FPSO Schiehallion Fatigue Life Extension of Stringers

During the first campaign the bottom transversal frames were treated by ultrasonic peening. In total five brackets/frames were treated.
From subsequent analysis of the treated brackets it was recommended to extend the scope of ultrasonic peening treatment to include the lower welds on the bracket to the transversals. It is still recommended to develop a local FEA model for the treated weld details in order to increase the accuracy of the areas recommended for treatment as well as the life extensions achieved so far.
From FE analysis of the treated welds, at stringer level 13700mm, it was recommended to treat both toes of the new implemented bracket at stringer level during the next campaign and to check the sizes of any new implemented bracket against a local FEA model with solid elements.
During coming offshore campaigns it is recommended that a LETS Global senior engineer is able to carry out an inspection by previous to ultrasonic peening treatment in order to re-assess and/or confirm the locations and extensions for the proposed treatment.

Ultrasonic peening of bracket at stringer level

General view of working are at COT (Cargo Oil Tank)

Local FEM of concerned area

Fin meshing and constraints origins of UP treated area

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