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Conversion of pipe diameter

Sep 03, 2018

1.Conversion of pipe diameter in inch and mm units:

1 inch =25.4 mm =8 GB (GB/ t50106-2001)

Pipe diameter shall be expressed in the following way :(pipe diameter shall be in mm)

① Water gas transmission pipe (galvanized or non-galvanized), cast iron pipe and other pipe, pipe diameter should be denoted by nominal diameter DN.

② Seamless steel pipe(Seamless Bend),, welded steel pipe (straight or spiral joints), copper pipe, stainless steel pipe and other pipe, pipe diameter should be expressed as outside diameter x wall thickness.

③ Reinforced concrete (or concrete) pipe, clay pipe, acid-resistant ceramic pipe, cylinder tile pipe and other pipe materials, the pipe diameter should be expressed in the inner diameter d;

④ Plastic pipe, pipe diameter should be expressed according to the product standard method;

⑤ When the design USES the nominal diameter DN to represent the pipe diameter, there should be a comparison table between the nominal diameter DN and the corresponding product specification.

The specification of rigid PVC pipes for building drainage is expressed by DE (nominal outer diameter) x e (nominal wall thickness) (GB 5836.1-92); Specification of polypropylene (PP) pipe for water supply

Seamless Bend

2. About the difference between DN and De:

1、DN refers to the nominal diameter of the pipe. Note: this is neither the outside diameter nor the inside diameter; It should be related to the British system at the beginning of the development of pipeline engineering; Generally used to describe galvanized steel pipe, its correspondence with British units is as follows:

4 in. : 4/8 in. : DN15;

6 in. : 6/8 in. : DN20;

1 inch tube: 1 inch: DN25;

Inch 2 tube: 1 1/4 inch: DN32

Inch and a half tube: 1 1/2 inch: DN40;

Two inch tube: 2 inches: DN50;

3-inch tube: 3 inches: DN80 (also labeled DN75 in many places);

4 inch tube: 4 inches: DN100; 

De mainly refers to the outside diameter of the pipe, which is generally marked by De.

Mainly used for description: seamless steel pipe, PVC and other plastic pipes, and other pipes that require clear wall thickness.

Taking galvanized welded steel pipe as an example, two labeling methods of DN and De are as follows:

DN20 De25X2.5mm

DN25 De32X3mm

DN32 De40X4mm

DN40 De50X4mm ………

① We are accustomed to use DN to label welded steel pipe, and rarely use De to label pipe without involving wall thickness.

② But labeling plastic tubes is a different matter; Or is it related to the industry habit? In the actual construction process, the pipe named 20, 25 and 32 refer to De, not to DN. There is a difference of one specification. It is easy to cause losses in the process of procurement and construction if we do not make clear.

③ The two types of pipe materials are connected in the same way: thread connection and flange connection. Other connections are used less frequently.

Galvanized steel pipe (Galvanized Threaded Elbow) and PPR pipe can use the above two connections, only less than 50 pipe thread more convenient, more than 50 flange more reliable.

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