The galvanized steel pipe is identified by its excellent benefits such as corrosion resistance, lengthy life, low first expense as well as upkeep costs, has actually been wieldy utilized in outdoor and also interior, aquatic and underground applications
Galvanized steel pipe is a 20um thick zinc covering on the outside of the reduced carbon steel pipeline. The melting point of zinc goes to 419 ° C and the boiling point is around 908 ° ℃. In welding, zinc is thawed on the surface of the molten pool or at the root of the weld. Given that zinc has a relatively high strong solubility www.wldsteel.com in iron, the zinc liquid will deeply erode the weld steel along the grain boundary, forming "liquid steel embrittlement". At the exact same time, zinc as well as iron can form an intermetallic breakable compound, which lowers the plasticity of the weld metal and also causes splits under the activity of tensile stress.
When welding galvanized steel, the surface of groove as well as the edge of the zinc layer under the action of arc heat, oxidation, melting and also evaporation of white smoke and also vapor quickly lead to weld porosity. ZnO created by oxidation has a high melting point, above 1800 ° C. If the criteria are also little in the welding procedure, ZnO slag inclusion will certainly be created. At the same time, as Zn ends up being a deoxidizer, FeO-MnO or Feo-Mno-Sio2 oxide slag incorporation with low melting factor will be created. It has to be kept in mind that the white dust of zinc volatilization is damaging to body and the galvanized layer at welding must be gotten rid of.
Action 1: Polishing
The galvanized layer should be gotten rid of at the welding part, or else will occur bubbles, trachoma, incorrect welding and also various other flaws, which causes weak welding seam and rigidness decreases.
Step 2: Weld groove
The prep work of galvanized steel before welding resembles the basic low carbon steel, it is necessary to pay attention to the groove dimension and also galvanized layer. The groove dimension is normally 60 ~ 65 ° and there is a certain gap, generally 1.5 ~ 2.5 mm; In order to reduce the penetration of zinc right into the weld, the galvanized layer in the groove can be removed prior to welding and afterwards bonded. In practical welding, the groove is usually focused and also no blunt side is left. Two-layer welding reduces the opportunity of incomplete welding. The welding rod need to be picked according to the base product of galvanized steel tube. Typically talking, J422 is an ideal option.
GL weld groove
Action 3: Welding
In the very first layer of multilayer welding weld, attempt to melt the zinc layer as well as make it vaporized, dissipation, this can considerably decrease the zinc liquid continued to be in the weld. The same technique is utilized for fillet welds. First relocate the electrode tail ahead about 5 ~ 7mm, and afterwards go back to the original position to proceed welding after thawing the zinc layer. If the choice of brief slag electrode such as J427, there will be a really small bite edge propensity; Backward and forward input electrode can get the welding high quality without problems