Re: Stress Analysis of FPSO with Caesar II

Dear Ali,
This is the most difficult question in stress analysis for FPSO lines. Where is this FPSO situated (ambient temp. can also be -30C in some conditions)? Here are some factors; combination of which are to be done judiciously. In order to reduce the no. of cases to a minimum; discuss with team members and take collective decission. I am mentioning here some factors (matrics of these variable will give rise to some 250 cases of combination) which are to be cosidered while deciding stress analysis specifications/ methodology for your project. Some figures are taken just to show the range( figures are realistic). Eleminate the least sever cases. Make combination of worst cases.

1. Temperature: Operating (T1=55C), design hot (T2=65C ), design cold {could be -30C(T3) depending upon location of FPSO, as in case of Norway}, upset condition (T4=80C) and shut down condition(T3= -30C or 21C ambient temp).
2. Thermal Growth of Nozzles:Thermal Growth of nozzles are to be taken for above temteratures. Movement to be superimposed with movement of nozzles and supports due to pitiching, rolling and vertical movment of ship.
3. Deflection of all supports and nozzles due to Pitching, Rolling and vertical motion of ship for 100 or 50 year storm condition . Please note that for 100year storm condition consider only operating case and not design, upset cases etc. After certain rolling/ pitching angle plant will trip. In our case axial movent for flare line was -100mm and +100mm (i.e. 200mm). We reduced the factor "f" of stress range to 0.7 to take of fatigue cycle.
4. Wind load: Selection of direction of wind. It could be +X,-X, +Z, -Z. Y direction can be neglected for wind load.
5. Explosion load: In case of explosion application of wind load in all direction i.e. +x,-x, +y (-y can be neglected as it will be compressive load and is rare also) +z and -z. But in explosion load we can go for higher allowable loads and stress i.e. upto yield stress.
6. Acceleration: Acceleration is to be applied in different direction individually (x,y,z). Wind dierction and acceleration direction can be diffrent.
7. Snow load: Loading due to snow in addition to insulation is also to be considered by application of UDL. But this can be excluded by calculation of basic span for each spec. and schedule.

So no. of cases will be:
A) Operating: With operating temp., Design (hot) temp, design (cold) temp. and Upset temp. with combination of
i) wind ii) without wind iii) acceleration iv) without acceleration vi) with movements due to pitching rolling yawing. B) Hydrotestig
C) Explosion

Dynamic analysis may be done only for lines with two phase flow and for compressor line (for crude injecting module).

To take care of such extreme cases we indicated in MR itself (and also in stress analysis basis) for higher nozzle allowable loadings: 4 times of API610 for pumps and 8 times of API617 for compressors.

Dear Ali my reply may not solve your problem rather may complicate it but may highlight some factors which you may be forgetting. I could have attached the stress analysis specification but now I am on foreign assignment to Qatar and all my refrence doc. are lying in India. I request you to email me the final methodology of analysis (rakesh8193@yahoo.co.in) of this job which will be interesting indeed. Dear Ali I attended one lecture on stress analysis and in that I cam to know that around 250 cases are analysed in nuclear power plant. However we were also not very sure about the no. of cases to be performed in our FPSO job. But every one was willing to analyse minimum no. of cases and min. no. of runs. After great arguments we land up for at least 3 no. of runs containg around 9 caeses each. Exact sequence and combination no of cases I dont know now as I did it in 1998.
Please reply back to me and please write your reaction/ action on this issue.

Regards
Rakesh Kumar
Engineers India Limited, Qatar
Manager, Piping

• Original Message ----- From: "Ipakchi, Ali" <AIpakchi@hanover-co.com> To: <PipingDesign@yahoogroups.com> Sent: Friday, July 15, 2005 1:08 PM Subject: [PipingDesign] Stress Analysis of FPSO with Caesar II

> Dear All,
>
> Can anyone cast a light on this:
>
> What are the most common load cases which to be considered for stress
> analysis of piping systems on a FPSO and how normally we define these
> loads for CII?
>
> Is it possible to just go for Static analysis with some Dynamic load
> factors or Dynamic analysis is manentury.
>
>
> Thanks
>
>
>
> Ali
>
> ***** CONFIDENTIALITY NOTICE *****
>
> This message (including any attachments) contains confidential information
> intended for a specific individual and purpose, and is protected by law.
> If you are not the intended recipient, you should delete this message. Any
> disclosure, copying, or distribution of this message, or the taking of any
> action based on it, is strictly prohibited.
>
>
>
>
>
> =========================================
> PipingOffice - Excel Spreadsheets for Piping Calculations
> http://www.pipingoffice.us/
> =========================================
> Main site: http://www.pipingdesign.com
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
Received on Sat Jul 16 04:38:00 2005