Hot dip galvanized seamless steel pipe

Date:2024-08-27Tags:seamless steel pipe, galvanized steel pipe
Hot-dip galvanizing (galvanizing) is also called hot-dip galvanizing and hot-dip galvanizing: it is an effective way to prevent metal corrosion, mainly used in metal structural facilities in various industries. It is to immerse the rust-removed steel parts in a zinc solution melted at about 500°C, so that the zinc layer adheres to the surface of the steel components, thereby achieving the purpose of corrosion protection.

Hot-dip galvanized seamless steel pipe: The amount of hot-dip galvanizing is high, and the average galvanized layer thickness is above 65 microns. Its corrosion resistance is much higher than that of hot-dip galvanized pipes. Hot-dip galvanized seamless steel pipe is to make the molten metal react 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 an ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to the hot-dip galvanizing tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life.

Hot-dip galvanized seamless steel pipes are made of: Q195, Q215, Q235, Q235B, 20# steel, 45# steel, Q345B, Q345C, Q345D, Q355B, Q355C, Q355D, 16Mn, Q390, Q460, 12Cr1MoVG, 40Cr, 35CrMo, 42CrMo, T91, 20G, 15CrMoV, 27SiMn, 45CrMo, 15CrMoG, 12CrMoV, 45Cr, etc.
seamless steel pipe
Seamless steel pipes can be divided into two categories according to the production method: hot-rolled seamless steel pipes and cold-rolled (pulled) seamless steel pipes. Galvanized steel pipes also have hot-dip seamless steel pipes and cold-dip seamless steel pipes. Cold-dip galvanized steel pipes have been banned.

Hot-dip seamless pipes:

Hot-dip seamless pipes are made by reacting molten metal with the iron matrix to produce an alloy layer, thereby combining the matrix and the coating. 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 an ammonium chloride or zinc chloride aqueous solution or a mixed ammonium chloride and zinc chloride aqueous solution tank, and then sent to the hot-dip galvanizing tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life.

Cold-dip galvanizing seamless pipe:

Cold-dip galvanizing is electro-galvanizing. The amount of galvanizing is very small, only 10-50g/m2, and its corrosion resistance is much worse than that of hot-dip galvanized pipes. In order to ensure quality, most regular galvanized pipe manufacturers do not use electro-galvanizing (cold plating). Only small enterprises with small scale and outdated equipment use electro-galvanizing, and of course their prices are relatively cheaper. In the future, cold-dip galvanized pipes are not allowed to be used as water and gas pipes.

Differences between hot and cold galvanizing:

Hot-dip galvanized seamless pipe: The steel pipe matrix undergoes complex physical and chemical reactions with the molten plating solution to form a corrosion-resistant and tightly structured zinc-iron alloy layer. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix. Therefore, it has strong corrosion resistance.
Cold-dip galvanized seamless pipe: The zinc layer is an electroplated layer, and the zinc layer is independently layered from the steel pipe matrix. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe matrix and is easy to fall off. Therefore, its corrosion resistance is poor. In newly built houses, it is forbidden to use cold-dip galvanized steel pipes as water supply pipes.

How to distinguish the authenticity of galvanized seamless pipes?

There is now a so-called hot-dip galvanized fluid pipe on the market, also called de-galvanized seamless pipe, which is actually a processed high-frequency welded pipe. The original weld is either planed or ground off with special equipment and then galvanized. Now I will share the identification method with you:
(1) Anything that is planed or ground off will leave traces, and some are very obvious;
(2) Hot-dip galvanized seamless steel pipes are all 6 meters, 9 meters or 12 meters in length. Genuine hot-dip galvanized seamless steel pipes are very rare in length because they have to be priced much higher when shipped out of the factory;
(3) Manufacturers of such pipes are afraid of taking responsibility, so their quality certificates are all fluid pipes and they dare not say they are seamless steel pipes;
(4) Check whether the wall thickness is uniform. Since seamless steel pipes are made of round steel hot-rolled and perforated, the wall thickness of seamless steel pipes will generally have deviations (with the continuous improvement of technology, the wall thickness deviation of seamless steel pipes is getting smaller and smaller, but there are still some). Although welded pipes have undergone welding rib treatment or heat expansion, their raw materials are strip steel, so their wall thickness is very uniform.

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