De、DN、d、 ф Respective representation range of

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

ф--  The nominal diameter of seamless steel pipe is ф 100:108 X 4

Difference between pipe diameter DE and DN

1. DN refers to the nominal diameter of the pipe, which is neither the outer diameter nor the inner diameter (it should be related to English units at the early stage of pipeline engineering development, and is usually used to describe galvanized steel pipes). Its corresponding relationship with English units is as follows:

4/8 inch: DN15;

6/8 inch: DN20;

1 inch pipe: 1 inch: DN25;

Two inch pipe: 1 and 1/4 inch: DN32;

Inch half pipe: 1 and 1/2 inch: DN40;

Two inch pipe: 2 inch: DN50;

Three inch pipe: 3 inch: DN80 (also marked as DN75 in many places);

Four inch pipe: 4 inch: DN100;

2. De mainly refers to the outer diameter of the pipe (generally marked by De, which should be marked in the form of outer diameter X wall thickness)

It is mainly used to describe: seamless steel pipes, PVC and other plastic pipes, and other pipes that require clear wall thickness.

Taking galvanized welded steel pipe as an example, DN and De marking methods 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; It is also related to the industry habits. In the actual construction process, the 20, 25, 32 and other pipelines we call simply refer to De, not DN.

According to the practical experience on site:

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

b. Galvanized steel pipe and PPR pipe can be connected by the above two methods, but the screw thread is more convenient for pipes smaller than 50, and the flange is more reliable for pipes larger than 50.

c. If two metal pipes made of different materials are connected, whether galvanic cell reaction will occur shall be considered, otherwise the corrosion rate of active metal pipes will be accelerated. It is better to use flanges for connection, and use rubber gasket insulation materials to separate the two metals, including bolts, with gaskets to avoid contact.

Differences among DN, De and Dg

DN Nominal diameter

De external diameter

Dg diameter gong

a. Different marking methods for various pipes:

1. 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);

2. Seamless steel pipe, welded steel pipe (straight seam or spiral seam), copper pipe, stainless steel pipe and other pipes, the pipe diameter should be D × Wall thickness (such as D108 × 4、D159 × 4.5, etc.);

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

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

5. 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.

b. Relationship of DN, De and Dg:

De is the diameter of the outer wall of the pipe

DN is De minus half the thickness of pipe wall

Dg is generally not used

1 Pipe diameter shall be in mm.

2 The expression of pipe diameter shall comply with the following provisions:

1 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;

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

3 For reinforced concrete (or concrete) pipes, clay pipes, acid resistant ceramic pipes, liner pipes and other pipes, the pipe diameter should be expressed by the inner diameter d;

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

5 When the nominal diameter DN is used to represent the pipe diameter in the design, a comparison table between the nominal diameter DN and the corresponding product specifications shall be provided

Unplasticized polyvinyl chloride pipes for building drainage - de (nominal outside diameter) for specification × E (nominal wall thickness) means (GB 5836.1-92).

Polypropylene (PP) pipes for water supply × E stands for (nominal outer diameter × Wall thickness)

Marking of plastic pipes on engineering drawings

Metric dimension size

Represented by DN

Commonly referred to as "nominal size", it is not the outer diameter of the pipe nor the inner diameter of the pipe. Is the average of the outside diameter and the inside diameter, which is called the average inside diameter.

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

ISO metric dimension size

Take Da as the outer diameter of PVC pipe and ABS pipe

Take De as the outer diameter of PP pipe and PE pipe

For example, the metric mark of plastic pipe with an outer diameter of 63mm (mm dimension size)

Da63 for PVC pipe and ABS pipe