choosing shape of head

[dursosono]

What kind of consideration when choosing either semi ellipsoidal or thorisperical head for a pressure vessel? It would be use as Knoct Out Drum. Also the advantage & disadvantage of them.
This matter is regardless cost or fabrication schedule. It's pure technically assistance.

 

[TomBarsh]

If you disregard the cost and fabrication characteristics, then you are left with considerations of process performance. For a vessel not subjected to special flow characteristics then either head type should be acceptable. Aside from this there is little difference in structural characteristics between the two types of head.

(personally, I prefer working with semi-ellipsoidal heads, those special design rules in ASME Code for torispherical heads always trip me up and annoy me)

 

[jamesl]

F&D heads are for low pressure applications. Typically they are not used on a vessel with over 75 psi design pressure. Also nozzles supporting pumps, agitators, etc should not be located on F&D heads.

 

[roca]

james1 – by F&D I assume you mean torispherical? If yes then why can’t a torispherical end have nozzles supporting pumps, agitators, etc located on it?

 

[jamesl]

roca,

Yes. Toripherical heads are typically called F&D heads.

F&D heads have smaller knuckle radius. We don't want high nozzle load causes head buckling.

 

[dursosono]

Jamesl, in which Code/ Standard I can found your statement torispherical head are applied for design pressure not more than 75 psi?

 

[jte]

durosono-

You won't find a code or standard that answers your question. Codes and standards are about minimum requirements, not common design practices or good engineering judgment.

If you wanted to pay for the extra steel, you could put a torispherical head on a Section VIII Div. 1 vessel designed for 750 psi. The reasons not to do it are non-code reasons.

jt

 

[JStephen]

I suppose if cost wasn't an issue, we'd probably just build all the vessels rectangular instead of round. I don't think you can really get away from the cost aspect of it. Any time that you start to consider saving material or labor or freight or making it easier to build or design or making a more efficient design, you're looking at cost issues.

One consideration with using F&D heads is that you have excess plate thickness in the crown area that can be used for reinforcing if you know you'll have nozzles or manways there.

 

[MJCronin]

durso...

A couple of small things not mentioned above:

- F&D means "flanged & dished"

- ASME VIII has specific dimensional requirements (knuckle radius)for various heads. (I am not sure about other codes) Be careful if purchasing a head; you might get one that cannot be used for the code you choose)

- "80:20 heads" are an ASME code qualified compromise shape that exists to minimise material usage. Dimensionally, they are kind of fit "in between" ellipsoidal and F&D heads. They are sometimes specified for larger diameter heads made of more exotic materials.

Just my two cents....

-MJC

 

[roca]

MJCronin – I believe that most codes have checks on head geometry, BS5500 and AS1210 (which is basically ASME VIII) certainly do.

james1 – IMO your statement that pump / agitator nozzles should not be located on a torispherical (F&D) head is not correct. There are torispherical heads – as MJCronin has pointed out – that are close to 2:1 ellipsoidal in shape. I think you are sticking to the 6% minimum knuckle radius limit. It all depends on the load applied to the head, the head thickness used (of course). I have used several torispherical ends in the past supporting agitators with no issues whatsoever.
Check this link – from memory I believe that these are not 2:1 DE’s on these glass lined reactors.

http://www.dedietrichddz.com/equipments_reactors_din.htm

 

[r6155]

For internal pressure, the required thickness is appox. the same for semiellipsoidal head 2:1 and cylindrical shell. Then you can use the same plate for both.

regards