The Fire Resistance of Concrete Structures of a Typical LNG-Tank

The worldwide transportation of liquid gas requires tanks for storage in the producer and consumer countries. For the temporary storage and the transport by ship the gas is cooled down to about −165°C. By cooling down, the gas liquefies with a consequent reduction in volume of 1/600. On the coast, LNG-Tanks (Liquefied Natural Gas Tanks) are necessary for the interim storage. During storage, some liquid regasifies. This so called "Boil off Gas" is re-liquified and fed back into the tank. Pressure relief valves are placed in the roof as protection measure for the concrete structure against overpressure. The heat generated by the ignition of gas flowing out from a pressure relief valve is one determinant emergency load case for every LNG-Tank roof. Fire can also act from or to neighbouring structures; a so called "adjacent fire" affects primarily the prestressed wall of an LNG-Tank. In this paper, the calculation procedure for the heat radiation load of a valve fire and an adjacent fire is explained and the spatial distribution of the radiation for typical distances between flame and concrete surface is idealized. Furthermore, time dependent temperature analysis over a period of one to eight hours is carried out for typical roof and wall sections, which leads to nonlinear temperature gradients along the investigated sections of the concrete structure. These temperature gradients are used for the calculation of the sectional forces and especially for the evaluation of the material behaviour. The time limit is shown beyond which the material strength of concrete, reinforcement and prestressing strands has to be reduced for calculation or material protection systems must be used.