Knowledge of Galvanized Pipe Welding

Galvanized steel is widely used in all walks of life, the benefits of galvanized steel use in the air to form a dense oxide protective layer of zinc metal to protect the internal steel structure. In the case of welding, scratches, due to the presence of the original battery of the Zn-Fe, relative lively galvanized part as a sacrificial anode, delaying the corrosion of iron and steel, at the same time the respective structural Hassle can be reached, and good corrosion resistance. The traditional galvanized pipe threaded connection is easy to leak, resulting in the maintenance workload Ming tubing affect the exterior of the building and other shortcomings, seek new connections is an inevitable choice. Welding due to its good sealing and high strength as part of the city gas works. However, due to the presence of zinc coating, welding prone to cracks, pores, slag, the more difficult to get a good quality of welding. Therefore, how to ensure the quality of welding, a galvanized pipe installation a key.

Galvanized steel is generally in the low carbon steel plated with a layer of zinc, galvanized layer 20um thick. Zinc in the 419 ° C melting point, boiling point of 908 ° C or so. In welding, zinc melted into a liquid floating on the bath surface, or in the root of the weld location. Having a larger degree of solid solution of zinc and iron in zinc liquid depth etching along the grain boundary of the weld metal, the low melting point of zinc is formed liquid metal embrittlement. The same time, zinc and iron can form a brittle intermetallic compound, such Fe3Zn10 (delta phase), FeZn10 (epsilon). These brittle weld metal plasticity decreases and cracks under tensile stress. If the welding fillet welds, especially the T-joint fillet most prone to penetrate the cracks.

Low carbon steel galvanized pipe weld preparation is the same, the need to pay attention to seriously deal with the groove size and near zinc coating. Penetration groove dimensions should be appropriate Usually 60 to 65 °, to leave a certain gap is generally 1.5 ~ 2.5mm; in order to reduce zinc penetration of the weld, the weld can be galvanized inside the groove layer removal after welding. Actual supervision, focused on playing the groove, leaving no the blunt edge technology for centralized control, two layers of welding process, reducing the possibility of incomplete penetration.

Welding techniques: welding the first layer of the multi-layer welding try to make the zinc layer melting and vaporization, evaporation and escape the weld, which can greatly reduce the liquid zinc stay in the weld. In fillet welding, the same as far as possible in the first layer so that the zinc layer is melted and vaporized, evaporated and escape the weld, with its forward end portion of the first electrode out of from about 5 to about 7mm, when the zinc layer. melted and then move back to the original position welding. And horizontal and vertical welding, such as choice of short residue electrode such as J427, undercut tend to be small; if the front and rear and from the transport technology, but also can be non-defective welding quality.