What Is Galvanized Tube Steel?

Galvanized steel refers to the galvanizing process of ordinary carbon construction steel to effectively prevent corrosion and rust of the steel to prolong the service life of the steel. Among them, galvanization is divided into electrogalvanizing and hot-dip galvanizing. Generally used in building exterior walls, such as glass curtain wall, marble curtain wall, aluminum plate curtain wall as pillars and stress materials, or used in outdoor telecommunication towers, highways and other open-air construction steel is called galvanized steel. Dip galvanized.

Galvanized steel

Galvanized steel in Chinese

Nominal wall thickness mm 2.0 2.5 2.8 3.2 3.5 3.8 4.0 4.5 Coefficient parameter: c 1.064 1.051 1.045 1.040 1.036 1.034 1.032 1.028

Note: The mechanical properties of steel are important indicators to ensure the end-use performance (mechanical properties) of the steel, and it depends on the chemical composition and heat treatment system of the steel. in

Galvanized pipe, galvanized pipe is often said that the iron pipe used for gas and heating is also galvanized pipe. Galvanized pipe is used as water pipe. After several years of use, a large amount of rust is generated in the pipe, and the yellow water flowing out not only pollutes Sanitary ware, and mixed with bacteria that grow on the non-smooth inner wall, rust causes excessive heavy metal content in water, which seriously endangers human health.

The production process of galvanized pipe has the following production steps

a. Round steel preparation; b. Heating; c. Hot-rolled perforation; d. Cut head; e. Pickling; f. Dressing; g. Lubrication; h. Cold rolling; i. Skim; j. Solution heat treatment; k. Straightening; l. Pipe cutting; m. Pickling; n. Product testing.

Technical requirements of galvanized pipe

1. Grade and chemical composition

The grade and chemical composition of the steel for galvanized steel pipes shall comply with the grade and chemical composition of steel for black pipes as specified in GB 3092.

2. Manufacturing method

The manufacturing method of the black tube (furnace welding or electric welding) is selected by the manufacturer. Galvanizing uses hot-dip galvanizing.

3.Threads and pipe joints

a: For galvanized steel pipes delivered with threads, the threads should be turned after galvanizing. The threads shall comply with the provisions of YB 822.

b: Steel pipe joints shall comply with YB 238; malleable cast iron pipe joints shall comply with YB 230.

4. Mechanical properties The mechanical properties of steel pipes before galvanizing shall meet the requirements of GB 3092.

5. Uniformity of galvanized layer Galvanized steel pipe shall be used for the test of uniformity of galvanized layer. The steel pipe sample must not be reddened (copper-plated) for 5 consecutive immersions in the copper sulfate solution.

6. Cold bending test Galvanized steel pipes with a nominal diameter of not more than 50mm should be subjected to cold bending test. The bending angle is 90 °, and the bending radius is 8 times the outer diameter. The test shall be carried without filler, and the weld of the test specimen shall be placed outside or above the bending direction. After the test, there should be no cracks or zinc peeling on the sample.

7. Hydraulic pressure test The hydraulic pressure test should be carried out in a black tube. Eddy current flaw detection can also be used instead of the hydraulic pressure test. The test pressure or eddy current inspection comparison specimen size shall meet the requirements of GB 3092. The mechanical properties of steel are important indicators to ensure the end-use performance (mechanical properties) of the steel, and it depends on the chemical composition and heat treatment system of the steel. In the steel pipe standard, according to different usage requirements, tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indicators, as well as high and low temperature properties required by users are specified.

Tensile strength (b): The maximum force (Fb) that the sample is subjected to during breaking, the stress () obtained from the original cross-sectional area (So) of the sample is called the resistance Tensile strength (b), the unit is N / mm2 (MPa). It indicates the maximum ability of a metal material to resist damage under tensile forces. In the formula: Fb--the maximum force that the specimen can withstand, N (Newton); So--the original cross-sectional area of the specimen, mm2.

Yield point (s): Metal material with a yield phenomenon. The stress at which the specimen can continue to stretch without increasing the force during the tensile process (keep constant), which is called the yield point. If the force decreases, the upper and lower yield points should be distinguished. The unit of the yield point is N / mm2 (MPa). Upper yield point (su): The maximum stress before the first drop in the specimen yield force; Lower yield point (sl): The minimum stress in the yield phase when the initial transient effect is not taken into account. In the formula: Fs--yield force (constant) in the tensile process of the sample, N (Newton) So--the original cross-sectional area of the sample, mm2.

Elongation after breaking: () In the tensile test, the percentage of the length increased by the gauge length of the specimen after the sample is broken, is called the elongation. Expressed as , the unit is%. In the formula: L1-gauge length after the sample is broken, mm; L0-original gauge length of the sample, mm.

Section shrinkage: () In a tensile test, the percentage of the maximum reduction of the cross-sectional area at the shrinkage diameter of the sample after the sample is broken off is the percentage of the original cross-sectional area. Expressed in , the unit is%. In the formula: S0--the original cross-sectional area of the sample, mm2; S1--the minimum cross-sectional area at the reduced diameter of the sample after breaking, mm2.

Hardness index: The ability of a metal material to resist the depression of a surface by a hard object is called hardness. According to different test methods and applicable scopes, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro hardness and high temperature hardness. Brinell, Rockwell and Vickers hardness are commonly used for pipes.

A. Brinell hardness (HB): a steel ball or cemented carbide ball with a certain diameter is pressed into the surface of the sample with a specified test force (F), and the test force is removed after a specified retention time to measure the pressure on the surface of the sample Trace diameter (L). The Brinell hardness value is a quotient obtained by dividing the test force by the spherical surface area of the indentation. Expressed in HBS (steel ball), the unit is N / mm2 (MPa).

Elements that influence the properties of galvanized steel pipes

(1) Carbon; the higher the carbon content, the higher the hardness of the steel, but the worse its plasticity and toughness.

(2) Sulfur: It is a harmful impurity in steel. When steel with high sulfur content is subjected to pressure processing at high temperature, it is easily brittle, which is usually called hot brittleness.

(3) Phosphorus; can significantly reduce the plasticity and toughness of steel, especially at low temperatures, this phenomenon is called cold brittleness. In high-quality steel, sulfur and phosphorus must be strictly controlled. However, from another aspect, the low carbon steel contains higher sulfur and phosphorus, which can make its cutting easier, which is beneficial to improving the machinability of steel.

(4) Manganese; can improve the strength of steel, weaken and eliminate the adverse effects of sulfur, and improve the hardenability of steel. High alloy steel (high manganese steel) with high manganese content has good wear resistance And other physical properties.

(5) Silicon; it can increase the hardness of the steel, but the plasticity and toughness are reduced. The electrical steel contains a certain amount of silicon, which can improve the soft magnetic properties.

(6) Tungsten; can improve the red hardness and heat strength of steel, and can improve the wear resistance of steel.

(7) Chromium; can improve the hardenability and wear resistance of steel, and can improve the corrosion resistance and oxidation resistance of steel.

In order to improve the corrosion resistance of steel pipes, general steel pipes (black pipes) are galvanized. There are two types of galvanized steel pipes: hot-dip galvanized and electro-galvanized steel. The thickness of hot-dip galvanized layer is low and the cost of galvanizing is low.