Galvanized Pipe Classification And Production Process

First, galvanized pipe overview

In order to improve the corrosion resistance of the steel pipe, the general steel pipe is galvanized. Galvanized pipe (galvanized steel pipe) hot dip galvanized and cold galvanized two, hot galvanized galvanized layer thickness, with uniform coating, strong adhesion, long life and other advantages. Cold galvanized pipes have low cost and the surface is not very smooth. The corrosion resistance of the cold galvanized pipes is much worse than that of hot galvanized pipes and has been gradually eliminated.

Most of the old housing construction in China uses galvanized pipes, and now the common iron pipes for gas and heating are also galvanized pipes. Galvanized pipe as a water pipe, with the accumulation of the use of years, a large amount of rust in the pipe, which not only pollute the sanitary ware, but also mixed with bacteria that are not smooth inside the wall, more serious is the rust caused by high levels of heavy metals in the water, seriously harming the human body Health. In the 1960s and 1970s, some developed countries began to develop new types of pipes and banned galvanized pipes one after another. China's Ministry of Construction and other four ministries have also stipulated that galvanized pipes have been banned since 2000. At present, galvanized pipes have rarely been used for cold water pipes in newly built communities. Some hot water pipes use galvanized pipes.

Second, the classification and characteristics of galvanized pipe

Galvanized pipes are divided into hot dip galvanized steel pipes and cold galvanized steel pipes, among which cold galvanized steel pipes have been gradually phased out.

1, hot-dip galvanized pipe / hot dip galvanized steel pipe

Hot dip galvanizing reacts the molten metal with the iron matrix to produce an alloy layer, thereby combining the matrix and the plating layer. The manufacture of hot-dip galvanized pipe is to pickle the steel pipe first to remove the iron oxide on the surface of the steel pipe. After pickling, the steel pipe is cleaned by an aqueous solution of ammonium chloride or zinc chloride or an aqueous solution of ammonium chloride and zinc chloride. , and then into the hot dip coating tank.

Hot-dip galvanized steel pipe is a complex physical and chemical reaction between the steel pipe substrate and the molten bath to form a corrosion-resistant and compact zinc-iron alloy layer. The alloy layer is integrated with the pure zinc layer and the steel pipe substrate. Therefore, the hot-dip galvanized steel pipe has the advantages of uniform plating, strong adhesion, and long service life.

2, cold galvanized pipe / cold galvanized steel pipe

Cold galvanizing is electro-galvanizing, and the amount of galvanizing is very small, only 10-50g/m2, and its own corrosion resistance is much worse than hot galvanized pipe. Regular galvanized pipe manufacturers, in order to ensure quality, mostly do not use electro-galvanized (cold galvanized). Only those small businesses with small scale and outdated equipment adopt electro-galvanizing, and of course their prices are relatively cheap. The zinc layer of the cold galvanized steel pipe and the steel pipe substrate are layered independently. As the zinc layer is thin, the zinc layer is simply attached to the steel pipe base body and is easy to fall off, so the cold-galvanized steel pipe has poor corrosion resistance. Therefore, in newly built houses, the use of cold galvanized steel pipes as water supply and gas supply pipes has been banned.

Third, the production process of galvanized pipe

The production process of galvanized steel pipes belongs to the secrets of various manufacturers, so it can only provide the approximate process flow: a. Round steel preparation; b. Heating; c. Hot rolling piercing; d. Cut the head; e. Pickling; f. Grinding; g. Lubrication; h. Cold rolling processing; i. Degreasing; j. Solution heat treatment; k. Straightening; l. Cut tube; m. Pickling; n. Product testing.

Fourth, galvanized pipe technical requirements and standards

1. Grade and Chemical Composition Galvanized Pipe

The grade and chemical composition of the galvanized steel pipe steel should meet the grade and chemical composition of the black pipe steel specified in GB-3092.

2. Manufacturing method of galvanized pipe

The manufacturing method of the galvanized pipe (furnace welding or welding) is selected by the manufacturer. Galvanizing often uses hot-dip galvanizing.

3, galvanized pipe thread and pipe joints

(1) Galvanized steel pipes with threaded delivery, the threads shall be made after galvanizing, and the threads shall comply with the provisions of YB-822;

(2) Steel pipe fittings shall comply with YB-238, and malleable cast iron pipe fittings shall comply with YB-230.

4, the size of galvanized pipe

Nominal wall thickness (mm): 2.02.52.83.23.53.84.04.5 Weight coefficient c: 1.0641.0511.0451.0401.0361.0341.0321.028

5, the mechanical properties of galvanized steel pipe

The mechanical properties of the steel pipe before galvanizing shall comply with the provisions of GB-3092. The mechanical properties of steel are an important indicator to ensure the end-use performance (mechanical properties) of the steel. It depends on the chemical composition of the steel and the heat treatment system. In the steel pipe standard, tensile properties (tensile strength, yield strength or yield point, elongation), and hardness and toughness indexes, as well as high and low temperature performance required by users, are stipulated in accordance with different application requirements.

6. Uniformity of galvanized pipe galvanized layer

Galvanized steel pipes shall be tested for the uniformity of the galvanized layer. Samples of galvanized steel tubes shall not be reddish (copper plating) by dipping in a copper sulfate solution for five consecutive times.

7. Cold bending test of galvanized pipe

Galvanized steel pipe with a nominal diameter of not more than 50mm shall be subjected to a cold bending test. The bending angle is 90° and the bending radius is 8 times the outside diameter. The test shall be carried out without filler. The weld of the test specimen shall be placed on the outside or upper part of the bending direction. After the test, there shall be no cracks and zinc flaking on the specimen.

8, hydrostatic test of galvanized pipe

The hydrostatic test of the galvanized steel pipe should be conducted in the black pipe, and eddy current testing can also be used instead of the hydrostatic test. The test pressure or eddy current test specimen size shall comply with the provisions of GB-3092.