Fuel oil is one of the main by-products of petroleum refining. It is used as fuel for ocean liners and cargo ship engines. It is also used in power plants and industrial plants. Fluid catalytic cracking (FCC) is often found in the petroleum refining process to maximize the distillation of hydrocarbon with a high octane rate. Some contaminants such as nickel, iron, vanadium, silicon, aluminium, sodium and calcium are found in FCC and are transferred in fuel oil during the refining process. It is important to find the concentration of these elements because they are adhesive at certain temperatures and they cause corrosion on the reheater tube surfaces of boilers as well as on the combustion chamber and components of fuel oil engines. Corrosion should be avoided as much as possible because it causes wear and entails additional costs for maintenance or replacement.