FPSO Schiehallion Fatigue Life Extension of Transverse Brackets

The operator requires that this FPSO will be in service for 10 more years with an acceptable structural integrity.
Lloyds Register (LR) has localized two different fatigue sensitive areas in each of the six cargo tanks.
In order to ensure the structural integrity, the localized fatigue hot-spots must be strengthened in order prevent fatigue cracks to initiate.
LETS Global® Ultrasonic Peening Procedure (LGUPP) was selected to extend the service life of the fatigue hot-spots found and documented by LR.
LGUPP has successfully been used in the North-Sea in co-operation with Bureau Veritas and in the Gulf of Mexico in co-operation with Den Norske Veritas and American Bureau of Shipping.
The fatigue life extension achieved for the ultrasonic peening treated welded attachments for this specific location is four times, conservatively estimated.
Alongside this project LGUPP received an official approval of LR.

Without a localized and detailed Finite Element Analyses (FEA) model it is only possible to roughly estimate the benefit of the LGUPP. The benefit of the life extension method is strictly dependent on two main pillars; the as-build weld quality and the local stress.

UP treated welds on transversal brackets

Rope access to area
of treatment

UP tool

Transversal brackets weld previous to UP treatment

Typical crack modus for this type of bracket

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