Repair of floating offshore units using bonded fibre composite materials

Abstract

On ships, tankers and similar vessels structural defects such as cracks and corrosion damage are typically repaired by welding. However, welding is unwanted hotwork on floating offshore units (FOUs) such as floating, production, storage and offloading (FPSO) and floating, storage and offloading (FSO) vessels because it requires shutdown of parts of the vessel thus resulting in expensive production delays. Bonded fibre composite material patch repairs can be used as an alternative to overcome the hazards of hotwork associated with welding. The patches are bonded over the defect and the integrity of the original structure is hence restored. The patch repair technology can also be utilised to provide upgrades, such as life extensions and higher design requirements. A recommended practice (RP) has been developed that describes requirements for patch repairs used in FOUs. To provide flexibility and to fit different repair needs, the RP defines a range of Repair Classes that can be used depending on the urgency of the repair and the need for optimisation. The qualification effort increases with the degree of optimisation. The requirements are based on an extensive test program carried out in the laboratory (reported elsewhere) as well as experience from full-scale repair demonstrators. Two full-scale repair demonstrators were carried out on actual FOUs to demonstrate the feasibility of the RP for bonded composite patch repair. In addition the demonstrators also showed the viability of using bonded composite repairs under harsh conditions encountered in oil and gas exploration and production environments. The first repair was carried out to arrest a fatigue crack that had developed from the corner of a door, while the second repair was carried out to restore material loss on a heavily pitted deck floor. Both repair cases are used as examples to demonstrate the proposed qualification procedures whilst at the same time discussing the challenges and potential applications of this patch repair technology for FOUs in the oil and gas industry.