Grade and chemical composition. The grades and chemical compositions of steel used for galvanised steel pipes shall be in accordance with GB 3092 or GB/T 3091, which are applicable to steel used for black pipes.
Manufacturing method. The manufacturing method of black pipe (e.g. furnace welding or electric welding) is selected by the manufacturer, while galvanising is usually done by hot dip galvanising.
Threads and Fittings. For galvanised steel pipes delivered with threads, the threads shall be turned after galvanising and shall conform to YB 822. For steel pipe joints, they shall conform to YB 238; for malleable iron pipe joints, they shall conform to YB 230.
Mechanical properties. The mechanical properties of the steel pipe before galvanisation shall comply with the provisions of GB 3092 or GB 3091.
Uniformity of galvanised layer. Galvanized steel pipe shall be tested for uniformity of galvanized layer, e.g., the steel pipe specimen shall be dipped in copper sulphate solution for 5 consecutive times, and shall not turn red (i.e., shall not appear to be copper-plated).
Cold bending test. For galvanised steel pipes with a nominal calibre of not more than 50 mm, a cold bending test shall be carried out with a bending angle of 90° and a bending radius of 8 times the outside diameter. The test should not be carried out with filler, and the specimen weld should be placed on the outside or upper part of the bending direction. After the test, there should be no cracks and zinc layer flaking on the specimen.
Hydraulic test. The hydraulic pressure test shall be carried out in the black pipe or replaced by eddy current flaw detection. The test pressure or eddy current flaw comparison specimen size shall comply with the provisions of GB 3092 or GB 3091.
