The relative setting of the welding seam automatic tracking system needs to be used 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 arc stability is poor, which is not suitable for welding Thin parts with thickness less than 1mm. Submerged arc welding has been widely used for the welding of carbon steel, low alloy structural steel, and stainless steel. Because 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 shielded welding is an excellent method for connecting sheet metal and bottom welding because it can control heat input very well. This method can be used for welding almost all metals, especially for dry welding of aluminum, magnesium, metals that can form refractory oxides, and active metals such as titanium and beriberi: the welding quality of this welding method is high, but it is different from other arcs. Compared with 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/MAG welding are argon, helium, carbon dioxide, or a mixture of these gases. When argon and nitrogen are used as shielding gas, it is called molten extremely inert gas shielded welding (abbreviated as MIG welding in the world); when a mixture of inert gas and oxidizing gas (O2, CO2) is used, or with C02 and C02+ When the mixed gas of 02 is a shielding gas, it is collectively referred to as molten electrode active gas shielded welding (abbreviated as MAG welding internationally). The main advantage of MIG welding is that it can be easily welded in various positions, and it also has the advantages of faster welding speed and higher deposition rate. MIGAW can be applied to the welding of the most abundant 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 MIG/MAG welding. The welding wire used is flux-cored, and the core of the welding wire is filled with powders of various compositions. When welding, a protective gas is added, mainly CO2 gas, and the powder is decomposed or melted by heat, which plays the role of gas generation and slag generation 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 the powder as the protec

ve gas. The change in the dry elongation of the welding wire of this welding method will not affect the protective effect, and the range of change can be large. Flux-cored arc welding has the following advantages: good welding process performance, beautiful bead shape; fast deposition speed, high productivity, continuous automatic, and semi-automatic welding; easy adjustment of the alloy system The method adjusts the chemical composition of the deposited metal; the energy consumption is low; the comprehensive cost is low. The disadvantage is that the manufacturing equipment is complex, the manufacturing process and technical requirements are high, the storage requirements of the flux-cored welding wire are high, and the welding wire is easily damp. Flux-cored arc welding can be applied to the welding of most ferrous metals of various thicknesses and joints.

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