Crude oils and their heavy fractions tend, in storage tanks and vessels to deposit the so-called sludge. This sludge causes many troubles in handling of the crude oil whether in pipelines, storage tanks, or in the refineries. It leads to blockage of the pipelines especially in cold weather during transferring the crude oil through them, also causes blocking of the nozzles of the burners in refineries.

Sludge precipitation also interferes with accurate measurement of crude quantity, leading to serious problems in custody transfer.

Petroleum sludge consists of heavy organic materials such as paraffin waxes, Asphaltenes, resinous materials and other extraneous materials such as cotton pieces besides the organic materials, there is an inorganic substance as dust, scales and water.

There are many factors controlling the sludge formation in tanks of petroleum. The most importance one is the oxidation of organic materials present in the crude. The oxidation process occurs due to the change in the atmospheric temperature or due to the heating of the crude oils during pumping them in pipelines especially in winter. Also due to the effect of some oxidizing fungi on the organic petroleum compounds In addition, it may be due to the electrostatic charge formed on pumping the products, these electrical charges tend to oxidize the petroleum components.

Coagulation of heavy petroleum components with water is another factor leading to sludge formation. This factor is demonstrated by the presence of water in emulsion state with sludge in high percentage.
Sediments, sand, dust and scales also are other factors encouraging the precipitation of the sludge and these shows in their high percentage in the sludge on analysis.

The precipitation of paraffin wax is also one of the most important factors that cause sludge formation. It is well known that the precipitated waxes are very difficult to re- dissolve in the liquid crude oil. Precipitation of waxes may be due to the difference in temperature between day and night which leads to separation of waxes in a sludge-form.
The variation of temperature between summer and winter also has the same effect on precipitation of waxes.
The interruption in the material balance due to the losses in the volatile components is another factor leading to the formation of sludge. Some of the heavy components present in the crude oils such as asphaltenes, resins and polymeric compounds, tend to precipitate thus, disturb the material balance again.

Conventional sludge cleaning methods generally require that the tank is taken out of service for three to four months. Sludge removal is usually difficult. The sludge disposal also causes many environmental problems. These considerations, along with the amount of labor required to clean a tank, are the primary reasons why routine tank cleaning programs have never been widely accepted by the industry.

Some of the problems that may be attributed to sludge deposition in storage tanks include.

• Loss of sludge entrapped hydrocarbons.
• Reduced tank holding capacity
• Erroneous measurements of crude quantity
• High sediment concentration is found in the oil located in the bottom of the tank, this causes troubles in desalting operation.
• Sludge build up may interfere with the roof floating operation.
• Tank drain plug problems may occur.
• Increased transfer pump maintenance due to impeller erosion and blockage, may become a problem
• Corrosion cell often assemble in the sludge zone