ASME B16.34 valve pressure rating/ hydrostatic pressure

[dredre]

Hello all,

I have a 900lb valve that has a pressure/temp rating (mawp) in the ASME B16.34 that is below the design pressure of the sytem that it is installed in. Now I know normally the mawp > design pressure. The valve gets a hydrostatic shell test with the disc off its seat above design pressure. Is there anything in the ASME code that says if you hydro up to this point than it can take more pressure than what is shown in the pressure/temp rating for the class of valve. Or is there another way to tackle this problem?

Appreciate any suggestions.

 

[dtn6770]

The valve should be replaced with one rated for the service.

About the only option is to re-visit the system's design pressure to see if what it's based on is realistic. Basically, see if the system can be de-rated.

 

[JLSeagull]

Am I missing something?

For B31.3 the hydrostatic testing of the piping system is done at 1.5 times the design pressure. In B16.34, 2.5.3 valves may be exposed to the hydrotest pressure if open. Thus, the hydrostatic pressure would exceed the pressure temperature rating of the valve and flanges. This is normal. Cautionary notes exist if the valve were to be closed.

 

[BigInch]

If you test a valve at a higher hydrotest pressure than normal it will not upwardly rerate the valve. Example. testing a 600# valve to a 900# test pressure would not make it a 900# valve, it would probably make it a 600# valve ready to burst on any excuse.

As dtn says, replace the valve with a pressure and temperature rating at least equal to your system design pressure and temperature or derate the design P&T of your piping.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com