Why crude oil washing or COW is preferred over water washing?

As we know that cleaning with water gives reasonable good result only when water jets with sufficient impact force are directly hitting the surfaces within a tank. Accordingly the cleaning effect is almost non-existent as far as reflected jets and drainage’s are concerned. 

When using crude oil a surprisingly good cleaning result is obtained even from drainage’s and reflected jets of crude oil – the so-called “splash-back effect”. Maintaining a pressure of at least 10 bar assists the process of crude oil washing.

Crude oil has a latent ability to “clean up its own mess”. i.e. to dissolve and suspend the deposits. This process is facilitated by  the viscosity of the oil considerable reduced when being pressurized in pump(s), lines and  nozzles of tank washing machines.

As a result of viscosity property, crude oil used for tank washing drains effectively leaving only a surprisingly thin film upon the tank surface. The superiority of crude oil to water as a tank cleaning fluid is exclusively dependent upon the dissolving property of crude oil. It is not possible to dissolve sediments from crude oil cargoes with water. But the latent dissolving property alone, oil is not enough


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