Chemical Tankers / Day 3 / Day 3 Topic 5 Tank Cleaning Guidelines

5.3 Industry best practice in tank cleaning

The following is stated in Company VMS manual Chapter 11.4:

“In the absence of specific loading instructions, immediately after discharge, all tanks should be cleaned to Water White standard as a minimum in order to have the maximum flexibility for the stowage of the next cargo”.

5.3 Industry best practice in tank cleaning

The following points are considered when deciding if a tank has reached a Water White standard:

oNO trace of previous cargo in the tank or line system, including drop and stripping systems;

oNO odour;

oNO suspended particles (visual particles);

oNO discoloration from last cargoes or due to tank cleaning;

5.3 Industry best practice in tank cleaning

oNO free water or condensation in pump well, bottom, bulkheads,

overhead and all associated line systems;

oNO loose scale and blisters which could entrap previous cargo;

oHeating coils clean and bright;

oCargo pump and piping clean and bright;

5.3 Industry best practice in tank cleaning

oHatch packing clean and free from odor. Tank pump, lines etc must all be fresh water rinsed and dried to prevent damage to stainless steel components;

oFixed butterworth machine nozzles to be set in the point down position, and if drain hole fitted on bottom of machine, check that it is not blocked;

oCargo heat exchangers must be opened and visually inspected to confirm they are clean and free of previous product or water;

5.3 Industry best practice in tank cleaning

Type and condition of tank linings

Stainless steel – tanks lined with stainless steel. This tank requires less time and chemicals for cleaning. Traps lesser amount product than the rougher surface which is commonly used. Rough cleaning followed by a later final wash can lead to problems with stainless steel.

5.3 Industry best practice in tank cleaning

Type and condition of tank linings

Any residue remaining within the stainless profile will harden up and will be very difficult to remove when preparing the tank to wall wash. Almost any cleaning medium can be used without damaging the tank lining, but when cleaning stainless steel, it is important whenever salt water is used, fresh water must be used immediately for salt removal to avoid pitting of the tank.

5.3 Industry best practice in tank cleaning

Type and condition of tank linings

Epoxy/Phenolic linings – organic coating of tank. All organic coatings absorb the cargo. Some types of cargoes although permitted to be loaded and carried, may soften the lining and get trapped in the lining making it more difficult to clean. Always refer to tank coating resistancy list for such information.

5.3 Industry best practice in tank cleaning

Type and condition of tank linings

After transporting aggressive cargoes, the tank has to be ventilated until the cargo has been de-absorbed from coating film, which results in hardening and decreased swelling of coating. This can take up to several days, depending on type of cargo, type of coating and film thickness.

5.3 Industry best practice in tank cleaning

Type and condition of tank linings

Epoxy coating reaction after carriage of aggressive cargoes:

5.3 Industry best practice in tank cleaning

Type and condition of tank linings

Water may not be used for cleaning until this ventilation process is finalised. Otherwise the water can lead to blistering and subsequent serious damage of the coating. The more solvency power a cargo has, the more cargo residues could still be present in the coating.