Abstract: This study investigates the S-N fatigue behaviour of S355 double-V transverse butt welds used in offshore wind foundations. As-welded seams are analysed using PCA and Bayesian regression: the former filters non-relevant data, while the latter accounts for runouts, heteroskedasticity, and misalignment. Ground flush welds are also studied using Bayesian inference, but due to limited literature data, additional experiments are conducted to assess the role of microstructure.