What should be paid attention to in zinc steel pipe welding, galvanized steel pipe company will answer for you:
First, the premise is to polish but the galvanized layer at the welding place must be polished off, otherwise bubbles, trachoma, false welding, etc. will occur. It also makes the weld brittle and stiff down. 2. Welding characteristics of galvanized steel Galvanized steel is generally coated with a layer of zinc on the outside of low carbon steel, and the galvanized layer is generally 20um thick. The melting point of zinc is 419 °C and the boiling point is around 908 °C. In welding, zinc melts into a liquid that floats on the surface of the melt pool or at the root of the weld. Zinc has a large solid solubility in iron, and the zinc liquid will deeply impregnate the weld metal along the grain boundaries, and the low melting point zinc forms "liquid metal embrittlement". At the same time, zinc and iron can form intermetallic brittle compounds, and these brittle phases reduce the metal plasticity of the weld and produce cracks under tensile stress. Fillet welds, especially those of T-joints, are most susceptible to penetrating cracks. When galvanized steel is welded, the zinc layer on the surface and edge of the groove will oxidize, melt, evaporate and even volatilize white smoke and vapor under the action of arc heat, which can easily cause weld porosity.
The ZnO formed due to oxidation has a high melting point, about 1800 °C or more, if the parameters are small in the welding process, it will cause ZnO slag inclusion, and at the same time. As Zn becomes an oxygen absorber. FeO-MnO or FeO-MnO-SiO2 low melting point oxide slag inclusions are generated. Secondly, due to the evaporation of zinc, a large amount of white smoke is volatilized, which has an irritating and harmful effect on the human body, so the galvanized layer at the welding place must be polished and disposed of. 3. The welding process controls the pre-welding preparation of galvanized steel is the same as that of general low-carbon steel, and it should be noted that the size of the groove and the nearby galvanized layer should be carefully handled.
In order to weld through, the size of the groove should be appropriate, generally 60~65°, and a certain gap should be left, generally 1.5~2.5mm; In order to reduce the penetration of zinc into the weld, the galvanized layer in the groove can be removed before welding. In the actual supervision work, the centralized beveling is adopted, the blunt edge process is not left for centralized control, and the two-layer welding process reduces the possibility of non-penetration. The welding rod should be selected according to the substrate material of the galvanized pipe, and J422 is more common for low carbon steel due to the consideration of ease of operation. Welding method: When welding the first layer of multi-layer welding, try to melt the zinc layer and make it vaporize, evaporate and escape from the weld, which can greatly reduce the liquid zinc left in the weld.
