Tank Cleaning
Tank Cleaning is the operation of cleaning cargo tanks between cargoes on a tanker — removing the residues of the previous cargo so the tank is ready for the next one, meets the required cleanliness (from crude-dirty to chemical-clean), or is gas-free and safe to enter for inspection and repair.
It uses fixed and portable washing machines spraying water, hot or cold, or, for crude tankers, crude oil washing. The washings and residues go to the slop tank, and the tank atmosphere is controlled with the inert gas system and ventilation. Tank cleaning is one of the more hazardous routine operations, involving toxic and flammable atmospheres and enclosed-space entry.
Tank cleaning determines whether a ship can take the next cargo and whether tanks can be safely entered, so it is central to the commercial flexibility and safety of a tanker. It is also one of the most dangerous operations on board, combining flammable and toxic atmospheres with enclosed-space entry, so it is tightly proceduralised.
Where do the tank washings go?
To the slop tank, where the oil settles out and is retained on board; the separated water is discharged within MARPOL limits or landed ashore. Crude tankers reduce washings by using crude oil washing.