Rerate Valve to Higher Pressure
I want to operate a 900# ANSI valve up to say 2500 psi. This valve is normally limited to 2160 psi case pressure. The valve is WxW in both through conduit and horizontal swing check configurations.
If it is rated ANSI 900, then it is more than likely cast to the wall thicknesses listed in B16.34 for class 900. Your only chance to upgrade it is if it has weld ends, then you can radiograph the body and when the body is found not to be flawed, you could classify it 900 Special. That gives you a little more pressure capability.
If the the issue is worth of, I would suggest a Finite Elements Method (FEM) analysis by means of a computer simulation program, which would verify if the gate valve can withstand the specific pressure (and give an estimation of the relevant safety margin). Probably the valve Manufacturer itself can perform that...
In alternative, there are standards that give design verification formulas which can be filled with the specific input data of the case, such as the German DIN 3840 (even if it is rather elaborated and laborious: try to compare it, for example, with Annex F of ASME B16.34...!).
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