This paper presents ExxonMobil's evolution of a direct sloshing assessment methodology to resolve several challenging technical issues that are essential for evaluating integrity of LNG containment systems. Among the most significant developments is the introduction of a probabilistic-based framework that facilitates modeling of the high variability of sloshing impact pressures due to sloshing physics and insulation materials that is inherent in products from natural sources (e.g. plywood, etc.). This probabilistic-based framework also provides the basis for a reliability-based assessment of structural integrity. In addition, this methodology furthered the technical basis of Scaling Law that supports the use of sloshing test as the method for prediction of design sloshing loads, addressed tank sloshing and ship motion coupling effects in deriving inputs to drive the sloshing test rig, demonstrated the influence of membrane surface structures on sloshing pressures, and developed limit state structural capacities as a function of loaded area. The authors are hopeful that this methodology enhances the foundation for achieving continuous safe operation of LNG carriers and enables sound design of offshore LNG loading and receiving terminals.
Over the past four decades, the LNG industry has experienced two stepchanges that produced significant cost savings in delivering LNG. As shown in Figure 1(refer to the main paper), the first step-change occurred in the 1970s when scientists and engineers succeeded in increasing capacity of LNG carriers from ~75,000 m3 to ~130,000 m3. Jean et al. (1998) reported that sloshing of LNG inside the LNG carrier's insulated tanks was one of the key technical challenges for the step-change. Directionally, with the same number of tanks on an LNG ship, the larger the ship size, the larger the sloshing pressures impacting its tank insulation structures. Therefore, maintaining integrity of the insulated LNG tanks subjected to increased sloshing loads was the primary focus that challenged engineers to realize the step-change.
