DESIGN AND UPENDING ANALYSIS OF THREE-LEGGED JACKET STRUCTURE IN MAKASSAR STRAIT

• Main Author: Raihan Nafis, Muchamad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/58165
• Institution: Institut Teknologi Bandung

Onshore oil and gas reserves are increasingly scarce. The exploration of the primary energy source has begun to shift to the offshore area. Offshore platform is one of the supporting facilities for the upstream oil and gas industry. Offshore platform structures need to be carefully designed, to ensure safe operations on the structures. In this final project, a three-legged fixed jacket platform is designed to operate in the Makassar Strait. The structure is designed according to the API RP2A - WSD standard. The offshore platform structure design has to be assessed in terms of serviceability of the structure due to loading in the field. Initial assessment of the structure includes in-service analysis (in-place, seismic and fatigue analysis). From the analysis result, can be concluded that the designed structure is able to withstand operating and storm condition according to the results of in-place analysis, through checking member stress, deflection, joint can and pile capacity. The designed structure is also considered to be able to accommodate earthquake strength level (SLE) and rare intense (RIE) earthquake conditions, by checking the member stress, joint strength (joint can) and pile capacity. Also, the structure can last for 23.49 years (with a safety factor of 5.00) with a fatigue damage of 0.639 from the fatigue analysis result. After the structure is declared feasible to operate in the field, pre-service analysis is carried out in the form of lifting analysis on the topside and floatation and upending analysis on the jacket. The designed topside structure is able to meet the stress criteria of the API RP2A – WSD design criteria in both balanced and unbalanced lifting configurations. The entire design and selection of lifting components including sling rope and shackle properties, also dimensions of the padeye have also met the API RP2A – WSD design standard. Floatation and upending analysis was carried out to obtain a feasible scenario for upending activities based on the GL Noble Denton 0028/ND Guidelines for Steel Jackets Transportation and Installation criteria. Upending scenario was obtained with a combination method of controlled ballasting from the buoyancy tank and crane vessel lift. The buoyancy tank functions as an upending force, while the crane hook functions as a jacket load-controller. This scenario has met the criteria for seabed clearance and minimum stability of the GL Noble Denton 0028/ND criteria. Based on the force acting on the main hook during the upending process, the Bokalift 1 DP-2 3000 T vessel crane was selected with a maximum capacity of 1,200 MT for its main hook. It is concluded that the fixed platform structure of the three leg jacket type in this Final Project also meets the criteria at the pre-service analysis stage.