The main processing methods of large-diameter steel pipes are:
①Forged steel: A pressure processing method that uses the reciprocating impact of a forging hammer or the pressure of a press to change the blank into the shape and size we require.
②Extrusion: It is a steel processing method in which metal is placed in a closed extrusion cylinder and pressure is applied on one end to extrude the metal from a specified die hole to obtain a finished product of the same shape and size. It is mostly used to produce non-ferrous metal materials. steel.
③Rolling: A pressure processing method in which the steel metal blank is passed through the gap between a pair of rotating rollers (in various shapes). Due to the compression of the rollers, the material section is reduced and the length is increased.
④ Drawing steel: It is a processing method that draws the rolled metal blank (shaped, tube, product, etc.) through the die hole into a reduced cross-section and increased length. Most of them are used for cold processing. Large-diameter steel pipes are mainly completed through tension reduction and continuous rolling of the hollow base material without a mandrel.

The documents for standard setting and production of large-diameter steel pipes show that deviations are allowed when manufacturing and producing large-diameter steel pipes:
① Allowable length deviation: The allowable length deviation of steel bars when delivered to fixed length shall not be greater than +50mm.
②Bending and ends: The bending strain of straight steel bars does not affect normal use, and the total curvature is not greater than 40% of the total length of the steel bars; the ends of the steel bars should be sheared straight, and local deformation should not affect use.
③Length: Steel bars are usually delivered in fixed lengths, and the specific delivery length should be specified in the contract; when steel bars are delivered in coils, each coil should be one steel bar, and 5% of the coils in each batch are allowed to be composed of two bars. Composed of steel bars. The disc weight and disc diameter are determined by negotiation between the supply and demand parties.

Length description of large diameter steel pipe:
1. Ordinary length (also called non-fixed length): Any length within the length range specified by the standard and without a fixed length requirement is called ordinary length. For example, structural pipe standards stipulate hot rolled (extruded, expanded) steel pipes 3000mm ~ 12000mm; cold drawn (rolled) steel pipes 2000mm ~ 10500mm.
2. Fixed length: The fixed length should be within the usual length range and is a fixed length required in the contract. However, it is impossible to cut out the fixed length in actual operation, so the standard stipulates the allowable positive deviation value for the fixed length.
3. Double ruler length: The double ruler length should be within the normal length range. The single ruler length and the multiples of the total length should be indicated in the contract (for example, 3000mm × 3, which is 3 multiples of 3000mm, and the total length is 9000mm). In actual operation, an allowable positive deviation of 20 mm should be added to the total length, and a notch allowance should be left for each single ruler length. If there are no provisions for length deviation and cutting allowance in the standard, it should be negotiated between the supplier and the buyer and stated in the contract. The double-length scale, like the fixed-length length, will significantly reduce the finished product rate of the manufacturer. Therefore, it is reasonable for the manufacturer to propose a price increase, and the price increase range is basically the same as the fixed-length length.
4. Range length: The range length is within the usual range. When the user requires a fixed range length, it must be specified in the contract.