What is the key difference in design philosophy between a full containment and a double containment LNG storage tank?

The key difference in design philosophy between a full containment and a double containment LNG storage tank lies in how they manage potential LNG leaks and spills. A full containment tank is designed to contain any credible spill from the inner tank within the outer tank and its roof system. This means both the outer tank wall and the outer tank roof are designed to hold the full volume of the inner tank. The outer tank acts as a complete secondary barrier, preventing any LNG from escaping to the environment. The outer tank is typically made of reinforced concrete designed to withstand cryogenic temperatures and the hydrostatic pressure of the LNG. The roof is also designed to contain any vapor generated from a leak, directing it to a safe release point. In contrast, a double containment tank is designed to contain smaller leaks or spills from the inner tank within the area between the inner and outer tank walls, but its outer tank roof is not designed to contain a full-scale spill. If a larger spill were to occur, the vapor cloud may be vented through a safety release system. The outer tank in a double containment tank is typically made of carbon steel or concrete. The primary purpose of the outer tank is to provide a secondary liquid barrier for smaller spills and to prevent the rapid spread of any leaked LNG. The overall philosophy of full containment prioritizes preventing any release of LNG to the environment under any credible scenario, whereas the double containment design accepts that a full inner tank spill could potentially result in a controlled vapor release, but still provides significant protection against smaller leaks and spills.