Dear All:
thank you see this paper.

please see the attached CAESAR II file, i had a trouble.
the client want to know 40 years (2*10e8 cycles ) fatigue calculations, and i find the ASME 31.3 302.3.5 Stress Range Reduction Factor, f=0.15

now the question is coming, you see the CAESAR II model, and code stress check failed. all failed node in the knee joint part.

because my engineering experience is poor ,so who can tell me how can modifiy this model?

Hi aodi,

how is it posible for a system to undergo 2*10e8cycle for 40years? or 14,000cycle a day?... Do your client realy want to do this??

Regards!

Dear BOM:
yes, this is the client comment "The fatigue calculations are to be described. It can not be seen that fatigue loads from the wave bending moment is included (i.e. 2*10e8 cycles=40years for World Wide Operation) are not included. "

i am crazy about this comment.

Aodi,

Sorry to throw that comment but the number of cycle would be to imposible to perform in a day(14,000cycle) because this mean turning on and off your system to 10times/minute. and this will greatly reduce its life.

In my opinion in this case is that, you cannot reach the whole cycle with 6sec in interval. But if this is a special case then you have to provide much heavy duty material.

Regards!

Dear BOM:
thanks for you informaion,if this cycles changed 1*10e6(for example) and had failed node in the knee joint part too,
how can i do it?
BEST REG.

Aodi,

Please read your code or ask your senior for this. Or you can buy some book like Intro to Pipe Stress by Sam Kannapan and read the code requirement as a guide, it is currently available in its new edition.

Regards!

Dear Aodi,
I am not an expert on this but in my opinion these low amplitude, high frequency displacements from waves shall be treated as a fatigue case in Caesar and not an normal expansion case. Some companies also specify to do fatigue analysis as per PD5500

Once I had read an explanation about this from Mr. John Breen in this forum or engg-tips. You may get it if you search. I did a quick search now but could not get the link.

Siv

Daer Aodi,

I agree with Bom, this is a big cycle and life 40 years. I am very interesting to the case. Since I could not open the attachment, could you please send the *.CAESAR II file to my email: samsulpm@yahoo.com. Thank you very much.

I have a pdf file "High temperature flexible pipe joint" But not sure if this applicable for line pipe of the case.

aodi

Is this Wave Exceedance data you are talking about.

Hi aodi,

For simple case, this is not attainable, in my point of view but since you said, that this one deals with wave loading then this is out of my knowledge.. Maybe some of our experience engineer here in offshore could give us idea with this one.

Regards!

Thanks everyone.

Now my trouble is

this pipe system had sagging and hogging(a big quantity in displacement) and must be satisfy 40years(2*10e8 cycles) working, How do I modify model to fulfil the above conditions

best regards

Dear,
In my opinion your system is not going to face 2*10e8 cycles of maximum hogging and sagging.
Consider the hogging or sagging condition.The displacements will not be constant even if you are not doing any offloading or filling.Due to waves these will keep on changing by smaller amounts as compared to your hogging and sagging displacements. You can consider this as a sine wave with a non zero central amplitude.In my opinion your client is talking about these displacemnts when he mentions 2*10e8 cycles .
You need to consider the displacements from max hogging to max sagging for expansion stress range and consider these small displacements for fatigue analysis.
But again as I mentioned in my last post I have not done this type of analysis before.Hope somebody experienced reads this and advises you in right direction.
Regards
Siv