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


6" Dummy Leg Support on 12 " pipe

6" Dummy Leg Support on 12 " pipe

6" Dummy Leg Support on 12 " pipe

I'm having some trouble in performing a check on a dummy leg support within Caesar II.  I have a 12" horizontal run pipe, and a 6" vertical support pipe with no repad.  The info that I have seen so far does not impose any SIF's on the connection, and I think that there should be.  I have performed a WRC 107 check on the "nozzle", and all stresses are fine, but when I model the connection within Caesar, it fails miserably

RE: 6" Dummy Leg Support on 12 " pipe

Why not change it to  10"Dummy..It is a common practice to
use a one size smaller for a dummy support.The recommended size for a 12""run pipe is 8"dummy...and you could even go to a full size but it is better to put a pad.

RE: 6" Dummy Leg Support on 12 " pipe

Hi Porter

I am not in favour of oversized trunnions.

Acceptance criterion for trunnion is based on local stresses and Caesar II cannot handle that. MWKellogg's Design of Piping Systems Chaper 3 gives a methodology to calculate local stresses..it is quite straight forward and you can put it into a spreadsheel and off you go!

Most piping engineers have a copy (or a photocopy) of this great reference of the 1960's.

Good luck

RE: 6" Dummy Leg Support on 12 " pipe

When running C2, I used to model elbows with attachements (dead legs, elbowlets, etc.) as having being flanged on both ends.  This stiffened up the elbow as one would expect.  Remember that C2 (or triflex and other programs) cannot approach FEA for small areas.  If C2 is failing you on this design, I suggest you have something going on other than the size of the dead leg, or the stiffness of this elbow.  Even if the stresses were below the limits, I would still strive to get them as low as reasonably possible.  Going from "failing miserably" to "reasonable" requires more than changing the size of the trunnion support.

By the way, I assume you are in B31.3; just last week, I discovered that welding of attachments (shoes, trunnions, supports, etc.) in B31.4 is now strictly forbidden.

RE: 6" Dummy Leg Support on 12 " pipe

Hi  Hookem (Mechanical) and all members

I do agree with you, but I have found it faster to use FE/PIPE.

NimalJayaratne (Mechanical) Also, I have the MWKellogg's Design of Piping Systems sence 1973. RE: Chaper 3. Have check with FE-PIPE.

Leonard Stephen Thill

RE: 6" Dummy Leg Support on 12 " pipe

The FEA using Nozzlepro or FEPipe is aok to use if you have these tools.

A simple approach that I have used with round or structural attachment is the line load method given within section 7.6 of the Pressure Vessel Design Handbook - Bednar, 2nd. edition.

Good Luck.

RE: 6" Dummy Leg Support on 12 " pipe

Please see page 249 (of MWKellogg) top left para which says "local stresses for trunnion type attachments can be approximated by the approach outlined in chapter 3 Section 3.14"
I have also referred to a paper published by MWK later on the subject...I'll see whether I can dig it out from my museum...

RE: 6" Dummy Leg Support on 12 " pipe

Coming back to more authentic and detailed analysis, which is not easily possible manually, one may try WinNozl ( again Paulin software, marketted by Bentley, earlier Rebis). I have myself demonstrated the use in such trunion support cases and even for vertivcal vessel supported by pipe legs. Another to mention is FEPipe/ NozzlePro by Codeware.
Use these softwares, to reduce your complicated analysis burden. they make the analysis seem so easy.

Narendra K. Roy
Gramya Research Analysis Institute,
PO box 4016, Vadodara 390015, India
Website: www.gramya.com ; www.charismaglobal.com

RE: 6" Dummy Leg Support on 12 " pipe

Usually 6" support on 12" is good; however, there is not enough info. to determine whether you have problem elsewhere.  Also many pipe stress engineers refer dummy or trunnion as horizontal extension.  Most would call your support as a "base support".

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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close