Pipe diameter
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I study engineering; these days I’ve been working with pipes and valves. People usually talk about the nominal diameter, but the concept is quite complicated – it’s neither the inner diameter nor the outer diameter. I have a humble question: if we use an approximate value, then when connecting pipes, installing valves or gaskets, won’t there be any errors? Won’t it be possible to install them incorrectly? Why was the concept of nominal diameter introduced? How can the inner and outer diameters be indicated without being explicit? \ud83d\ude0a\ud83d\ude0a\ud83d\ude0a\ud83d\ude0a
This post was last edited by “Ten Plus One is Greater Than Eleven” on July 12, 2018, at 07:42. I’m really confused here. “Nominal diameter” is a commonly used term; for valves, flanges, gaskets, etc., we refer to their nominal diameter as DN value. For pipes and similar items, the symbol φ is usually used to indicate the outer diameter, which is equal to the inner diameter plus the thickness of the pipe wall. There’s no need to overthink this; just understanding it is enough. In practice, use whichever term or notation seems more appropriate and convenient； Another example: for valves, DN80 means φ89 – it is a valve with a diameter of DN80, and the inner diameter of the gasket is also DN80; there is no deviation. When ordering the gasket, if you specify φ89, the warehouse staff will usually ask to measure the outer diameter. This is also part of my work experience; I hope it can help you. Please correct me if there are any mistakes
Definition of nominal diameter: DN refers to the nominal diameter, which is the standard size used for various pipes and piping fittings. Tubes and piping fittings of the same nominal diameter can be connected to each other, offering interchangeability. It is not the actual outer or inner diameter of the pipe, although its value is relatively close to or equal to the pipe’s inner diameter. However, it is not exactly equal to the difference between the outer diameter of the steel pipe and twice the wall thickness; this is how GB-T1047-1995 defines it. Function of nominal diameter: To standardize the connection dimensions of pipes and fittings, the nominal diameter (also known as nominal bore or nominal size) is used. For example, welded steel pipes can be classified by thickness into thin-walled pipes, ordinary pipes, and thick-walled pipes. Its nominal diameter is neither the outer diameter nor the inner diameter, but rather a nominal size that is close to the inner diameter of ordinary steel pipes. For each nominal diameter, there is a corresponding outer diameter, while the inner diameter value varies depending on the thickness. The nominal diameter can be expressed in metric mm or imperial inches. Pipeline fittings are also indicated by nominal diameter, with the same meaning as welded pipes.