MarineLine 784: Advanced tank coating for long-term protection

Odfjell's MarineLine coated vessels are coated with MarineLine 784 which is a heat-cured polymer tank coating. This coating is applied in two coats and undergoes a thermal curing process which activates its full crosslinking potential. The resulting structure consists of up to 784 crosslinks per polymer molecule, significantly exceeding standard epoxy coatings which have only four crosslinks per molecule. 

Following the heat-curing, the coating surface becomes glossy and almost impermeable, resulting in a broad chemical resistance, low cargo and water absorption, and makes it significantly easier to clean than other coatings. 

To preserve the coating integrity, it is essential to prevent mechanical damage. Direct contact with objects such as tools, ejector hoses and portable tanks cleaning machines must be avoided. Any portable machines used should be fitted with rubber protection to minimize impact. 

The material cost for the coating is higher than other coatings, and the two-coat, heat-cured application process requires extended yard time which makes it extra important that the coating is treated correctly. Both with aspects of cargo resistance and mechanical damage. With proper maintenance and timely repairs, the coating can provide a long service life before recoating becomes necessary. 

Chemistry

MarineLine is a polysiloxane coating and is not classified as an epoxy coating because the backbone does not consist of carbon atoms. It is technically not even an organic coating because the silicon-oxygen (Si-O) backbone is derived from quartz sand (SiO2).

Methyl groups are introduced to adjust flexibility and reactivity, and silanol (-Si-OH) groups condensate to form cross-links.

MarineLine gets its excellent chemical and thermal stability from the very high bond energy of the silicon-oxygen bond, as it takes a lot of energy to break this bond. But there are some cargoes to which the coating is not resistant. For example, phenol and nitric acid cannot be carried in MarineLine. 

Aggressive cargos

Cargos such as alcohols (methanol, ethanol), chlorinated hydrocarbons (EDC) and vinyl acetate are aggressive to the coating because they soften the three-dimensional structure by interacting with the silanol groups.

These grades are still acceptable to carry but require extra handling precautions. Aggressive cargos should be kept under nitrogen blanket during the voyage and discharged with nitrogen to avoid condensation in the tanks. 

Discoloration

Certain products can cause discoloration to the MarineLine coating, particularly those with high levels of Free Fatty Acid such as PFAD, UCO and POME. The discoloration intensifies at higher temperatures and prolonged time and it is therefore recommended to limit the heating of these cargoes to the minimum requirements. 

A good practice can be to keep the cargo temperature in the lower part of voyage temperature, and before discharge slowly increase to minimum discharge temperature.  

The discoloration is limited to the surface of the coating and is primarily a visual concern. It does not compromise the coating’s chemical resistance or pose a contamination risk to subsequent cargos. 

Consequently, further cleaning to remove discoloration is not recommended, provided the tans meet the requirements for next cargo to be loaded.