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#18030 - 05/15/08 08:00 AM use of Hot elastic modulus
StressTechie Offline
Member

Registered: 09/05/06
Posts: 10
Loc: usa
Hi,
I’m quoting one of the requirements of our German client -

"To calculate the stress in the piping system the piping system should be analysed with modulus of elasticity at the room temperature(Ec),
but to calculate the forces and moment at equipment nozzle and forces at restraint points, modulus of elasticity at operating temperature (Eh) has to be used."

Can some one tell me how to implement this in CII.
I can see that there are Hot elastic Modulus (H1,H2,H3) fields in CII input but they are not enabled.

Regards,
_________________________
Pipe Stress -The Deep Abbys

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#18038 - 05/15/08 11:37 AM Re: use of Hot elastic modulus [Re: StressTechie]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 5975
Loc: Houston, Texas, USA
The "hot modulus" fields shouldn't be disabled, what Version of CAESAR II are you using?

If you want to use the "hot modulus" for equipment nozzles, the easiest thing to do is setup duplicate load cases, and for these cases go to the "Load Case Options Tab" and (a) select which hot modulus to use, and (b)in the output type, pick "displacement/force" - which means there won't be stresses available for these load cases.
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Richard Ay
Hexagon PPM (CAS)

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#27171 - 05/05/09 08:58 AM Re: use of Hot elastic modulus [Re: Richard Ay]
Perseus Offline
Member

Registered: 04/30/09
Posts: 77
Loc: Dorset, UK
As an adlib, I found that the analysis would crash if I didn't set all the hanger design cases to EH1 as well as the OPE case. Can anyone confirm that I am doing this correctly or if there is a workaround?

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#27181 - 05/05/09 12:14 PM Re: use of Hot elastic modulus [Re: Perseus]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 5975
Loc: Houston, Texas, USA
That isn't right at all. All cases should run fine with "EC".

If you want to send your job in to "techsupport@coade.com", we'll take a look at it.
_________________________
Regards,
Richard Ay
Hexagon PPM (CAS)

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#27197 - 05/06/09 02:35 AM Re: use of Hot elastic modulus [Re: Richard Ay]
Perseus Offline
Member

Registered: 04/30/09
Posts: 77
Loc: Dorset, UK
To be somewhat clearer I needed the EH1 OPE case but I could not obtain this without the hanger design cases being set to the equivalent modulus.

Richard I've sent the model as requested.

Cheers,

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#27234 - 05/07/09 03:50 AM Re: use of Hot elastic modulus [Re: Perseus]
RK Offline
Member

Registered: 02/24/09
Posts: 173
Loc: India
In my opinion the better way is to calculate all laod cases with the Young's modulus at operation temperature to get the correct loads and the multiply the calculated moments with the ratio Ec/Eh to get the correct stresses. Am i right or something is missing?

Regards,
RK

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#27235 - 05/07/09 03:51 AM Re: use of Hot elastic modulus [Re: RK]
RK Offline
Member

Registered: 02/24/09
Posts: 173
Loc: India
I forgot to mention that I am talking about EN-13480

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#27236 - 05/07/09 04:13 AM Re: use of Hot elastic modulus [Re: RK]
Perseus Offline
Member

Registered: 04/30/09
Posts: 77
Loc: Dorset, UK
I'm using B31.3, not sure Ec/Eh ratio gives the same result.

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#27237 - 05/07/09 04:49 AM Re: use of Hot elastic modulus [Re: Perseus]
RK Offline
Member

Registered: 02/24/09
Posts: 173
Loc: India
can any one in the forum answer to my last post?

Thanks & Regards,
RK

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#27241 - 05/07/09 06:28 AM Re: use of Hot elastic modulus [Re: RK]
MoverZ Offline
Member

Registered: 11/22/06
Posts: 1195
Loc: Hants, UK
RK,

Use of Ec/Eh to factor up hot modulus stresses to Ec values for B31.3 Code compliance may be acceptable, in a truly linear system. However if you introduce any non-linearity such as one way restraints you risk serious errors.

