Pipe specifications are commonly indicated using various methods such as DN, inch, D, Φ, De, dn, and d. This article introduces the basic specifications and typical application scenarios of pipes.
Meaning of various expressions
DN is an abbreviation for Nominal Diameter, representing the nominal diameter of a pipe. It is the standardized diameter of the pipe.
DN is neither the outer diameter nor the inner diameter, but a nominal diameter that approximates the actual size of the pipe. It is mainly used in pipeline engineering design and construction to facilitate the selection and matching of pipes and fittings.
For example, a pipe with a nominal diameter of DN100 generally corresponds to an outer diameter of 108 mm, while its inner diameter varies depending on the wall thickness.
Inch is an imperial unit of length. In pipe specifications, inches are commonly used to represent the nominal diameter of pipes, such as 1/2”, 3/4”, 1”, etc., which correspond to DN respectively.
1 inch = 25.4 mm, therefore 1 inch (1”) corresponds to DN25. In the imperial system, 1 inch equals 8 points, 1/2” is 4 points, corresponding to DN15 (commonly known as 4-point pipe); 3/4” is 6 points, corresponding to DN20 (commonly known as 6-point pipe). D generally represents the outer diameter of a pipe. In practical applications, it is usually used together with the wall thickness to indicate pipe specifications, such as D108×4, which indicates a pipe with an outer diameter of 108 mm and a wall thickness of 4 mm.
Φ is commonly used in engineering to represent the diameter of a common circle. Similar to D, it is used to represent the outer diameter of pipes, often for seamless steel pipes or non-ferrous metal pipes.
It is generally labeled in the form of “outer diameter × wall thickness,” for example, Φ108 x 4, indicating a pipe with an outer diameter of 108 mm and a wall thickness of 4 mm.
De is an abbreviation for External Diameter, mainly used for the nominal outer diameter of building water supply and drainage plastic pipes, with the unit being millimeters. It is generally labeled in the form of “outer diameter × wall thickness.” For example, De25×3 indicates a pipe with an outer diameter of 25 mm and a wall thickness of 3 mm.
dn is generally used to represent the nominal outer diameter of building water supply and drainage plastic pipes, similar to De, but dn is more commonly used in European standards or ISO standards. For example, DN50 indicates a plastic pipe with a nominal outer diameter of 50 mm.
The ‘d’ is typically used to indicate the inner diameter of pipes such as concrete pipes and clay pipes; it represents the internal diameter of the concrete pipe. For example, d300 indicates a concrete pipe with an inner diameter of 300 mm.
Differences between various representation methods
Scope of application and standard system
DN is a widely used designation in Chinese and many international standards, applicable to various pipe materials such as steel pipes, cast iron pipes, and plastic pipes, and used in multiple engineering fields including water supply and drainage, HVAC, and gas supply.
D and Φ are commonly used in domestic and international standards related to metal pipes, especially in fields such as machinery manufacturing and petrochemicals where high precision and strength of pipe dimensions are required.
d is mainly used in standards related to some traditional pipe materials where the inner diameter is the primary design parameter, such as concrete pipes and clay pipes.
De and dn are commonly found in standards related to plastic pipes. Different countries or regions may choose to use De or dn depending on their standard system. For example, De is commonly used in Chinese standards for building water supply and drainage plastic pipes, while dn is commonly used in European standards.
inch is mainly used in countries and regions that adopt imperial standards, as well as in some projects that have introduced technologies or equipment that are in line with international standards.
Indicates emphasis
DN focuses on standardizing pipe and fitting specifications from a nominal size perspective, facilitating selection and matching during design, manufacturing, and installation.
D, Φ, De, and dn emphasize the actual outer diameter of the pipe, providing more direct guidance for dimensional control during pipe manufacturing and installation.
d emphasizes the inner diameter of the pipe, which is crucial for pipe materials where parameters such as flow rate and velocity need to be determined based on the inner diameter.
inch is an imperial unit of measurement, allowing for better compatibility with equipment and fittings using other imperial units within a system that adopts the imperial standard.
Final Thought
When selecting a model, first determine the material (metal/plastic/concrete), then match the standard specifications (DN/De/d) based on pressure and flow rate, and finally confirm the specific dimensions in conjunction with the connection method and industry standards.
