ASME B16.5 Inch and Metric Flange Interchangeability and Raised Faces

[beh188]

I read in ASME B16.5 that the inch and metric flange dimensions are to be held as separate standards and should not be interchanged. Does this mean that an inch flange and a metric flange should not be mated together in a joint? From a quick scan it looks like the dimensions are almost equivalent.

Also, the raised face dimensions given in the standard are different for metric and inch. For a class 150 flange the raised face is 2mm or (0.06 in.). It seems that many flanges are commercially produced to metric dimensions but state a 1.6mm raised face, which is approximately 0.06 inches per the inch standard. What gives?

 

[gr2vessels]

There is no significant difference between the same type/size metric and imperial flanges. You can connect them together and you won't notice the difference. The manufacturing tolerances are larger than the dimensional differences from catalogue / standard.
The cautionary note in the standard refers to the practice of segregating the two systems, since they don't overlap always correctly, thus you can induce design errors.
Cheers,
gr2vessels