Large refineries and petrochemical companies hold heavy oils, as crude oil, in large tanks. With time, heavy sediments accumulate at the bottom of the tanks, partially obstructing the tank & preventing its proper and economical operation. Maintenance teams must shut-down operation & clean the sediments. They also perform routine maintenance, e.g., welding, that require a gas-free state within the tank.
Cleaning such tanks requires a massive work force & long shut-down periods of the tank, up to several months. Furthermore, petrochemical companies do not accept the sediments for re-use. Regulations classify these sediments as hazardous waste which requires disposal in special depositories. All this makes tank cleaning a costly operation.
