When purchasing seamless steel pipes, manufacturers often ask us some professional terms. For purchasing, it is unavoidable to see things in a fog. Now we have some simple terminology parsing, hoping to help our purchasing staff.
1.Nominal size and actual size
A. Nominal size: Is the nominal size specified in the standard, is the size that the user and the enterprise want to get, and is also the size indicated in the contract.
B. Actual size: is the actual size obtained in the production process, the size is often greater than or small Yu gong size, this is greater than or less than the phenomenon called deviation.
2. deviation and tolerance
A. deviation: there is a difference between the actual size and the nominal size. The difference is called positive difference, and the difference is negative.
B. tolerance: the sum of the absolute value of the positive and negative deviations specified in the standard is called the tolerance. Tolerance has no directivity.
3. Delivery Length
Delivery length is also called customer required length and contract length.
A. Usual length: also known as non-fixed length. Any length within the standard length range and without fixed length requirements is called the normal length.
Structural pipe standards stipulate that:
Hot rolled (extruded, expanded) steel pipe: 3000mm ~ 12000mm
Cold-rolled (drawn) steel pipe: 2000mm~10500mm
B. Length of fixed length: Usually within the normal length range, it is a fixed length size required in the contract, but the actual length is impossible to cut out; therefore, the standard stipulates that positive deviation is allowed for length of fixed length (only more can not be less).
Structural pipe standard: The price increase requirement is about 10% of the base price.
C. Length of multiple rulers: The length of multiple rulers should be within the normal range. The contract should specify the length of single ruler and the multiple of the total length (e.g. 3000X3, or 3 times of 3000mm, 9000mm). In practice, the allowable positive deviation of 20 mm should be added on the basis of the total length, and the allowance of incision should be left for each single length. (10%) structural pipe as an example: external diameter < 159 mm, 5-10 mm external diameter > 159 mm, 10-15 mm external diameter
D. Range Length: In the normal range, the user requires a fixed range length. It must be stated in the contract. (4%)
Example: Usually the length is 3000mm~12000mm.
The range length is 6000mm~8000mm.
4. uneven wall thickness
In order to control the uniformity of wall thickness, the allowable index of uneven is stipulated in some steel pipe standards, and the general rule does not exceed 80% of the wall thickness tolerance. (mutual negotiation)
5. degree of ellipticity
The difference between the maximum outer diameter and the minimum outer diameter is the ellipticity. In order to control the ellipticity, some steel pipe standards set the allowable index of ellipticity. 80% of the outer diameter tolerance shall be specified (mutual negotiation).
The steel pipe is curved in the length direction, and it is shown by the number that the curve is called bending degree.
A. partial bending (1m) H chord height
B. total total bending H chord height Max L total length (100%)
7. size deviation
The size is too bad or the size is allowed to exceed the standard allowable deviation. (mainly refers to the outer diameter and wall thickness of the steel tube).
The delivery state refers to the final plastic deformation of the product or the state of final heat treatment. Generally speaking, hot rolling or cold rolling (drawing) state or manufacturing state is not delivered after heat treatment. The state of heat treatment is called heat treatment, or normalizing (Chang Hua), quenching and tempering, solid solution and annealing according to the type of heat treatment.