Hot Dipped Galvanized Steel Pipe is widely used in all kinds of industries. The advantage of using Hot Dipped Galvanized Steel Pipe is to protect the internal steel structure by using zinc metal which forms a tight oxide protective layer in the air.  In the case of being welded and scratched, the relatively active galvanized part can be used as the sacrificial anode to delay steel corrosion and have good corrosion resistance due to the existence of zn-fe galvanic battery. However, due to the existence of a galvanized layer, cracks, pores and slag are easily produced during welding, which makes it difficult to obtain good welding quality.

Generally, Hot Dipped Galvanized Steel Pipe is coated with a layer of zinc on low carbon steel in the chemical reaction. The melting point of zinc in 419 ° C, the boiling point around 908 ° C. Zinc in iron has a high degree of solid solubility, zinc liquid will penetrate the weld metal along the grain boundary, low melting point zinc forms "liquid metal embrittlement". Meanwhile, zinc and iron can form brittle intermetallic compounds, such as Fe3Zn10 and FeZn10. These brittle phases reduce the plasticity of weld metal and make weld metal crack under tensile stress.

Penetration cracks are most likely to occur in fillet welds, especially int-joints. During the welding of Hot Dipped Galvanized Steel Pipe, the zinc layer on the surface and the edge of the groove produces oxidation, melting, evaporation and even volatilization white smoke and steam under the action of arc heat, which can easily cause weld porosity. The ZnO, which is formed due to oxidation, its high melting point is above 1800 ° C. If the welding process parameters are smaller, it will cause the ZnO slag. At the same time, as zinc become deoxidizer, the FeO-MnO or FeO-MnO-SiO2 low melting oxide slag will be produced.

If the welding specification is not appropriate and the operation method is not appropriate, it is easy to melt the galvanized layer at the edge of the weld and expand the melting area, which may damage the galvanized layer, especially in the case of elongating the arc and large swing operation, widen the melting area and damage the galvanized layer more seriously. At the same time, due to the evaporation of zinc, a large amount of white smoke is emitted, which has a stimulating and harmful effect on the human body. Therefore, the selection of welding methods and materials with low smoke and dust is also a factor that must be considered.

The pre-welding preparation of Hot Dipped Galvanized Steel Pipe is the same as that of normal low carbon steel. It should be noted that the groove size and the adjacent galvanized layer should be carefully handled. To weld complete penetration, the groove size should be appropriately arranged, generally 60 ~ 65°. The groove should leave some space, certainly, a gap generally is 1.5 ~ 2.5 mm. To reduce the penetration of zinc into the weld lines, the zinc layer in the groove should be removed before welding. In the actual work, the concentrated beveling and the dull edge technology are adapted to take centralized control. Two-layer welding process reduces the possibilities of incomplete welding penetration.

Welding rod should be selected according to the base material of Hot Dipped Galvanized Steel Pipe pipe. Generally, J422 is a common choice for low carbon steel due to its easy operation. Welding technique: when welding the first layer of multilayer welding, try to make the zinc layer melt and vaporize, evaporate and escape the welding line, which can greatly reduce the liquid zinc remaining in the welding line. When weld fillet weld, also try to make the zinc layer melting and evaporation on the first layer, evaporation and escape welding lines. It's a method including removing the electrode end forward about 5 ~ 7 mm. When the zinc layer is melted, return to the original position and continue welding. After the completion of welding, the welding line should be cleaned in time, and coated with zinc - rich primer with good anti-corrosion measures.

For more information about ADTOMALL'S high-quality Pre Galvanized Steel Pipe, please click here. Wishing for your visit.