This is a very clear explanation of DN, De and Φ! (Friends who do engineering please come in)
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发布日期:2020-06-15
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作者:ESPA
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This is a very clear explanation of DN, De and Φ! (Friends who do engineering please come in)

01 DN refers to the nominal diameter of the pipe


The nominal diameter can be expressed in metric mm or imperial in. Pipeline accessories are also expressed by the nominal diameter, the meaning is the same as the seam pipe. The corresponding relationship between it and imperial units is as follows:

单位对应表

The nominal diameter (nominal diameter), also known as the mean outer diameter (meanoutside diameter). This is because the wall of the metal pipe is very thin, and the outer diameter of the pipe is almost the same as the inner diameter of the pipe, so the average value of the outer diameter of the pipe and the inner diameter of the pipe is called the pipe diameter.


DN is the nominal diameter, and the nominal diameter (or nominal diameter) is the universal diameter of various pipes and pipeline accessories. The nominal diameter is a convenient round integer for reference, and it has only a loose relationship with the processing size. Pipes and accessories of the same nominal diameter can be connected to each other and are interchangeable. It is not a pipe outer diameter or inner diameter in a practical sense, although its value is close to or equal to the pipe inner diameter.


For example: Welded steel pipe can be divided into thin-walled steel pipe, ordinary steel pipe and thickened steel pipe according to thickness. Its nominal diameter is not the outer diameter nor the inner diameter, but a nominal size that approximates the inner diameter of ordinary steel pipes. Each nominal diameter corresponds to an outer diameter, and its inner diameter value varies with thickness.



ESPA  Engineering case drawing


02 De mainly refers to the outer diameter of the pipe

Mainly used to describe: seamless steel pipes, PVC and other plastic pipes, and other pipes that require a clear wall thickness


Generally, those marked with De need to be marked in the form of outer diameter X wall thickness.


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


DN20 De25X2.5mm


DN25 De32X3mm


DN32 De40X4mm


DN40 De50X4mm


We are accustomed to using DN to mark welded steel pipes, and De is rarely used to mark pipes without involving wall thickness; however, marking plastic pipes is another matter; it is still related to industry habits. In the actual construction process The 20, 25, 32 and other pipes we call simply refer to De, not DN.


In addition, according to the practical experience on site:





a. The connection method of the two pipe materials is nothing more than: screw connection and flange connection.


b. Both the galvanized steel pipe and PPR pipe can be connected by the above two methods. However, the thread buckle for pipes less than 50 is more convenient, and the flange more than 50 is more reliable.


ps: If two metal pipes of different materials are connected, it is necessary to consider whether there will be a galvanic reaction, otherwise it will accelerate the corrosion rate of active metal material pipes. It is best to use flange connections and use rubber gaskets to insulate the two. All kinds of metals are separated, including bolts should be separated by gaskets to avoid contact.


Φ can also represent the outer diameter of the pipe, but at this time it should be multiplied by the wall thickness behind it.


 03 Φ represents the diameter of an ordinary circle


Of course, Φ can also represent the outer diameter of the pipe, but at this time it should be multiplied by the wall thickness behind it. Such as: Φ25×3, which means that the outer diameter is 25mm and the wall thickness is 3mm.


For seamless steel pipes or non-ferrous metal pipes, "outer diameter x wall thickness" shall be marked. For example: Φ107×4, where Φ can be omitted.


Some steel pipes in China, ISO and Japan are marked with wall thickness to indicate the series of steel pipe wall thickness. For this type of steel pipe, the method is expressed as pipe outer diameter × wall thickness. Such as: Φ60.5×3.8


Comparison table of nominal diameter and outer diameter of each pipe





The difference between DN, De, Dg, Φ▼

DN Nominal diameter


De external diameter


Dg diameter gong (the initial consonant of the Chinese pinyin "gong") Now you will understand that Dg is a domestic product and a Chinese product with Chinese characteristics, which is no longer used.


  Relation of DN, De, Dg, Φ


De measures the diameter of the outer wall of the pipe


DN is the number of De minus the thickness of the pipe wall

Dg is generally not used

Φ represents the diameter of an ordinary circle


The pipe diameter should be in mm, and the expression of the pipe diameter should meet the following requirements:


Water and gas transportation steel pipes (galvanized or non-galvanized), cast iron pipes and other pipes, the pipe diameter should be expressed by the nominal diameter DN;


Seamless steel pipe, welded steel pipe (straight or spiral seam), copper pipe, stainless steel pipe and other pipes, the pipe diameter should be expressed by the outer diameter × wall thickness Φ;


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


For plastic pipes, the pipe diameter should be expressed according to the product standard method;


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 specifications.


The specifications of rigid PVC pipes for building drainage are indicated by de (nominal outer diameter)×e (nominal wall thickness) (GB 5836.1-92), and the specifications of polypropylene (PP) pipes for water supply are indicated by de×e (nominal outer diameter× Wall thickness) Marking of plastic pipes on engineering drawings.


Metric dimension (metric dimension size)


Represented by DN is generally called "nominal size", it is not the outer diameter of the pipe, nor the inner diameter of the pipe. Is the average value of the outer diameter and inner diameter, we call the average inner diameter.


For example: metric mark (mm dimension size) of plastic pipe with outer diameter of 63mm DN50



ESPA  Engineering case drawing

ISO metric dimension size


Denote the outer diameter of PVC pipe and ABS pipe by Da


De means PP pipe, PE pipe diameter


For example: metric marking of plastic pipes with an outer diameter of 63mm (mm dimension size)

Da63 is for PVC pipes and ABS pipes.


Summary: De, DN, d, ф's respective representation range!


De-- PPR, PE pipe, polypropylene pipe


DN-- nominal diameter of polyethylene (PVC) pipe, cast iron pipe, steel-plastic composite pipe, galvanized steel pipe


d - nominal diameter of concrete pipe


ф-- Seamless steel pipes or non-ferrous metal pipes should be marked "outer diameter x wall thickness"


Source: We power plant people, ESPA finishing


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