Outer diameter of pipeline corresponding to DN250 flange
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For flanges of PN250 specified in the GB/T 9115 standard, the outer diameter of the welded end for flanges with a DN of 80 or higher differs from the outer diameter of pipes as defined by that standard. So which standard governs this outer diameter?
Is it a problem with Series A and Series B? For example, for DN100, there are two outer diameters: 108 and 114.
This outer diameter refers to the outer diameter at the junction where the flange meets the steel pipe; it does not necessarily have to be exactly the same as the outer diameter of the seamless steel pipe, and that’s completely fine
The pipe is chosen according to the requirements for pipes, and the flange is selected based on its own specifications; it’s not necessary nor appropriate for the outer diameter of the pipe to be exactly the same as that of the flange
There are three series for the outer diameter of steel pipes connected to flanges: the DN100Ⅰa series has a diameter of 114.3 (the Ⅰa series corresponds to Series A of flanges); the Ⅰb series has a diameter of 114, with this value being the rounded version of that of the Ⅰa series. Both of these series belong to the imperial pipe system. The II series has a diameter of 108 (the II series corresponds to Series B of flanges)
There are three series for the outer diameter of steel pipes connected to flanges: the DN100Ⅰa series has a diameter of 114.3 (the Ⅰa series corresponds to Series A of flanges); the Ⅰb series has a diameter of 114, with this value being the rounded version of that of the Ⅰa series. Both of these series belong to imperial-sized pipes. The II series has a diameter of 108 (the II series corresponds to Series B of flanges), and it refers to metric-sized pipes
It depends on which series the outer diameter of the steel pipe you are using belongs to
There are issues with this; for example, in the case of DN100 flanges, the weld sizes for Series A and Series B flanges are different. The flange must match the outer diameter of the pipe it is connected to, otherwise welding will not be effective and serious problems will arise
In fact, for pressures below PN160 (including PN160), the outer diameter of steel pipes is still divided into Series I and Series II, and these diameters are all quite common sizes. However, for steel pipes with PN250, PN320, and PN400 ratings, there is only one value provided for the outer diameter. I guess the reason might be as follows: DN250 generally refers to the nominal size of the pipe, and this value of 250 is close to – or may be greater than or smaller than – the inner diameter of the steel pipe. For example, in the case of DN250 PN160, according to the data sheet, the outer diameter of the steel pipe is 273, the wall thickness is 20, and the inner diameter is 233. DN250 PN100, outer diameter of the steel pipe is 273, wall thickness is 10, inner diameter is 253. The data is more or less like this. With a fixed outer diameter, the higher the pipeline pressure, the thicker the wall thickness and the smaller the inner diameter. When the inner diameter becomes small enough, it may affect the flow rate of the pipeline. In the table provided by the original poster, for DN250 PN250, the outer diameter of the steel pipe is 298.5, the wall thickness is 32, and the inner diameter is 234.5. This inner diameter is almost the same as that of PN160. Let’s take the DN80 case for comparison again: under PN160 conditions, the outer diameter of the steel pipe is 89, the wall thickness is 6.3, and the inner diameter is 76.4. Under PN250 conditions: the outer diameter of the steel pipe is 101.6, the wall thickness is 11, and the inner diameter is 79.6.
The last edit to this post was made by Baoji ChaoSheng Titanium Industry on 2019-5-8 at 17:18. You mentioned this; what standard does the outer diameter follow? The table you sent is the standard itself. ;P;P The data in the table has all been calculated!