Dear Rakesh Kumar
You missed the fatigue analysis which is very important for FPSO's.
Regards
Tanmoy Saha
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Subject: Re: [PipingDesign] 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.
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
> 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
>
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Yahoo! Groups Links Received on Sun Jul 17 00:03:00 2005
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