The galvanized pipe and the galvanized pipe are often used. The iron pipe used for gas and heating is also a galvanized pipe. The galvanized seamless steel pipe is used as a water pipe. After a few years of use, a large amount of rust is generated in the pipe, and the yellow water flows out. It not only pollutes sanitary ware, but also is mixed with bacteria that grow on the inner wall of the slick. The rust causes the heavy metal content in the water to be too high, which seriously endangers the health of the human body.
Production steps
a. Round steel preparation; b. Heating; c. Hot rolled perforation; d. Cut the head; e. Pickling; f. Grinding; g. Lubrication; h. Cold rolling processing; i. Degreasing; j. Solution heat treatment; k. Straightening; l. Cutting tube; m. Pickling; n. Product testing.
Skills requirement
1. Grade and chemical composition? The grade and chemical composition of steel for galvanized steel pipe should meet the grade and chemical composition of the steel for black pipe specified in GB/T3092.
2. Manufacturing method The manufacturing method of black tube (furnace welding or electric welding) is selected by the manufacturer. Galvanizing is performed by hot dip galvanizing.
3. Thread and pipe joints
a: Galvanized steel pipe with thread delivery, thread should be made after galvanizing. The thread shall comply with the provisions of YB?822.
b: Steel pipe joints shall comply with the provisions of YB?238; malleable cast iron pipe joints shall comply with the provisions of YB?230.
4. Mechanical properties? The mechanical properties of steel pipes before galvanizing should meet the requirements of GB?3092.
5. Uniformity of 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.
6. Cold bending test The galvanized steel pipe with a nominal diameter of not more than 50 mm shall be tested for cold bending. The bending angle is 90° and the bending radius is 8 times the outer diameter. The test shall be carried out without filler and the weld of the specimen shall be placed on the outside or the upper part of the bending direction. After the test, there should be no cracks on the sample and the same phenomenon as the zinc layer peeling off.
7. Hydraulic test The hydraulic test shall be carried out in a black tube, or an eddy current test may be used instead of a hydrostatic test. The test pressure or eddy current test comparison sample size should meet the requirements of GB?3092. The mechanical properties of steel are important indicators to ensure the ultimate performance (mechanical properties) of steel.
Mechanical properties
1. Tensile strength (σb): The maximum force (Fb) that the specimen is subjected to during the stretching process, divided by the original cross-sectional area (So) of the specimen (So), called the resistance Tensile strength (σb) in N/mm2 (MPa). It represents the maximum ability of a metal material to resist damage under tensile forces. Where: Fb–the maximum force to be taken when the sample is broken, N (Newton); So–the original cross-sectional area of the sample, mm2.
2. Yield point (σs): a metal material with a yielding phenomenon, the stress of the sample does not increase (maintains constant) during the stretching process, and the stress at the time of elongation can be continued, which 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 maximum stress before the specimen yields and the force first drops; the lower yield point (σsl): the minimum stress in the yielding phase when the initial transient effect is not counted. Where: Fs–the yield force (constant) during the tensile process of the specimen, N (Newton) So–the original cross-sectional area of the specimen, mm2.
3. Elongation after break: (σ) In the tensile test, the percentage of the length of the gauge length increased after the sample is broken and the length of the original gauge length is called the elongation. Expressed in σ, the unit is %. Where: L1–the length of the gauge length after the sample is broken, mm; ?L0–the original gauge length of the sample, mm.
4. Section shrinkage rate: (ψ) In the tensile test, the maximum reduction of the cross-sectional area of the reduced diameter after the sample is broken and the percentage of the original cross-sectional area, called the section shrinkage. Expressed in ψ, the unit is %. Where: S0–the original cross-sectional area of the sample, mm2; ?S1–the minimum cross-sectional area at the reduced diameter after the sample is broken, mm2.
5 Hardness Index?: The ability of a metal material to resist the indentation of a hard object is called hardness. According to the test method and the scope of application, the hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. Commonly used for pipes are Brinell, Rockwell and Vickers hardness.
A, Brinell hardness (HB): with a certain diameter of the steel ball or carbide ball, with the specified test force (F) into the surface of the sample, after the specified retention time, remove the test force, measure the surface of the sample Indentation diameter (L). The Brinell hardness value is the quotient obtained by dividing the test force by the spherical surface area of the indentation. It is expressed by HBS (steel ball) and the unit is N/mm2 (MPa).