A Safe and Cost Effective Diverless Method for Hull Wetted Surface Side Shell Repairs Executed On FPSO Fluminense

Abstract

The Bijupira and Salema oil fields in the Campos Basin, Brazil, are tied-back to the FPSO Fluminense. The design life of FPSO Fluminense was 15 years, first oil was in 2003. In 2017, Shell as operator and partner Petrobras decided to execute a 5 year life extension project to extend production until 2023. Although the life extension project encompassed many vessel, moorings, and production facility renovation projects, this paper will focus on the repairs of cracks in the wetted surfaces of the hull. Crack repairs were executed during production operations using a novel methodology designed to eliminate the risks of diving operations, while significantly reducing the costs of the offshore hull repairs. Earlier attempts using traditional methods with divers to deploy cofferdams were unsuccessful due to the high safety risk of diving in the persistent 2-plus knot Brazil current. In early 2019, the operator and a team of engineering consultants concluded that a novel repair approach that eliminates diving operations was feasible. The concept methodology was developed, one element of which included positioning and securing a cofferdam over a cracked area of the FPSO side shell. The cofferdam was lowered from the FPSO deck while being guided into position and secured in place by guide wires passed through holes in the side shell. Water ingress into the void spaces was eliminated via a hot tap and winching system that penetrates the side shell from inside the tank. Following the concept development, a step-by-step procedure was written, vetted with the classification society and subsequently used in the tendering process to select an execution contractor. The selected execution contractor constructed a test tank that replicated the actual hull structure. The prototype was used to test the method at full scale, including procedures, communication protocols, and equipment. The learnings were incorporated into both the procedures and equipment. This process was repeated as a training exercise for the offshore personnel and HSSE leaders prior to offshore execution. The execution contractor was mobilized offshore in the first quarter of 2020 and successfully performed the hull repairs. The job was completed as planned, including removal and replacement of several independent sections of stiffened hull plating, which included both flat and curved surfaces. Based upon successful execution, this method has been proven to be a technology that can be used to eliminate the risks of diving and to significantly reduce the costs of future offshore hull repairs. This paper will address the methodical approach taken to develop and integrate the various elements of this novel technology developed jointly by the operator and consultants, as well as the phases testing, pre-mobilization surveys, project execution, and other activities that drive success.