【Y2025】Various ways of denoting pipe diameters such as DN, inch, D, Φ, De, dn, d, and their application scenarios
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This post was last edited by zhoudingshengs on 2025-4-21 09:43. The attachment contains information on various ways of denoting pipe diameters such as DN, inch, D, Φ, De, dn, d, along with the situations in which they are used.
This post was last edited by zhoudingshengs on 2025-4-21 09:25. The following replies are for reference only: DN–nominal diameter of polyethylene (PVC) pipes, cast iron pipes, steel-plastic composite pipes, and galvanized steel pipes.
De-- Outer diameter of PPR, PE pipes, and polypropylene pipes.
d -- Nominal diameter of the concrete pipe.
ф-- the nominal diameter of the seamless steel pipe; its specifications are given as, for example, ф100: 108 X 4.
DN refers to the nominal diameter of a pipe – it is neither the outer diameter nor the inner diameter (it is likely related to imperial units from the early days of pipeline engineering, and is commonly used to describe galvanized steel pipes).
De mainly refers to the outer diameter of the pipe (it is generally denoted by De, and it must always be specified in the form of outer diameter X wall thickness). It is mainly used to describe: seamless steel pipes, PVC and other plastic pipes, as well as other pipe types for which the wall thickness needs to be specified.
We are *accustomed to using DN to denote welded steel pipes; we rarely use De to denote pipes when the wall thickness is not relevant； But labeling plastic pipes is another matter altogether ； It still relates to industry conventions; in the actual construction process, the terms 20, 25, 32, etc., which are used informally, refer to De rather than DN.
1. Pipe materials such as water gas transmission steel pipes (galvanized or ungalvanized), cast iron pipes, etc., should have their diameter indicated by the nominal diameter DN (e.g., DN15, DN50)； 2. For pipes such as seamless steel pipes, welded steel pipes (with straight or spiral seams), copper pipes, and stainless steel pipes, the diameter should be indicated as outer diameter D × wall thickness (e.g., 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 (e.g., d230, d380, etc.) ； 4. For plastic pipes, the pipe diameter should be indicated in accordance with the methods specified in the product standards ； 5. When the pipe diameter is specified using the nominal diameter DN in the design, there should be a table correlating the nominal diameter DN with the corresponding product specifications.
The specifications for rigid polyvinyl chloride pipes used for building drainage are expressed as de (nominal outer diameter) × e (nominal wall thickness) (GB 5836.1-92).
Inches (") are a commonly used unit of measurement in the American system, for items such as steel pipes, valves, flanges, elbows, pumps, tees, etc.; for example, the specification might be 10". The inch (abbreviated as in.) originally meant thumb in Dutch; one inch is the length of one thumb. Of course, the length of people’s thumbs also varies. In the 14th century, King Edward II introduced the \"Standard Legal Inch\". It is specified that the length of one inch is equal to the length of a row formed by arranging three of the largest barley grains selected from the middle of a barley ear in sequence. Generally, 1\" = 2.54 cm = 25.4 mm