Test result of safety valve using lifting assist device compare with actual popping pressure 1

[raa2125]

Dear gentlemen,

In one of the audit of local authorities on the on-going boiler erection, they raised a question regarding the safety valve as follow;

"How could you confirm if the test result of safety valve using lift assist device is the same with actual popping pressure".

We could not think of any possible answer but I have this idea;

"No method that we knew has existed to confirm the test result of safety/relief valve using lifting assist device is the same with the actual popping result. Possibly by instance, if any of the safety/relief valve had popped up during the normal operation. Take the actual pressure when it popped up and compare it with the previous test result using the lifting assist device."

Any idea guys?

Any input will be highly appreciated.

Thanks

 

[Dhurjati Sen]

Dear raa2125,

Check Link

Regards.

DHURJATI SEN

 

[raa2125]

Dear Dhurjati Sen,

I read thru the link you sent. This procedure may not be advisable to our boiler.

Here, we used the hydraulic lift assist device.
Our boiler is supercritical with MAWP stamp on the nameplate as "26.7Mpa". Maxium set pressure we have is over 31 Mpa.
It may be dangerous to raise the boiler at this pressure.

Anyway, we will let our Designer/safety valve vendor to answer this comment from local authorities.

Thank you for the link.

 

[DBreyer]

Dear raa2125,

The hydaulic/pneumatic lift assist simulates a higher pressure underneath the valve seat (by adding a lifting force through a piston acting on the valve stem), so that the following is true:
hydraulic pressure*(hydraulic piston active area/safety valve seat area) + boiler pressure = popping pressure.

An easy way to test where the valve would open without hydraulic force is wto do 2 tests with 2 different boiler pressures while measuring the hydraulic pressure applied to pop the valve.

If you now draw a graph with the boiler pressure on the x-axis and the hydraulic pressure on the y-axis, and enter your 2 data points you can draw a straight line thorugh the 2 points. At the intersection with the x-axis you have your actual popping pressure without hydraulic help.
That's basic math/ physics.

According to german boiler regulation that is also the appropriate way to test those valves.
Typically the safety valve manufacturer has also Instructions describing these steps.

Additionally, if you want to re-test the safety valve at a later date, you can do it at any boiler pressure, measure the hydraulic pressure and see if you are still on the line drawn at the first test.

Hope that helps

Daniel Breyer
Inspection Engineer

http://lnkd.in/dFcQA-w

 

[raa2125]

Dear Daniel,

Before I saw your message, we are actually discussing the same thing, that is to test using two different boiler base pressure. It makes us more interested after I saw your message and shared it with my colleague.

Thank you very much,

raa2125