×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

choosing shape of head

choosing shape of head

choosing shape of head

(OP)
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.

 

RE: choosing shape of head

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)

RE: choosing shape of head

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.
 

RE: choosing shape of head

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?

RE: choosing shape of head

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.
 

RE: choosing shape of head

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

RE: choosing shape of head

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

RE: choosing shape of head

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.

RE: choosing shape of head

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

   

RE: choosing shape of head

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
 

RE: choosing shape of head

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources