Non-metallic tanks are reservoirs for oil and oil products storage, made of synthetic, earth, stone, brick, concrete and reinforced concrete materials. The shape and design of such tanks can be very diverse.
In most cases non-metallic tanks are designed to be in the ground, that is, subterranean or semi-subterranean. But there are also surface-mounted reservoirs.
Generally non-metallic tanks’ service life is longer than metallic ones due to low susceptibility to corrosion.
Construction materials for non-metallic tanks has requirements of strength, frost resistance and water- and oil-resisting properties.
Storing volatile petroleum products with high content of gasoline could only be in reinforced concrete tanks, since they provide impermeability due to gasoline- and oil-resistant coating. Storing viscous petroleum products and heavy oils with low content of gasoline is permitted without special coating. Oil residues are allowed to store in earthen tanks.
Most of the materials, used in practice for non-metallic tanks, do not fully comply with the impermeability requirements. It is compensated by tanks internal insulation. For insulation it is possible to use cement-sand, metal and synthetic.
Spatter dash for tanks is a cement-sand insulation, which is used for oil and dark oil storage tanks.
Spatter dash insulation can be performed in several layers. Each subsequent layer is applied after hardening of a previous one. Spatter dash insulation has one disadvantage: a probability of cracking.
In order to obtain a proper oil resistant insulation – it is necessary to use synthetic and natural resins, thiokol as well as diphenylacetylene varnishes. Researches on new non-metallic materials with gasoline- and oil-impermeability, are still ongoing. Tanks with coating of vinyl enamels, thiokol, latex, neoprene, teflon, etc have been tested in the USA, France and Germany.
The main disadvantage of these insulating materials is a long period of application, due to many layers and long drying period of each of them.
Reinforced concrete tanks insulation and sealing. Reinforced concrete tanks insulation and upper covers are sealed by adhesion of film material to prepared surface. The disadvantage of this method – is high cost of non-metallic insulating coating, especially in comparison with steel cladding.
The solution could be in development of high performance heavy density concrete. The tanks, made of concrete with additives of ferric hydroxide, calcium chloride, sodium chloride with admixture of spent sulfite-alcohol liquor, furfuryl alcohol, phenyl-amine chloride, etc – have shown success in laboratory testing.
Non-metallic tanks are monolithic and modular. Monolithic construction is used for tanks with capacity of up to 5000 gl. There are special requirements for temperature and expansion joints for tanks with larger capacity due to concrete shrinkage and potential settlement of soil. It is necessary to set the expansion joints every 30-40 ft. of tank length, forming sections.
There are non-metallic tanks of circular, rectangular, spherical and other shapes. The choice of a specific shape depends on building material and on financial considerations.