Technical requirements that galvanized pipes should meet.
2013-11-18
1. Grade and Chemical Composition Galvanized Pipe GalvanizationSteel PipeThe grade and chemical composition of the steel used should comply with the specifications for black pipe steel as stipulated in GB 3092. 2. Manufacturing Method The manufacturing method for black pipes (furnace welding or electric welding) is chosen by the manufacturer. Galvanization is done using the hot-dip galvanizing method. 3. Threads and Pipe Joints 3.1 Galvanized with ThreadsSteel Pipe, threads should be machined after galvanization. The threads should comply with the provisions of YB 822. 3.2 Steel pipe joints should comply with YB 238; ductile iron pipe joints should comply with YB 230. 4. Mechanical PropertiesSteel PipeThe mechanical properties before galvanization should comply with the provisions of GB 3092. 5. Uniformity of Galvanized LayerSteel PipeTests for uniformity of the galvanized layer should be conducted.Steel PipeSamples must not turn red (copper color) after being continuously immersed in copper sulfate solution for five times. 6. Cold Bending TestSteel PipeGalvanized pipes with a nominal diameter not greater than 50mm should undergo cold bending tests. The bending angle is set at 90°, and the bending radius is eight times the outer diameter. During testing, no filler material is used, and the weld seam of the sample should be placed on the outer side or upper part in the direction of bending. After testing, there should be no cracks or zinc layer peeling on the sample. 7. Hydrostatic Test (Hydrostatic tests should be conducted on black pipes; eddy current testing can also replace hydrostatic tests.) The test pressure or dimensions for eddy current comparison samples must comply with GB 3092 specifications.Steel Pipe(The mechanical properties of steel are important indicators that ensure its final usage performance (mechanical performance), which depends on its chemical composition and heat treatment process.) In standards, tensile properties (tensile strength, yield strength or yield point, elongation) as well as hardness, toughness indicators, and high/low temperature performance required by users are specified based on different usage requirements. (1) Tensile Strength (σb) (The maximum force (Fb) endured by a sample during stretching at fracture divided by its original cross-sectional area (So) gives rise to stress (σ), known as tensile strength (σb), measured in N/mm² (MPa). It indicates the maximum ability of metal materials to resist failure under tensile forces.) The calculation formula is: (Where: Fb -- Maximum force endured by sample at fracture, N (Newton); So -- Original cross-sectional area of sample, mm².) (2) Yield Point (σs) 具有屈服现象的金属材料，试样在拉伸过程中力不增加(保持恒定)仍能继续伸长时的应力，称屈服点。若力发生下降时，则应区分上、下屈服点。屈服点的单位为N/mm2(MPa)。 上屈服点(σsu)：试样发生屈服而力首次下降前的最大应力; 下屈服点(σsl)：当不计初始瞬时效应时，屈服阶段中的最小应力。
