Instructions
The commonly mentioned galvanized steel pipe is also used for gas and heating. The iron pipe used for galvanized steel pipe is also galvanized steel pipe. As a water pipe, after several years of use, a large amount of rust is generated inside the pipe. The yellow water flowing out not only pollutes the sanitary ware, but also contains bacteria that grow on the unsmooth inner wall. Rust causes high heavy metal content in the water, seriously endangering human health.
Production steps
The process flow is as follows: black pipe – alkali washing – water washing – acid washing – water rinsing – soaking agent – drying – hot dip galvanizing – external blowing – internal blowing – air cooling – water cooling – passivation – water rinsing – inspection – weighing – storage.
technical requirement

1. Brand and chemical composition
   The grade and chemical composition of steel used for galvanized steel pipes should comply with the grade and chemical composition of black pipe steel specified in GB/T3091.
2. Manufacturing methods
   The manufacturing method of the black tube (furnace welding or electric welding) is chosen by the manufacturer. Galvanizing adopts the hot-dip galvanizing method.
3. Thread and pipe joint
   (a) For galvanized steel pipes delivered with threads, the threads should be turned after galvanizing. The thread should comply with the provisions of YB 822.
   (b) Steel pipe joints should comply with the provisions of YB 238; Malleable cast iron pipe joints shall meet the requirements of YB 230.
4. The mechanical properties of steel pipes before galvanizing should comply with the provisions of GB 3091.
5. The uniformity of the galvanized layer should be tested on galvanized steel pipes. The steel pipe sample shall not turn red (copper plated) after continuous immersion in copper sulfate solution for 5 times.
6. Galvanized steel pipes with a nominal diameter of no more than 50mm shall undergo a cold bending test. The bending angle is 90 °, and the bending radius is 8 times the outer diameter. During the test, there should be no filler, and the weld seam of the sample should be placed on the outer or upper side of the bending direction. After the test, there should be no cracks or zinc layer peeling on the sample.
7. The hydraulic test should be conducted on a black tube, or eddy current testing can be used instead of the hydraulic test. The test pressure or eddy current flaw detection comparison sample size should comply with the provisions of GB 3092. The mechanical properties of steel are important indicators to ensure the ultimate performance (mechanical properties) of steel,
   mechanical property
   ① Tensile strength（ σ b) The maximum force (Fb) that the specimen bears during the tensile process at break, divided by the stress obtained by dividing the original cross-sectional area (So) of the specimen（ σ）， Called tensile strength（ σ b) , in N/mm2 (MPa). It represents the maximum resistance of metal materials to failure under tensile force. In the formula: Fb – the maximum force borne by the specimen during fracture, N (Newton); So – Original cross-sectional area of the sample, mm2.
   ② Yield point（ σ s) The stress at which a metal material with yield phenomenon can continue to elongate without increasing (maintaining a constant) force during the tensile process is called the yield point. If the force decreases, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa). Upper yield point（ σ Su): The maximum stress of the sample before yielding and the first decrease in force; Lower yield point（ σ SL): The minimum stress in the yield stage when the initial instantaneous effect is not considered. In the formula: Fs – yield force during the tensile process of the specimen (constant), N (Newton) So – original cross-sectional area of the specimen, mm2.
   ③ Elongation after fracture:（ σ） In a tensile test, the percentage of the length increased by the gauge length of the specimen after breaking compared to the original gauge length is called elongation. with σ Represented in%. In the formula: L1- gauge length of the sample after fracture, mm; L0- Original gauge length of the sample, mm.
   ④ Reduction of area:（ ψ） In a tensile test, the maximum reduction in cross-sectional area at the reduced diameter of the specimen after fracture, as a percentage of the original cross-sectional area, is called the reduction in area. with ψ Represented in%. In the formula: S0- Original cross-sectional area of the sample, mm2; S1- The minimum cross-sectional area at the reduced diameter of the specimen after fracture, mm2.
   ⑤ Hardness index: The ability of a metal material to resist surface indentation by hard objects, known as hardness. According to different test methods and application scope, hardness can be divided into Brinell hardness hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high-temperature hardness. There are three commonly used types of hardness for pipes: Brinell, Rockwell, and Vickers.
   Brinell hardness (HB): Use a steel ball or carbide ball with a certain diameter to press into the sample surface with the specified test force (F), remove the test force after the specified holding time, and measure the indentation diameter (L) of the sample surface. The Brinell hardness hardness number is the quotient obtained by dividing the test force by the spherical surface area of the indentation. Expressed in HBS (steel ball), in N/mm2 (MPa).