Hi all,

I am doing static analysis for a 12" oil line running on a offshore bridge of 60m long connecting two platforms.
The client asked for fatigue analysis to be done for this line.

As per DNV, The bridge pipe is subjected to fatigue.

But, I would like to propose if the number of cycles calculated based on PD 5500 code is well within the limit of max cycles in S-N curve for the max code stress from static analysis, the detailed fatigue analysis is not required.

Please refer attached image for the criteria from PD 5500.

Is there any other simplified way in other codes to check the fatigue damage without detailed analysis? please do share your experience.

Fatigue analysis is never simple. DNV requires Miner's Rule and application of relevant S-N curves, and should be considered a minimum requirement for offshore bridge pipework.

It's not rocket science, but is does deal with the respective damage levels from the various wave height and occurance combinations.

IMHO, PD 5500 is not relevant to offshore bridge piping.

Finally remember that a hydrocarbon pipe fatigue failure on a bridge might cause a catastrophic fire and block a primary escape route. At least, it would be a nightmare to repair.