Anticorrosion Additives. Anticorrosion additives are special substances mixed with fuel to give it protective properties. The result is the formation of a protective film on metal surfaces, preventing corrosion.
There are two types of anticorrosion additives. The first type includes alkyl sulfonate and nitrate oil. These promote the creation of a strong chemisorption layer on the protected surface, isolating air and moisture. The second type are the salts of organic acids and esters, which reduce the interfacial tension on the boundary between fuel and water and improve the affinity of metal and fuel.
The corrosive properties of diesel fuel are determined by the presence of chemicals, which cause electrochemical and chemical corrosion of fuel system components. Fuel can also become contaminated by the products of corrosion, reducing system throughput, as well as lubricity of the fuel.
In standard diesel fuel the amount of contaminants which may cause corrosion of metal parts is strictly limited. Such contaminants as bases, water-soluble acids and hydrogen sulfide are prohibited.
Electrochemical corrosion is usually caused by water and electrolytes. When oil products are shipped from the refinery, their copper strip test must be negative. This is only possible in the absence of hydrogen sulfide or free sulfur or their presence in such concentrations which cause no chemical corrosion of metal surfaces in the fuel system.
Modern oil refining technologies do not involve separate mixing of anticorrosion additives into diesel fuel. This is due to the fact that such additives are already present in lubricating and multifunctional additives.