Schedule 10S & 5S Piping 1

[MJCronin]

Is CAESAR-II an appropriate tool for use on large diameter, stainless steel, schedule 5S and 10S piping systems ?

The ASME code calculated stress intensification factors are very high, and probably not realistic.

I believe that B31.1, B31.3 and CAESAR should, in some way, address the issue of limitations in a "beam-type" stress analysis. At what point (i.e. a D/T ratio) do the local effects of bending take over and make a CAESAR-II analysis invalid ?

I feel that this issue has been addressed before and industry references exist.

I would appreciate any comments, discussions, informal company "analysis guidleines, rules-of-thumb etc.

Thanks in advance !!!............................MJC

 

[rjstephens]

Hi MJCronin,
I have previously used CII for the flexibility analysis only for large bore thin walled piping(D/t>100). I have calculated the SIF's from FE pipe along with the stiffness and inputted the data into CII at the fabricated intersections and bends. The wall thickness requirements have been calculated to a pressure vessel code, ie BS 5500 or ASME VIII. I hope this helps.

 

[MJCronin]

To all,


Is there anyone out there with experience on CAESAR-II modelling of thin walled systems ?


MJC

 

[LSThill]

MJCronin (Mechanical)

Re-post on COADE FORUMS

http://www.coade.com

Leonard@thill.biz

http://www.thill.biz

 

[xhpipe]

Spend some time reading the B31.3 code... There are some very specific D/t ratios mentioned as being limiting considerations when it comes to SIF's if your D/t ratio exceeds or comes close to those limits NO BEAM ELEMENT PROGRAM is appropriate.

Higher ratios require 3d analysis... check the notes in the SIF appendix.

Regards,
XHPIPE

 

[MJCronin]

XHPIPE,

Spend some time reading my question......

I am asking about the limitations of CAESAR-II not about the validity of the computer program nor am I asking about the validity of the notes within the appendicies to B31.3.

I am fully aware of the code's D/t< 100 limitation.

Some mechanics of materials texts state that, for thin walled cylinders, with D/t of about 90, the effects of localized instabilities take over. The piping materials, temperature, modulus etc all have an effect.

Again, my question is: &quot;At what point (i.e. a D/T ratio) do the local effects of bending take over and make a CAESAR-II analysis invalid ?&quot;

Additionally, a reasonable person would ask, why doesn't CAESAR-II prohibit the running of an analysis when the D/t makes the model unstable/invalid....???????


MJC

 

[xhpipe]

CAESAR II as well as all other beam element programs, is based on the B31 codes, which have simplified rules for analysis. The D/t ratio listed in the codes is not a pass fail limit. In other words some people taking precautions in what and how they do things can work above those D/t ratios using good engineering judgement (as well as some FEA help). Others get in trouble below that limit. The code and CAESAR II are not simple design cookbooks or tools, both require an in-depth feel and understanding of whats being evaluated.

Your desire for a simple answer to this complex issue i.e, &quot;above this value X don't proceed,&quot; is reminiscent of how complex problems are viewed by management.

Regards,
XHPIPE

 

[richay]

Also note that for a given D/t ratio (above 100), the local/stability issue is sensitive to the overall system geometry. For a given ratio, you may have stability issues in a &quot;tight&quot; system, while in a geometrically loose system dominated by bending you won't. &quot;3D beam&quot; elements are great in bending, but poor in other modes. Also important to remember is the fact that the &quot;3D beam&quot; element is completely oblivious to buckling.

Richard Ay
COADE, Inc.