dimpled jackets

[adiem]

I read in a previous post that if a dimpled jacket is used for a vessel with an external pressure of 1 barg (F.V.), the pressure in the jacket does not have to be included in the vessel wall thickness calc, Is there a paper or reference that states this, somebody I know suggested 'Neale'.

 

[adiem]

Can anybody help with this? I am desparate for an answer!

 

[prex]

Never did such a calculation, but let me try to put things in correct order:
1)Vessel wall is subject to FV only: it must be checked for this condition. You may safely use wall thickness only to do this, or base your analysis on UG-29(f), where it is stated that a construction with a jacket connected to shell with closure bars and rings has adequate inherent stiffness. However you still need to determine a stiffness ring spacing to calculate the wall to vacuum, so, depending on dimples disposition, this could be easy to do or could require a test.
2)Jacket is subject to its internal pressure, but the inner wall is also suject to vacuum: it would be simple (and wise) to check the jacket with design pressure + vacuum.
3)How to check the dimpled jacket to pressure is another matter: Div.1 requires a proof test for this, if I recall it correctly.

prex

http://www.xcalcs.com

Online tools for structural design

 

[adiem]

Thanks for your reply.

I was always going to check the vessel wall for F.V. the question (although not very weel worded) was do I have to include the jacket internal pressure of 3 barg and check the vessel wall for 4 barg external over an effective length equal to the jacket length? Is there a value I can equate for an effective length of shell subject to the external pressure that takes into account the pitch of the dimpled jacket welds?

 

[prex]

In my opinion you don't need to check vessel wall under an external pressure of 4 bar: the jacket internal pressure is resisted by the dimples. Of course you can do that, as it is by far on safe side...
Vessel wall need be checked also between dimples against jacket pressure: if it was a flat wall, it would be checked per UG-47 using a pressure of 4 bar. As it is not, I wonder what method you intend to use: you need to check against buckling the wall portions between dimples with a pressure of 4 bar, but this will have much less impact on thickness than checking the full unsupported shell against buckling. If the dimples are quite close to each other, I suppose it would not be too severe to check vessel wall as a flat wall.

prex

http://www.xcalcs.com

Online tools for structural design

 

[rmw]

If I were looking for this answer, I would go to

http://www.tranterphe.com/phe/platecoil/platecoil.htm

and search their site for the answer.

When you said "dimple" plate, you obviously referred to their competition, but their style of weld on or clamp on jacketing would face the same problem you are facing, if that were what you were using.

It has been a long time, but as I remember it, when the jacket was weld on, the plate to which it was welded was a coded part, since it was the ultimate pressure boundary for the process, and the only thing that had to be considered from the perspective of the outside was the pressure imposed on the boundary plate by the heating medium in the jacket. But, it has been a long time.

Hope you find something here.

rmw

 

[adiem]

Thanks guys for your responses, they have given me some leaders. Any further info would be greatly appreciated.