6" Dummy Leg Support on 12 " pipe 2

[Porter]

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

 

[piping1971]

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.

 

[NimalJayaratne]

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

 

[Hookem]

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.

 

[LSThill]

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

http://www.thill.biz

 

[hiliter]

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.

 

[NimalJayaratne]

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...

 

[gramya]

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:

http://www.gramya.com

;

http://www.charismaglobal.com

 

[Jsquare]

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".