Floating boiler Safety valves after an overhaul - query
Floating boiler Safety valves after an overhaul - query
(OP)
In Australia, when a boiler has been down for an inspection or overhaul, or for a safety relief valve overhaul, it's standard practice to do a controlled lift of the safety valve [boiler firing against the blocked stop valve with superheater vents open to keep some flow]. We record lift and reseat pressures. We try not to lift and or adjust the SV settings more than 3 times, otherwise the SV will leak on line.
There is a move by occupational health and safety folk to stop this practice because of the noise involved. In my experience, trevi testing is not a total answer - so I'm on the side of floating SV's.
Is this "floating" a common Australian practice? If not, has anyone gone from floating to not floating when recommissioning their boilers?
Thanks
Rob
There is a move by occupational health and safety folk to stop this practice because of the noise involved. In my experience, trevi testing is not a total answer - so I'm on the side of floating SV's.
Is this "floating" a common Australian practice? If not, has anyone gone from floating to not floating when recommissioning their boilers?
Thanks
Rob





RE: Floating boiler Safety valves after an overhaul - query
While installed and in service, a Boiler Inspector will sometimes require that the boiler undergo a capacity test like you described. Such a test is used when total valve relief capacity is suspect. Or when installation configuration might restrict or hinder proper valve operation including valve reseating.
If you elect to not op test your valves, but instead send them out for test, then you need to take a close look at how the valves are installed. Ensure escape piping is properly configured. Do not allow escape piping to place loads or stresses on the valve body or it may effect valve operation. Provide plenty of capacity beyond output calculations.
You should consider locating a SV repair/retest concern to recertify your valves vice testing them in operation if noise is a problem.
RE: Floating boiler Safety valves after an overhaul - query
You're totally right. An offsite overhaul by a mob with a test rig is the answer. Obviously, you're satisfied with the capacity test tagging but are the valves being tested on steam or air?
I'm only aware of two mobs in Australia that have a capacity test rig, however both operate on air. To my mind, air is not steam.
I've looked at these mobs and have not been convinced that their correction factors are sufficient. In our case, we operate right on 95% of set [very tight] and small margins of error mean a big difference to valve life. The other thing is that the mobs are over 1000 kms away and I'm mindful that the valves are likely to take some knocks and vibration during transportation - quite possibly destroying all the good overhauling effort. Unfortunately, offsite overhauling does not seem to be the answer in our case.
RE: Floating boiler Safety valves after an overhaul - query
I also live 3 miles from a Dresser Valve plant where they operate 6 Vapor steam generators. One of their boilers operate at 2250 PSI. The boilers are used to test their steam SV's and other products. I can easily hear their tests from 3 miles distant. It's never a problem unless they work a third shift.
You present testing is certainly the best way to go, but if you must stop op testing, then you really have no alternative but to send them off.
RE: Floating boiler Safety valves after an overhaul - query
and lifting light.
RE: Floating boiler Safety valves after an overhaul - query
Yes its common practice and again its mandatory to do it at least on your boiler interlock check maximum period which is 2 years in Australia.( and any other time the psv gets worked on ) The environmental watchdogs wont let you do it at night , but they cant stop you doing it
RE: Floating boiler Safety valves after an overhaul - query
One path forward to consider, provided jurisdictional authorities are agreeable, is to perform the repairs yourself, or contract to have them repaired, in place using the following scenario:
Step 1: Perform Live Steam Testing on the Boiler prior to a scheduled outage (Maintenance shutdown). Make any necessary Adjustments to Set Pressure and Blowdown.
Step 2: Perform Repairs during Shutdown. Be careful to record all adjustments during disassembly in order to return the PRV to its "as found" adjustment.
Step 3: Following Repairs, when the unit is back on line for at least 24 hours (Heat Soak for Springs), Test the PRVs using Trevitest or another Auxiliary Lift Device to reestablish (confirm) set pressure.
The Logic of this method is the Blowdown should not change if the Adjustments are returned to the proven settings from before the shutdown. Then perhaps once every five years one or more PRVs could be live tested to demonstrate the accuracy of the set pressure & blowdown settings.
J. Alton Cox
President
DeLuca Test Equipment
www.delucatest.com