Valve Flange Face Parallelism Standard 1

[marklobo]

Does anyone know of a published standard for straight-pattern valve body flange face parallelism? When flanges are welded to a butt weld glove valve body, there is no assurance of inherent parallelism as there would be if the facings were machined on a cast or forged body.

I've been to the piping forum to find out if there is a standard for perpendicularity of flange faces to pipe, which of course would work with that of a valve to assure that excess strain is not induced when the flanges are mated. Nothing there so far, though weld-neck flanges are butt-welded to pipe "all the time", and I can't imagine there is no standard. Don't weldments ever get rejected for being out-of-square? If they do, why?

 

[rneill]

I would apply the same tolerance criteria as in Code for normal flange alignment tolerance. If you are mating up two flange then the allowable misalignment should be the same whether welded to pipe or if one of them is on a valve. Actually, I'd think there would be a tougher standard for the valve but if not then I'd default to your piping code.

 

[marklobo]

Thank you, rneill. You raise an interesting issue. To borrow from NORSOK L-CR-004, a 2" to 10" flange face must be square with the pipe it is welded to within 1.5 mm. If the valve body was considered a very short piece of pipe, that would allow paralellism to be 3 mm. That's huge.

What "Code"? I'm very familiar with ASME B16.34 and somewhat familiar with B&PV and B31.3 and have yet to find a standard there. A specific reference would be a very "valuable post"

I'm wondering if parallelism between faces is simply established by face-to-face or end-to-end tolerance, typically +/- .06"(B16.10, API 6A) for valves to 10" size. For a 2" Class 1500 RF flanged valve, that would permit the angle to be 1.9 degrees, which may cause the customer to quiz the manufacturer.

 

[rneill]

How about Para 335 of B31.3 Item (c) "before bolting up, flange faces shall be aligned to the design plane within 1 mm in 200 mm measured across any diameter; flange bolt holes shall be aligned within 3 mm maximum offset".

If I have a perfectly straight and true piping installation and the flanges on the valve were such that it could not be dropped into a square and true set of piping flanges, within the tolerance specified in B31.3, I would reject it.