Water-Soluble or Water-Miscible products Water-Soluble substances and water-miscible substances are easy to clean with water, and the solubility of the substances might increase at higher temperatures. The use of a cleaning agent is only advisable for reduction of the cleaning time.
Products with a high melting Point These products should be washed at a temperature of 15-20 C above the melting point. During washing there should be no ballast water or cold cargoes adjacent to the tank to be cleaned. During cleaning special attention must be given to liquid and vapor line systems to avoid freezing/solidification at cold line segments. Washing as soon as possible after discharge is recommended.
Products with a high viscosity These products should be washed at higher temperatures. In general the viscosity is closely related to the temperature and will decrease at higher temperatures. During washing there should be no ballast water or cold cargoes adjacent to the tank to be cleaned. Washing as soon as possible after discharge is recommended.
Vapor Pressure/Boiling Point Products with a high vapor pressure (higher than some 50 mbar at 20 C) can be removed from the tank by evaporation. As always during ventilation, special care must be taken to prevent the risk of explosion (flammable products) and emission (toxic vapors). All safety ans environmental precautions must be taken.
Flash Point/Flammable Range The flashpoint is the lowest temperature at which a product gives off sufficient gas to form a flammable gas mixture that can be ignited. The pre-cleaning temperature must be well below the flashpoint. If this is not possible, avoid any ignition source.
Density / Specific Gravity Is the ratio of the mass of a volume of a product to the mass of an equal volume of freshwater (1.0). For a product with limited or no solubility in water the specific gravity indicates whether the product will float on water or sink.
Polymerisation The initial wash of products that tend to polymerise should be carried out with cold (ambient) water. Washing with hot water may result in polimeric residues being left in tanks and lines, which are very difficult to remove.
Evaporation of volatile substances Cargoes consisting of mixtures with different vapor pressures should neither be cleaned by evaporation, nor prewashed hot. The evaporation of the light substances from a mixture could result in non-volatile residues, which are very difficult to remove.
Reaction with waterIsocyanates must never come into contact with water, not even the residues, because the reaction product and insoluble urethane (plus CO2) are very difficult to remove. Such products must be washed with a suitable solvent, that does not contain any water.
Reaction with Oxygen Drying and semi-drying vegetable and animal oils react with oxygen to form a varnish-like polymeric film. This is very difficult to remove from the bulkheads etc. Since heat increases the reaction speed the initial washing of these products must be done with water at ambient temperature without any delay after unloading the cargo.
Reaction with water hardness compounds Water hardness is formed by the calcium and magnesium content of the water. Sea water has a very high water hardness. Some products like fatty acids and vegetable oils with a high free fatty acid content will form white sticky residues, if they are cleaned with a water of a high water hardness (e.g. sea water).
Smell Minor residues of a smell-producing cargo left in lines, valves and pumps (including pump cofferdams) can contaminate a sensitive cargo. To neutralise the smell of some chemicals (e.g. Acrylate, Nitrobenzene or Pygas) the use of a smell killer may be recommended.