The galvanized steel pipeline is defined by its excellent advantages such as corrosion resistance, lengthy life, reduced preliminary cost and maintenance expenses, has been wieldy utilized in outside as well as indoor, aquatic and underground applications
Galvanized steel pipe is a 20um thick zinc finishing outside of the low carbon steel pipe. The melting factor of zinc is at 419 ° C as well as the boiling factor is around 908 ° ℃. In welding, zinc is melted on the surface of the molten pool or at the root of the weld. Since zinc has a fairly high strong solubility in iron, the zinc liquid will deeply erode the weld metal along the grain border, creating "fluid metal embrittlement". At the exact same time, zinc as well as iron can form an intermetallic breakable substance, which minimizes the plasticity of the weld metal and also results in fractures under the action of tensile stress and anxiety.
When welding galvanized steel, the surface area of groove and also the edge of the zinc layer under the action of arc heat, oxidation, melting and also dissipation of white smoke and also steam conveniently lead to weld porosity. ZnO formed by oxidation has a high melting factor, over 1800 ° C. If the specifications are too small in the welding process, ZnO slag inclusion will certainly be caused. Meanwhile, as Zn ends up being a deoxidizer, FeO-MnO or Feo-Mno-Sio2 oxide slag inclusion with low melting point will certainly be produced. It must be kept in mind that the white dirt of zinc volatilization is unsafe to human body and also the galvanized layer at welding must be gotten rid of.
Action 1: Polishing
The galvanized layer should be gotten rid of at the welding component, otherwise will certainly happen bubbles, trachoma, incorrect welding as well as other issues, which causes weak welding seam and rigidity decreases.
Action 2: Weld groove
The prep work of galvanized steel prior to welding resembles the basic low carbon steel, it Check over here is necessary to take note of the groove size and also galvanized layer. The groove size is normally 60 ~ 65 ° and also there is a certain void, normally 1.5 ~ 2.5 mm; In order to reduce the infiltration of zinc right into the weld, the galvanized layer in the groove can be removed prior to welding and then bonded. In practical welding, the groove is normally focused and no blunt edge is left. Two-layer welding minimizes the possibility of insufficient welding. The welding pole must be selected according to the base product of galvanized steel tube. Typically speaking, J422 is a perfect selection.
GL bonded groove
Action 3: Welding
In the very first layer of multilayer welding weld, attempt to thaw the zinc layer and make it vaporized, dissipation, this can substantially reduce the zinc liquid continued to be in the weld. The exact same method is made use of for fillet welds. First move the electrode tail ahead concerning 5 ~ 7mm, and after that return to the initial position to proceed welding after thawing the zinc layer. If the choice of brief slag electrode such as J427, there will certainly be a really tiny bite edge tendency; Back and forth input electrode can obtain the welding quality without issues