Hot galvanized pipe is molten metal and reacting the iron matrix alloy layer. So that the substrate and coating combination of both. Hot-dip galvanizing is the first steel pickling. In order to remove iron pipe surface. After pickled, ammonium chloride or zinc chloride aqueous solution of ammonium chloride and zinc chloride mixed aqueous solution tank or cleaning. And then into the hot dip tank. HDG has a uniform coating. Strong adhesion. Long life and other advantages.

1. Grades and chemical composition

Galvanized steel pipe steel grades and chemical composition should be consistent with GB 3092 stipulated clarinet steel grades and chemical composition.

2. Manufacturing method

Manufacturing method clarinet (furnace brazed or welded) selected by the manufacturer. Galvanized hot dip galvanizing.

3. And threaded fittings

Galvanized steel with threaded delivery. Thread should be galvanized after car system. Threads shall comply with the provisions of YB 822.

Steel pipe fittings shall comply with the provisions of YB 238. Malleable cast iron pipe fittings shall comply with the provisions of YB 230.

4. Mechanical properties of galvanized steel pipe before mechanical properties shall comply with the provisions of GB 3092.

5. Uniformity of galvanized steel zinc coating uniformity test should be galvanized layer. Steel sample was immersed in a copper sulfate solution, five times in a row can not be red (copper color).

6. Cold bending test is not greater than the nominal diameter of 50mm galvanized steel pipe should be cold bending test. Bending angle of 90 °. 8 times the bending radius of the outer diameter. Without filling the test sample weld should be placed on the outside or the upper bending direction. After the test, the sample should not have cracks and flaking same as the zinc layer.

7. Hydrostatic test pressure test should be carried out in clarinet. Eddy current testing can also be used instead of the hydrostatic test. Test pressure or eddy current testing comparative sample size shall comply GB 3092's.

Mechanical properties of steel is to ensure that the steel end-use properties (mechanical properties) is an important indicator. It depends on the chemical composition and heat treatment of steel system. In the steel standard, according to different requirements. Provisions of the tensile properties (tensile strength, yield strength or yield point elongation) and hardness, toughness index. As well as user requirements of high and low temperature properties.

Tensile strength (σb)

During the tensile specimen. Pull off when exposure to the most vigorous (Fb). The stress to a sample of the original cross-sectional area (So) obtained (σ). It called the tensile strength (σb). Units of N / mm2 (MPa). It represents a metal material to resist damage under tension maximum capacity. The formula is:

Where: When Fb-- specimen pull off the maximum force N (Newton); So-- original specimen cross-sectional area, mm2.

Yield point (σs)

Having a yield phenomenon of metal materials. Specimen during the tensile force does not increase (constant) could continue elongation stress, said yield point. If power down occurs, it should distinguish between the lower yield point. Yield point of the unit N / mm2 (MPa).

The yield point (σsu): sample yield and maximum stress occurs force before the first drop; lower yield point (σsl): When excluding the initial transient effects, the yield phases of minimum stress.

Yield point is calculated as follows:

Where: Fs-- process of tensile yield strength (constant), N (Newton) So-- original specimen cross-sectional area, mm2.

The Elongation (σ)

In the tensile test, the specimen fractured its gauge of the percentage increase in the length of the original gauge length, called elongation. In σ expressed in units of%. The formula is:

Where: L1-- specimen fractured gauge length, mm; L0-- original specimen gauge length, mm.

Section shrinkage (ψ)

In the tensile test, the specimen fractured its biggest percentage reduction in the amount of the original cross-sectional diameter of the cross-sectional area reduction, known as section shrinkage. In ψ expressed in%. Calculated as follows:

Where: S0-- original specimen cross-sectional area, mm2; S1-- specimen fractured necking at least cross-sectional area, mm2.

Hardness index

Metal material to resist indentation capacity hard surface objects, called hardness. According to the test method and scope differ. It can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro hardness and high temperature hardness. Commonly used for pipe Brinell, Rockwell, Vickers hardness of three.

Brinell hardness (HB)

With a certain diameter steel balls or carbide ball. In a predetermined test force (F) is pressed into the pattern surface. After a predetermined hold time removable test force. Indentation diameter measurement sample surface (L). Brinell hardness value is spherical indentation test force divided by the surface area of ​​the resulting quotient. In HBS (ball), in units of N / mm2 (MPa).