Validation of the corrected Dang Van multiaxial fatigue criterion applied to turret bearings of FPSO offloading buoys

In engineering practice, multiaxial fatigue analyses are often avoided due to their complexity and computational intensity. However, damages have been encountered in turret bearings of Floating Production Storage and Offloading vessel (FPSO) offloading buoys which were likely caused by multiaxial fatigue. The Dang Van criterion has often been used to assess problems with multiaxial fatigue in rolling contacts. Therefore, this study set out to validate the application of the Dang Van criterion to turret bearings of FPSO offloading buoys. For this purpose, the criterion was corrected with a horizontal conservative locus for compressive hydrostatic stresses. Three load cases were identified based on the seakeeping analysis of an FPSO offloading buoy equipped with a wheel-rail turret bearing. For each load case, the surface pressure distribution and sub-surface stress states were determined analytically. Staircase tests were used to determine the characteristic parameters (α and β) of the Dang Van curve. Then, the Dang Van criterion was corrected and used to perform a multiaxial fatigue analysis in the critically stressed area of the wheel-rail contact. Finally, full-scale, long-duration fatigue tests were used to validate the results. The corrected Dang Van criterion shows agreement with the experimental results and is not rejected as multiaxial fatigue criterion for application to turret bearings in FPSO offloading buoys