∅ the difference from DN

If DN is not shown, it should be indicated in the schedule; the inner diameter is specified there. In the drawings, only φ is used to denote the inner or outer diameter of circular components.

DN refers to the nominal diameter, which is neither the outer diameter nor the inner diameter. It is a rounded method of specifying cylinder dimensions; it can only be considered an “approximate inner diameter”. Each DN value corresponds to a fixed outer diameter value, which can be found in the standards for flanges and pipe fittings.

It is specified in the regulations for preparing chemical engineering drawings

This post was last edited by Guxi Village on 2018-10-31 at 10:51. The same thing is expressed in different ways in various files. In technical documents, DN or Φ can be used; DN refers to the nominal diameter, while Φ denotes the actual diameter. However, when marking on drawings, only Φ is used to represent the diameter. Next, the person on the 3rd floor said that for each nominal diameter of DN, there is one corresponding diameter (outer or inner diameter), but there are many different wall thicknesses that correspond to it. Therefore, when DN corresponds to the inner diameter, different wall thicknesses result in different outer diameters. So when designing, special attention needs to be paid to the areas that need to be matched :)

This post was last edited by FishCan’tDesign on 2018-10-31 at 11:37. For example, if the inner diameter of a tank is 2000 and the wall thickness is 8, should it be marked as Φ2000 or Φ2016 on the drawings? It is marked as DN2000x8 in the schedule; can it be marked as DN2016 instead? If DN is not shown, it should be indicated in the schedule; the inner diameter is specified there. In the drawings, only φ is used to denote the inner or outer diameter of circular components. According to this statement, Φ2000 indicates the inner diameter; is DN the only value that can be used in the specification sheet?

This post was last edited by FishCan’tDesign on 2018-10-31 at 11:50. The first image shows the inner diameter, while the second shows the outer diameter. But why are they distinguished in this way? I don’t quite understand it, because there’s an ‘x’ on the first one, in the wall thickness section, so it indicates the inner diameter. Can we then also remove the wall thickness and simply indicate ∅1210?

This is the difference and definition between pipes and cylinders; only when there is a surname and a given name does it constitute a full name

As long as the markings are correct and in place, there’s no need to worry that those who receive the drawings won’t be able to understand them. If I don’t understand, I’ll come to you; you have control over the conversation. The nominal diameter of pressure vessels can refer to GB/T9019, but other diameter series are not restricted. Both an outer diameter of 159 and an outer diameter of 168 correspond to DN150; for relevant details, refer to the general provisions in HG/T20592. Both standard DN values are followed by integers; in simple terms, this makes them “easy to remember”! There are DN values that are not integers; for example, the 2001 version of GB/T9019, but it has been revoked. I haven’t checked other standards in detail, but I believe these are all remnants of the past. In my opinion, DN values should ultimately be standardized to be integers.

Whether it is marked as 2000 or 2016, the wall thickness of 8 must be indicated. Anyone who gets the drawings will instinctively assume that the inner diameter is 2000; there’s no confusion possible here, as no one would use complicated numbers to calculate values such as the volume of the tank. There are two benchmarks in the design: based on the inner diameter and based on the outer diameter. Based on the inner diameter, the wall thickness is adjusted to meet the requirements, while the outer diameter changes ； Based on the outer diameter, the wall thickness is adjusted to meet the requirements, while the outer diameter remains unchanged. Taking an inner diameter of 2000 as an example, whether the wall thickness is 10 (resulting in an outer diameter of 2020) or 40 (resulting in an outer diameter of 2080), there is only one specification available, namely DN2000. The change in design wall thickness due to variations in parameters should not lead to the emergence of specifications such as DN2016/2020/2024/2036. Taking an outer diameter of 159 as an example, it is DN150 regardless of the wall thickness.