Operability Analysis of Topside Platform Removal Using Dynamic Method

Topside removal is one of the main activities in the offshore platform decommissioning process, with one of the methods in this process being reverse installation-single lift. Corrosion is considered in this research as a parameter to reduce the strength of topside structures. The structural strength analysis is executed to check the integrity of the members and joints of the structures to avoid collapse of the structure during lifting process. The impacts of the dynamic responses to the hoisting line and sling tension are to be identified, such as due to the motions of the crane barge. The length of the hoisting line can influence significantly the members and joints tension as impacts of the changes of the stiffness, velocity and acceleration of the topside motions, thereby can increase probably the snap force of the hoisting. These conditions are considered in the determine the dynamic amplification factor (DAF) and factor of safety (FOS) of the sling. The operability analysis of the topside lifting is determined based on DnV Standards. The Cinta platform in the SES block, which is operated since the 1970s in Natuna area, is used as a research object in this study. The operability of the system is found 89.4%, at significant waves of 1.0-3.5 m and a zero up-crossing (Tz) period of 8.0 and 9.0 seconds.