Nigel,

I only ask because the client wanted to know what other design options were considered. They specifically asked about flexible pipe. Since flexible pipe is so expensive per foot, that pretty much killed it there. Another problem using flexible pipe involves keeping the flexible portion out of the "splash zone". For an equivalent 16" OD pipe, the minimum bend radius would be on the order of 13 feet. Technically the platforms were not high enough above mean sea level to accommodate the flexible pipe hanging down AND stay out of the 25' maximum wave height. Also, rollers were not used. Opted instead for guided shoes.

With regards to the fatigue analysis, I used an approximation based on data provided for storm deflections and everyday deflections. I seem to remember there being a pretty comprehensive write up in the CAESAR manual, but I may be thinking of another reference. The difficult part of the fatigue analysis was devising a deterministic analysis of a stochastic system. Finding the worst case of wave height, wave direction and frequency and then using that for each "segment" of the fatigue analysis. Not to mention extrapolating beyond the published stresses.

All in all, a very interesting and enlightening exercise.