When valves are pressure tested by the manufacturer, they're pretty much just testing the body of the valve, with the valve open. They may do a leak test on the valve seats up to the rated pressure of the valve, but not up to hydrotest pressure.
It's advisable to use screwed plugs, blind flanges, or weld caps where you can. I would even go as far as to say that you can remove valves from the test section and replace them after the test.
I am guessing you want to basically close the valve and pressure up against it to preform your test?
Certain types of valves, soft seated ball valves in particular, could be damaged by doing this.
Using a blind flange or some other expendable "plug" is the safest course of action. If that is just not an option, contact the valve manufacturer, and find out if their valve's seating/sealing mechanisim will handle the test pressure required. For certain types of valves, like certain plug valves, or metal seated valves, it may not really be a problem.
You should also take into consideration that the manufacturer will very likely void the warranty if your test pressure is above 1.1 times the valve's room temp MOP. So if you do damage the valve, you may very likely be replacing it out of pocket.
That's right,I'm testing against the closed valve. In this case the valve is the limit between two different piping classes. The valve is on the CL 300 side, the test system on the CL 150. The test pressure is lower than the CL 150 flange rating so given the difference between the two classes ratings I think the closed valves will be able to pass the test. I'm not sure for how long the test pressure could be maintained.
Where can I get the MAWP of the valve from?
Thank you very much, your answers are very helpful.
ANSI working pressures for most types of valves are established in ASME B16.34. The spec is really meant to provide a minimum pressure temperature curve for the valve bodies, based on the ability of various materials to handle temperature fluctuation.
For your purposes, you should only consider the pressure rating shown @ 100 deg. F. At a very minimum, the valve seats will be able to handle that pressure. For any other temperature, you should consult the manufacturer and ask for a pressure temperature chart.
Or, if you have direct access to the valve, it should be tagged or marked with the 100 deg. F MOP.
