Coatings and Corrosion

At war with nature


Malcolm Latarche
Malcolm Latarche
ShipInsight

18 December 2018

At war with nature

Shipping’s battle with the forces of nature is one that has been fought from the days of wooden ships. Over time, preventing biofouling has involved the use of many different materials and chemicals from sheets of copper to poisonous compounds. Some of these were very successful but their undesirable side effects attracted the attention of science and the environmental movement which wanted to see them controlled and prohibited from use.

Unlike so much IMO regulation which details what ships must do or carry, the International Convention on the Control of Harmful Anti-fouling Systems (AFS) on Ships, which was adopted in October 2001 but only came into force on 17 September 2008, is totally geared to preventing the use of certain products. The convention covers all vessels including FSUs and FPSOs. Initially the product at which the convention was aimed was tributyltin (TBT), a substance developed through the 1960s and first used in the 1970s and which the IMO itself concedes is probably the most effective biocide so far devised for the maritime industry.

TBT belongs to a wider family of chemical compounds called organotins. Other compounds within the organotin family are still permitted in coatings as a catalyst for the curing process if organotin content does not exceed the allowable limit of 250mg/kg of paint. Some concerns have been raised that the quantities in some products are increasing and could be having a similar effect to TBT on mollusc reproductive systems. This is an ongoing issue that is being monitored at the IMO.

Before the AFS Convention came into force, all of the leading coatings manufacturers had already ceased production of TBT products and were developing replacement products. Not all of the new coatings used on the hulls are affected by the convention because the technologies that have been developed sometimes are designed not to kill but merely to make attachment to the hull more difficult.

There are now three different methods used in products for coating for the underwater parts of a ship: antifoulings, which contain a biocide to kill organisms that adhere to the hull; foul-release coatings, which are designed to prevent organisms attaching by a variety of methods; and hard coats, which present a smooth surface that can be cleaned using equipment that would remove or damage the other two types of coating. The technologies employed in each case may vary from product to product and some manufacturers describe some products as having more than one means of operation.

As with most IMO treaties, there is provision for countries to opt out of it but should they do so their vessels will not be welcome in most parts of the world. Any party to the treaty is obliged to apply it to vessels flying its flag or which it would otherwise have some control over, and to prevent any vessel of whatever flag entering its ports. Since most of the world’s major economies are parties to the treaty, only a very few domestic vessels and some trading between adjacent countries that are not signatories can afford to ignore the treaty.

Testing for banned products by Port State Control inspectors is allowed under the convention but there is very little evidence to suggest that this is done on any great scale. Ships above 400gt are obliged to undergo an initial survey before they are put into service or before their International Anti-fouling System Certificates required under regulation 2 or 3 of the convention are issued for the first time. Ships are also obliged to undergo surveys when their anti-fouling systems are changed or replaced and the details of their survey recorded on the certificate.

The certificate records the type of anti-fouling used, its manufacturer, where it was applied and by whom and even extends to the colour of the coating. Generally, as long as the certificate appears to be in order, PSC inspectors are unlikely to order tests on the coatings although this can never be discounted. The convention includes a clause which states that a ship shall be entitled to compensation if it is unduly detained or delayed while undergoing inspection for possible violations of the convention.

The Black List

The International Convention on the Control of Harmful Anti-fouling Systems on Ships does not approve any products but is purely a prohibiting convention with a black list of banned substances. Today, TBT organotin is still the only substance on the banned list, which is contained as Annex I to the convention. However, there are expectations that other products may be added over time.

Copper-based products which now feature in many biocidal anti-fouling products are often mentioned as being likely candidates for future banning. However, in August 2016 the prospect of an imminent ban on copper receded when it was announced that, after thorough scientific evaluation of the use of dicopper oxide, copper thiocyanate and coated copper flake as antifouling substances within the EU Biocidal Products Regulation 528/2012, the European Chemicals Agency’s Biocidal Product Committee determined that these copper compounds should be approved for use as active substances in commercial and yacht (pleasure craft) antifouling products. The committee also allowed its application by both professional and nonprofessional users. These three compounds are the only copper compounds to have received approval to date but importantly they are the forms of copper most commonly used in current antifouling paints, either as a sole biocide or in conjunction with a co-biocide.

As always with EU regulations, things are not straightforward and the regulations required that manufacturers submitted applications for approval of all their copper-based antifouling products by 1 January 2018 after which acceptance was not guaranteed. Products containing zinc pyrithione have a later deadline. Paints must be approved by each country in which they will be marketed.

For any product to be added to the IMO’s black list, an amendment is required under article 16 of the convention which will first be subject to a lengthy investigation process described in articles 6 and 7. As the shipping industry in general and coatings manufacturers in particular are likely to be aware of any move to add a substance to the banned list well in advance of any action actually being taken, the length of time needed for the process is not likely to cause headaches for operators. Even so the convention does allow any vessel affected by an amendment to Annex I a period of grace of up to 60 months or until the coatings were due for renewal, whichever is the earlier.