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The Standard Size of Stainless Steel Pipe and Summarize

The standard size of stainless steel pipe and summarize.
1) nominal size and actual size
A, nominal size: size is specified in the standard name, is the ideal size of users and manufacturers hope to get, is also stated in the contract to the order of size.
B, the actual size:  is given in the production process of actual size, the size is often greater than or less than the nominal size. This is greater than or less than the nominal size of the phenomenon known as deviation.
(2) the deviation and tolerance
A, deviation: in the process of production, due to the difficult to meet the requirements of nominal size, actual size is often greater than or less than the nominal size, so the standard stipulated there is a difference allowed between the actual size and nominal size. The difference is positive is called a positive deviation, the difference is negative is called negative deviation.
B, tolerance: standard specified in the positive and negative deviation absolute value sum is called tolerance,also called "tolerance zone".
Deviation is directional, that is "positive" or "negative" indicates; tolerance is not directional, so the deviation value called "positive tolerance" or "negative tolerance" is wrong.
(3) Delivery length
Delivery length, also known as the length of user requirements or contract length. There are several provisions of the standard length for delivery:
A, normal length (also known as non-random length): when the length is in the length of the standard and no fixed length requirements are referred to as normal length. Such as structural pipe standard: hot-rolled (extrusion, expansion) steel 3000mm ~ 12000mm; cold drawn (rolled) steel 2000mmm ~ 10500mm.
B、specified length: Length should be within the range of usual length,  is a fixed-length size requested in the contract,
C、Range length: range length is in the usual length range, need to be indicated in the contract when the user requires a range of fixed length.
(4) uneven wall thickness
Steel pipe wall thickness is not the same, wall thickness range phenomenon exists objectively may in the cross section and longitudinal pipe body, that is uneven wall thickness. In order to control this unevenness, in some steel standards specified in the uneven wall thickness allows indicators, general provisions do not exceed 80% of the wall thickness tolerance (negotiated by both sides before execution).
Circular in cross section of the pipe there is an outer diameter ranging phenomenon,  i.e., there is not necessarily perpendicular to each other of the maximum outer diameter and the smallest diameter, the difference between the maximum and minimum outer diameter is ovality (or roundness). In order to control the ovality, some steel standards specified allowable ovality indicators, generally no more than  80%  of the outside diameter tolerance (negotiated by both sides before execution).
(6) size out-of-tolerance
Size out-of-tolerance or dimensions beyond the standard tolerances. Here the "size" refers to the steel pipe outer diameter and wall thickness.