dished end with small convex

[andy74]

Hello
How to calculate a dished end with small convex? ratio H/D=0,12(H-height of end, D-diameter of end). I can't find any formulas covering this type of dished ends.
Thank you for any help.
Andy

 

[JStephen]

Is this a conventional dished head with a portion at the center inverted? Or is the whole head turned with pressure on convex side?

 

[andy74]

It's some kind of torispherical head similar to DIN 28011, (you can see here for example:

http://www.weisstaler.de/en/sites/weisstaler.html)but

flattened, with small ratio H/D. It looks like Standard-type/flat dished head (3rd row on this web site)

Andy

 

[JoeTank]

Andy74
ASME VIII, Div 1, Appendix 1 has design formulas for torispherical heads of various proportions. In UG-32 the standard ASME Torispherical head has a dish radius that is 100% of the vessel diameter. The knuckle radius is 6% of the vessel diameter. This gives an H/D ratio of about 0.17, so clearly your vessel head is even flatter than that. I was not aware that there were any veseel codes that permitted shallower heads than that. My impression was that the euro codes did not allow heads as shallow as the ASME Codes.

Joe Tank

 

[andy74]

Yes, but this type of dished head is used for non pressure vessel for Diesel fuel, gasoline. This type of vessel is not covered by PED, but they are supervised by technical office inspector, and inspector wants to see a strength calculation. Some firms make a storage vessel for gasoline using this type of dished, and I was wondering how did they calculate this.
Andy

 

[SnTMan]

andy74, if you are talking about a flat head with a knuckle and skirt, I beleive it is commonly called "Flanged Only", see UG-34.

Regards,

Mike

 

[prex]

In the site below under Vessels -> EN13445 -> int.pressure -> Dishes there's a sheet for calculating torispherical heads.

prex

http://www.xcalcs.com

Online tools for structural design

 

[andy74]

http://www.cgh.com.pl/eng/g_prodblank.htm-

here you can see what i'm talking about, (also see technical details)
regards
Andy

 

[andy74]

It's not a flat head with a knuckle and not a typical torispherical head, it's looks like torispherical head but very flattened (out of range of any known by me formulas)
Andy

 

[SnTMan]

andy74, torispherical heads are also called F&D heads (Flanged & Dished). The shallower heads are often not ASME heads, because they do not meet the dimensional requirements of ASME as to dish radius, etc. but are still commercially available. I would calculate as a sphere of whatever the dish radius is, as that portion of the head is spherical. Add forming allowance as recommended by the head vendor. See this link for variety of styles and give them a call. They may be able to steer you to a rating.

http://www.bakertankhead.com/products.htm

Regards,

Mike

 

[JStephen]

I'm still not clear on the exact profile. However, if it's small enough and unpressurized, check it as a flat plate (possibly using large-deflection equations) per Roark's Formulas for Stress and Strain. If that shows it's adequate, it should be close enough for just about any kind of shallow dish. You could also look at just a strip across the diameter as a beam or catenary and check strength that way.

Part of engineering judgment is knowing when something doesn't need engineering, although that's kind of hard to get across sometimes.

 

[SnTMan]

"and inspector wants to see a strength calculation"

It needs it in this case.

Regards,

Mike

 

[andy74]

"The shallower heads are often not ASME heads, because they do not meet the dimensional requirements of ASME as to dish radius, etc. but are still commercially available." That's what i'm talking about, if they do not meet the dimensional requirements of ASME and PED and DIN how they are commercially available? How it is possible?

I can't calculate this as a flat head, thickness is too big.

 

[SnTMan]

andy74, you can buy all kinds of things that do not meet a given code or specification, because they are intended for other purposes. Plate, sheet, tubing, bolting, flanges, heads, you name it.

Have you tried calculating as a sphere of whatever your dish radius is?

Not clear what code you're working to, but ASME Sec VIII Div 1 also has a formula for dish only heads in Appendix 1-6

Regards,

Mike

 

[mammut74]

Perhaps if all fails can you do a proof test to determine its pressure limits?

 

[SnTMan]

In such a case, you stand beside your work, not behind it