Piping stress analysis for FPSO

[nickcaiyh]

Dear all professionals,

I have put this post in COADE forum but not got anwsers yet, so I came here for more help.

Would you please do me a favor on piping stress analysis issue for marine case?
Is there a recommended load case combination for FPSO? I understand there would be many factor need to be considerred, such as wave motion, deck deflection, wind, etc. I also checked the DNV-RP-D101 for some information, but the recommended load combination does involved the sagging and hogging case.

As onshore, the wind and accelaration will be treated as OCC load, and we will take the factor 1.33 on considering stress range, however for FPSO, I think the wind and wave motion should not be seperated, if I treat this comination as OCC, does that means the factor should be 1?

For the wave motion, I simulated it as uniform load as G accelartor, should I need to confirm about the wave main direction and input it as a vector? Considering on wave accelaration, how serious case we normally used for calculation? Once in a 100 years or else?

I also concerned about fatigue analysis for piping, but not figure out a solution, does any professionals here have good suggestions?

Thanks a million in advanced!

 

[DSB123]

nickcaiyh,
Forum rules are that you do not "double post". I know you have not had any response on the other forum but it is the most appropriate one. The questions you ask are probing ones but I do not think you will get many if any responses since the methods for analysing FPSO pipework are generally closely guarded.

 

[nickcaiyh]

Dear DSB123,
I apologize for breaking the rules, I post the topic here was that I found people here are more willing to talk and dicuss, I really got many good suggestions here.
It seems that the piping stress analysis on a FPSO is kind of "esoteric", while, I googled and gathered a lot seperated information for this topic, I prepare to intergrate them into a reasonable piping stress analysis spec.

I would like to share some:

1),"RP-D101_2008-10 STRUCTURAL ANALYSIS OF PIPING SYSTEM", this standard given the detail infomation, in APPENDIX G, a recomended load case combination listed, however, deck deflection does not involved, and does not clear on how to determin the Max wave motion direction and also for Max wind direction.

2),"FPSO related piping and pipe stress aspects" it was a PDF I found on google search, it shows to devide the calculation into two parts to avoid numerous combinations of load. First to decide the Max wave motion direction, then perform the rest calculation.

3),A video downloaded from Intergraph website,"

http://www.intergraph.com/global/eu/go/Intergraph-Analysis-Webinars.aspx",

it was a exsiting project which use CAESAR II for piping stress analysis on FPSO.

I would continue on the study next.

Thanks and Best regards,

Nickcaiyh

 

[DSB123]

nickcaiyh,
The video in 3) does not cover the Fatigue aspect of the analysis of FPSO pipework. I watched the webinar as it was given and posted several questions as to how Aibel covered the fatigue aspects. So really it provided you with no information.

So you are going to use Caesar II to analyse the systems and then how do you propose to use the "Code" calculated stresses to perform a fatigue analysis. You cannot use Caesar to perform the analysis since Intergraph have acknowledged that Caesar does not perform a fatigue analysis in accordance with ASME VI Div 2 (latest edition). Are you going to adopt the method in DNV D101 because that is in accordance with PD 5500 and requires stress ranges NOT "Code" stresses.

 

[nickcaiyh]

DSB123,

Thank you very much for you kind reminding.

CAESAR II will be applied to perform the calculation with code B31.3 for piping system topside. Fatigue analysis is really a big problem, however, I got to know that someone dealing with the fatigue in CAESAR II was to fill the "Fatigue Cuves" data in the classic piping input dialog box, and then combine to load case. I am not quite clear if it was reasonable, but I would like to try. As I have limited experiences on fatigue analysis, I planed to reduce the stress level as much as possible for help.

We also separated the piperack into seveal structure parts recommended from the hull manufactory, maybe it could help on metal fatigue performance.

Best regards,

Nickcaiyh

 

[DSB123]

nickcaiyh,
The stresses you calculate using Caesar are Code Stresses whereas to perform a fatigue analysis you need to use actual stresses. Also where are you getting the fatigue curves for input to Caesar?

 

[LSThill]

(FPSO & Topside Facilities Piping Stress/Fatigue Analysis)
• Hogging-Sagging and acceleration (towing) Analysis - Piping Stress Caesar II & Fe-Pipe
• FPSO Piping Stress & Fatigue Analysis - Piping Stress Caesar II & Fe-Pipe
• Topside Facilities Piping Stress & Fatigue Analysis - Piping Stress Caesar II & Fe-Pipe
• PDMS- Piping Stress Caesar II & Fe-Pipe
• OS (On-Site): D1,D2,D3,D4,D5; Analysis - Piping Stress Caesar II & Fe-Pipe
• TC (Towing Condition): D1,D2,D3,D4,D5; (towing) Analysis - Piping Stress Caesar II & Fe-Pipe
• FS (Fatigue Stress): D1,D2,D5; Fatigue Analysis - Piping Stress Caesar II & Fe-Pipe
• FSTC (Fatigue Stress -Towing Condition): D1,D2,D5; (Fatigue / Towing) Analysis - Piping Stress Caesar II & Fe-Pipe
• Vendor Skied Package Review {FE/PIPE v5.0, Nozzle.PRO v7.5, MatPRO v2.0,}

 

[XL83NL]

Leonard, can you explain what (in general) is the contribution of any of your posts to any topic, apart from providing a literature list of some sort?

 

[DSB123]

XL83NL,
Good observation. Maybe I can answer your question - None. The guy bnever actually answers a question just contributes a Bibliography or "cuts and pastes" references etc. No specific responses are ever given!!!

 

[nickcaiyh]

DSB123,

I recently found another dicussion with the link below:

http://www.linkedin.com/groups/Fatigue-Curve-SN-Piping-Stress-1924654.S.171183961

I found the topic was discuss much, but seldom found a clear answer, I am not quite that if I could treat it as a hign cycle fatigue case, as the cycle does not come from temperature but from the deck deformation.
Just as you said, I really can not find the fatigue curve suit for my case. I would like to know if I could make the total piping stress level lower than 80%, the fatigue case then could be omitted?

Best regards,

Cai Yunhe

 

[LSThill]

hope this will help

Efficiency and Economy of Automating Displacements for FPSO Pipe Stress Analysis
OTCpowerpoint(FPSO pipe stress)[1]

 

[LSThill]

Efficiency and Economy of Automating Displacements for FPSO Pipe Stress Analysis