Dear Ingrid,
With only one seed per wind-speed bin, I would be a bit concerned that the calculated fatigue loads would depend on the seed. I would suggest running more seeds to assess the sensitivity–ideally the fatigue solution would be seed independent.
There is some discussion on how to choose LUlt in our FAQ: nwtc.nrel.gov/FAQ#TypeLMF. For a simple cylindrical steel cross section, you should be able to calculate LUlt analytically see e.g. my post dated Feb 23, 2016 in the following forum topic: MLife/Interpretation of DEL and LUlt - #2 by Jason.Jonkman.
For steel, often the fatigue analysis is performed over a range of material exponents e.g. m = 3, m = 4, and m = 5.
Best regards,