Steel Pipe Dimensions term knowledge
① nominal size and actual size
A nominal size: the nominal size specified in the standard, users and producers hope to get the ideal size is also stated in the Contract Order size.
B, the actual size: is the actual size of the obtained in the production process, the size is often greater than or less than the nominal dimension. This is greater than or less than the nominal size of the phenomenon known as deviation.
② deviation and tolerance
A, deviation: In the production process, since the actual size is difficult to achieve the nominal size requirements, i.e. often greater than or less than the nominal dimension, so specified in the standard to allow a difference between the actual size and the nominal dimensions. The positive difference is called a positive deviation, the difference is negative is called negative deviation.
B, tolerance: the standard set forth in the positive and negative absolute value of the deviation and called tolerance, also called "tolerance zone".
Deviation is directional, that is, to "positive" or "negative" indicates; tolerance is not directional, therefore, the deviation value is called "positive tolerance" or "negative tolerance" is called an error.
The ③ delivery length
Delivery length, also known as the length of user requirements or contract length. Delivery length standard has the following provisions:
A, the usual length (also known as random length): Where the length of the standard specifies the length within and fixed length requirements are referred to as the usual length. For example, structural pipe standards: hot-rolled (extrusion, expansion) steel pipe 3000mm ~ 12000mm; cold drawn (rolled) steel pipe is 2000 mm-10500mm.
B Length Length: Length Length should be the usual length range, the size of a fixed length of the contract requirements. But the actual operations are cut out absolutely definite length is unlikely, therefore, the standard provides for definite length allowed positive deviation.
To structural pipe standard:
Production of definite length tube than usual length tube finished product rate decline, producers proposed fare increase is a reasonable request. The enterprises of the fare increases are not consistent, generally the base price on the basis of a 10% fare increase.
C, double length: double length should be in the range of usual length, the contract should specify haplotypes length and a total length of multiples (for example 3000mm x 3, namely 3 multiples of 3000mm, a total length of 9000mm). The actual operation, should be on the basis of the total length of plus allowed positive deviation 20mm, plus the length of each of the haplotype Ft cutting margin. Structural tube, for example, require cutting margin: ≤ 159mm to 10mm outside diameter; outside diameter> 159mm of 10 to 15mm.
By supply and demand if the standard deviation of multiple lengths and cutting the margin provisions negotiated and specified in the contract. Times longer scale with definite length, will give a significant reduction in production enterprises to bring the rate of finished production enterprises proposed fare increase is reasonable, its rate of increase is basically the same as the rate of increase of definite length.
D, the range of length: the range of length in the usual length range, when the length of a fixed range of user requirements which need to be clearly indicated in the contract.
For example: usually a length of 3000 ~ 12000mm, Range Length Length 6000 ~ 8000mm or 8000 ~~ 10000mm.
Seen, the length of the range is more lenient than the cut to length and double length requirements, but more than the usual length tightened many, and also to bring about the reduction of the rate of finished production enterprises. The so manufacturers proposed fare increase is justified, its rate of increase is usually in the base price on the fare increase by about 4%.
④ uneven wall thickness
The pipe wall thickness can not throughout the same objective wall thickness ranges phenomenon exists in its cross-sectional and longitudinal tubular body, i.e. the thickness unevenness. In order to control this heterogeneity, uneven wall thickness allows indicators specified in some steel standards, general provisions (after consultation between the execution) does not exceed 80% of the wall thickness tolerance.
⑤ ovality
Exists in the circular pipe cross section of the outer diameter ranging phenomenon, namely the existence of necessarily mutually perpendicular maximum outer diameter and the smallest outer diameter, the difference between the maximum outer diameter and the smallest outer diameter is ovality (with or without roundness). In order to control the ellipticity some steel standards specified allowable ovality indicators, generally defined as no more than 80% of the diameter tolerance (consultation between).
⑥ curvature
Pipe in a curved shape in the longitudinal direction, that is called the degree of curvature is shown using the number of its curve degrees. The standard provisions curvature is generally Pided into the following two:
A partially curved: by the amount of one meter long ruler at the maximum bending of the steel pipe, measuring the chord high (mm) is the local bending degree value in units of mm / m, that the methods, such as 2.5mm / m . The method is also applicable to the bending of the tube end portion.
The percentage of B, full-length total curvature: a piece of string from both ends of the tube taut, measuring pipe bend chord high (mm), and translation of length (in meters), is the length of pipe direction the entire length of bending.
For example: Pipe length of 8m, maximum chord 30mm, full-length bending the pipe should be:
0.03 &Pide; 8m × 100% = 0.375%
The ⑦ size of tolerance
Dimensions of tolerance or called standard size exceeds allowable deviation. "Size" refers to the diameter and wall thickness of the steel pipe. Usually someone the size of the ultra-poor habits called "tolerance outrageous, this is called deviation and tolerance equated imprecise, should be called" deviation outrageous. Deviation here may be "positive" and "negative" rarely appear in the same batch of steel pipe "positive and negative" deviation outrageous phenomenon.
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