Flat Head Design Pressure
Flat Head Design Pressure
(OP)
When designing a Flat Head vessel that will be atmospheric and ambient, what should I use as the design pressure? Technically speaking atmospheric will be 14.7psi, but if I use that in lieu of 0psi, the vessel will require a 1.25" plate. This vessel will have a 1/4" shell, and be supported on < legs. It will be 108" overall length and made of 304SS.





RE: Flat Head Design Pressure
RE: Flat Head Design Pressure
You didn't say what is the shell diameter, however, per Bobfromoh's recommendation just make the head out of .25" thk 304L plate and weld some stiffeners over it. You should ask the process engineer if there is any other design conditions you should consider such as condensing, exothermic reaction, etc. that could create a vacuum or pressure. The other thing is, would anyone be walking on the cover plate? If so, you may want to use a 50 lb/ft2 load as a design load for the cover and design it for deflection, for example.
RE: Flat Head Design Pressure
Be careful with the way you specify your design parameters. If the vessel is at atmospheric pressure, then there is ZERO differential pressure (Inside = Outside = 14.7 psia). The walls and heads are designed to withstand DIFFERENTIAL pressure, not absolute pressure, so I worried when you seem to indicate a design to withstand 14 "psi" when at atmospheric pressure. I like to always think in terms of absolute, gauge, and differential pressures and to label them appropriately (psia, psig, & psid in the FPS system). Avoid psi without a sufix. It will help avoid a lot of heartache (i.e. confusion, misinterpretation) later.
Doug
RE: Flat Head Design Pressure
RE: Flat Head Design Pressure
RE: Flat Head Design Pressure
Then there surely is pressure in the tank. The equivalent of a 9ft head is (9 x 0.4335) =3.9 psi at the bottom and varying linearly to zero at the top.
Paul Ostand
www.ostand.com
RE: Flat Head Design Pressure
the vessel has a flat cover in the top (it could be welded to the shell, but that's still irrelevat) and the internal pressure is equal to the external pressure (atmospheric) or zero gauge pressure at the top, as you indicated.
cheers
RE: Flat Head Design Pressure
This vessel seems to be an atmospheric tank, doesn´t it?
API 650 has lots of interesting points on the issue, specially about safety. I see that you should be conserned with venting, over filling, weak joint between cover and sidewall, and the like. STD 650 will lead you to the thickness of side walls, if needed - but 1/4" will fit.
About the bottom of the vessel, I´d design a stand with a top grid, small enough to allow me to use 1/4"
Carlos Filgueiras