Minimum Flange Thickness and B16.5 Dimensions

[valvepuke]

I have a flange joint made up of a 4" Class 150 pipe flange connected to a pressure safety valve (PSV) inlet. The PSV comes standard with an as-cast Class 300 flange on its inlet. The manufacturer machines the inlet flange just enough to conform to the fit up requirements of the Class 150 flange(bolting and raised face). The result is that the PSV inlet flange is a bit larger on the OD and it is thicker. My customer is saying that this is not acceptable. B16.5 lists MINIMUM dimensions for flange thickness based on pressure class and also gives tolerances. I am not sure how to approach this. My PSV flange thickness is beyond the thickness tolerance shown in B16.5. I am not concerned with the pressure retention as I know that the Class 300 flange is heavier than the Class 150 requirements. Just want to reconcile this with my customer, based on B16.5. Can anyone help on this?

 

[pennpiper]

"My customer is saying that this is not acceptable."

1). Make darn sure that the two flanges will in fact mate.

2). Require the Customer explain why it is not acceptable.

The thicker flange and a slightly larger O.D. should not be an issue as long as the ID and the OD of the gasket surface is the same (Class 150) and the number of bolts and bolt circle match.

 

[valvepuke]

Thanks for the quick reply. The two flanges mate up fine in that the PSV flange is machined with the proper bolt holes, bolt circle, and raised face dimensions. My experience with cast components says that leaving heavier castings unmachined if it is not necessary is common. My client says that the heavier flange does not conform to the dimensions for a Class 150 flange per B16.5. From what I see in B16.5 the thickness stated is "minimum". There are tolerances given in B16.5 for the dimensions. Leaving the Class 300 flange unmachined on the OD and doing minimum machining on the face results in the OD and thickness exceeding the tolerances for these two dimensions. I guess I need more help interpreting the intent of B16.5.

 

[11echo]

Well "if" you want the flanges to match, you have two choices. 1.) Cut off the 150# flange and weld on a 300# ...spec break at the weld.
2.) Weld a 150# weld-neck flange to a 300# weld-neck (back to back) and bolt the PSV this assembly ...again spec break at the weld seam of the two flanges.
...Only time I've seen where different flange rating assembly was acceptable was mating up a 150# to a 125# or a 300# to a 250# ...ALL flat faced in both situations