The main processing methods of large-diameter steel pipes are:
Forging steel: a pressure processing method that uses the reciprocating impact force of a forging hammer or the pressure of a press to change the blank into the shape and size we need.
Extrusion: It is a processing method for steel to place metal in a closed extrusion box and apply pressure at one end to make the metal extrude from the specified die hole to obtain a finished product with the same shape and size. It is mostly used for the production of non-ferrous metal steel.
Rolling: A pressure processing method in which the steel metal billet passes through the gap between a pair of rotating rolls (various shapes), and the cross-section of the material is reduced and the length is increased due to the compression of the rolls.
Pulling steel: It is a processing method in which the rolled metal blank (type, pipe, product, etc.) is pulled through the die hole to reduce the cross-section and increase the length. Most of them are used for cold working. Large-diameter steel pipes are mainly completed by tension reduction and continuous rolling of hollow base metal without mandrel. The standard formulation and production of large-diameter steel pipe documents show that deviations are allowed in the manufacture and production of large-diameter steel pipes.
Allowable deviation of length: The allowable deviation of the length of the steel bar when it is delivered according to the fixed length shall not be greater than +50mm.
Bending degree and end: The bending strain of the straight steel bar should not affect normal use, and the total bending degree should not exceed 40% of the total length of the steel bar.
The end of the steel bar should be cut straight, and the local deformation should not affect the use. Length: steel bars are usually delivered according to the fixed length, and the specific delivery length should be specified in the contract; when the steel bars are delivered in coils, each coil should be one steel bar, and 5% of the coils in each batch are allowed to consist of two steel bars composition. The weight and diameter of the disc are negotiated and stipulated by the supply and demand sides.
Description of the length of large-diameter steel pipes:
1. Normal length (also known as non-fixed length): Any length within the length range specified by the standard and without fixed length requirements is called normal length.
2. Length to length: The length to length should be within the normal length range, which is a certain fixed length dimension required in the contract. However, it is impossible to cut out the cut-to-length length in actual operation, so the standard stipulates the allowable positive deviation value for the cut-to-length length.
3. Double-foot length: The double-foot length should be within the normal length range, and the single-foot length and the multiple of the total length should be specified in the contract. In actual operation, an allowable positive deviation of 20mm should be added to the total length, plus a cutout allowance should be left for each single ruler length. If there is no specification for the length deviation and cutting allowance in the standard, it should be negotiated by both the supplier and the buyer and indicated in the contract. The double-length scale is the same as the fixed-length length, which will greatly reduce the yield of the production enterprise. Therefore, it is reasonable for the production enterprise to raise the price, and the price increase range is the same as the fixed-length length increase.
4. Range length: The range length is within the usual length range. When the user requires a fixed range length, it must be specified in the contract.
Mechanical properties of large-diameter steel pipes:
1. Tensile strength: the stress (σ) obtained from the original cross-sectional area (So) of the sample from the force (Fb) that the sample bears when it is broken during the stretching process is called the tensile strength ( σb), the unit is N/mm2 (MPa). It represents the maximum ability of metal materials to resist damage under tension.
2. Yield point: For metal materials with yield phenomenon, the stress at which the sample can continue to elongate without increasing the force (keep constant) during the stretching process is called the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).
3. Elongation after the break: In the tensile test, the percentage of the increased length of the gauge length after the sample is broken and the original gauge length is called elongation. Expressed in σ, the unit is %.
Post time: Aug-22-2023