There are two types of galvanizing methods for seamless tubes: hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing includes wet method, dry method, lead-zinc method, redox method, etc. The main difference between different hot-dip galvanizing methods is what method is used to activate the surface of the pipe body after acid dip cleaning of the steel pipe to improve the quality of galvanizing. The dry method and redox method are mainly used in the production.
1. Hot-dip galvanized seamless tube
The hot-dip galvanized seamless tube is made by reacting the molten metal with the iron matrix to produce an alloy layer, so that the matrix and the coating are combined. 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 cleaned in the tank of ammonium chloride or zinc chloride aqueous solution or mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to the in the hot dip bath. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. It is widely used in gas pipelines, natural gas pipelines, heating pipeline systems, and some outer wires of galvanized steel pipes are also used in hot water pipe network systems and domestic drainage systems.
2. Cold galvanized seamless tube
Cold galvanizing is electro-galvanizing. The amount of galvanizing is very small, only 10-50g/m2. Its corrosion resistance is much different than that of hot-dip galvanized pipes. In order to ensure the quality, most regular galvanized pipe manufacturers do not use electro-galvanized (cold plating). Only those small enterprises with outdated equipment use electrogalvanizing, and of course their prices are relatively cheap. At present, cold galvanized pipes have been banned from being used as water and gas pipes.
3. The difference between hot and cold galvanized tubes
Hot-dip galvanized seamless tube: complex physical and chemical reactions occur between the steel pipe matrix and the molten plating solution to form a corrosion-resistant zinc-iron alloy layer with a tight structure. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix. Therefore, it has strong corrosion resistance.
Cold galvanized seamless tube: The zinc layer is an electroplating layer, and the zinc layer is independently layered with the steel pipe substrate. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe substrate and is easy to fall off. Therefore, its corrosion resistance is poor. In newly built houses, it is forbidden to use cold galvanized steel tubes as water supply pipes.