Hi,
It was told by our process department that in a segment of Flare Header, magnitude of ρV2 is equal to 212,000 kg/m/sec2 which is slightly higher than allowable (200,000 kg/m/sec2) as per process design practice. Now they are asking piping stress group to confirm whether this is acceptable.
(where ρ-density, V - velocity of flow)

I guess this is the surge pressure at one of the operating situation of flare system. My question is as follows:
1. What is the limiting criteria of &#961;V2 and what about those lines where &#961;V2<200,000 kg/m/sec2 ?
2. Do we really consider surge load in flare header analysis?

Appeciate your suggestion / advice.

Regards

Dear Manoj Sarkar,

Go to first topic in the list "Piping disaster and incident" Raed the post regarding to Salah incident.Search in google using keyword Carucci & Mueller paper.xtrados.com also provides salad. I am not expert in this field but this only I have relate to that Q. This regards to vibration of piping.

Manoj,

Flare lines can be subjected to two phase flow for obvious reasons. Talk to Process group for the same. Analysis methods are well established.

I am not sure of the rho v^2 issue on the flare system. Rho v^2 is typically a parameter which industry prefers to associate with a phenomenon known as as " flow induced vibration". Lexically, flow induced vibration can be anything which is flow related. However, the above terminology is used to designate the flow transient which results due to pressure pulsations due to flow separation at elbows and flow restrictive devices.The remedy induces, controlling rho v^2 , separation of mechanical and acoustic frequencies ( for an understanding of what acoustic frequenices are , read Fundamentals of Noise and Vibration analysis for engineers by Norton and Karczub. To mention simply , they are the solution of the Eigenvalue problem resulting from the Homogeneous eqn. known as Hemlholtz eqn. and are the frequencies at which standing wave patterns are generated)and computation of Forces due to pulsation ( there are empirical relations ships for the computation of these forces) and the resulting bending stresses at TEE JOINTS. These bending stresses are checked against endurance limit.

Flare lines are subjected ( mostly ) to Acoustic induced Vibration for which the paper mentioned by Samsul is the bible.AIV is a function of D/T ratio and a product of M X Delta P where M is the Mach no. of Flow and Delta P is the pressure drop at restrictive devises.Rho v^2 is not a parameter for AIV as AIV is related to gas flow only and rho is negligible for gas.

Hence, I am not sure why Rhov^2 should be a yardstick for Flare lines which contain gas only ( except for the liquid bolus which results in two phase flow).

Regards

Anindya,Samsul,

Thanks for your help.

I understand that the criteria of ρV2<200,000 kg/m/sec2 for flare line is as per NORSOK P-001 to avoid flow turbulance and acoustic vibration.

Request experts guidance on calculation methodology for lines having higher ρV2> 200,000 kg/m/sec2.

Regards,

Refer the MTD guideline. This will give you qualitative but not quantitative solutions.Actually if the LOF is greater than 1, bending stresses have to be computed ( the otjer corrective actions are increase in all thickness, increase in diameter etc, more supports etc )as suggested by me in my previous post.However I will not be able to reproduce these equations.

However flow induced vibration is a low frequency vibration as opposed to acoustic vibration which is high frequency and in flow induced vibration, it is basically planar wave propagation and hence confined to smaller diameter pipes ( typically) less than 10 inch. Hence I don't see possibility of flow induced vibration in large flare systems but there is every possibility of acoustic vibration( high frequency acoustic vibration is not that dependent on rhov^2 but is dependent on Mach no times pressure drop)

Regards

I will summarize my views and recommendations in the following way:

1) Flare lines ( besides two phase flow) can be subjected to two different kinds of vibration , both of which are flow related.

2) The first type which is known as acoustic induced vibration is more probable.This does not depend on rhov^2. It depends on the product of Mach No. and Pressure drop at valve stations. It is a high frequency vibration which excites the " circumferential modes" of vibration. This type of vibration is addressed by the paper by Carucci and Mueller and the paper by Francis. Francis's paper puts a D/T restriction of 64 for systems where sound power level exceeds that of what is max. allowable for a D/T ratio.

The other solutions are use of anti-vibration trims,special valves,avoidance of weldolets, use of welding tees, use of full encirclement reinforcement at welded pipe supports ( or use of clamped pipe supports at non axial stop locations ) etc.

MTD also provides guidelines for the same.

3) The other type of vibration ( less probable)due to flow is what is known as Flow induced vibration ( an industry name ). This is a low frequency vibration and excites the planar modes. This is a function of rhov^2 as well as the stiffness of the system. MTD guidelines provides formula for calculation of L.O.F or likelihood of failure ( refer second edition of MTD as first edition provides a conservative estimate for gaseous systems) where the term rhov^2 appears.

