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Fixed roofs are used for tanks with low and middle storage volumes. The most of them are for tanks with diameter D from 6,0 m to 60,0 m but there are not any obstacles to be used for bigger diameters.
Fixed roofs could be used in these cases:
a) of all kinds of products (crude oil, gasoline, benzene, fuel oil, water, beer, molasses, etc.);
b) when the temperatures are raised (asphalt, liquid silphur, etc.) by normal and lower temperatures (when liquefied gases are stored in the tank);
c) when there are serious loads from snow and ice there and when ambient conditions are very severe;
d) when requirements about internal hygiene in the tank are exacting. Then roof structure will be placed over the roof plates. Steel plates will be painted with special covers.
1. According to used materials fixed roofs are:
a) aluminum roofs - they begin to be more popular around the world. Their advantages are:
- decreased self weight. They are very light and beautiful structures;
- it is not necessary to be painted;
- aluminum roofs have better resistance to any products that are used in chemical industry;
- they could cover cylindrical tanks with diameter D up to 120,0 m.
b) steel roofs - the most predominate kind of roofs in the world and only one type in Bulgaria by the moment. Their advantages are:
- they have lower basic price;
- they are more convenient to prefabrication and mounting;
- the steel has bigger strength than aluminum and clear pronounced yield strength. When a element of structure is overloaded it receives large displacement and re-distribute loads to another members of steel roof structure.
2. According to type (shape) of fixed roof:
a) cone roof;
b) dome roof - it is necessary radial girders to be bended
c) hanging roofs;
d) fixed roofs (dome or cone) with internal floating roof.
 Cone roof with internal floating roof
| The advantages of using of internal floating roofs are as follow: - level of evaporation of storaged product is decreased; - risk of fire is lower - there almost are not cases of fire in the world practice; - internal floating roof could be aluminum. It has low height and storage capacity is increased; - the internal floating roof is protected from ambient climatic conditions and they could be used in various earth regions; - it is not necessary mounting of roof drain. |
 Dome roof with internal floating roof
| Tanks with cone or dome roofs and internal floating roofs have reduction loss of evaporation of the product. When the internal pressure is increased the loss is less. Internal floating roofs could be: - made of steel - they are similar to external floating roof, but roof drain is not necessary; - made of aluminum - they are the most popular in the world; - synthetic - they could not be used when fire is extinguished under layer product. |
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