1. Brand and chemical composition
The grade and chemical composition of HDG pipe steel shall conform to the grade and chemical composition of black pipe steel specified in GB 3092.
The manufacturing method of black tube (furnace welding or electric welding) shall be selected by the manufacturer. HDG pipes are hot-dip galvanized.
3. Thread and pipe joint
(1) For galvanized steel pipes delivered with thread, the thread shall be machined after galvanizing. Threads shall be in accordance with Yb 822.
(2) steel pipe joint shall conform to Yb 238; malleable cast iron pipe joint shall conform to Yb 230.
4. Mechanical properties
The mechanical properties of steel pipe before galvanizing shall comply with the provisions of GB 3092.
5. Uniformity of zinc coating the uniformity of zinc coating shall be tested for galvanized steel pipes. The steel pipe sample shall not turn red (copper plating) after being immersed in copper sulfate solution for 5 times.
6. Cold bending test shall be carried out for galvanized steel pipe with nominal diameter no more than 50mm. The bending angle is 90° and the bending radius is 8 times of the outer diameter. During the test, without filler, the weld joint of the sample shall be placed on the outside or upper part of the bending direction. After the test, there should be no crack and zinc layer peeling on the sample.
7. Hydrostatic test shall be carried out in black pipe or eddy current inspection, and also can be used instead of hydrostatic test. The size of test pressure or eddy current flaw detection contrast sample shall conform to the provisions of GB 3092.
The mechanical property of steel is an important index to ensure the final use performance (mechanical property), which depends on the chemical composition and heat treatment system of steel. In the steel pipe standard, according to different requirements, the tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indexes, as well as the high and low temperature properties required by users are specified.