We are doing an Offhore bridge line analysis. While carrying the fatigue analysis we have stuck up at fat file cycles.

There is a cycle due to Ocean waves, there is a cycle available in the ASME Section 3. Please advice us how shall we calculte the Offshore Bridge piping line cycles for fat files in Caesar II fatigue load cases

JANARDHANA,

Your question is not clear? Are pipes submerged in water or laying on bridge? Is this bridge between 2 platforms?

Ya, the bridge is between two platforms.
The Ocean cycle (for jackets) is say x Cycles.

And ASME cycle is say Y Cycles.

Now Fat file has a provision for cycle entry.

This could be a Temp/Process/Operation based/Material/Ocean cyles or all combined together.

Do we have any means for the same?

Ya, the bridge is between two platforms.
The Ocean cycle (for jackets) is say x Cycles.

And ASME cycle is say Y Cycles.

Now Fat file has a provision for cycle entry.

This could be a Temp/Process/Operation based/Material/Ocean cyles or all combined together.

Do we have any means for the same?

As you know bridge is fixed at one end and sliding at another end. Any relative displacement due to temp. change with anticipated cycles must be considered. As long as jackets are fixed and exposed to ocean wave and current, fatigue wave load is appleid to jacket's structure not piping.

Farhad, you are wrong, and I think you have seriously misled this guy. Yours is very dangerous and very poor advice.

You are correct in that most inter-platform bridges are fixed on one and sliding on the other platform. However, movement of EITHER jacket due to wave load in the direction of the bridge axis will either COMPRESS or EXTEND the pipe between the two platforms. This is usually accommodated in loop arrangements. The worst case has to be both jackets moving exactly out of phase due to a large wave height, giving the maximum movement range and thus stress range. In my experience this has been as large as +/-750mm absorbed in loops.

Such massive movements will occur only due to large and infrequent waves, so contribute little to fatigue damage. Mid sized, high occurence waves will cause the most fatigue damage.

You should be thinking about a Miner's Rule assessment of fatigue life. Excellent guidance can be found in DnV documents.

MoverZ,

Thanks for your advice. But this guy didn't mention any relative displacement of two platforms, if you read his posts. In the case of platform movements, you are absolutely correct.

Farhad,

It was your assertion that somehow, fatigue loads applied to the jacket would not translate to pipe stress that concerned me. All platforms, just like every other structure, deflect under load. I have been on many 'fixed' platforms in North Sea storm conditions, when it was difficult to stand still due to deck movement caused by waves and wind and have observed very large movements of teflon sliding supports around bridge loops.

Given that piping crossing a bridge from one platform to another will often be production and test headers, from wellhead to process areas and thus very high pressure and stiffness, they will be some of the most critical lines on the plant.

Again, DNV-RP-D101 is a very good material.

I really do apreciate the people that contribute to this reccomended practice.

Best regards,

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

Thanks & good reply.

Ya, DNV can give very good explanation.

Since huge dispalcements to the bridge piping have been given including the fatigue case displacements of the structural analysis, the CYCLE need not tbe the same as that of the Ocean wave cycles for the piping inside the bridge.


Look ASME cycles would be around 10 rasie to 5 & real wave cyles would be 10 rasie 7 & there is a structure in whcih piping is safely put-in.
The only argument would be the piping cycles need not be the same as that of the cycles that occur due to the damage by the waves.

Hi all, more suggestions are welcome to make Piping Engineers design confortable by the structural and wave inputs.

regards,
Janardhana Acharya Gurugundi

It is not easy to evaluate. Refer BS5500 fatigue curves and apply in evaluating.