Containment system for reduced boil-off

Det Norske Veritas (DNV) now classifies this new technology called Mark III Flex. The containment system has been enhanced to reduce the boil-off rate from 0.15% to 0.10% of the cargo volume per day.
The common industry practice has been to build LNG carriers with boil-off rates of 0.15% of the cargo volume per day, reflecting the typical need for boil-off gas as fuel on board. Now the Mark III Flex system has been advanced in response to the reduced need for fuel gas due to the improved efficiency and changed operational practice of LNG carriers. For current standard LNG carrier designs with a cargo capacity between 160,000m³ and 170,000m³, the 0.05% reduction in the boil-off rate is equivalent to 85m³ or 36 tonnes per day.
All improvements have been achieved by increasing the containment tanks’ insulation thickness from 270mm to 400mm. This change in thickness effects the design of system elements that penetrate the insulation, such as the lower pump tower support and gas dome. The modified proportions of the insulation panels have a potential effect on the loading of the secondary barrier. The new system also implements GTT’s modified liquid dome design.
GTT has carried out an extensive qualification programme for the new system to ensure that the safety and reliability levels remain equivalent to or better than those of the conventional Mark III system. So far, 27 new vessels with the Mark III Flex system have been ordered from South Korean yards. Twenty of these will be built to DNV class.