FSO Vega Oil is a 250.000 DWT captive tanker permanently moored at an SPM serving Vega field production, offshore Sicily. In January 2001, due to a mismaneuver in cargo moving, the FSO has suffered from damages in the central area of the vessel structure and permanent deformations in the frames, which could have led to the jeopardizing of the vessel's stability. To minimize the loss in production, considering a tight work schedule, it was decided not to take the ship to the harbour for dry dock. The repair activities were carried out while the FSO was moored to SPM, with significant considerations to certain technical and safety aspects. To position the vessel in a safe condition and allow the cutting and the replacement to fit the original damaged structures, an additional skeleton structure was installed first. To define all the project's aspects it was necessary to carry out a complete survey of the damaged structures within the 6 tanks and the residual thickness of the structural elements. The project was submitted for approval to RINA, Minister of Production Activities and Minister of Transportation who succeeded to maintain the repair job under strict control throughout all the phases of the project. The repair works focused on 6 damaged tanks and involved the stiffening of the vessel with 110 tons of additional structures first and then the removal of the damaged / corroded sections and immediate replacement of the same with 585 tons of new steel. During the working period, up to 110 people were simultaneously working on the vessel and the assignment was completed in 10 months with zero accidents and 260.000 man-hours. During the project the stress in the structures was reduced by the control of the ballasting conditions, shearing force and bending moment. In addition, the stress was continuously monitored in real time with the aid of strain gauges installed on the structures and a computer system. At the end of the work a final test was carried out in order to monitor the stress in the newly built structures under the effect of different ballast and weather conditions.

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