Test media for thermal relief valve

[PAN]

Can we use nitrogen as test media for thermal relief valve (liquid service) ? One supplier informs that only water shall be used for testing. However, I understand that nitrogen can also be used for tighness test and pop test. Please comment.

 

[abeltio]

The viscosity of water, is several times higher than that of N2.
A few years ago I had a similar situation with a relief valve for use with lube oil... we had an N2 bottle and all the gear so ahead we went with the testing...the valves seemed to be completely out of spec (started to discharge at a significant lower pressure).
Went back to land, grrr!! (it was on an offshore rig) got a manual pump with oil similar to the actual working fluid and: lo and behold!!! the valves were right on the money.
HTH.
On the same token, when testing a valve that must be tight for H2 service (the smallest molecule of all), you cannot use air or N2, it will seem tight with those fluids but it may leak like hell with H2.
Bottom line: do what the supplier says.
HTH
Saludos.
a.

 

[valvetech]

Abeltio is right look at the attached ANSI test Standards for valve shut off. They are very specific as to what the test media is. By changing the test media you change the shutoff of the valve as Abeltio pointed out.
The manufacturer of the valve should be able to assist you if you need to test the valve in how it is tested.

ANSI CLASS Maximum Seat Leakage Test Conditions

Class III 0.1% of rated valve capacity Air or water @ 50 - 125 F. 45 - 60 psig or Maximum operating differential pressure whichever is less


Class IV 0.01% of rated valve capacity Air or water @ 50 - 125 F. 45 - 60 psig or Maximum operating differential pressure whichever is less


Class VI 1" Port Diameter
0.15 ml per minute or 1 bubble per minute
Air or Nitrogen @ 50 - 125 F 50 psig or Maximum operating differential pressure whichever is less

 

[packdad]

In my inexperienced opinion, I would think that, if all you want to do is check the set (popping) pressure and leakage, that you could substitute nitrogen for liquid since viscosity, momentum, etc., won't become a factor until after the valve has lifted. However, I would agree that you should adhere to the manufacturer's recommendations.

 

Liquid valves should be tested on a liquid. There will be a difference in opening point if tested on a gas. If these are ASME Code valves then it is required that liquid service valves be tested on liquid and gas valves tested using gas. In addition, the definition of the opening point varies with the manufacturer. Some manufacturers define opening as first steady stream while others may define it as first heavy flow. Also, ANSI/API RP527 is the standard for seat tightness for pressure relief valves. The pressure for seat tightness is typically 90% of the set pressure but could be lower if so specified by the manufacturer. The manufactures instructions should be followed carefully when testing pressure relief valves.

 

[PAN]

Dear Sirs,
I heard that we can test both liquid and gas application with air according to DIN Standard. However, we must test the safety relief valve for liquid application with water according to API/ASME. Please comment about the difference.

 

I'm not familiar with the DIN Standard requirements. However, there can be a significant difference in results between testing on a gas and with water. The manufacturer's instructions should be followed to insure accurate settings.