Concept of Half-Jacket and Retractable Joints to Restore Offshore Platform's Structural Integrity

Abstract

This paper presents a new approach of offshore jacket strengthening with rigidly connected members with minimum number of clamps and bolts. Horizontal and diagonal braces between two successive elevations of a jacket in a plane may be combined to form a prefabricated X-frame which will be able to replace a set of existing damaged members. To facilitate easy installation, X-frame will be assembled along with its connecting half-clamps and one side of the X-frame will be provided with retractable ends. The annulus portion of the movable ends of the X-frame will be grouted to make rigidly joined new braces. Additionally, the concept of half-jacket has been utilized to create additional deck space required for operational purpose. The half-jacket will be integrated to the existing structure by rigid subsea connections. The case study involves an aging offshore platform that undergoes a large amount of horizontal movement due to environmental loads. In spite of earlier upgrade with new piles and clamped braces, the substructure is found to be considerably flexible as a result of loose clamps and construction tolerance provided at the ends of each member. A detailed analytical study has been performed with the proposed strengthening scheme that shows significant improvement of the platform movement due to extreme environmental loads.