Hi guys,
I’m trying to find out something. Currently, I’m making a pipe spec, with a corrosion allowance of 1 mm and a(n extra) mechanical allowance of 0,5 mm.
I use B31.3 for the design of the spec.
Usually, the flange rating is lower than pipe rating (even with a mechanical allowance of 0.5mm), hence the flange makes the spec.
However, now with a total allowance of 0.5 + 1 = 1.5 mm., the pipe (or fitting, however one may see it) rates the spec, the flange usually is stronger.
Of course this depends on what schedule is used for which pound class flange.
My question now is; if you set a total allowance of 1.5 mm (this is allowance is called ‘c’ in B31.3, para 304.1.1), how is the flange then rated?
Are you allowed to keep/use the standard B16.5 rating?
I’m especially/specifically interested in weld neck raised face ASME B16.5 flanges, a typical flange we use.
My feeling is that (but I’m not sure though) that as long as the flange is rated lower than the pipe/fitting, your good, since (in the case of Weld Neck Raised Flanges) the smallest part of the flange, where the wall thickness is the bevel at the weld neck, which is of the same wall thickness as the pipe/fitting …
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