The galvanized steel pipeline is defined by its outstanding benefits such as corrosion resistance, long life, low initial expense and maintenance expenses, has actually been wieldy made use of in outside and interior, aquatic as well as below ground applications
Galvanized steel pipeline is a 20um thick zinc layer outside of the reduced carbon steel pipe. The melting point of zinc is at 419 ° C and also the boiling point is around 908 ° ℃. In welding, zinc is thawed externally of the molten pool or at the origin of the weld. Because zinc has a fairly high solid solubility in iron, the zinc liquid will deeply erode the weld metal along the grain boundary, developing "fluid steel embrittlement". At the exact same time, zinc and iron can create an intermetallic weak substance, which minimizes the plasticity of the weld steel and brings about splits under the activity of tensile stress.
When welding galvanized steel, the surface area of groove and also the side of the zinc layer under the activity of arc heat, oxidation, melting and also evaporation of white smoke and also vapor easily bring about weld porosity. ZnO formed by oxidation has a high melting point, above 1800 ° C. If the specifications are also little in the welding process, ZnO slag inclusion will certainly be triggered. Meanwhile, as Zn ends up being a deoxidizer, FeO-MnO or Feo-Mno-Sio2 oxide slag addition with low melting factor will be created. It needs to be noted that the white dust of zinc volatilization is damaging to human body and the galvanized layer at welding need to be gotten rid of.
Step 1: Polishing
The galvanized layer must be polished off at the welding part, or else will occur bubbles, trachoma, false welding and also other problems, which leads to fragile welding seam as well as rigidity decreases.
Step 2: Weld groove
The preparation of galvanized steel before welding is similar to the basic low carbon steel, it is necessary to pay attention to the groove size and galvanized layer. The groove dimension is usually 60 ~ 65 ° and also there is a certain void, usually 1.5 ~ 2.5 mm; In order to minimize the infiltration of zinc into the weld, the galvanized layer in the groove can be removed prior to welding and after that welded. In practical welding, the groove is generally concentrated and no blunt side is left. Two-layer welding minimizes the possibility of insufficient welding. The welding pole should be selected according to the base product of galvanized steel tube. Generally speaking, J422 is a suitable option.
GL weld groove
Step Additional hints 3: Welding
In the initial layer of multilayer welding weld, attempt to thaw the zinc layer as well as make it vaporized, dissipation, this can significantly minimize the zinc liquid continued to be in the weld. The exact same technique is used for fillet welds. First move the electrode tail ahead about 5 ~ 7mm, and then return to the original placement to continue welding after thawing the zinc layer. If the selection of short slag electrode such as J427, there will certainly be a really little bite edge tendency; Backward and forward input electrode can obtain the welding high quality without defects