LSAW steel pipe: introduction of steel pipe dimensions
Nominal size and actual size
1. Nominal size: It is the size specified in the standard, which is the ideal size that users and manufacturers hope to obtain, and is also the order size indicated in the contract between the two parties.
2. Actual size: is the size obtained during the production process, which is often larger or smaller than the nominal size. This phenomenon of being larger or smaller than the nominal size is called deviation.
Deviation and tolerance
1. Deviation: In the production process, since the actual size is difficult to achieve the nominal size requirement, that is, it is often larger or smaller than the nominal size, the standard specifies that a difference is allowed between the actual size and the nominal size. The difference is positive, called positive deviation, the difference is negative, called negative deviation
2. Tolerance: The sum of the absolute values of the positive and negative deviation values specified in the standard is called the tolerance, also called the “tolerance zone”.
Deviations are directional, expressed as “positive” or “negative”; tolerances are not directional, and therefore, the term “positive tolerance” or “negative tolerance” is incorrect.
The length of delivery is also known as the length of the user or the length of the contract. There are several provisions for the length of delivery in the standard:
1. Normal length (also known as non-fixed length): Where the length is within the length specified by the standard and there is no fixed length requirement, it is called the normal length. For example, the structural pipe standard stipulates: hot-rolled (extruded, expanded) steel pipe 3m ~ 12m; cold drawn (rolled) steel pipe 2m ~ 10.5m
2. Fixed length: The length of the fixed length should be within the normal length and is the fixed length size required in the contract. However, it is not possible to make an absolute length in actual operation, so the standard deviation length is specified for the length of the scale.
The production rate of steel pipe with fixed length is larger than that of normal length steel pipe. It is reasonable for manufacturers to raise the price. The rate of increase is not the same for all companies, generally about 10% based on the base price.
3. Double-length length: The length of the double-length should be within the normal length. The length of the single-length ruler and the multiple of the total length should be indicated in the contract (for example, 3m×3, that is, 3 times of 3m, the total length is 9m).
In practice, the allowable positive deviation of 20 mm should be added to the total length, plus the remaining allowance should be left for each single-length length. Taking the structural tube as an example, the remaining amount of the incision is specified: the outer diameter is less than or equal to 159 mm, which is 5 to 10 mm; and the outer diameter is greater than 159 mm, which is 10 to 15 mm.
If there is no ruler length deviation and cutting allowance in the standard, it shall be negotiated by the supplier and the buyer and specified in the contract. The double length scale is the same as the length of the fixed length, which will bring the finished product rate to the production enterprise to be greatly reduced. Therefore, it is reasonable for the production enterprise to raise the price, and the price increase is generally about 10% of the base price.
4. Range length: The range length is within the normal length range. When the user requests a certain fixed length, it must be indicated in the contract.For example, the length is usually 3m to 12m, and the length of the range is 6m to 8m or 8m to 10m.
It can be seen that the length of the range is looser than the length of the fixed length and the multiple length, but it is much stricter than the usual length, and it will also bring the reduction of the finished product rate to the production enterprise. Therefore, it is reasonable for the production company to raise the price, and the price increase will generally increase the base price by about 4%.