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Large opening in flat plates

Large opening in flat plates

Large opening in flat plates

(OP)
In a cylindrical PV, the material removed for an opening must be replaced per usual methods. If not, the remainder of the vessel wall carries a greater portion of the the hoop and longitudinal forces, so the stress is increased in those portions. That's my understanding. But in a flat cover (round or rectangular), there are mostly bending stresses. What does reinforcing of openings in flat plates guard against. To reduce the bending stresses? If the opening is very large compared to the body of the vessel, wouldn't the bending stresses be low?

RE: Large opening in flat plates

If the opening is very large, then the cover becomes a flange, and the bending stresses are not very low in a flange. You are possibly forgetting that the opening does only remove material: the end force due to pressure on the opening is still there and is applied on opening's edge.

prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads

RE: Large opening in flat plates

(OP)
Hi Prex
I agree there are radially outward pressure forces on the hole's surface, like the pressure on the inside of the pressure vessel acting on it's inner walls. This is what you explained?
It is also understandable that the opening is similar to a flange, but in a flange, the bending stresses are as a result of the moments of force taken about (usually) the bolt holes. This example I refer has no such moments. Is my understanding consistent with yours?

RE: Large opening in flat plates

No, sorry, it isn't.
The pressure force acting on the opening I'm speaking about is the pressure thrust: it is equal to PxA (A=opening area) and it acts at opening's edge (by means of the nozzle neck) in the axial direction.
In a flange the bending moment results (substantially) from the pressure thrust times the radial distance from the pipe wall to the bolt circle. In a flat head with a large opening it's the same, except that the radial distance is from the nozzle neck to the vessel wall.

prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads

RE: Large opening in flat plates

(OP)
Ok, I got it. Now I have a way of evaluating the bending stresses due to the pressure thrust (or other mechanical loads). Thanks. And it is further understood that the additional reinforcing or thickening of the head will act to reduce the bending stresses.
So to prove compliance to show that reinforcing is or is not required, I should do a flange calculation using the moment arm distance you describe? Is this the norm/acceptable way of addressing my situation?

RE: Large opening in flat plates

This will depend on the governing code. ASME VIII Div.1 has a specific appendix (App.14) for this situation: it is called for from UG-39(c).

prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads

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