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　　Boiler pipe refers to the steel with openings at both ends and hollow section, and its length is larger than that of the surrounding. According to the production method, it can be divided into seamless steel pipe and welded steel pipe. The specification of boiler pipe is based on the overall dimension.

　　DN refers to the nominal diameter of the boiler pipe. Note: This is neither the outer diameter nor the inner diameter; It should be related to British units in the early stage of pipeline engineering development; It is usually used to describe galvanized steel pipe, and its corresponding relationship with British units is as follows:

　　4. Branch pipe: 4 / 8 inch: DN15;

　　6. Branch pipe: 6 / 8 inch: DN20;

　　1 inch pipe: 1 inch: DN25;

　　Two inch pipe: 1 and 1 / 4 inch: DN32;

　　Half inch pipe: 1 and 1 / 2 inch: Dn40;

　　Two inch pipe: 2 inches: DN50;

　　Four inch pipe: 4 inches: DN100

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