This guideline also provides correction actions. However a better approach is to compute the pulsating forces( flow induced vibartion is more related to flow velocity and the pressure pulsation due to flow separation at elbows and valves where as acoustic induced vibartion is more realted to pressure drop at valve stations) and thereby compute the flexural stresses at tee points.These flexural stresses are checked against endurance limit. Computation of such forces are based on empirical relationships which I cannot reproduce in the forum.If this approach is not possible, then MTD guideline recommendations can be followed or to put in more general way, recommendations that are valid for acoustic induced vibration are also valid for flow induced vibration and same can be followed.

Hope this helps.

Anindya,

Thank you very much for the excellent advice.

As recommended by you, I am looking for a copy of the paper by Carucci & Mueller, the paper by Francis and MTD guideline. If the above said documents are readily available with you, may I request you to mail at Manoj.Sarkar@sbmoffshore.com

Reagrds,

I have responded at your email address.

Regards

Dear Aanindya/manoj please send me the papers too.

thank you

lee

Manoj,
This is one (Momentum criteria)of the methods used for sizing the pipe / pipe line . I do not know why process engr. thrown this issue to a stress engineer whose involvement is NIL in this case . If &#961;V2 exceeds the limit, let him(process) check if velcoity is within the "erosion" limit.
It is his baby , not yours so throw back to him.

However, Keep in mind that the higher fluid velocity might induce vibration hence, try to keep this line with minimum natural frequency of 4HZ.at least .

MSM,
You are quite right. I know, acoustic analysis also addressed by process department of all of my previous companies.

Some companies consider a addition load of (ρV2)A (multiplied by a suiable DLF) while disigning line stop at flare header, but never input this force in Caesar file , as such, no pipe stress check performed considering this force. Do anybody have any experience about this practice?

Regards,

Unless process says there is a possibilty of slug, no need to consider this force. Unnecessary increasing the support memeber / cost .

Dear Anindya,

Same with me, I am looking for a copy of the paper by Carucci & Mueller, send to yohanesw@gmail.com

regard's

Yudi
KBRI

MSM,

The issue is not only with momentum criteria but also with low and high freqency vibration which is outside the area of expertise of process engineer and hence he has correctly passed it on to the stress engineer.The stress engineer from his /her side can of course pass the baton to noise specialist who mostly address the issue of high frequency vibration ( acoustic vibration mentioned and explained in my response. The type explaiend in Carucci's and Franci's paper). The low frequency vibration ( flow induced vibartion mentioned in my response)which involves turbulence and flow separation is the regime of the expertise of pipe stress engineer ( albeit this also requires computation of some acoustic modes , which , luckily being the planar modes can be generally computed w/o a detailed coupled acoustuc-structural analysis).Regarding high frequency vibration, instead of rhov^2 the process engineer should compute the sound power level which is a function of Mach No, Pressure drop, Molecular weight and Temperature .

Regards

Anindya,

I think you did not read the last paragraph of my earlier response. Conisdering the flow induced vibration i notified that the system to be kept atleast with min. natural frequency of 4HZ.
Acosutic analyis is out of stress Engineer's boundry.

Dear Anindya,

I am also looking for a copy of the paper by Carucci & Mueller.,
Pls send to geesree79@gmail.com
Thanks & regards
gs

Dear MSM,

Please read link below and read Anindya posting there:
http://www.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=10625&page=1#Post10625

Go to xtrados.com, download AIV.pdf there. We all know that it is out of piping stress analysis. The 4 Hz natural freq, fn is not subjected to this case. This is special case.

Hope oneday COADE will add module relates to it in under analysis menu and add introduction theory. Salad uses the model file generated by Caesar as its input. Is it possible?

Dear MSM, Samsul, Anindya,

MSM's way is the way most of stress group follow in industry. Most of the engineering company assign this task to specialist third party (in absence of inhouse experts)to handle acoustic analysis who liase with process department, in tern process intimate piping about necessary modification in pipe size, thickness, RF pad, min.frequency etc.

I personally feel that stress group should be encouraged to carry out acoustic analysis in house with help of process gruop to obtain cost effective and most practical design of flare system.

I once again appreciate Anindya for guiding us. In line with Samsul, I also hope that one day COADE will add module for acoustic analysis.

Regards,

Majoj,

Perhaps it will not be possible for COADE to do so as or the higher order acoustic modes, we need to use shell elements . My undertanding is that COADE will stick to beam element based FEA only ( Richard/Dave correct me if I am wrong).

MSM , as pointed out by others, 4Hz has nothing to do with higher acoustic modes which excites the shell modes, frequencies sometimes reach as high as 3000 Hz.


