The relationship between American, European, and Chinese standards regarding steel pipe diameters
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I’ve looked up a lot of information, and it seems that the diameter series are rather confusing; I hope someone experienced can help explain them in detail.
For HG20553, you can check the outer diameters of the Ia series and the Ib series; these are part of the American standard series. The Ib series features outer diameters that have been rounded off. This specification corresponds to the 20615 American standard flange or the A series flanges of the European standard 20592. The outer diameters of the II series were commonly used in China in the past, and they correspond to the B series flanges of the European standard 20592. Actually, you don’t need to worry about whether to use American or European standard pipes; as long as your pipes, flanges, and fittings all belong to the same series, that’s sufficient.
What I mean is the relationship between GB and American/European standards, not the HG standards for use in the chemical industry
National standards refer to European and American standards. The standard on the 2nd floor can be taken a look at.
GB17395 also uses a similar classification method, dividing the outer diameter of pipes into different series; you can take a look at the preface sections of these standards.