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) is divided into hot dip galvanized and cold galvanized two, hot dip galvanized galvanized layer is thick, with uniform coating, strong adhesion, long service life and other advantages. Cold galvanized pipe has low cost, the surface is not very smooth, and its corrosion resistance is much different than that of hot galvanized pipe, and it has been gradually phased out.

Most of the old houses in our country are used in galvanized pipes, and the iron pipes commonly used in gas and heating are also galvanized pipes. Galvanized pipe as a water pipe, with the accumulation of service life, the pipe produces a large number of rust and scale, which not only contaminates sanitary ware, but also contains bacteria that are not smooth inside the wall, more serious is the corrosion caused by high heavy metal content in the water, seriously endangering human health. In the 1960s and 1970s, some developed countries began to develop new types of pipes and gradually banned galvanized pipes. China's Ministry of Construction and other four ministries and commissions have also explicitly stipulated that galvanized pipes have been banned since 2000, and the cold water pipes in new residential areas have rarely used galvanized pipes, and the hot water pipes in some residential areas use galvanized pipes.

Technical requirements and standards for galvanized pipes

1. grade and chemical composition galvanized pipe

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

2. galvanized pipe manufacturing method

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

3. galvanized pipe thread and pipe joint

(1) Galvanized steel pipe with thread delivery, the thread shall be made after galvanized, and the thread shall comply with the provisions of YB-822;

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

4. galvanized pipe specifications and dimensions

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 important indicators to ensure the final service performance of steel (mechanical properties), which depends on the chemical composition of steel and heat treatment system. In the steel pipe standard, according to different requirements, tensile properties (tensile strength, yield strength or yield point, elongation) and hardness, toughness indicators, as well as high and low temperature properties required by users.

6. the uniformity of the galvanized layer of galvanized pipe

Galvanized steel pipe should be tested for uniformity of galvanized layer. The galvanized steel pipe sample shall not turn red (copper plating color) after continuous immersion for 5 times in copper sulfate solution.

7. Cold bending test of galvanized pipe

The galvanized steel pipe with nominal diameter not more than 50mm should be cold-bending test. The bending Angle is 90° and the bending radius is 8 times the outside diameter. Test without filler, the specimen weld should be placed on the outside or above the bending direction. After the test, there should be no cracks and zinc layer spalling on the sample.

8. Hydraulic test of galvanized pipe

The hydraulic test of galvanized steel pipe should be carried out in the black tube, and eddy current testing can also be used to replace the hydraulic test. Test pressure or eddy current test specimen size should conform to the provisions of GB-3092.