Chemical Tankers / Day 3 / Day 3 Topic 6 Tank Cleaning Chemicals & Best Industry Practi

6.3 Use of cleaning chemicals

Hand spraying

An air-operated drum pump is used to supply the neat chemical to a hand spray gun and nozzle. The correct type of spray equipment is vital. High pressure operated hose should be used and spray gun chosen must incorporate a nozzle which produces a jet rather than a spray.

6.3 Use of cleaning chemicals

Hand spraying

6.3 Use of cleaning chemicals

Hand spraying

When contact period of chemical applied to the bulkheads is complete, the tank should be flushed with water by tank cleaning machines or by hand held hose connected to the washing system (with exception of Light Solvents like Methanol, MEK and Acetone spray).

6.3 Use of cleaning chemicals

Hand spraying

The following cleaning agents are suitable for hand spraying method:

•Carious emulsifiers, degreasers and oil removers;

•Butyl Cellosolve (contains Glycol - on dry bulkheads only);

•alkaline cleaners (don’t allow to dry on bulkheads);

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6.3 Use of cleaning chemicals

Hand spraying

•Acid based or Metal Bright agents;

•Methanol (for chlorides removing only, non-static);

•Acetone, MEK (for slight hydrocarbon, chlorides removing, non-static);

6.3 Use of cleaning chemicals

Steaming

Steaming means introduction of saturated steam into the tank. Steam should never be introduced into the tank containing flammable vapours.

The steam will condense on the tank surfaces. The use of steam in a tank is two fold:

1 - To remove the chlorides

2 - For smell/odour removal.

6.3 Use of cleaning chemicals

Steaming

If it is intended to eliminate Odour/ smell, then it mostly desired to raise the temperature as high as possible during steaming. This is enhanced if the adjacent tanks are empty.

If the low chloride content fresh water is limited on the ship, the use of steam for removal of chlorides is often the only possible option.

6.3 Use of cleaning chemicals

Steaming

Steaming is a good method to reduce chlorides level.

If the steam is used to remove chlorides, the wall temperatures should be cool in contrary to Odour / smell removal method. This results in increased condensation and water drops running down the tank walls and wash the chlorides off.

6.3 Use of cleaning chemicals

Special methods – Toluene re-circulation

In certain cases it will be necessary to use the Toluene re-circulation or floating method. Toluene has a good solvency power, but is a static accumulator because of it’s low electrical conductivity. Toluene

wash always results in a flammable mixture in the tank.

Thus the tank must be inerted down to oxygen level content of

less than 5%.

6.3 Use of cleaning chemicals

Special methods – Dye out

Discolouration of the tank or the coating could be removed by the dye out method. In some cases it could be removed by spraying or recirculation with 10%-15% Sodium Hypochlorite solution. If this does not work, steaming could help.