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PSV Set Point Tolerance ASME SEC 1

PSV Set Point Tolerance ASME SEC 1

(OP)
Hi All,

Per ASME SEC 1 code, set pressure tolerance for a PSV setting between 301 PSI to 1000 PSI is +/- 10 PSI.
For a Consolidated model# 2755B-2-X1-F1-WSC-RL PSV (Flange), do we need to follow ASME SEC 1 or SEC VIII code if same is being tested using air as the medium at our local valve repair shop?
It’s understood, if we are to follow SEC VIII during shop testing, the allowable tolerance would be much higher than SEC 1.
The valve repair shop is not equipped for testing safety valves with steam(non-ASME certified),however, when installed on site, they verify set pressure using the EVT equipment and make the necessary adjustments per ASME code SEC 1.
Is there a correlation calculation for shop testing of 2700 safety valves like 1900 PRVs?

Thank you kindly and appreciate your feedback.


RE: PSV Set Point Tolerance ASME SEC 1

Hi. Basically you have a ASME I section installation so you should test to that specification requirements. One of the reasons for testing on live steam is that the valve is actually "hot" hence no temperature correction is necessary - one of the reasons also these valves are open bonnet. Since you will be testing using verification device on the live application, I would follow the tighter ASME VIII requirements at the shop since you should be closer to target set pressure. HOWEVER, since you will not be getting a flow of sorts with the test pressure,you run the risk of seat damage due to effectively introducing rapid opening and closing when reaching set point. You best talk to the manufacturer on this since at least you should exercise and observe ring settings for bench testing which would be different to installed settings.

Correlation testing on air Vs steam (or ait Vs liquid), very often discussed. Does not really exist. Only in the wisdom of experienced site personnel testing same over many years. Not recommended, but unavoidable in a lot of cases.

Per ISO, only the term Safety Valve is used regardless of application or design.

RE: PSV Set Point Tolerance ASME SEC 1

Hi Avalveman. This is my first time posting, so bear with me if the topic was discussed somewhere else (I did search and came upon some related but incomplete explanations!).

Regarding correlation factors of air vs steam and air vs liquid. You say that it does not really exist. Our regulator has queried our correlation factors for bench testing our SVs, since ASME OM code requires that the SV be tested on the system medium and temperature otherwise correlation factors must be provided. The correlation factors we have were provided by the various valve OEMs, however it was mostly temperature related, not test medium. Why do you say it does not really exist when ASME OM requires it?

Also, is test medium correlation even required? The point at which the valve opens should not be affected by a difference in medium (temperature of course, due to variance in valve disc surface, etc.). Pressure is pressure. Valve response after the initial lift will of course vary between water, steam and gas, however then the interest shifts from set pressure to whether a SV flutters or chatters.

RE: PSV Set Point Tolerance ASME SEC 1

Thanks for your comments. My sentiment on "correlations does not exist" is the fact there is no known or published data advising factors to be used by all. Hence provided by vendors wisdom and experience. It is a manufacturer by manufacturer science. Every manufacturer will advise on different temperature correction factors, and then they are best compromise. Same with air Vs steam Vs liquid setting.

As regards set pressure, I understand the point you are making, but invariably the valve will react acc to the ring settings at test. This is to reduce the seats slamming (damaging) due to no sustained flow during bench test, effectively floating the valve open until closed. Set pressure is defined differently around the world, from first audible sound to initial pop etc. My favourite definition is "when the spring force is equal to the pressure in the valve inlet", which is effectively what you have stated.

There is no better method to get accurate set pressure than to have the valve set on a live, hot system if possible. Hence the manufacturers advice can only be recommended.

Per ISO, only the term Safety Valve is used regardless of application or design.

RE: PSV Set Point Tolerance ASME SEC 1

Thanks you for your guidance! I have gone through our various manufacturers' maintenance manuals. All the nuclear related safety relief valves provide guidance regarding correlation, except for one. I am waiting for a response from them too see if they have any specific guidance to provide.

RE: PSV Set Point Tolerance ASME SEC 1

Constantinople1990 This was not your original post, but I need to comment against your last posting. OK. Great you found the earlier guidance of use. You now mention Nuclear service.

If this installation is within the Nuclear reactor (island) then probably the SV specification is ASME III not ASME I. This is a different set of rules and contact with manufacturer is well recommended.

Per ISO, only the term Safety Valve is used regardless of application or design.

RE: PSV Set Point Tolerance ASME SEC 1

I do agree that correlation factors do not exist between media.
If the valve is to be tested on steam and is tested on air, will give you a whole different set of results when retested on steam.
A relief valve is set for a certain set pressure for the specific media (and capacity certified), be it air, steam or liquid. For any other compressible or incompressibles, correction factors with respect to air or water are available, but not between steam and air.

Also, within a nuclear power plant, there are non nuclear systems that do use Section I or Section VIII relief valves. Section III relief valves are only used on the primary nuclear systems.

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