Safety Relief Valves - Typical Failure Modes?? 3

[matreid]

Hello.
I am new to this site and just hope I have posted this thread correctly!!

I am trying to educate myself on Safety Relief Valves at the moment, and although I can find plenty of information regarding operating principles etc, I cannot seem to find anything regarding typical failure modes??

The following are my areas of focus:

1. Spring-Loaded Design, (Gland Packing)
2. Spring-Loaded Design, (Bellows)
3. Pilot Operated

Any advice would be greatly appreciated...

Many thanks......

 

[Goahead]

A query on Google on
"safety relief valve failures"
returns many articles some of which may be relevant to your research.

Regards,

http://www.welding-advisers.com/

 

[matreid]

Goahead,
Thanks for the advice.....

 

[JimCasey]

Failure mode:
1. Seat leakage. Usually caused by wire-drawing through a scratch left by foreign-object impingement. Restoring the seats is a periodic maintenance activity.

2. Decrease of setpressure due to thermal effects on the spring. Usually an applications error, or change ion process conditions. High-temperature construction is available. Both alloy springs and/or open bonnet construction adddress elevated temperatures to different extents.

3. Failure to open at setpoint. Usually due to mineral deposits in a leaky valve. Has caused some spectacular disasters, but code requirements(Lifting levers) and advances in boiler water treatment have made this almost unheard of in recent years.

4. Foreign object blocking valve. Not a valve failure, but an administrative failure. Adherence to code addresses this.

BTW: non-bellows valve usually are not packed.

 

[matreid]

Thanks Jim - Your advice is much appreciated....Matt

 

[AusSteelMan]

I am a maintenance strategist in a steel plant in the Energy and Cryogenics department. I have seen various types of failures, but most common include:

Seat Leakage - from (as previously described) foreign objects, associated equipment vibration (chatter), maintenance induced (from pulling test handles etc)

Altered set points - from relaxing springs (age, material but mainly high temps), seizing spindles, jammed springs, back pressure on outlet (that was not taken into account)

Some other issues include – incorrect transporting – valves (esp. large and low set pressure) need to be transported vertically so that the plug and spindle weight does not “bend” the spindle causing the plug and seat to rub on each other and therefore scratch the seat over every bump in the road. We have developed some “best practice” type requirements. Basically any valve under 50mm inlet may be transported laying down if packed properly and if set point is over 250kPa – we use foam packed cases (like what expensive cameras etc are sometimes packed in). Valves over 50mm inlet (up to our large valves of 500mm inlets) are bolted vertically to pallets. These pallets are specially built.

For transport, we use steel bases with plywood covers to protect from external environment (this helps with loading and unloading and does a lot for preventing the pallet being laid down). The bases have channels welded underneath to provide forklift capabilities and lifting lugs on the top to allow for lifting to the work area (or just off the truck if there is no forklift available) prior to lifting valve off the pallet.
For storage, large valves are usually on a steel pallet with its cover or heavy plywood pallets with covers. These allow the valve to be bolted down (drillings to suit PCD etc) providing security.

At times we may sprag a large or very low pressure valve to prevent seat / plug vibration but, YOU MUST HAVE A WAY OF ENSURING THAT THE SPRAG IS REMOVED BEFORE PUTTING THE LINE INTO SERVICE. If not the valve becomes just a very expensive and intricate piece of pipe and will not save your plant (and possibly your life) in the event of a process excursion.

Ok, I think I have crapped on enough for now.

Regards,
ASM