Galvanized pipe standard

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

standard:
1. Brand and chemical composition
The grade and chemical composition of the steel for galvanized steel pipes should comply with the grade and chemical composition of the steel for black pipes as specified in GB 3091.

2. Manufacturing method
The manufacturing method of the black pipe (furnace welding or electric welding) is selected by the manufacturer. Hot-dip galvanizing is used for galvanizing.

3. Thread and pipe joint
3.1 For galvanized steel pipes delivered with threads, the threads should be machined after galvanizing. The thread should comply with YB 822 regulations.
3.2 Steel pipe joints should comply with YB 238; malleable cast iron pipe joints should comply with YB 230.

4. Mechanical properties The mechanical properties of steel pipes before galvanizing should meet the requirements of GB 3091.

5. Uniformity of galvanized layer Galvanized steel pipe should be tested for uniformity of the galvanized layer. The steel pipe sample shall not become red (copper-plated) after being immersed in a copper sulfate solution for 5 consecutive times.

6. Cold bending test The galvanized steel pipe with a nominal diameter of not more than 50mm should be subjected to a cold bending test. The bending angle is 90°, and the bending radius is 8 times the outer diameter. There is no filler during the test, and the weld of the sample should be placed on the outside or upper part of the bending direction. After the test, there should be no cracks or peeling of the zinc layer on the sample.

7. Water pressure test The water pressure test should be carried out in the clarinet. Eddy current flaw detection can also be used instead of the water pressure test. The test pressure or the size of the comparison sample for eddy current testing shall meet the requirements of GB 3092.
The mechanical properties of steel is an important index to ensure the final use of performance (mechanical properties) of the steel, which depends on the chemical composition of the steel and the heat treatment system. In the steel pipe standard, according to different application requirements, the tensile properties (tensile strength, yield strength or yield point, elongation), hardness, toughness indexes, and high and low-temperature properties required by users are specified.

①Tensile strength (σb)
In the tensile process, the force (Fb) that the sample bears when it breaks, and the stress (σ) obtained by the original cross-sectional area (So) of the sample is called the tensile strength (σb), and the unit is N /mm2 (MPa). It represents the ability of metal materials to resist damage under tensile force.

②Yield point (σs)
For a metal material with a yield phenomenon, the stress at which the sample can continue to elong without increasing the force during the stretching process (remaining constant) is called the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).
Upper yield point (σsu): the stress before the sample yields and the force drops for the first time; Lower yield point (σsl): the minimum stress in the yield stage when the initial transient effect is not taken into account.

③Elongation after breaking (σ)
In the tensile test, the percentage of the length of the gauge length increased after the sample is broken to the original gauge length is called the elongation. Expressed in σ, the unit is %.

④Reduction of area (ψ)
In the tensile test, the reduction of the cross-sectional area at the reduced diameter of the sample after the sample is broken and the percentage of the original cross-sectional area is called the reduction of area. Expressed in ψ, the unit is %.

⑤ Hardness index
The ability of metal materials to resist the indentation of hard objects on the surface is called hardness. According to different test methods and scope of application, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness, and high-temperature hardness. There are three commonly used pipes: Brinell, Rockwell, and Vickers hardness.

Galvanized welded steel pipe for low-pressure fluid transportation (hot-dip galvanized part)
1. Uniformity of the galvanized layer: the steel pipe sample shall not turn red (copper-plated) after being immersed in the copper sulfate solution 5 consecutive times
2. Surface quality: the surface of the galvanized steel pipe should have a complete galvanized layer, and there must be no unplated black spots and bubbles, and small rough surfaces and local zinc tumors are allowed.
3. Galvanized layer weight: According to the requirements of the buyer, the galvanized steel pipe can be used to determine the weight of the zinc layer. The average value should not be less than 500g/square meter, and any sample must not be less than 480g/square meter.