Fatigue Design of Roller Bearing for Large FPSO Turrets

Abstract

The present report presents the fatigue design and a fatigue life prediction method for large roller bearings applied in the turret turn table for large Floating Production Storage and Offloading (FPSO) units. The contact point between wheel and rail in these bearings is subjected to a multi-axial stress situation and both surface wear and fatigue cracking may occur. Stress analyses with contact elements are carried out and a methodology based on the Dang Van fatigue criterion is adopted. The criterion is based on an equivalent stress defined as a combination of the fluctuation of the shear stress from its mean value and the associated hydrostatic stress at a critical plane at any time. The criterion has been used in the railway industry and is regarded as an appropriate approach for the crack initiation phase in the high cycle fatigue regime. A realistic case study is included where material combinations with high strength stainless steel S165M and high strength carbon steel 42CrMo4 are applied. It is demonstrated that a favorable wheel-rail design is characterized by an extreme load condition with a stress situation within the linear elastic behavior of the steel. Furthermore, the Dang Van equivalent stress function shall be below the shear stress fatigue limit. These two design criteria will ensure robust design and long durability of the turret bearings.