What is the difference between hot-galvanized pipe and cold-galvanized pipe?
Hot-galvanized pipe
The hot-dip galvanized tube is obtained by reacting a molten metal with an iron matrix to produce an alloy layer, thereby combining the substrate and the plating layer. Hot-dip galvanizing is to pickle the steel pipe first, in order to remove the iron oxide on the surface of the steel pipe, after pickling, it is washed by ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then fed. Hot dip plating tank. Hot-dip galvanizing has the advantages of uniform plating, strong adhesion and long service life.
Cold galvanized pipe
Cold galvanizing is electrogalvanizing. The amount of galvanizing is very small, only 10-50g/m2, and its corrosion resistance is much worse than that of hot-dip galvanized pipe. Regular galvanized pipe manufacturers, in order to ensure quality, most do not use electro-galvanizing (cold plating). Only small companies with small equipment and old equipment use electro-galvanized steel, of course, their prices are relatively cheaper. At present, the Ministry of Construction has officially laid down the cold-galvanized pipe with backward technology, and the cold-galvanized pipe is not allowed to be used as water and gas pipe in the future.
Hot-dip galvanizing and cold-dip galvanizing differ in the way they work: one is zinc plated in a molten zinc bath at 450-480 degrees, and the other is zinc plated by electroplating or other methods at normal temperature.
Compared with cold-dip galvanizing, the hot-dip galvanized zinc layer has better corrosion resistance due to the zinc-iron alloy layer.
In general, the hot-dip galvanized zinc layer is thicker and the corrosion resistance is better. The zinc layer of electro-galvanized is relatively thin and has poor corrosion resistance. (unless the cold-galvanized zinc layer also reaches the level of a thick zinc layer)
Which one is better? Can't generalize, see what you use. For example, the support wire in the water pipe is better than the plating. It looks good and the cost is low. If it is a power tower, it is a big mistake to use electroplating zinc. It should definitely be hot-dip galvanized. Because hot-dip galvanizing has good corrosion resistance, it can be used for decades.