Corrosion is a negative process, which is basically a destruction of metal surfaces at the influence of environment.
Ground-based metal tanks are subjected to atmospheric (external surfaces), air-vapor (roof inner surfaces and tank top rings) and soil (external surface of the tank bottom) corrosion.
Atmospheric corrosion is a result of electrochemical processes. Thin film of moisture or its separate droplets appearing at the tank surfaces in humid atmosphere act as electrolytes. In order to protect external surfaces of tanks from corrosion it is advisable to paint them with special weather-resistant paint coatings.
Corrosion of inner surface of the roof occurs with presence of sulfur compounds in gas phase, or when moist air gets into a tank during the process of ventilation. The moisture, that penetrated the inside of the tank, condenses, and the presence of oxygen and hydrogen sulfide create all prerequisites for galvanic corrosion.
Corrosion of inner surfaces of the walls occurs as a result of chemical interaction of metal with sulphurous oil-products.
Tank apron and bottom ring are subjected to corrosion more than any other parts, caused by their contact with water settled at the top and bottom. These types of water usually contain aggressive acids, gases and salts; which provokes intense corrosion of metal that comes in contact with these substances.
The following measures can be applied to protect internal surfaces that contact with gaseous phase:
- aluminum spraying;
- treatment by cement-based coating followed by surface coating with magnesium-fluoride-silicon solution;
- coating with chemically stable insoluble polymerizing substances.
Tank bottom protection is achieved by:
- adding alkalis or corrosion inhibitors into bottom settled water in order to neutralize acids;
- asphalt coating or coal and sand coating below the layer of water at the bottom;
- cement grout coating;
- metallized coating;
- ground protection.
Soil corrosion is a process of metal destruction which occurs as a result of metal and electrolyte interaction. Intensity of such corrosion depends on soil composition as well as its humidity and aeration.
Dry sand has minimal corrosive effect on metal tanks, so it is recommended to use sand as the base to install tanks on.
How to protect ground-based tanks? Bituminous insulation is most commonly used to protect ground-based tanks. But it should be noted that it is not sufficient. Bitumen coating may lose its insulating properties with time and soil electrolytes may penetrate into metal surface of tank bottom.
Therefore it is recommended to protect tanks bottoms using electrochemical methods (galvanic anodes, cathodic protection) in addition to bituminous insulation.
Cathodic protection from soil corrosion is a fairly effective and cheap method. Its aim is to artificially turn the tank surface, which contacts with soil, into a cathode by connecting it with a DC source circuit.
Cathodic protection is creation of an electrical circuit in which tank bottom acts as cathode, and protectors act as anode. Protectors are metal rods with a higher negative potential and electrochemical equivalent. Therefore, protectors corrode first, and not tank bottom.
Cathode protection is worth using where tanks service life is 10 years and more.
Protection of inner surfaces of the walls
Purity of stored oil-product protects tank walls from corrosion. GlobeCore UVR oil purifiers regenerates and purifies oil. It cleans dark diesel and heating oil, makes it lighter colored, removes sulfur and hydrosulfuric compounds as well as removes gum, dirt and gas condensate. The final oil-product fully conforms to normative cleanliness level after purification. It is freed from unpleasant odour and does not darken and oxidize for a long time.
The great advantage of UVR oil recycling plants over other similar equipment is their versatility i.e. ability to work with practically all types of oil-products such as transformer, turbine and industrial oils, diesel and heating oil, gasoline, kerosene.
GlobeCore equipment removes unwanted components that cause corrosion. Thus UVR oil purifier not only improves purity of processed oil, but also protects oil storage tanks.
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