1. Brand and chemical composition
The grade and chemical composition of the steel used for galvanized steel pipes shall 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. Galvanization adopts the hot-dip galvanizing method.
3. Thread and pipe joint
(a) Galvanized steel pipes delivered with threads should have their threads 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 comply with the provisions 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 specimen shall not turn red (copper plated) after being continuously immersed in copper sulfate solution for 5 times.
6. Galvanized steel pipes with a nominal diameter not exceeding 50mm shall undergo a cold bending test. The bending angle is 90 °, and the bending radius is 8 times the outer diameter. During the experiment, there should be no filling material, and the weld seam of the specimen should be placed on the outer or upper side of the bending direction. After the experiment, there should be no cracks or zinc layer peeling on the sample.
7. The water pressure test should be conducted on a black pipe, or eddy current testing can be used instead of water pressure test. The test pressure or eddy current testing 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
