The seamless pipe has a hollow cross-section and is widely used as a pipeline for conveying fluids, such as octg pipes for conveying oil, natural gas, gas, water, and pipes for certain solid materials. Compared with welded pipes, seamless pipes have higher bending and torsional strength and better compression resistance, and are economical section steels. Widely used in oil, natural gas, water, steam, gas and other high, medium and low pressure fluid transmission pipelines and steel pipes for piling, bridges, buildings and other structures
Manufacturers often ask us some technical terms when purchasing seamless steel pipes.
1. Nominal and actual dimensions
(1) Nominal size: It is the nominal size stipulated in the standard, the size desired by users and enterprises, and the size specified in the contract.
(2) Actual size: It is the actual size obtained during the production process. This size is often larger or smaller than the nominal size. This phenomenon of being larger or smaller is called deviation.
2. Deviations and Tolerances
(1) Deviation: A difference is allowed between the actual size and the nominal size. A positive difference is called a positive difference, and a negative difference is called a negative difference.
(2) Tolerance: The sum of the absolute values of positive and negative deviations specified in the standard is called tolerance. Tolerances are non-directional.
3. Delivery length
The delivery length is also called the user's required length and the contract length.
(1) Normal length: also known as non-cut length. Where the length is within the length range specified in the standard and there is no fixed length requirement, it is called the normal length.
(2) Fixed length: usually within the usual length range, it is a certain fixed length dimension required in the contract, but the actual length is impossible to cut out; therefore, the standard stipulates that positive deviations are allowed for the fixed length.(It can only be more, not less).
Structural management standard: The price increase requirement is generally about 10% of the base price.
(3) Double ruler length: The double ruler length should be within the normal range, and the single ruler length and the multiple of the total length should be specified in the contract (for example, 3000X3, which is 3 times of 3000mm, is 9000mm). In actual operation, an allowable positive deviation of 20mm should be added to the total length, plus a cut allowance should be left for each single ruler length.
(4) Range length: In the usual range, the user requires a certain fixed range length. must be specified in the contract.
4. Uneven wall thickness
In order to control the uniformity of wall thickness, some steel pipe standards stipulate the allowable index of unevenness, which generally does not exceed 80% of the wall thickness tolerance. (negotiation between both parties)
The difference between the largest outer diameter and the smallest outer diameter is the ovality. In order to control the ovality, some steel pipe standards stipulate the allowable index of ovality. No more than 80% of the outside diameter tolerance is specified (by mutual agreement).
The steel pipe is curved in the length direction, and the degree of curvature represented by numbers is called curvature.
(1) Local bending (1m) H Chord height
(2) Total total curvature H Chord height max L Total length (100%)
7. Size deviation
The size is out of tolerance or the size exceeds the allowable deviation of the standard. (mainly refers to the outer diameter and wall thickness of the steel pipe)
8. Delivery status:
The delivery state refers to the final plastic deformation or final heat treatment state of the product. Generally, delivery without heat treatment is called hot rolling or cold rolling (drawing) state or manufacturing state. Delivery after heat treatment is called heat treatment state, or normalized (normalized), quenched and tempered, solid solution, annealed state according to the type of heat treatment.