Structural analysis for heavy lift removal of offshore module

Abstract

This report presents a study of the structural analysis for removal operation of the Frigg TCP2 M32 Module with a new lifting arrangement situated at the top of the M32 Module. During the removal of the M32 from the Frigg TCP2 platform performed in 2005 a planned delay to the lifting operations was required, due to installation and welding of the M32 module lifting points at the bottom frame of the module. The intention of this study is to investigate if the interruption could have been avoided. This is done by performing structural analysis and verification of the M32 Module and the feasibility of installing padeyes at the top of the M32 Module. Global and local analysis covers the ultimate limit state and is carried out in accordance with prevailing design rules and standards. The global analyses are performed by using the Sesam software package and local analysis are performed by a combination of finite element analysis, analytical stress analysis and code checks. The lifting operation is defined as a heavy lift operation. Data from the Saipem S7000 semi-submergible crane vessel is used for defining load input for lifting and transportation of the M32 module. In this study the lifting arrangement is defined as a single crane lift with 3 loose spreader bars. The first global analysis showed failure of columns connected to the lifting points. To maintain the structural integrity of the module during lifting, these columns were reinforced by adding reinforcement plates to the failing structural elements. After that the reinforcements for the lifting operation are made the transportation condition is the governing condition for the global analysis of the M32 module, however it does not have a significant effect on the analysis result for the transportation condition, if the padeyes are top or bottom mounted. Analysis of the padeyes was performed as an analytical stress and showed that the padeye design has the sufficient strength to carry the lifting load. The joints in the module are analyzed and found to have the required strength to withstand all forces during lifting and transport of the module. Based on the analysis and considerations performed in this report, I consider it possible to perform the lift of the M32 module with a lifting arrangement situated at the top of the module. I consider all collected data and sources used in this thesis accurate and reliable. If errors of any kind occur I can assure that this is not of my intention as my aim is to present the results as accurate and realistic as possible. If however any inaccuracies have occurred it is my hope that these are minor and do not effect the final conclusion of this thesis.