Manufacturing Method Of Hot-dip Galvanized Steel Pipe
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The method of manufacture of the clarinet (furnace welding or electric welding) is at the manufacturer's option. Hot dip galvanizing, hot dip galvanizing, hot dip zinc.
3. Thread and pipe joint
3.1 Galvanized steel pipes delivered with thread shall be made after galvanizing. Threads shall conform to YB 822.
3.2 Steel pipe joints shall meet the requirements of YB 238; Malleable cast iron pipe joints shall comply with YB 230.
4. Mechanical properties The mechanical properties of steel pipes before galvanizing shall conform to the provisions of GB 3092.
5, galvanized layer uniformity galvanized steel pipe should be galvanized layer uniformity test. The steel tube sample shall not turn red (copper plating color) after dipping in copper sulfate solution for 5 consecutive times.
6, cold bending test galvanized steel pipe nominal diameter is not greater than 50mm should be cold bending test. The bending Angle is 90°, and the bending radius is 8 times of the outer diameter. The test without filler, the sample weld should be placed on the lateral or upper bending direction. After the test, there should be no cracks and spalling of zinc layer on the sample.
7, water pressure test water pressure test should be carried out in blackpipe, hot dip galvanizing, hot dip galvanizing, hot dip zinc can also be used instead of eddy current testing water pressure test. Test pressure or eddy current test sample size should be in accordance with GB 3092.
The mechanical property of steel is an important index to ensure the final serviceability of steel. It depends on the chemical composition of steel and the heat treatment system. In the steel pipe standard, according to different use requirements, stipulated the tensile properties (tensile strength, yield strength or yield point, elongation) and hardness, toughness indicators, as well as user requirements of high and low temperature performance.
Tensile strength (σ B)
In the tensile process, the maximum force (Fb) of the specimen at fracture is derived from the stress (σ) of the original cross-sectional area (So) of the specimen, which is called the tensile strength (σb), expressed in N/mm2 (MPa). It represents the maximum capacity of a metal material to resist damage under tension. The calculation formula is:
Where: Fb-- the maximum force borne by the specimen when it breaks, N (Newton); So-- Original cross-sectional area of the sample, mm2.
② Yield point (σ S)
Metal materials with yield phenomenon, the specimen in the process of tensile force does not increase (keep constant) can continue to extend the stress, called the yield point. In case of force decline, upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).
The upper yield point (σ SU) is the maximum stress before the specimen yields and the force drops for the first time. Lower yield point (σ SL) : the minimum stress in the yield stage when the initial transient effect is not considered.
The yield point can be calculated by:
Where Fs is the yield force (constant) of the specimen during tensile process, N (Newton) So is the original cross-sectional area of the specimen, mm2.
③ Elongation after fracture (σ)
In the tensile test, the percentage of the length increased by the standard distance after the specimen is pulled and the length of the original standard distance is called elongation. The unit is %. The calculation formula is:
Where: L1-- the distance of the specimen after breaking, mm; L0-- Original distance length of sample, mm.
Area reduction (ψ)
In tensile test, the percentage of the maximum reduction of the cross-sectional area at the reduced diameter of the specimen after being pulled and the original cross-sectional area is called the area reduction rate. ψ is expressed in %. The calculation formula is as follows:
Where, S0-- the original cross-sectional area of the sample, mm2; S1-- The minimum cross-sectional area at the reduced diameter of the specimen after breaking, mm2.
⑤ Hardness index
Hardness is the ability of a metal material to resist hard objects pressing into a surface. According to the test method and scope of application, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro hardness and high temperature hardness. Commonly used to pipe material have brinell, rockwell, Vickers hardness 3 kinds.
A, Brinell hardness (HB)
A steel ball or carbide ball of a certain diameter is pressed into the sample surface with a specified test force (F), and the test force is removed after a specified holding time to measure the indentation diameter (L) on the sample surface. The Brinell hardness number is the quotient of the test force divided by the surface area of the indentation sphere. Expressed in HBS, the unit is N/mm2(MPa).
