Can galvanized steel pipe be welded? What should I pay attention to?

First, the premise should be polished

However, the galvanized layer of the weld must be polished off, otherwise it will produce bubbles, trachoma, false welds and so on. It will also make the weld brittle and less rigid.

Second, the welding characteristics of galvanized steel

Galvanized steel is generally in the low-carbon steel outside a layer of zinc, galvanized layer is generally 20um thick. The melting point of zinc in 419 ° C, boiling point of 908 ° C or so. In welding, zinc melts into a liquid floating on the surface of the molten pool or in the root position of the weld. Zinc in iron has a large solid solubility, zinc liquid will be along the grain boundaries in-depth erosion of the weld metal, low melting point of zinc to form a “liquid metal embrittlement”.

At the same time, zinc and iron can form a brittle intermetallic compounds, these brittle phase to reduce the plasticity of the weld metal, under the action of tensile stress and cracks.

If welding fillet welds, especially T-joint fillet welds are most likely to produce penetration cracks. Galvanized steel welding, bevel surface and edge of the zinc layer, under the action of the arc heat, oxidation, melting, evaporation and volatile white soot and steam, very easy to cause weld porosity.

Due to oxidation and the formation of ZnO, its melting point is high, about 1800 ° C or more, if the parameters in the welding process is small, will cause ZnO slag, at the same time. As Zn becomes a deoxidizer. Produce FeO-MnO or FeO-MnO-SiO2 low melting point oxide slag. Secondly, due to the evaporation of zinc, volatilization of a large number of white soot, irritating and harmful effects on the human body, therefore, the galvanized layer of the weld must be polished off.

Third, welding process control

Galvanized steel welding preparation and general mild steel is the same, need to pay attention to is to carefully deal with the bevel size and the nearby galvanized layer. In order to weld through, the bevel size should be appropriate, generally 60 ~ 65 °, to leave a certain gap, generally 1.5 ~ 2.5mm; in order to reduce the penetration of zinc on the weld, before welding, can be beveled within the galvanized layer removed before welding.

In the actual supervision of the work, the use of a centralized beveling, do not leave a blunt edge process for centralized control, two-layer welding process, reducing the possibility of unwelded through.

Welding rod should be selected according to the base material of the galvanized pipe, general low carbon steel due to consider the ease of operation, the selection of J422 is more common.

Welding practices: in welding the first layer of multi-layer welding seam, try to make the zinc layer melting and vaporization, evaporation and escape from the weld, can greatly reduce the liquid zinc stay in the weld.

In welding fillet weld, the same in the first layer as far as possible to make the zinc layer melting and vaporization, evaporation and escape from the weld, the method is to move the end of the electrode forward about 5 ~ 7mm or so, when the zinc layer melting and then return to the original position to continue forward to continue to weld.

And then horizontal and vertical welding, such as the choice of short slag welding rod such as J427, biting tendency will be very small; if the use of back and forth to the transport technology, more can be obtained without defects in the quality of the weld.