For many decades DYWIDAG, a member of STRABAG Group, has been in the forefront of the development, design and construction of prestressed concrete containments for the storage of liquefied gases. The current safety standards for containment systems were to a large extent influenced by DYWIDAG’s engineering work. Various gases require storage at low temperatures e.g. from – 20°C for Propane gas to -165°C. for natural gas (LNG).

LNG is an abbreviation for liquefied natural gas and is liquefied by cooling it to around -162°C to -165°C depending on the exact chemical composition. This reduces the volume by a factor of 600. As a result, the volume required for storage and transport is reduced and LNG has become an economical solution for countries which are not connected to a gas pipeline network.
Liquefaction is a technically safe and economical solution to the problem of storing large quantities of gas and transporting them by ship over large distances.

At both ends of the transport chain storage tanks are required, i.e. prior to loading of the vessel and after off-loading at the destination. Given the size of the available vessels, the common tank size is currently 140–160.000 m³ net storage capacity. In selected markets tanks of 200.000 m³ and in future maybe 270.000 m³ will be realised.

Other markets where storage tanks for liquefied natural gases are needed are for energy suppliers using peak-shaving tanks to cover peak demands and bunker stations with truck loading facilities located at harbours for the supply of ferries and vessels. In general, the capacity of these tanks is much smaller and defined by the available space, demand and local regulations.


Storage Systems

Due to various aspects and requirements related to the storage at low temperatures and the high energy potential of liquefied gases, planning of LNG Tanks is a complex task. In the early years LNG was stored for in single wall steel tanks, as was common practice for oil. Subsequently double containment l steel tanks were introduced. Due to more demanding safety consideration and in some locations lack of space, the overall concept for liquefaction plants included full containment tanks and this has become the worldwide industry standard today. In simple terms, the tank resemble a thermos flask, with insulation between the inner and outer containments to maintain the temperature of the stored liquid at the required level.

The outer containment, a prestressed concrete shell provides the protective component as an integral part of the full containment tank. The inner tank, fabricated with special steel as a stand-alone component, forms the primary storage tank, and the thermal insulation between the inner and outer tank prevents cold loss, thus limiting the vaporisation rate. The inner and outer tanks are designed with separate hydrostatic stability.

In addition, the concept of the tank system is designed to restrict all the effects of any conceivable accident to the inner storage tank. The outer tank protects the primary tank from potential operational disturbances from external sources and, conversely, also protects people and the environment from a potentially explosive gas-air mix, forming as a result of a leak in the inner tank.

In this system the outer concrete tank has to fulfil the following protective functions:

• Physical protection e.g. against pressure waves from explosions, impact caused by parts of the plant flying through the air, helicopter collision and (cold) liquid impact.
• Thermal protection e.g. against fire in adjacent tanks, fire on the tank roof, cold shock
• Collecting and retaining fluids or gases e.g. escaping from a leak in the inner tank.