When not to use Fire case for PSV design
When not to use Fire case for PSV design
(OP)
Hello all,
I'm sizing a PSV for an atmospheric tank containing 35% HCl. The fire case is by far the largest relief requirement, and would require a new nozzle to be cut into the tank. If the contents are not flammable, and there are no other flammable sources nearby, do i have to size for the fire case? Does anyone know which codes govern this decision. API-2000 doesn't offer too much up in this area.
Thanks in advance
Scall
I'm sizing a PSV for an atmospheric tank containing 35% HCl. The fire case is by far the largest relief requirement, and would require a new nozzle to be cut into the tank. If the contents are not flammable, and there are no other flammable sources nearby, do i have to size for the fire case? Does anyone know which codes govern this decision. API-2000 doesn't offer too much up in this area.
Thanks in advance
Scall





RE: When not to use Fire case for PSV design
RE: When not to use Fire case for PSV design
RE: When not to use Fire case for PSV design
they might not remember to check the sizing for other tanks in the dike when doing the sizing for the new tank.
but if you have no valid scenarios, that is likely why you have the nozzle size you do.
best regards, ben
RE: When not to use Fire case for PSV design
I want to add a little additional experience to this thread because the subject matter, albeit basic, is so very important.
Two key individuals have contributed the basic, true facts:
Phil Leckner - "There is no Code that dictates the criteria for sizing relief cases....it's totally up to you."
BenThayer - "..be careful that you do not create a scenario in the future."
These two pieces of advice are pearls of wisdom. Now let me add something else: What Ben has pointed out is precisely why Management Of Change (MOC) was instituted and mandated by OSHA and some smart and experienced companies. As Phil indicates, it's your responsibility; therefore, the way you plan, organize, and control any future change is in your hands and if you are smart, you too will find a way to make sure you don't create a potential or fatal hazard by introducing a possible Fire Case in the future. Document any and all changes and continuously control them.
Merely installing the correct PSV is not the total answer when you are operating the unit. That attitude is reserved for those of us who are now contracted designers or work for engineering companies - we don't operate the units; we just design them, then walk away. If you operate, you have to live with the results and any future changes.
RE: When not to use Fire case for PSV design
does an atmospheric tank need at all a PSV? not only pressure vessels?
regards,
roker
RE: When not to use Fire case for PSV design
In my opinion all enclosed vessels receiving and supplying fluids should be scrutinized for needing a Pressure or Vacuum (lack of pressure) relief device. Any API storage tank described as "atmospheric" probably will be found to require a device of one sort of another - even an overflow nozzle. It all depends on what you're doing with it and how you operate it.
Do not be naive and simply apply generalities to any application - even one as "mundane" as an atmospheric tank. I can show you photos of such "benign" applications that would raise the hair on your head. It doesn't take much pressure (or lack there of) to destroy such a piece of equipment - and it can be fatal.
A Pressure Safety Valve (PSV) is normally used on Pressure Vessels (reference API 520 & 521). A conservation vent and emergency relief (we call them PVSV and PSE where I work at) are used on API storage tanks. You can use whatever acronym you like - but make sure you acrutinize the safe operation of the tank, just as you would a pressure vessel - especially for vacuum scenarios.
RE: When not to use Fire case for PSV design
IF your "atmospheric" tank is one that is totally opened to the atmosphere via a vent, then you only need to make sure the vent size and piping (if existing) are sized appropriately to account for pump-in, pump-out, breathing and any other credible over pressrue scenario that you can think of, including fire. If the open vent pipe is not capable of handling it all then you would install some type of emergency relief device on the tank as well.
If the tank is designed to be an "atmospheric" tank but is totally enclosed for process or environmental reasons, then as Art points out, some device is absolutely required to protect the vessel from the same conditions, I state above.
RE: When not to use Fire case for PSV design
An atmospheric aboveground storage tank does require a means of pressure relief based on a fire scenario if it contains flammable or combustible liquids. NFPA 30 contains extensive requirements. It should be noted that NFPA 30 does not define it as pressure relief but instead defines it as emergency venting.