Advances in Assessment of LNG Sloshing for Large Membrane Ships

Large ships are a strategic element to reducing cost for delivery of liquefied natural gas to worldwide markets. They reduce delivery cost through economies of scale and they will help meet the demand for ship volume with the existing construction capacity. The excellent performance history of LNG ships over the past 40 years is a well-established fact. However, the introduction of large LNG ships poses new technical challenges for our industry. One of the challenges in moving to larger ships is the potential to have higher cargo sloshing loads with larger ship tanks. Since membrane insulation systems are installed inside the tank, they are in direct contact with the LNG and must be capable of withstanding all loads from sloshing. Qatargas II and ExxonMobil have led a major technical effort with collaboration with Gaztransport & Technigaz S.A.s to enable the safe design of a new class of cost effective large LNG membrane ships for our projects. This paper highlights our recent advances in sloshing load prediction and membrane capacity assessment. These advances were essential to establishing requirements for the industry's first application of LNG ships up to 216,000m3, a significant increase in size over the 155,000 m3 LNG ships recently ordered by industry, and will enable the safe design of even larger, 250,000m3 LNG ships