Regards

Anindya,

Exactly. The "3D Beam" element used in CAESAR II is not capable of addressing this type of analysis. This sort of evaluation would require a completely different software package.

Pl. find attached the papers by Carucci and Mueller and the one by Francis.

My recommendation will be : to properly comprehend both the papers , one should read Fundamentals of Noise and Vibration analysis for Engineers by Norton and Karczub.

Regards

Dear Anindya i am not able to download the pdf files can u just mail to me palanidex@gmail.com or palanimech06@yahoo.co.in

Hi Anindya, I am in the same situation that Paldex, it is not possible to download the Carucci and Mueller papers nor Acoustic Fatigue document, please send them to:
dagoberto.gonzalez@kbr.com or dgl94@hotmail.com

Thanks in advance.

Anandiya, please upload again.

many thanks
lee

I have tried tp upload again. Let's hope it is all right this time.

Regards

Dear Anindya

Still same problem. Not able to download the file.
Pls send to geesree79@gmail.com.
Thanks
GS

Hi,
Please include me also in your mailing list for these papers.

piper11@walla.com

Regards
Siv

I have made a list of all email ids who require this document.I will send it to all of you asap.

Regards

Anindya Sir,

I hope you can send me some copy.. thanks a lot...

my email silman_re22@yahoo.com.

Regards,

Mr.Anindya,

Please add me in your mail list.
mvp2k6@gmail.com.

Thanks,
Paddy.

Dear Anindya,

Same with me, please send to yohanesw@gmail.com

Thank's

Yudi

As the list is ever increasing, I have not yet send the documents to anybody. I will do it by Monday to all who have requested the same.

Regards

If I am not too late please include me in the distribution
robinchandy@msn.com
Thank you.

Mr. Anindya,
please send me too those paper to rois_s@yahoo.com.
Thank you


Regards,

Rois

Guys,

Many of you have got the paper by Carucci & Mueller now - can one of you (or all ) forward it to sanjay.banerjee@aee-australia.com.au please?

cheers,

Dear Anindya i am not able to download the pdf files can u just mail to me palanidex@gmail.com or palanimech06@yahoo.co.in

I know that i am too late... can anyone forward the papers to vikas_ud@yahoo.co.in?
please..

Dear Anindya,

Can you please send the files at saurabh.2001@gmail.com


I'll be really grateful to you.


Hope I'm not troubling you.


Thanks in Advance,

Regards,

SJ


“One of the most responsible things you can do as an adult is to become more of a child.”

Hi Manoj,

Myself also facing same problem of limiting criteria of rhoV2<100,000kg/m/sec2, indicated in total process specification for vibration and support checks.

I have understood basics from valuable previous post from Mr.Anindya.

Can you kindly send me the information, papers and MTD guideline if you have.

mnjnyk@gmail.com

Please, let me know how did you solve the problem and your exp as well.
Thanks
Manjunath

Dear Anindya,

Can you please send me the files at gspatil08@gmail.com.

I will be greatly thankful to you.

Regards,

GSP

dear anindya,

please send the files to satheesvictory@gmail.com.


thanks in advance
A.Sathees kumar

Dear Anindya,

Can you please send me the files at karmakar.tp@gmail.com
I will be greatly thankful to you.

Regards,

tpkarmakar

Dear Anindya ,

my queries is given below
1) is the flare header line required stress analysis ?
2) is the flare header line required surge analysis or slug flow analysis ?
3) or it require thermal shock analysis?

which type of analysis is subjected to the above subjected matter , to confirm the system is adequate to sustain all cases.

with Regards

Dear Anindya,
I'm working on Acoustic vibration study for a gas plant. I think the papers you mentioned can help me for doing vibration study.
Can you please send these files at swapnilymeshram@yahoo.com

1. 424-CARUCCI.pdf
2. 425-AcousticFatigue.pdf

Thanks in Advance,

Regards,

Swapnil

Hello Anindya,

Kindly send me the file also at tibor121774@yahoo.com.....Many thanks in advance......

Dear Anindya,

Can you please send me the files at gspatil08@gmail.com
I will be greatly thankful to you.

Regards,

PDSE

Dear Anindya,

Can you please send me the files at ozmaian@yahoo.com
I will be greatly thankful to you.

Regards,
javad

Mr. Anindya,
Can you please send me too those papers to emreysl@yahoo.com.
I will be greatly thankful to you.

Regards,

Emre

Could some of you send me:

1. 424-CARUCCI.pdf
2. 425-AcousticFatigue.pdf

my mail il mignemi.francesco@libero.it

Thanks in advance for your help

Regards

Dear Anindya,

Can you please send me the files at lorry_001@yahoo.com
I will be greatly thankful to you.

Regards,

Pandoraer