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1 Scope This standard specifies the dimensions, shape, weight, and allowable tolerances of seamless steel pipes. This standard is applicable when formulating standards for flat seamless steel tubes for various uses, to determine the dimensions, surface condition, weight, and allowable tolerances. 2 Outer Diameter and Wall Thickness 2.1 Size Categories Pipe sizes are classified into the ordinary steel pipe size group (see Table 1), the precision steel pipe size group (see Table 2), and the stainless steel pipe size group (see Table 3). 2.2 Outer Diameter The outer diameter of steel pipes is divided into three series. First series: Standardized steel pipes ； Second series: Steel pipes primarily of non-standardized type ； Third series: Steel pipes for special purposes. The outer diameter of ordinary steel pipes is classified into series 1, 2, and 3; the outer diameter of precision steel pipes is classified into series 2 and 3, while the outer diameter of stainless steel pipes is classified into series 1, 2, and 3. 2.3 Permissible dimensional tolerances 2.3.1 Selection of permissible dimensional tolerances 2.3.1.1 The selection of permissible dimensional tolerances should take into account the purpose of the steel pipe and the manufacturing equipment used for producing it. 2.3.1.2 The allowable dimensional tolerances specified in the product standards should preferably be standardized relative tolerances; however, depending on the customer’s requirements and the specific characteristics of the product, non-standardized dimensional tolerances may also be used. 2.3.1.3 For the allowable dimensional tolerances, either unilateral or bilateral tolerances can be used; symmetric tolerances are generally preferred, and relative tolerances are advisable. 2.3.2 Allowable deviation of outer diameter 2.3.2.1 The allowable deviation of outer diameter is divided into standardized and non-standardized types; standardized allowable deviations should be preferred (see Table 4). 2.3.2.2 Recommended non-standard outer diameters with allowable tolerances (see Table 5). Table 4 Allowable deviations for standardized outer diameter. Deviation grade, Allowable deviation for standardized outer diameter: D1 ±1.5%, minimum ±0.75 mm; D2 ±1.0%, minimum ±0.50 mm; D3 ±0.75%, minimum ±0.30 mm; D4 ±0.50%, minimum ±0.10 mm. Table 5 Allowable deviations for non-standardized outer diameter. Deviation grade, Allowable deviation for non-standardized outer diameter, %: ND1 +1.25 to –1.50; ND2 ±1.25; ND3 +1.25 to –1.0; ND4 ±0.8. 2.3.2.3 For steel pipes intended for special purposes and cold-rolled (drawn) steel pipes, absolute deviations may be used as the allowable deviations for the outer diameter. 2.3.3 Allowable deviation of wall thickness 2.3.3.1 The allowable deviations of wall thickness are divided into standardized and non-standardized types; standardized allowable deviations should be preferred (see Table 6 for details). 2.3.3.2 Recommended allowable deviations for non-standard wall thicknesses (see Table 7). Table 7: Allowable deviations for non-standard wall thicknesses. Deviation grade; Allowable deviation for non-standard outer diameter, %: ND1: +15, –12.50; ND2: +15, –10; ND3: +12.5, –10; ND4: +12.5, –7.5. 2.3.3.3 For special applications, absolute deviations can be used as the allowable deviations for the wall thickness of steel pipes and cold-rolled (drawn) steel pipes. 3 Length 3.1 Normal length: Steel pipes are generally delivered in their normal length. The usual length should comply with the following specifications: Hot-rolled (expanded) tubes: 3000–12000 mm Cold-rolled (drawn) tubes: 2000–10500 mm. The length of hot-rolled (expanded) short tubes must be at least 2 m, while the length of cold-rolled (drawn) short tubes and pipes must be at least 1 m. 3.2 Fixed length and multiple-length: The fixed length and multiple lengths should fall within the normal range of lengths; the allowable deviation for the total length is divided into three grades (see Table 8). A cutting allowance is to be provided for each scale length as follows: Outer diameter ≤ 159 mm: 5–10 mm ； Outer diameter > 159mm: 10–15mm. Table 8 Allowable Deviations for Total Length. Grades of allowable deviations for total length, in meters: L10–20, L20–10, L30–5, 3.3. For steel pipes used for special purposes, such as ultra-thin-walled stainless acid-resistant steel pipes and small-diameter steel pipes, the length requirements can be specified separately. 4 Appearance 4.1 Bendability The bendability of steel pipes is divided into total length bendability and bendability per meter. 4.1.1 Total length curvature The curvature measured along the entire length of the steel pipe is referred to as total length curvature, which is classified into five grades (see Table 9). Table 9: Overall bending degree grades – Overall bending percentage, %: not more than E10.20, E20.15, E30.10, E40.08, E50.06. 4.1.2 Bending per meter: The bending measured per meter of length of the steel pipe is referred to as bending per meter, and this value is classified into five grades (see Table 10). Table 10: Bend per meter – Bend grade, bend per meter, in mm/m; minimum values: F13.0, F22.0, F31.5, F41.0, F50.5, 4.2. Ellipticity: The ellipticity of steel pipes is classified into four grades (see Table 11). Table 11: Ellipticity of steel pipes – Ellipticity grades. The ellipticity shall not exceed the allowable deviation of the outer diameter, in %. NR180, NR270, NR360, NR450: 5. Weight: Steel pipes can be delivered based on their actual weight, or based on their theoretical weight. Actual mass delivery can be divided into single-piece weight or batch weight. The theoretical weight per meter of steel pipe is calculated using equation (1):……………………(1) Where: W —— theoretical weight per meter of steel pipe, kg/m ； π——3.1416 ； ρ —— density of steel, kg/dm3; the density of steel is given in Table 5 ； D — the nominal outer diameter of the steel pipe, in mm. S — nominal wall thickness of the steel pipe, mm ； 5.1 For steel pipes delivered based on theoretical weight, the allowable deviation between the theoretical weight and the actual weight of each individual steel pipe is divided into five grades (see Table 12). Table 12 Permissible weight deviations. Grades of permissible weight deviations: Permissible deviation for the weight of a single steel pipe, %: W1±10, W2±7.5, W3+10, -5, W4+10, -3.5, W5+6.5, -3.5; 5.2 For steel pipes delivered based on their theoretical weight, each batch must contain at least 10 tons, and the permissible deviation between the theoretical weight and the actual weight is ±7.5% or ±5%. **Approved by the Quality and Technical Supervision Bureau on 1998-05-28, effective as of 1998-12-01