The melting point of zinc oxide formed by oxidation is higher than 1800 C. If the welding parameters are small, the inclusion of zinc oxide will occur. At the same time, the inclusion of low melting point oxides such as FeO-MnO or FeO-MnO-SiO 2 will occur because zinc becomes a deoxidant. If the welding specification is not suitable and the operation method is not appropriate, it is easy to melt the galvanized layer at the edge of the weld and even expand the melting area, which may destroy the galvanized layer, especially in the case of elongated arc and large swing operation, widening the melting area and destroying the galvanized layer more seriously. At the same time, due to the evaporation of zinc, a large amount of white smoke and dust is volatilized, which has stimulating and harmful effects on human body. Therefore, the selection of welding methods and materials with low smoke and dust content must also be considered.
Welding method of galvanized pipe:
Gas welding, manual arc welding, CO2 gas shielded welding, submerged arc automatic welding and tungsten argon arc welding are commonly used in galvanized steel structures.
In the past, it was often used to weld galvanized pipes. Because the heat input of gas welding was not centralized, it was easy to produce defects, and the mechanical properties of welds were poor, so it was basically eliminated in the installation industry. Gas welding has great damage to galvanized coating.
CO2 gas shielded welding:
The welding performance of galvanized steel is good. When appropriate welding specifications and matching protective gases and welding materials are adopted, high quality welding joints can be obtained. This method is seldom used in engineering practice.
Tungsten Arc Welding Arc:
Energy concentration, less damage to galvanized layer, and easy to form a good one-sided welded double-sided formed joint, is a welding method worth adopting, but the welding speed is slow and the cost is expensive.
Manual arc welding:
At present, pipeline installation is the most common welding method. In the case of correct selection of electrodes, such as J421, J422, J423 and other titanium oxide and titanium-calcium electrodes, the melting rate of the electrodes is higher and the melting speed is relatively increased because of the large amount of rutile and ilmenite in the coating of these electrodes. If only the galvanized layer such as the front of the molten pool can be destroyed without oscillation, the melting area will not be enlarged and the penetration of zinc liquid into the weld metal will be reduced. Under the correct operation method and welding materials, the mechanical properties of the joints will be better and the welding quality without defects will be obtained. Because manual arc welding is cheaper and faster than tungsten argon arc welding, manual arc welding technology is adopted in the case of skilled welders.
Pre-welding preparation of galvanized pipe:
It should be noted that the groove size and the galvanized layer near the groove should be carefully handled. In order to penetrate, the groove size should be appropriate, generally 60-65 degrees, leaving a certain gap, generally 1.5-2.5 mm. In order to reduce the penetration of zinc into the weld, before welding, the galvanized layer in the groove can be removed and then welded. In practical work, centralized grooving without blunt edge is adopted to centralize control, and two-layer welding process reduces the possibility of non-penetration.
Welding rod should be selected according to the base material of galvanized pipe. J422 is a common choice for low carbon steel due to its easy operation. Welding manners: When welding the first layer of multi-layer welding seam, try to make the zinc layer melt and vaporize and evaporate out of the weld, which can greatly reduce the liquid zinc left in the weld. When fillet weld is welded, the zinc layer is melted in the first layer and vaporized and evaporated to escape from the weld. The method is to move the end of the welding rod forward about 5-7 mm, and then return to the original position after melting the zinc layer and continue to weld forward. After welding, the weld seam should be cleaned up in time, and zinc-rich primer should be brushed to prevent corrosion.
Welding quality assurance measures:
Control from five aspects: human, material, machine, law and ring.
The human factor is the key point of welding control. Therefore, before welding, we should select skilled welders with welding license, and carry out necessary technical training and submission. It should not be replaced at will to ensure the relative stability of welders.
(2) Welding material control: to ensure that the purchase of regular channels of welding materials, quality assurance, certification, in line with technological requirements; tightly control the recovery of electrode head to ensure flow direction, dosage; welding materials should be strictly baked in accordance with the process, and once issued not more than half a day of dosage.
Welder: Welder must ensure reliable performance and meet process requirements; Welder must have qualified current and voltage meters to ensure the correct implementation of welding process. Welding cable should not be too long. Welding parameters should be adjusted for a long time.
(4) Welding process methods: to ensure the strict implementation of special operation methods for galvanized pipes, to inspect the groove before welding, to control the welding process parameters and operation methods, to inspect the appearance quality after welding, and to increase the non-destructive testing after welding if necessary. Control welding level and welding material consumption per pass.
Correct welding process is adopted in the construction of hot-dip galvanized pipe, inspection and acceptance are carried out strictly in accordance with the specifications, and anticorrosion treatment of weld seam is done in time after the completion of welding. It has certain feasibility in the operation of air-conditioned open and closed systems, which can improve the construction speed and the firmness of pipeline connection. Therefore, under the permissible construction conditions, on the premise of doing well the relevant protective and anti-corrosion measures, the welding connection of hot-dip galvanized pipes is the best way to connect the overall quality.
The highlights of this article are provided by Jinan Galvanized Pipe. For more information, you can click on http://www.jnxjm.com.