Typical Operator checks on a "Pressure/vacuum breather valves" ? 1

[mrtangent]

Dear sirs,

We have a couple of "Pressure /vacuum relief valves -- breather valves" on site. They are the ones which are totally covered. We generally inspect them at our "normal frequencys" and have no history of issues/failures, ie 1-2 years during shutdowns.

On our normaly relief dutys we perform weekly operator checks for premature failure of busting discs benefit relief valves and relief valves for signs of usage.

However on these breather valves for operator checks is anyone aware of what you can actually check ?, or should check ?

Any comments / expereince appreciated.

 

[Montemayor]

Jim:

Nice to hear from you again. I’ve had a lot of background in applying and operating Pressure /vacuum relief valves (aka: “conservation vents”) on storage tanks and perhaps I can contribute some help in this area.

You’ve expressed my past and present concerns for the proper operation of these rather simple devices. I also share your thoughts on making sure these devices (albeit simple) don’t cause trouble. My main concerns have centered on their inherent characteristics:

1) they are traditionally located in remote, elevated, and often inaccessible sites;
2) They depend on nothing else but a gravity-operated pallet to function;
3) They too frequently are taken for granted – due primarily to their simplicity and remoteness.

In the case of hazardous or toxic fluids, I have found no technique or manner that I could reasonably recommend to check on their operation – other than a complete, safe turn-around. The inherent awkward and remote, elevated location of these devices present some risk involvement in their inspection and maintenance. It is not a routine task, and certainly one that should be supervised and carefully planned. Gaining and maintaining access on the roof of an industrial storage tank is not something that should be decided on the spur of the moment or taken lightly. Tank roof conditions are sometimes very risky and perilous. Some of these devices – especially those on large tanks – are bulky and very big in size and, as such, require special equipment, tools, and techniques.

It is only in the case of the smaller, “pipe-away” models that I have been able to monitor if there is any positive pressure leaks occurring. What I have done in some services is to pipe the discharge into a water level inside a vat or drum beside the tank and scrutinize the water to detect gas bubbles which would indicate a leaky pallet or seat. There is virtually nothing one can do with the vacuum side to verify of detect faulty operation.

There are of course, some common sense engineering one can design into an installation, such as bird screens and safe, accessible platforms and ladders. The structural location of these devices – especially the larger ones – can (or should) be done away from the actual tank roof where a workman does not suffer the risk of having to step on the actual roof itself while servicing the device. I realize this is an expensive proposition; but what do we, as engineers, think about the possibility of us having to walk across the roof of a storage tank filled with something like sulfuric acid? I certainly wouldn’t do it - and I couldn’t expect anyone else to.

These types of simple devices are going to suffer some leaks while in operation – however minimal. This is their nature and a lot depends on the proper vertical installation, the fluid involved, and the quality of fabrication. What I recommend is simply trying to keep a methodical yearly turn-around inspection on these devices. I perfectly understand the economic pressure today in keeping storage tanks operating profitably around the clock as long as one can. But there comes a time when we all have to weight the negative results of not inspecting and maintaining our equipment properly and in time. In my opinion, after witnessing serious failures in the field due to lack of inspections, the downstream price to pay is too risky and expensive.

I hope some of this experience helps – although I realize it isn’t much to offer.

 

[mrtangent]

Thanks Montemayor,

You've confirmed our suspictions. Basically you need to ensure these valves are on a regular inspection program. If the inspections idenfity further issues/reliability conserns then pressure monitoring and may be further protection maybe an issue.

It is our normal pratice for the operators to perform work based inspections on relief valves weekly, ie is the bursting disk gone, drain valve down stream of valve showing signs of any leakage, pressure guages show any signs of problems, catch tanks show signs of any level build etc... but with these valves a visual inspection for degrading of the surfaces seems about the best you can do.

Thanks

James