Lifting activity has been usually employed to deploy subsea equipment, especially for huge structures. In one target field of China South Sea, there was one 3D “M” shaped, long and massive jumper being lowered to 200 meter water depth. The jumper was nearly 90 meters long, 22 inches in diameter, deployed by using a spreader frame. The total weight of jumper and frame has been up to nearly 400 Te in air. The whole lifting system mainly includes spreader frame, jumper, two connectors, wire rope and serial slings, etc. Two connectors were welded on both ends of the jumper, and jumper was lifted under spreader by several slings. The deployment operation was proposed by deepwater pipelay crane vessel Hai Yang Shi You (HYSY) 201. To ensure a successful installation, COTEC Offshore Solutions, together with its mother company, China Offshore Oil Engineering Company, have developed an advanced analysis by considering practical offshore field procedure and accurate modeling technology.
In this paper, firstly, wet lift capacity of wire rope and natural period of the hosting system have been obtained for certain circumstances including axial resonance caused by hostile environment. In addition, lowering though the splash zone operation procedure was simulated by OrcaFlex 9.8a. Allowable Max crane tip tension force, Dynamic Amplification Factor (DAF), Min wire rope force, Max Cranemaster® stroke motion and heave velocity at jumper were obtained during the numerical analysis. Also, allowable values of these key factors are further studied.
According to the above analysis, COTEC provides a series of environmental parameters such as the optimum wave direction and period for the offshore lifting operation.