First, the main processing methods for large-diameter steel pipes include.
- Forging: A pressure processing method that uses the reciprocating impact force of a forging hammer or the pressure of a press to change the billet into the desired shape and size.
- Extrusion: A processing method in which steel is placed in a closed extrusion chamber, pressure is applied to one end, and the metal is extruded from a specified die to obtain a finished product with the same shape and size. It is mostly used in the production of non-ferrous metals and steel.
- Rolling: A pressure processing method in which steel billets (of various shapes) are passed through the gap between a pair of rotating rollers, and the material’s cross-section decreases while its length increases due to the compression of the rollers.
- Drawing: A processing method in which rolled metal billets (profiles, tubes, products, etc.) are drawn through a die to reduce their cross-section and increase their length. It is mostly used for cold working. Large-diameter steel pipes are mainly produced by tension reduction, continuous rolling of hollow base material without a mandrel. The standard for manufacturing large-diameter steel pipes specifies the following permissible deviations:
- Length tolerance: The permissible length deviation for steel bars delivered in fixed lengths shall not exceed +50mm.
- Bending and ends: The bending deformation of straight steel bars shall not affect normal use, and the total bending shall not exceed 40% of the total length of the steel bar; the ends of the steel bars shall be cut straight, and local deformation shall not affect use.
- Length: Steel bars are usually delivered in fixed lengths, and the specific delivery length shall be specified in the contract; when steel bars are delivered in coils, each coil shall contain one steel bar, and 5% of the coils in each batch are allowed to consist of two steel bars. The coil weight and diameter shall be agreed upon by the supplier and the buyer.
Second, an Explanation of the length of large-diameter steel pipes.
1. Normal length (also known as non-fixed length): Any length within the range specified in the standard and without a fixed length requirement is called normal length. For example, structural pipe standards specify: hot-rolled (extruded, expanded) steel pipes 3000mm～12000mm; cold-drawn (rolled) steel pipes 2000mm～10500mm.
2. Fixed Length: Fixed length should be within the usual length range and is a specific length dimension required in the contract. However, in practice, it is unlikely to cut to the fixed length every time. Therefore, the standard specifies an allowable positive deviation for fixed length.
3. Multiple Length: Multiple lengths should be within the usual length range. The contract should specify the single multiple length and the multiples constituting the total length (e.g., 3000mm × 3, i.e., 3 times 3000mm, total length 9000mm). In practice, an allowable positive deviation of 20mm should be added to the total length, plus a cutting allowance for every multiple length. If the standard does not specify multiple length deviations and cutting allowances, they should be negotiated by both the supplier and the buyer and specified in the contract. Similar to fixed-length, double-length specifications significantly reduce the yield rate for manufacturers. Therefore, it is reasonable for manufacturers to request a price increase, and the increase is basically the same as that for fixed lengths.
4. Range Length: The range length is within the usual length range. When the user requires a specific range length, it must be specified in the contract.
Third, Mechanical Properties of Large-Diameter Steel Pipes.
1. Tensile Strength: The stress (σ) obtained by dividing the maximum force (Fb) a specimen withstands during tensile testing by the original cross-sectional area (So) is called tensile strength (σb), with units of N/mm² (MPa). It represents the maximum ability of a metallic material to resist fracture under tensile force.
2. Yield Point: For metallic materials exhibiting yielding, the stress at which a specimen continues to elongate without an increase in force (remaining constant) during tensile testing is called the yield point. If the force decreases, the upper and lower yield points should be distinguished. The unit of yield point is N/mm² (MPa).
3. Elongation after fracture: In a tensile test, the percentage increase in gauge length after the specimen breaks relative to the original gauge length is called elongation. It is denoted by σ, and the unit is %.
Post time: Dec-03-2025