Zinc Silicate Coatings

Typical properties are:

Zinc coatings tend to absorb and retain oil-like cargoes.
Not resistant against acids and bases (pH range generally 5.5 – 9.5)
Retained residues can be detected by wall wash test.
Retained residues can result in the contamination of subsequently carried cargoes.

Removal of oil-like residues retained in the profile of the coating is a very difficult subject. It depends on many influencing parameters such as properties and characteristics of the previous cargoes that led to the adsorption, the type and condition of the coating, technical possibilities of the vessel, the experience of the crew, just to name the most important ones.

General rules for the removal of oil-like cargoes from zinc coatings:

These residues could be removed by a solvent. Most solvents are flammable and/or toxic. Procedures involving the application of such solvents requires a risk assessment and risk mitigation which should be carried out by experienced personnel.

Epoxy Coatings

Typical properties are:

Epoxy coatings tend to absorb and retain solvent-like cargoes. This absorption leads to swelling and subsequent softening of the coating.
Solvent like cargoes are not completely desorbed after ventilation.
Retained residues can be detected by wall wash test.
Retained residues can result in the contamination of subsequently carried cargoes.

Washing epoxy coatings with water after the carriage of certain solvent like cargoes before thorough ventilation and desorption of absorbed residues could result in serious damage of the coating, especially at elevated temperatures. Always refer to the coating manufacturers guidelines in the event of any uncertainty.

Removal of solvent-like residues absorbed and retained by epoxy coatings is a very difficult subject. It depends on many influencing parameters such as properties and characteristics of the previous cargoes that led to the absorption, the duration of the exposure to the coating, the resistance of the coating, the condition of the coating, just to name the most important ones. Therefore the description of such procedures goes beyond the scope of this publication.

General rules for the removal of solvent-like cargoes from epoxy coatings: Check the instructions of the coating manufacturer. It may be necessary to ventilate the cargo tanks before washing with water. Even after ventilation, according to manufacturer’s instructions and the carriage of intermediate cargoes, previously carried cargo residues could be retained in the coating, which could lead to contamination of the subsequently carried cargoes.

Phenolic Epoxy Coatings

Cross-linked polymer structures do not allow a chemical cargo to permeate the tank lining. This improves the chemical and temperature resistance compared with other Epoxy coatings.