Outer diameter of small-diameter pipes and fittings, as well as flange standards

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This post was last edited by meinijiuok on 2018-9-28 at 10:21. Dear colleagues: 1. In HG/T20553-2011, the minimum nominal diameter for pipes in Series II is DN10. If pipes with DN6 or DN8 diameters are to be used, what should their outer diameter be? Although the standard includes pipes of DN6 and DN8, they are not of Series II but rather of Series I. However, for pipes larger than DN10, I choose the II series; if DN6 or DN8 must be used, then only the I series is an option. Then there will be a mixing of Series I and II. This is not conducive to design and engineering installation. Do any of you have the outer diameter standards for small pipes such as DN6 and DN8 in the II series? 2. In HG20592, the minimum standard for flanges is also DN10; if DN6 or DN8 pipes are used, must threaded connections be employed? Additionally: I am not very familiar with threaded connections. If threaded connections are used, will they be able to meet the sealing requirements at 20 MPa? Are there also standards for II series pipes with DN6 and DN8 in the threaded connection standards? 3. In GB/T14383, the standards for socket-welded pipe fittings and threaded pipe fittings include data for small pipes such as DN6 and DN8 in Series I. However, regarding the fittings of Series II, there is a statement stating that when using pipes from Series II, their socket and flow aperture sizes should be determined in accordance with the dimensions of Series II pipes. The question is: There are no sizes for small-diameter pipes such as DN6 and DN8 in the II series of pipes. Then, how should the fittings be designed according to the sizes of the II series pipes? ? ? ? ? I hope fellow sailors can answer these three questions!