Do you know the units of diameter Φ, diameter DN, and inches? | Fleyenda Flow
Nov.07.2024
The different measurement units used in specifying pipe sizes and diameters, particularly focusing on inches (") in the American system, DN in the Chinese and European systems, and the general unit Φ for outer diameters. Fleyenda Flow introduces the units and conversion formula.
What is an inch?
Inch (") is a common specification unit in the American system, such as steel pipes, valves, flanges, elbows, pumps, tees, etc. For example, the specification is 10".
Inch (abbreviated as in.) originally means thumb in Dutch, and one inch is the length of one thumb. Of course, people’s thumbs also vary in length. In the 14th century, King Edward II promulgated the "Standard Legal Inch". The stipulation is: select the three largest wheat kernels from the middle of the barley ear and arrange them in a row, the length of which is one inch.
Generally 1"=2.54cm=25.4mm
What is DN?
DN is a specification unit commonly used in Chinese and European systems. It is also a specification for identifying pipes, valves, flanges, pipe fittings, and pumps, such as DN250.
DN refers to the nominal diameter of the pipe (also called the nominal diameter). Note: This is neither the outer diameter nor the inner diameter. It is the average of the outer diameter and the inner diameter, which is called the average inner diameter.
What is Φ?
Φ is a general unit, which refers to the outer diameter of pipes, elbows, round steel and other materials. It can also be said to be the diameter. For example, Φ609.6mm means that the outer diameter is 609.6mm.
Now that we have figured out what these three units represent, what is the connection between them?
First of all, "The meaning of "DN" is almost the same. Basically, it means nominal diameter, which indicates the size of this specification. Φ is a combination of the two.
For example: If a steel pipe is of DN600 specification, and the same steel pipe is marked with inches, it becomes 24". Is there any connection between the two?
Generally, inches are integers that are directly multiplied by 25 to equal DN, such as 1"*25=DN25, 2"*25=50, 4"*25=DN100, etc. Of course, there are also different ones, such as 3"*25=75, which can be rounded. DN80 also has some inches with semicolons or decimal points, such as 1/2" 3/4" 1-1/4" 1-1/2" 2-1/2" 3-1/2", etc. These cannot be like that Forget it, but the calculation is roughly the same. They are basically the prescribed values:
1/2"=DN15
3/4"=DN20
1-1/4"=DN32
1-1/2"=DN40
2-1/2"=DN65
3-1/2"=DN90
Expression of pipe diameter
1. Water and gas transportation steel pipes (galvanized or non-galvanized), cast iron pipes, plastic pipes and other pipes should be marked with the nominal diameter "DN" (such as DN15, DN50).
2. For seamless steel pipes, welded steel pipes (straight seam or spiral seam), copper pipes, stainless steel pipes and other pipes, the pipe diameter should be expressed as outer diameter × wall thickness (such as De108×4, De159×4.5, etc.); for seamless steel pipes or Non-ferrous metal pipes should be marked with "outer diameter × wall thickness". For example, Φ108×4, ф can be omitted.
3. For pipes such as reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, cylinder tile 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 in accordance with product standards.
5. When the design uses the nominal diameter DN to express the pipe diameter, there should be a comparison table between the nominal diameter DN and the corresponding product specifications.
Other Instructions
Nominal diameter, also known as average outer diameter. In order to unify the connection sizes of pipes and pipe fittings, DN is used to represent their nominal diameter (also called nominal diameter, nominal diameter).
Because the units are divided into metric (mm) and imperial (inch), there are the following ways of calling them.
1. Based on the metric system (mm), it is called DN (metric unit)
2. Based on the imperial system (inch), it is called NB (inch unit)
3. DN (nominal diameter) NB (nominal bore) OD (outside diameter)
4. [Example] Galvanized steel pipe DN50, sch 20 Galvanized steel pipe NB2”, sch 20
Note: The pipe number (Sch.) is not the wall thickness, but the wall thickness series. The actual wall thickness, the same pipe diameter, has different thicknesses in different pipe numbers.
The 1938 American National Standards Institute ANSIB36.10 (welded and seamless steel pipe) standard stipulates: The pipe number (Sch.) is the ratio of the design pressure to the allowable stress of the material at the design temperature multiplied by 1000, and rounded value after.
ISO metric dimension size is expressed in Da as the outer diameter of PVC pipes and ABS pipes. De represents the outer diameter of PP pipe and PE pipe.
For example: the metric mark (mm dimension size) of a plastic pipe with an outer diameter of 63mm is: Da63, which is for PVC pipes and ABS pipes.
New materials and plastic pipes are used, please note that it is in lowercase.
Dn is mainly used in cast iron pipes, galvanized steel pipes and steel-plastic composite pipes. In addition, Dn100 is equivalent to de110, and Dn150 is equivalent to the pipe diameter of de160.
