01 DN refers to the nominal diameter of the pipe
Usually used to describe: galvanized steel pipe.
The nominal diameter can be expressed in metric mm or in imperial. Pipe accessories are also expressed in nominal diameter, which has the same meaning as seamed pipes. Its correspondence with imperial units is as follows:
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Nominal diameter, also known as mean outside 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 and the inner diameter of the pipe is taken as the pipe diameter.
DN is the nominal diameter, and the nominal diameter (or nominal diameter) is the common diameter of various pipes and pipe accessories. The nominal diameter is a convenient round integer for reference, and it is only loosely related to the processing size. Pipes and pipe accessories of the same nominal diameter can be connected to each other and are interchangeable. It is not the outer diameter or inner diameter of the pipe in the actual sense, although its value is close to or equal to the inner diameter of the pipe.
For example: welded steel pipes can be divided into thin-walled steel pipes, ordinary steel pipes and thickened steel pipes according to thickness. Its nominal diameter is neither 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.
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 clear wall thickness are generally marked with De, and all need to be marked in the form of outer diameter x wall thickness.
Take 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 used to using DN to mark welded steel pipes, and rarely use De to mark pipes without involving wall thickness, but marking plastic pipes is another matter, which is still related to industry habits. In the actual construction process, the pipes we simply call 20, 25, 32, etc. all refer to De, not DN.
In addition, according to practical experience on site:
a. Connection methods of two pipe materials: threaded connection and flange connection.
b. Both galvanized steel pipes and PPR pipes can be connected by the above two methods, but it is more convenient to use threads for pipes less than 50, and it is more reliable to use flanges for pipes greater than 50.
ps: If two metal pipes of different materials are connected, it is necessary to consider whether a galvanic reaction will occur, otherwise it will accelerate the corrosion rate of the active metal material pipe. It is best to use flange connection and use insulating materials such as rubber gaskets to separate the two metals, including bolts, 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.
03 φ represents the diameter of a common 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. For example: φ25×3, indicating a pipe with an outer diameter of 25mm and a wall thickness of 3mm.
For seamless steel pipes or non-ferrous metal pipes, "outer diameter × wall thickness" should be marked. For example: φ107×4, where φ can be omitted.
Some steel pipes in China, ISO and Japan are marked with wall thickness dimensions to represent the steel pipe wall thickness series. For this type of steel pipe, the representation method is pipe outer diameter × wall thickness. For example: φ60.5×3.8.
Comparison table of nominal diameter and external diameter of various pipe materials
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Differences between DN, De, Dg, and φ
DN Nominal diameter;
De external diameter;
Dg diameter gong (the initial consonant of the Chinese pinyin "gong") Now you understand that Dg is a domestic product, a domestic product with Chinese characteristics, and it is no longer used now.
Relationship between DN, De, Dg, and φ:
De measures the diameter of the outer wall of the pipe;
DN is De minus half 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 comply with the following provisions:
For pipes such as water-gas transmission steel pipes (galvanized or non-galvanized), cast iron pipes, etc., the pipe diameter should be expressed in nominal diameter DN;
For pipes such as seamless steel pipes, welded steel pipes (straight seams or spiral seams), copper pipes, stainless steel pipes, etc., the pipe diameter should be expressed in outer diameter × wall thickness φ;
For pipes such as reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, and tile pipes, the pipe diameter should be expressed in inner diameter d;
For plastic pipes, the pipe diameter should be expressed in accordance with the product standard method;
When the design uses nominal diameter DN to express the pipe diameter, there should be a comparison table between nominal diameter DN and corresponding product specifications.
The specifications of rigid polyvinyl chloride pipes for building drainage are expressed in De (nominal outer diameter) × e (nominal wall thickness) (GB 5836.1-92), and the specifications of polypropylene (PP) pipes for water supply are expressed in De × e (nominal outer diameter × wall thickness) Plastic pipes are marked on engineering drawings
Metric dimension size
DN is generally called "nominal size". It is not the outer diameter or inner diameter of the pipe. It is the average value of the outer diameter and the inner diameter, which we call the average inner diameter.
For example: the metric dimension size of a plastic pipe with an outer diameter of 63mm is DN50.
ISO metric dimension size
Da is used to represent the outer diameter of PVC pipes and ABS pipes;
De is used to represent the outer diameter of PP pipes and PE pipes.
For example: the metric dimension size of a plastic pipe with an outer diameter of 63mm; Da63 is for PVC pipes and ABS pipes.
Summary: The respective ranges of De, DN, d, and φ:
De--Outer diameter of PPR, PE pipe, and polypropylene pipe;
DN--Nominal diameter of polyethylene (PVC) pipe, cast iron pipe, steel-plastic composite pipe, and galvanized steel pipe;
d--Nominal diameter of concrete pipe;
φ--Seamless steel pipe or non-ferrous metal pipe should be marked with "outer diameter × wall thickness".
Source: New Vision of Environmental Protection
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