Shape and size term of steel pipe-Boiler Tubes,Heat-Exchanger Tubes,Superheater Tubes,Supplier,Beite

Shape and size term of steel pipe

Shape and size term of steel pipe

Commonly used terms in the technical requirements of steel pipes-the shape and size of steel pipes

Yesterday we introduced the general terms of steel pipes, and today we introduce the shape and size terms of steel pipes.

Shape and size terms of steel pipes.

1 Nominal size and actual size

A Nominal size: It is the nominal size stipulated in the standard. It is the ideal size that users and manufacturers hope to obtain. It is also the order size specified in the contract.

B Actual size: It is the actual 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.

2 Deviations and tolerances

A deviation: In the production process, because the actual size is difficult to meet the nominal size requirements, that is, it is often larger or smaller than the nominal size, the standard stipulates that there is a difference between the actual size and the nominal size. Positive deviations are called positive deviations, and negative deviations are called negative deviations.

B Tolerance: The sum of the absolute values of the positive and negative deviation values specified in the standard is called tolerance, also called "tolerance zone".

The deviation is directional, that is, it is expressed as "positive" or "negative"; the tolerance is non-directional, so the deviation value is called

The term "positive tolerance" or "negative tolerance" is wrong.

3 Delivery length

The length of delivery is also called the length required by the user or the length of the contract. The standard has the following provisions on the length of delivery:

A Ordinary length (also known as non-fixed length): Any length within the range specified by the standard and without a fixed length requirement is referred to as the normal length. For example, the standard for structural pipes stipulates: hot-rolled (extruded, expanded) steel pipes 3000mm to 12000mm; cold-drawn (rolled) steel pipes 2000mmm to 10500mm.

B fixed length: The fixed length should be within the normal length range, which is a fixed length dimension required in the contract. However, it is not possible to cut out the absolute fixed length in actual operation, so the standard specifies the allowable positive deviation value for the fixed length.

Take the structural pipe standard as an example: the production rate of fixed-length pipe is larger than that of ordinary pipe, and it is reasonable for the manufacturer to raise the price. The rate of increase is not consistent among enterprises, and is generally about 10% based on the base price.

C. Ruler length: The ruler length should be within the normal length range. The contractor should indicate the length of the multiple ruler and its multiples that constitute the total length (for example, 3000mm × 3, which is 3 times the 3000mm, and the total length is 9000mm). In actual operation, the allowable positive deviation of 20mm should be added to the total length, and the cut margin should be left for each single length. Take the structural tube as an example, the allowance for notch is specified: the outer diameter ≤159mm is 5 ～ 10mm; the outer diameter> 159mm is 10 ～ 15mm.

If there is no rule for length deviation and cutting allowance in the standard, it should be negotiated between the supplier and the buyer and specified in the contract.

D Range length: The range length is within the normal length range. When the user requires a fixed range length, it must be specified in the contract.

For example: Usually the length is 3000 ～ 12000mm, and the range length is 6000 ～ 8000mm or 8000 ～ 10000mm.

It can be seen that the length of the range is looser than the fixed length and the double length, but it is much stricter than the usual length.

4 Uneven wall thickness

The wall thickness of the steel pipe cannot be the same everywhere, and there is an objective unequal wall thickness on its cross section and longitudinal pipe body, that is, uneven wall thickness. In order to control this non-uniformity, the allowable index of uneven wall thickness is specified in some steel pipe standards. Generally, it does not exceed 80% of the wall thickness tolerance (implemented after consultation between the supply and demand parties).

5 Ovality

There is a phenomenon of unequal outer diameter on the cross section of the circular steel pipe, that is, there is a maximum outer diameter and a minimum outer diameter that are not necessarily perpendicular to each other. The difference between the maximum outer diameter and the minimum outer diameter is the ovality (or not Roundness). In order to control the ovality, some steel pipe standards stipulate the allowable index of ovality, which is generally set to not exceed 80% of the outer diameter tolerance (implemented after consultation between the supply and demand parties).

6 Curvature

The steel pipe is curved in the length direction, and the degree of curve is called the degree of curvature. The bending degree specified in the standard is generally divided into the following two types:

A Local bending degree: Use a ruler of one meter to measure the maximum bending point of the steel pipe, and measure its chord height (mm), which is the value of local bending degree. The unit is mm / m, and the method is 2.5mm / m. This method is also applicable to tube end bending.

B. Total total bending degree: Use a thin rope to tighten from both ends of the pipe, measure the maximum chord height (mm) at the bend of the steel pipe, and then convert it to the percentage of length (in meters), which is the length of the steel pipe. Full length curvature.

For example: the length of the steel pipe is 8m, and the maximum chord height is 30mm.

7.Size out of tolerance

The size is out of tolerance or the allowable deviation of the size beyond the standard. The "size" here mainly refers to the outer diameter and wall thickness of the steel pipe. The deviation here may be "positive" or "negative". Rarely, the "positive and negative" deviations appear in the same batch of steel pipes.