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What should be paid attention to when welding galvanized steel pipe?

Update:2020-03-30   View(s):438   Keywords :welding galvanized steel pipe

1. the premise must be polished

However, the galvanized layer at the weld must be polished away, otherwise air bubbles, trachoma, and false welding will be generated. It also makes the weld seams brittle and reduces rigidity.

 

2. the welding characteristics of galvanized steel

In welding, zinc melts into a liquid and floats on the surface of the molten pool or at the root of the weld. Zinc has a large solid solubility in iron. Zinc liquid will deeply attack the weld metal along the grain boundary, and low melting point zinc will form "liquid metal embrittlement".

 

At the same time, zinc and iron can form inter-metallic brittle compounds. These brittle phases reduce the plasticity of the weld metal and cause cracks under the action of tensile stress.

 

If fillet welds are welded, especially T-joints, penetration cracks are most likely to occur. When galvanized steel is welded, the zinc layer on the bevel surface and the edge will be oxidized, melted, and evaporated under the action of arc heat, and even white smoke and steam will be volatilized, which will easily cause weld pores.

 

3. welding process control

The preparation of galvanized steel before welding is the same as that of ordinary low carbon steel. It is necessary to pay attention to carefully handle the groove size and the nearby galvanized layer.

 

In the actual supervision work, a centralized beveling process is adopted, and a blunt edge process is not used for centralized control. The two-layer welding process reduces the possibility of unpenetration.

 

Welding method: When welding the first layer of multi-layer welding, try to melt the zinc layer and vaporize and evaporate to escape the weld, which can greatly reduce the liquid zinc remaining in the weld.