ASME standard B16.5 (2003 Edition) provides dimensions and ratings in metric units (these are the primary tables, the US units are secondary in Annex F). But the bolt sizes remain specified in US units ("inches") rather than converted or transformed to metric size. For example, Table 10, page 78, for Class 300 flanges shows metric dimensions for drilling but shows bolt sizes (and holes) as inches.

For vessels constructed in Europe, or intended for installation in Europe, would the B16.5 flanges be installed with bolts in "inch" sizes? or metric? I cannot imagine the former situation but the latter leads to some more conversion problems.

For example, a 24" Class 300 flange indicates 1-1/2" bolt (1.5" bolt). This is about 38.1 mm but there is no similar size metric bolt (eg: there is no 38 mm bolt by my study).

What is customary please?

Using other fasteners than those specified in B16.5 renders the use of a flange not allowed to use under UG-44, so it must follow Appendix 2. But it is quite likely that a B16.5 flange will not meet all applicable requirements. Believe me, it's much easier to find inch studs.

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Konrad Anikiel

Thank you Konrad. I hope that finding those "inch" bolts in EU is easier than finding Whitworth screws for my old bicycle here in the US.

Tom,
Sure, they can be bought off the shelf. Usually more expensive, sometimes hard to find (When you want, say UNF 2" with heavy hex head, particularly long one)- but people understand that they go with B16.5 flanges so there is a market for them.

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Konrad Anikiel