In order to unify the connection size of pipes and fittings, DN is used to represent their nominal diameters (also called nominal diameters and nominal diameters). Chemical plants are used to transport fluids with general pressure, such as water, gas, air, oil and steam, for heating. Welded steel pipes are often used as pipes, which are called slotted pipes.

For example, a seamless steel pipe with an outer diameter of 108, with a wall thickness of 5MM, is represented by D 108*5, and a plastic pipe is also represented by an outer diameter, such as De63. Others, such as reinforced concrete pipes, cast iron pipes and galvanized steel pipes, are represented by DN, and are generally represented by nominal diameters in design drawings. Nominal diameter is an artificially specified standard for the convenience of design, manufacture and maintenance, also called nominal diameter.

Extended data:

Generally speaking, the diameter of a pipe can be divided into outer diameter, inner diameter and nominal diameter. The outer diameter of the pipe made of seamless steel pipe is indicated by the letter D, followed by the size and wall thickness of the outer diameter.

Grooved pipes can be divided into thin-walled steel pipes, ordinary steel pipes and thickened steel pipes according to their thickness. Its nominal diameter is neither outer diameter nor inner diameter, but a nominal size similar to the inner diameter of ordinary steel pipe.

Each nominal diameter corresponds to an outer diameter, and its inner diameter value varies with thickness. (The pipes are divided into English pipes and metric pipes. The nominal diameter of the pipeline is DN 100. If the pipe is an international series (commonly known as English pipe), its outer diameter is114.3mm. ..

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