The grade and chemical composition of the steel for galvanized pipe shall comply with the grade and chemical composition of the steel for black pipe specified in GB 3092. The uniformity of the galvanized layer The galvanized steel pipe shall be tested for the uniformity of the galvanized layer. The steel pipe sample shall not be reddened (copper plating) by continuously immersing it in the copper sulfate solution for 5 times.
First, the standard classification of galvanized pipe
In order to improve the corrosion resistance of the steel pipe, the general steel pipe (black pipe) is galvanized.
Galvanized steel pipes are divided into hot-dip galvanizing and electric steel zinc. The hot-dip galvanizing galvanized layer is thick and the cost of electro-galvanizing is low.
The galvanized pipe is divided into two types: hot-dip galvanizing and electro-galvanizing. The hot-dip galvanizing galvanized layer has the advantages of 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.
Galvanized steel pipes are divided into cold-plated pipes and hot-plated pipes. The former has been banned, and the latter has been promoted temporarily by the state.
1, hot-dip 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.
Hot-dip galvanized steel pipe: The steel pipe matrix and the molten plating solution undergo complex physical and chemical reactions to form a corrosion-resistant structure of a zinc-iron alloy layer. The alloy layer is integrated with the pure zinc layer and the steel pipe base. Therefore, its corrosion resistance is strong.
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. 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.
Cold-galvanized steel pipe: The zinc layer is an electroplated layer, and the zinc layer and the steel pipe substrate are layered independently. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe base and is easy to fall off. Therefore, its corrosion resistance is poor. In newly built houses, the use of cold-galvanized steel pipes as water supply pipes is prohibited.
Second, the application of galvanized pipe:
The galvanized pipe has the advantages of uniform plating, strong adhesion and long service life.
The surface of the galvanized pipe is welded with hot dip or galvanized steel. Zinc plating can increase the corrosion resistance of steel pipes and prolong their service life. Galvanized pipes are widely used, in addition to pipelines for general low-pressure fluids such as water, gas, oil, etc., and also used as oil well pipes and oil pipes in the petroleum industry, especially in offshore oil fields, and oil heaters and condensation of chemical coking equipment. The cooler, the tube for the coal-distilled oil-washing exchanger, the bridge tube pile, the support tube for the mine tunnel, and the like.
Third, the unique cleaning process of galvanized pipe
The galvanized pipe adopts the sulphate electroplating zinc-iron alloy process, in which the production line groove and the groove are pierced straight through without any carry-over or overflow of the solution. Each process in the production process consists of a circulation system. Each tank solution is an acid-base solution, a plating solution, a light-emitting and a passivation solution, etc., and only recycles and leaks to the outside of the system, and only 5 cleaning tanks are used in the production line. Reuse of regular discharge, especially the production process without waste water after passivation.
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