Generally, the diameter of stainless steel tubes is classified into outer diameter, inner diameter and nominal diameter. The seamless steel pipe diameter using the letter D to that in diameter attached to the size and thickness, such as diameter is 108 seamless steel pipe, wall thickness of 6MM, is expressed as D108 * 6, another plastic tube with outer diameter is also said, such as De63, such as reinforced concrete pipe, cast iron pipe and galvanized steel pipe also is to use DN to represent, in the design drawings are usually used to represent the nominal diameter, nominal diameter is a standard in order to design and manufacture and maintenance convenient set artificially, also called nominal diameter, such as stainless steel pipe fittings is most specification name.
DN is nominal diameter, nominal diameter, also known as nominal diameter, that is, all kinds of pipe fittings and pipe accessories of the general caliber. The same nominal diameter of the pipe and piping accessories can be connected with each other, with interchangeability. It is not a real sense of pipe diameter or diameter, although its value is closer with the pipe diameter or equivalent; in order to make the tube, pipe connection size uniform, with nominal diameter (or nominal diameter, nominal diameter). For example, welded steel pipe can be divided into thin walled steel pipe, ordinary steel pipe and thickened steel pipe according to the thickness. Its nominal diameter is not an outer diameter, nor an inner diameter, but a nominal size similar to the diameter of ordinary steel pipe. Each nominal diameter corresponds to an outer diameter, and its inner diameter varies with the thickness. Nominal diameter can be expressed in metric mm, and can also be expressed in Imperial in. With nominal diameter pipeline accessories, which means the same and seamed tube.
Such as stainless steel pipe fittings nominal diameter and the inner diameter and the outer diameter are not equal, such as the nominal diameter is 100mm seamless steel pipe is 1025, 1085 and 108 of them are several, the outer diameter of pipes, 5 stainless steel tube wall thickness, so the pipe diameter is (108 * 5-5) = 98mm, but this result is not completely equal to two times the wall thickness difference, reducing the pipe diameter in other words, just close to the nominal diameter of a stainless steel inner diameter, but not exactly the same to the diameter of pipe diameter specification name, so the need for nominal diameter on the design drawings, the purpose is to determine according to the nominal diameter of the pipe and pipe fittings valve, flange, gasket structure dimensions and connection dimensions, nominal diameter is represented by the symbol DN, if the diameter is used to represent the design drawings, also need to give the size of pipe The nominal diameter and wall thickness of a pipe are indicated by a comparison table.
The design and construction of a series of standard pressure pipes for stainless steel pipes, the first step is to consider the selection of the standard series of pressure piping and its components. In this regard, although the application of standard systems in many countries, but can be divided into two categories.
Nominal steel tube diameter, also known as the average diameter of steel pipe. The nominal diameter is followed by a number to represent the letter. Because the tube is thinner, the outer diameter of the pipe is almost the same as the inner diameter of the pipe, so the diameter of the steel pipe can be used as the average value of the inner diameter of the pipe.
Source: China Stainless Steel Tube Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)