FPSO Triton: UP treatment of Side Shell Longitudinal
FPSO Triton: UP Treatment of Side Shell Longitudinal
Finite Element Analysis (FEA)
Finite Element Analysis (FEA) calculations revealed significantly lower fatigue lives for certain welded connections in the water ballast tank (WBT) on both the Portside (P) and Starboard(S). To address this, six WBTs will undergo ultrasonic peening treatment, with the primary objective of extending the fatigue life of these critical weld connections.
The specific weld locations requiring attention are the side shell longitudinal welds near the typical web frame and those adjacent to the transverse bulkhead. The fatigue life assessments for these connections—15 years and 7 years, respectively—fell significantly short of the targeted structural service life of 20 years for the FPSO Triton. As a result, it was determined that ultrasonic peening would be implemented to enhance the fatigue life of these welds.
Based on internal fatigue testing, SN design curves, and IIW recommendations for improved welds, ultrasonic peening is expected to extend fatigue life by a factor of 4 (for high stress ranges) to a factor of 10 (for low stress ranges). This estimation is a conservative approximation.
The effectiveness of the ultrasonic peening treatment is predicated on the assumption that the affected welded connections do not contain fatigue cracks at the time of blast cleaning and/or subsequent ultrasonic peening. By applying this treatment, the original fatigue life of these connections is expected to be restored or improved.