Rerate Valve to Higher Pressure

[roderick]

What would the steps be, or is it possible to perform an analysis of existing valves to qualify it to operate at a 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.

 

[Ashereng]

A105 Carbon Steel, ANSI 900#, at -20 = 100 °F, is only rated to 2220 psig.

I don't think you can use a 900# valve at 2500 psig. I would think you need to go to 1500#.

 

[JimCasey]

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.

 

[abscott]

roderick,
In many valve styles the ANSI Class 900 & 1500 are not sold in large volumes and manufacturers make both the CL900 and CL1500 from a CL1500 casting. If you are not a manufacturer I would check with your valve supplier.

I agree with Jim Casey, you can perform the additional NDE required to qualify the valve for the Special Class rating.

There is one other method. The required wall thicknesses list in ANSI B16.34 are the absolute minimum and are used for inspection purposes. Valve manufacturers and foundries add considerable extra wall thickness for manufacturing. If you can determine how much extra wall thickness you have, you can re-rate the valve using the method described in sections 2.1.4 and 6.1.4 of ANSI B16.34.

I would rely on your valve supplier for help. You are just over the Class limit and most manufacturers are able to rerate the valve and provide the documentation.
Hope this helps,
ABScott

 

[Ashereng]

abscott,

The increase in this case is an additional 280 psi.
Would this still fall under "just over the limit"?

 

[unclesyd]

One thing that you need to do is make sure that no one interprets the valve's special rating for 2500 psig as a Class 2500 valve.

 

[roderick]

Thank you to everyone that has commented so far.
I should point out that the valves to be rerated are 30" in size. The gate valve body is of the fabricate body design.

 

[unclesyd]

A fabricated design complicates the rerating. I believe that everyone was thinking of a monobody valve, casting.

Can you comeback with the make and model with a little better description of the valve body?

 

[NGiLuzzu]

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 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...!).


Hope this helps, 'NGL