The demand of floating type offshore structures has been being increased since the last several decades in offshore construction field. Generally, the fabrication and assembly of floating offshore structures have been carried out in the dry dock of the shipyard by stacking unit blocks sequentially from lower to upper levels. However the use of dry dock facilities has great dependency on deck schedule and tight fabrication process of yard. So it is difficult to incorporate any design change or modification required by client.
For that reason, the on-ground fabrication methodology was used for several offshore floating structures to reduce total construction schedule and have flexibility in fabrication phase since hull and topside part can be fabricated at the same time. As of now the on-ground built is not an option for construction of large offshore floating structure. Nonetheless, the guide lines for on-ground fabrication methodology have not been established.
Therefore this paper discusses the optimum design, structural validation and practical operation method for Superlifting system and Loadout System based on successfully performed GK-FPS (41,060mt dry weight GUMUSUT KAKAP Semi FPS) project in April 2012 and April 2013 respectively.
The major characteristics of Superlifting technology, which depend on configuration of the object to be lifted, were its heavy weight(22,531mt), high lifting height(45.5m) and big size(90m*90m) based on GK-FPS project. So special consideration should be required for safe Superlifting operation since its scale is remarkable compared with previous cases of other offshore structures.
The Superlifting technology is very comprehensive, challenging and perilous work. for that reason, the first, the ground foundation should be verified and monitored during Superlifting operation as well as its settlement should be considered for structural integrity check of Superlifting Structure. The second, a lot of hinge connections such as knife edge bearing (KEB) and tension plate should be inevitable for optimum design even though these designs are very complicated and have inherent risk. The third, pre-load test for structural validation of Superlifting structure should be done by using topside weight, which is required to check the topside integrity. The last, the topside modules should have enough strength to have the practicable twist value during going up to target lifting height since the lifting point might be controlled by strand jacks independently.
Loadout operation looks like easier work compared with Superlifting operation. but it is misjudgment in case of skidding heavy weight structure. For the effective Loadout operation, the concept design should be preceded with regard to the pulling force flow considering the stability of quay and capacity of vessel.
Generally, the fixed anchor is located on the vessel and specified fenders is between vessel and quay to transfer pulling force to quay, which sometimes causes many reinforcement of quay and vessel for skidding heavy structure. In order to solve this problem, the new concept was developed and presented based on viewpoints of costwise in this paper, which is named as“Direct Connection Method” since pulling force flows only skidbeam connection to offset pulling force by itself.
Foresaid developed methodologies for Superlifting and Loadout operation have been verified through successfully accomplished GK-FPS project done at MMHE (Malaysia Marine and Heavy Engineering) yard, which broke the world record.
Therefore, this paper describes the developed effective method and enhanced engineering technology for Superlifting and Loadout Operation to be going to be guidelines of efficient on-ground fabrication of heavy structure in offshore field for the future application.