Polskie LNG: Roof Concreting on First Tank Starts
On December 20th 2012, an extremely difficult and complicated operation of concreting the first tank’s roof has been started at the construction site of Swinoujscie liquefied natural gas (LNG) receiving terminal.
Covering the roof with concrete is a continuous operation and will take approximately 48 hours. All work is performed over 40 meters above the ground level. The convex shape of the roof is an additional challenge. The approximate weight of the concrete mixture used for this operation is 5000 tons. Is that much? To compare, the maximum weight of “Polish” Boeing 787 – “Dreamliner” – is 230 tons, thus the structure will weigh more than 20 aircrafts of this type!
„This is an extremely important operation, and we are happy that we managed to start it still before Christmas. Despite unfavourable weather conditions, the Consortium was professionally prepared for the operation and all the work was performed to the highest quality standards. I hope that success of this operation heralds another accomplishments in 2013”, said Rafał Wardziński, Polskie LNG CEO.
During concreting, the air blowers will be used (as it was done during roof raising operation), producing the pressure of 40 mbar in tank’s confined space. The resulting pressure will also “push up” (support) the roof, balancing the weight of the concrete, thus ensuring stability of the entire structure during concreting and maturing of concrete (i.e. until the concrete reaches the proper strength).
And there is pretty much to hold! The steel roof structure, raised 42 meters high using the force of compressed air, weighs approximately 600 tons. Subsequently, the reinforcement was placed on the steel roof structure, adding another 800 tons. The most significant load is concrete mixture which weighs over 5000 tons! Therefore the total weight of the roof will approximate 6,500 tons. It is almost the weight of metal structure of Eiffel Tower in Paris (about 7000 tons)! Concreting will be performed with 5 pumps together with concreto poured from containers using two or three cranes. About 80 persons will be directly involved in roof concreting operation.
In the first stage of the operation, approximately 800m3 of concrete will be poured (creating the layer 40 cm thick around the rim and 20 cm thick in the central part of the dome). The concrete will be heated to +15 Centigrades. During this operation, the first layer of concrete will be poured. In the coming weeks, a similar operation on the second tank is planned, and subsequently both roofs will be covered with the second layer of concrete.
In order to commence the process of concreting, a special procedure has been prepared to allow the work in winter conditions. Under this procedure, a special system of heating the roof was prepared (inside and outside the tank), and the entire roof is covered with special canvas. The system involves also 16 electric heaters installed inside the tank on a special working platform, and the heat is distributed through a piping system mounted on a suspended roof. In addition, hot air blowing system from the outside was put in operation; involving four oil heaters situated on the tank’s rim of the crown, from which the heat is distributed around the perimeter of the roof through pipes. Such a system ensures average air temperature inside the tank between +17 and +20 Centigrades.
LNG World News Staff, December 20, 2012; Image: Polskie LNG