Dear Members,

While performing Modal Analysis, we came to have one query as below, request to look once & help us.

Bases on Piping Code 31.3, for Stress & force calculations in Static Analysis, the Modulus of Elasticity at Cold Temp (EC) shall to use. NOT EH at OPE/ DESIGN TEMP.

1) Can this EC / EH affect to Natural Frequency in Dynamic Analysis?

2) After Static Analysis, save the file as Dynamic & IF we change from EC to EH at OPE temp,since,in Modal analysis user has to check the LNF(Low Natural Frequency) of Piping system output, here in Modal analysis, no external forces are to be considered like same as time history & spectrum analysis.

As per my knowledge, Modal analysis is based on distribution of Masses of Piping (Concentrated, Insulation, Fluid Density) thru proper supporting & fine breakdown of piping via additional nodes only.

So, question is whether we can use EH at( Hot Design / OPE)case where LNF need to check based on project specification for MODAL ANALYSIS?

We tried here to check, the output LNF at EH (elastic modulus at high temp) is lower than the use of EC (elastic modulus at Cold temp)

Is this correct approach or my understanding is not correct?

Hope to have your experts thoughts for this query.

Regards
SND

Ask yourself ... Is it possible for excitation to exist in piping when it is cold ? If not, then as you are not complying with any Code requirement in doing a modal analysis, you should use 'Eh' as a basis, since this is the real world.

Dear Richard / Dave san /all members

Please give your views @ EC & EH for Modal Analysis.

Whether need to change the "EH" value in cell of "EC" for Frequency Check.
Means, the load case on which Fn need to check, that EH value copy into the "EC" cell.?

Moverz, if you go for "real world" why we are using "EC" for static analysis.There also use "EH", why we go conservative side to check the force/ moments/ stresses.?

This forum is open for all to the doubts what we have & the problems what we are facing.

The Code is made by the humans & CAESAR is also made by the people who follow the codes & Stds to perform stress analysis.Hence, don't reply such fullish answers. Every stress engineer knows the code rules & CAESAR application.


Request to all dear members to help this query with your expert views.

Regards
SND

Snd,

My question was relevant, but seems to have given you the hump. If, for example you are dealing with a drain from a reciprocating pump, then imposed vibration when the pipe is not in service may be a primary consideration.

By 'the real world' I meant just that. 'Eh' (if it makes any difference) is actually the correct stiffness controlling parameter to apply to a dynamic run representative of the operating mode. In most cases I think 'Ec' would be acceptable, given the many other inaccuracies attandant to a stress calculation.

Incidentally, the application of 'Ec' to static analysis in accordance with B31.3 has been covered in previous posts, and in various other places.

Moverz

We have also the same understanding as you mentioned, see my 2nd point,however there is no strong basis/back up found to consideration for

" The same piping system will follow"
Dynamic Analysis - EH
Static Analysis - EC

Request to other members to share views for this one.

Regards
SND

Sorry for correctness,

" The same piping system will follow"
Dynamic Analysis - EH (Modal Analysis - Frequency Check ONLY)
Static Analysis - EC

Regards
SND

At the present time, the only way to use Eh in the Dynamics modules is to overwrite the value of Ec (with Eh) in the Piping Input. Note that this would affect subsequent Static re-runs.