PSV online Testing limitations

[Hosseinmah]

What size of PSV can be tested by online testing devices?
What are other limitations of PSV online testing method?

 

[bevjones2009]

Hi,

From my days of testing online we were really only governed by our load cell size and if the PSV had a threaded spindle that we could pull.

 

[bevjones2009]

Oh sorry I forgot to mention that it's sometimes hard to distinguish a solid set point of valves on a process medium other than gas, this is differs by manufacturer of the test equipment.

 

[nasim123]

Hi, Dresser is doing the online testing from valve size 1" onwards. While conducting the online test, you can verify only set pressure, No leak test or back pressure test.

Most of the companies prefer to test steam service valves, not process psvs.

Thanks
Nasim

 

[The Obturator]

Just to add, relevant or not, regardless of what the various in-situ SRV manufacturers claim, you cannot "test" for SRV blowdown (closing) using these devices. Sure you get a nice looking graph but it is not reality.

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

 

[bevjones2009]

@avalveman - absolutely correct, a lot of valve companies try to use the nice little graph with lift and reseat markers on as a selling point. You could always use the Hot Float method if you wanted to measure the blowdown.

 

[pawan797]

You can use TREVI testing online tool. Trevi testing of steam relief valves is an accepted method of RV testing for all type of safety relief valves. A load cell is mounted with hydraulic puller on the valve's stem top. This pulls the stem thereby trying to lift the disc. The net result is that the valve pops at a pressure set pressure less hydraulic pressure calculated on the basis of disc area. We do not have to actually raise system pressure to the set point of the RV. But , as far as I know, Trevi Test puller cannot apply more than 20 kg/cm2 pressure on the valve disc depending on disc area. Still, since the system pressure remains very less than set pressure when the valave pops, it is safer . This method is normmally used for stem relief valves. However , there may be slight variation in the set pressure done through actual testing as compared to Trevi testing methods.

 

[The Obturator]

Trevitest, Sesitest, ValveCheck etc., they are all brand and trade names of manufacturers in-line safety relief valve in-situ test devices. basically the principal between them is the same. In addition to my previous comments on this thread regarding blowdown, I felt it apt to add a few further comments specifically to make users aware of such devices usage. I am not renouncing or promoting the method, but making some observations as an ex SRV manufacturing guy.

* Some users are led to test their newly acquired SRV's prior to initial installation, since they are informed that the new SRV is at a factory setting and correct (OK a few users bench test first). However, with the result obtained with the in-situ device, they calculate back what the pressure area is on the seats of the SRV (Sometimes defined as the area between the outer and inner lapped nozzle seat). The reason for this is because a) They have not had the the areas provided by the SRV vendor (note these areas should be as actual measured and can be sometimes put on manufacturers test certification if requested, and b) require the areas calculated for future on system. in-situ test.

However, in doing this, and sometimes with less than 75 % of set pressure in the inlet of the SRV, the user runs a real risk of damaging the spindle by stretching (this is also why ASME states not to use a lifting lever at less than 75 % set pressure). Result, distorted seating, wrong set pressure etc. Since the user wishes to save time and money, the future testing now carried out without any maintenance, may well be providing in accurate results with the user thinking he had a good accurate initial test.

* The test will never indicate to the user the condition of the critical internal parts (disc, guide, spindle) which must be sound to ensure a proper full lift during a real overpressure excursion.

* The lack of an extended threaded spindle to allow device attachment is not a regular feature on all SRV's. It is known some users have drilled and tapped spindles on an assembled SRV damaging the seats and other parts.

+ And finally, only the point of set pressure is tested, not the lift or blowdown.

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