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 in. Pipeline accessories are also expressed by nominal diameter, which is the same as seamed pipe. It corresponds to imperial units as follows:

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

DN is the nominal diameter, and the nominal diameter (or nominal diameter) is the general diameter of various pipes and pipeline accessories. The nominal diameter is a convenient round integer for reference, and has only a loose relationship with the processing size. Pipes and pipeline accessories of the same nominal diameter can be connected to each other and are interchangeable. It is not the actual outside diameter or inside diameter of the pipe, although its value is closer to or equal to the inside 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 varies with thickness.

02 De mainly refers to the outer diameter of the pipe

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

Generally, those marked with De are required 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 rarely use De to mark pipes when wall thickness is not involved; but marking plastic pipes is another matter; it is still related to industry habits, in the actual construction process The pipes 20, 25, 32, etc. that we call simply refer to De, not DN.

In addition, according to the practical experience in the field:

a. The connection methods of the two pipeline materials are nothing more than: thread connection and flange connection.

b. Both galvanized steel pipes and PPR pipes can use the above two connections, but it is more convenient to use threads for pipes smaller than 50, and flanges for pipes larger than 50 are more reliable.

ps: If two metal pipes of different materials are connected, it is necessary to consider whether a galvanic reaction will occur, otherwise the corrosion rate of active metal pipes will be accelerated. All kinds of metals are separated, including bolts, which must be separated by gaskets to avoid contact.

Comparison table of nominal diameter and outer diameter of each pipe

DN, De, Dg difference

A. Different marking methods for various pipes

For water gas transmission steel pipes (galvanized or non-galvanized), cast iron pipes and other pipes, the pipe diameter should be indicated by the nominal diameter DN (such as DN15, DN50);

For seamless steel pipe, welded steel pipe (straight seam or spiral seam), copper pipe, stainless steel pipe and other pipes, the pipe diameter should be expressed as outer diameter D × wall thickness (such as D108 × 4, D159 × 4.5, etc.);

3 For pipes such as reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, and cylinder tile pipes, the pipe diameter should be indicated by the inner diameter d (such as d230, d380, etc.);

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

When the nominal diameter DN is used to represent the pipe diameter in the design, there should be a comparison table between the nominal diameter DN and the corresponding product specifications.

Relationship between B, DN, De, Dg

De is the diameter of the outer wall of the pipe

DN is the number obtained by subtracting half the thickness of the pipe wall from De. Dg is generally not used.

The pipe diameter should be in mm.

The expression of the pipe diameter should meet the following requirements:

For water gas transmission steel pipes (galvanized or non-galvanized), cast iron pipes and other pipes, the pipe diameter should be indicated by the nominal diameter DN;

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

For pipes such as reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, and cylinder tile pipes, the pipe diameter should be indicated 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 expressed by de (nominal outer diameter) × e (nominal wall thickness) (GB 5836.1-92).

The specifications of polypropylene (PP) pipes for water supply are represented by de×e (nominal outer diameter×wall thickness) The marking of plastic pipes on engineering drawings

metric designation ( metric dimension size )

Expressed in DN, it is generally called "nominal size", which is neither the outer diameter of the pipe nor the inner diameter of the pipe. Is the average of the outer diameter and the inner diameter, we call the average inner diameter.

For example: Metric designation (mm dimension size) DN50 for a plastic pipe with an outer diameter of 63mm

ISO metric designation ( ISO metric dimension size )

The outer diameter of PVC pipe, ABS pipe is expressed in Da

Denote the outer diameter of the PP pipe and the PE pipe

For example: the metric designation of a plastic pipe with an outer diameter of 63mm ( mm dimension size )

Da63 for PVC pipe, ABS pipe.