What is a galvanized steel pipe?

Galvanized pipe, also known as galvanized steel pipe, is divided into hot-dip galvanizing and electro-galvanizing. The hot-dip galvanizing layer is thick, with uniform plating, strong adhesion and long service life. The cost of electroplating is low, the surface is not very smooth, and its corrosion resistance is much worse than that of hot-dip galvanized pipes.

1. Hot dip galvanized pipe

The molten metal is reacted 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. Most of the northern processes use galvanized strips to directly coil the zinc.

2. 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 pipes. 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. In newly built houses, the use of cold-galvanized steel pipes as water supply pipes is prohibited.

Difference hot-dip galvanizing and cold galvanizing

Hot dip galvanizing process:
Workpiece degreasing → washing → pickling → washing → drying solvent dip fluxing preheated hot dip galvanized → cooling → finishing → rinsing → drying → passivation test

Cold-galvanized process:
Chemical degreasing → washing → hot water electrolysis degreasing → washing → washing → strong corrosive galvanized iron alloy → washing  → light → washing → drying passivation

Appearance of Hot Dip Galvanizing And Cold Galvanizing

Cold galvanizing looks more smooth, bright, color passivation process plating layer is yellow-green in color, was colorful. Plating layer was bluish-white or white with white passivation process was green, white coating passivation process and the sun was significant Colorful angle. The complex workpiece angular edges parts prone to “electrical burning” from gloomy, the parts of the zinc layer thick. Yin corner site is easy to form a current dead undercurrent gray area and the area zinc layer is thinner. The workpiece overall zinc tumor, caking phenomenon.

Hot dip galvanized look a little rough compared to the electro-galvanized, silvery white, look prone process waterlines and a few drops of tumor is more obvious, especially in the one end of the workpiece. Hot dip galvanized zinc layer than a few times of the electro-galvanized thick corrosion protection is several times that of the electro-galvanized.

Advantages of galvanized pipes

1. Galvanized pipe after being hot dip galvanized surface can be protected, and inside the cavity of the pipe or any other coating the corner is difficult to enter, deepen the zinc can easily cover to the top, make whole galvanized pipe can be protected.

2. After being galvanized pipe galvanized its impact resistance and anti-wear properties are very good, because the zinc coating hardness values larger than the hardness of steel, and therefore the impact resistance of hot-dip galvanized after and abrasion resistance is quite good. Furthermore galvanized biggest advantage is in the corner of the zinc layer will be relatively thick and good toughness and abrasion resistance, while other coatings are often in this corner of the thinnest most difficult construction, and therefore are vulnerable injury. 

3. There is a major feature of hot-dip galvanizing that is occasionally subject to considerable mechanical damage or other causes a small portion of the zinc layer off, the iron-based nudity, then it will play around the zinc layer and other coatings not the same spirit of sacrifice to protect the steel here, so from erosion. 

4. The hot-dip galvanizing and other aspects of life and aesthetics of art, life expectancy is in a particular environment, the main agency of the thickness of the coating, and the coating thickness of it but also by the thickness of the galvanized pipe and decisions, and therefore thicker galvanized pipe is more easily coating. Second, in terms of aesthetics and art, at the time it is certain severe corrosive environments, galvanized layer above Zaishi paint to deal with, as long as the selection of the correct paint system, easy construction of its anti-corrosion effect will be very good.

Standards of galvanized pipes