MARINELINE® & CHEMLINE® COATINGS FOR INDUSTRY

APC Article Reprints

TANKS AND TANK COATINGS
AS SEEN IN :
the FOFSA International Newsletter

During the last two years, the topics 'Ships Tanks' and 'Tank Coatings' have become the subject of investigation in several areas. The design and spacial position of tanks was critically reviewed during discussions within the revision of the Marpol II regulations by the International Maritime Organisation (IMO). This resulted in a derogation for animal and vegetable fats and oils to be carried in IMO Type 3 ships with a narrower cofferdam than that required for other 'noxious liquid substances'.

The performance of tank coatings has also been discussed within Codex circles with respect to the Codex proposed list of acceptable previous cargoes. It is well accepted that tank coatings can absorb up to 10% of their weight of a cargo during a long voyage. The fact that this material may desorb during the subsequent voyages is one of the main reasons for trading on 'acceptable terms'. It is also recognised that stainless steel tanks do not absorb their cargoes during a voyage, and it was this major difference in absorption properties which prompted the initiation of two projects within the Oils and Fats Committee.

A member proposed to the committee that there had been a development within polymer technology which meant that it was now possible to produce organic polymer coatings which absorbed very little of the cargo during the voyage. It was suggested that the very extensive cross-linking within the new polymers prevented the molecules of the cargo from penetrating the coating. If this were the case, then it may be that the use of this coating need only be restricted to the same carriage conditions as stainless steel. Some trials have been carried out and the report has been considered by the working group of the Oils and Fats Committee. This group has asked for further investigations to be made to demonstrate the comparative improvement over standard organic coatings.

The fact that liquid cargoes are not absorbed into the body of stainless steel tank walls forms the basis of another proposal from a member. This concerns the use of wall wash tests to confirm the cleanliness of stainless steel tanks. These tests are routinely used within the chemical trade before loading high purity materials. The member feels that if an appropriate wall wash test can be used to show that there is no residue from the previous cargo, then even if it was a banned list cargo, it should be possible to load a subsequent food grade cargo without risk of contamination. A sub-committee has carried out tests on three voyages where the washing and testing have been closely monitored. The report of this sub-committee is currently being considered within the Oils and Fats Committee working group. Members will be kept informed of developments within these two projects.