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#27285 - 05/08/09 02:35 AM Re: use of Hot elastic modulus [Re: MoverZ]
Perseus Offline
Member

Registered: 04/30/09
Posts: 77
Loc: Dorset, UK
Thankyou MoverZ

Clearly a system with friction does not allow this ratio either.

Anyone had issues with hanger design for EH? Setting the OPE case to EH(1) necessitates (as far as i'm aware) all other cases being set to EH1 to run - certainly the hanger design cases.

Still don't have a definitive response confirming or denying this.
I would love to be able to run all the cases I need in one go, rather than 2 or 3 jobs.

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#27291 - 05/08/09 07:13 AM Re: use of Hot elastic modulus [Re: Perseus]
CraigB Offline
Member

Registered: 05/16/06
Posts: 378
Loc: Denver, CO
The long and short of it is that, if you run your analysis with Eh, you have to go adjust all your support loads by Ec/Eh. If, instead, you run the analysis using Ec in all cases, you have to correct your terminal point loads by the ratio of Eh/Ec. Since this second approach requires you to do much less hand calculation, and a procedure is given in B31.1 Paragraph 119.10, this is what you should do. In B31.3, Paragraph 319.5, the analyst is specifically directed to calculate all support forces and terminal point reactions using Ec.

So I am not quite sure why you are asking this. You are being directed to calculate support loads using Ec. Fine, run your analysis using Ec. You are being directed to calculate terminal point loads using Eh. Fine, adjust the terminal point reactions as permitted by B31.1, Paragraph 119.10, equation 9. Note that, if you are using B31.3, you are not permitted (see 319.5) to use Eh for any reason other than to calculate the amount of required cold spring.

If you had spent half the effort reading the codes that you have spent asking other people to read them for you, you'd be done by now.
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CraigB

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#27293 - 05/08/09 07:48 AM Re: use of Hot elastic modulus [Re: CraigB]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 5975
Loc: Houston, Texas, USA
RK -

I just ran a job with EH1 for OPE1. I then went back and changed the two hanger design cases from EC to EH1. The job ran fine with no problem.

If you're running EN-13480, this Code states that you should use the "modulus at temperature" for the flexibility analysis. The Code makes no mention of what modulus should be used for hanger design, so (in my humble opinion) you should use EC unless specfically directed otherwise (for hanger design).
_________________________
Regards,
Richard Ay
Hexagon PPM (CAS)

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#27300 - 05/08/09 08:43 AM Re: use of Hot elastic modulus [Re: Richard Ay]
Perseus Offline
Member

Registered: 04/30/09
Posts: 77
Loc: Dorset, UK
Craig,

Thankyou for a good explanation.

Reading the code and applying it are different entities, that's why forums like these are useful to clarify code practice. Unfortunately I don't have the privelege of a pipe Guru to consult, so I use all other resources to hand and maintain a conservative route.

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#73302 - 05/21/19 02:28 AM Re: use of Hot elastic modulus [Re: Richard Ay]
whm Offline
Member

Registered: 08/29/05
Posts: 101
Loc: China
If run a job with EC for OPE1 and with EH1 for OPE2,
change the NO.2 hanger design case from EC to EH1. The job run ,the hangerloads of OPE1 and OPE2 are all have some difference with the load of NO.1 hanger design case.

Why?

Is it wrong to use different elastic modulus for the NO.1 and NO.2 hanger design cases?



Edited by whm (05/21/19 02:34 AM)
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whmwhm

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#73309 - 05/21/19 10:40 PM Re: use of Hot elastic modulus [Re: StressTechie]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 5975
Loc: Houston, Texas, USA
The elastic modulus is a term used in the formation of the stiffness matrix. Once the stiffness matrix (and load vector) are formed, CAESAR II solves the matrix equation [K]{x} = {f}, for {x}.

If you change E, you change [K], therefore {x} changes. This applies to the hanger load cases as well.

Almost all piping codes state that the flexibility analysis be performed using the cold modulus of elasticity. The exception to this statement is EN-13480 (and those codes based on 13480). However, even these codes don't discuss hanger cases with regard to the elastic modulus.

I suggest you use Ec for your hanger design load cases.
_________________________
Regards,
Richard Ay
Hexagon PPM (CAS)

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