Where does the nominal diameter of the pipe come from?
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As we all know, the nominal diameter is neither the outer diameter nor the inner diameter. Since it is nothing, why was it done like this in the first place? Can't we just use the outer diameter or inner diameter as the nominal diameter? Or when the outer diameter of the pipe is manufactured, wouldn't it be okay to make the outer diameter as large as the nominal diameter?
The nominal diameter is also called the nominal diameter. It is a quantity related to the mechanical strength of the pipeline. It is just a scale, so it cannot be used for direct calculation. It is a benchmark for unifying pipe fittings, valves, etc. on the pipeline. It is also a benchmark used by manufacturers. Based on a nominal diameter, pipes with different wall thicknesses can be produced.
The nominal diameter simplifies the specification of pipe diameters, unifies the connection dimensions of pipe equipment components, and standardizes the classification of pipe diameters. The nominal diameter represents the nominal inner diameter of pipes, pipe fittings and other pipe equipment components. For pipe flanges with the same standard, nominal pressure and nominal diameter, they have the same connection dimensions. Nominal pressure The nominal pressure of a pipeline component refers to the design given pressure related to its mechanical strength. It generally represents the maximum allowable working pressure of the pipeline component at the specified temperature. To sum it up, haha
Take a look at the standard GB/T1047-2005 to deepen your understanding.
None of the people mentioned above got to the point. What I meant was the reason why the people who set the standards did so in the first place. What I asked was why, not what.
The host is worrying too much! ! ! This is very confusing
In fact, the definition of nominal diameter given on the third floor already tells you the reason. There are several series of steel pipe outer diameters (standards vary from country to country). If we name the outer diameter, take the DN15 pipe as an example. The outer diameter is 21.35 in the American standard, 21.7 in the Japanese standard, 21.3 in the German standard, 18 in the metric system, 22 in the metric system, etc. You can name as many types as you want. Similarly, naming based on the inner diameter is inappropriate. Pipes with the same outer diameter and the same DN have different inner diameters with different pressure levels. Therefore, in order to unify the differences between national standards, the concept of nominal diameter was introduced.
Friends on the 7th floor, I have a little question: As you said, pipes under different standards will have different outer diameters, such as metric 18 and German standard 21.3, but both are DN15 pipes. Can I understand that during design and construction, pipes with metric 18 and German standard 21.3 are allowed to be directly connected (or welded) together. Note: I'm not a piping designer, so please forgive me if I ask a very unprofessional question.
This post was last edited by w9002 on 2015-3-15 19:42 My understanding of pipelines is this: The inner diameter and wall thickness are very important. When piping in a process, first perform process calculations to determine the inner diameter, determine the material according to the material properties, and determine the wall thickness according to the actual working pressure. In this way, the outer diameter of the pipe is determined. If I first consulted the manual on metric pipes, I selected the metric DN15, which is a pipe with an outer diameter of 18mm. If the German standard DN15 is selected in the subsequent design, there will be two different sizes of pipes (different outer and inner diameters) in the same system. I think this choice is inappropriate. I don't know if my understanding is correct.