Study and Checking of Adequacy of Pinion Stiffness for Jacking Systems of Self Elevating Units during the Conversion Jobs

Bh. Nagesh; I.N. Niranjan Kumar; N. Madhu Latha

doi:10.3759/joost.v6i1.554

Abstract

Jacking systems are used to elevate and lower the hull of self-elevating units in the elevated condition and to raise and lower the legs in the floating condition. In one of a conversion job of a Jack-up Rig from MODU to MOPU, which has been considered here as a case study, in which during conversion it has been identified that the inadequacy of the pinion stiffness could be one of the causes of impending future failure of the rig when installed as a future offshore platform. The hull of the unit is maintained stationary in the elevated condition by means of a holding mechanism. The same mechanism is used to maintain the legs stationary in the floating condition. It is therefore, necessary to have a thorough check of the entire jacking system and identify the pinion stiffness for the jacking system. In this paper, a meticulous checking procedure has been shown to identify the adequacy of the pinion stiffness. The Finite Element Method is used to determine the stresses and strains in various support sections of the jacking system of legs, by modelling the entire structure in SACS modelling and FE analysis software which is extensively used in offshore industry. The analyses have been done on the existing leg lattice structure of a three legged drill rig with spud cans which had been undergoing conversion process from Mobile Offshore Drilling Unit (MODU) to Mobile Offshore Production Unit (MOPU) for installation at Mumbai High.