The IMO resolution MSC.215(82) or PSPC for coating performance in sea water ballast tanks has raised considerably the profile of coating activities for yards, owners and regulatory authorities. The prospect of additional IMO resolutions on coatings to deal with other critical vessel areas is focussing the attention of many people.

The PSPC details the needs for coating ballast tanks to achieve a 15 year target life. It clearly focuses on the current preferred solution, which is based on epoxy coating systems. However, tantalisingly, the regulation opens another door and that is the systems that can be used to achieve the 15-year target life are not limited to the epoxy, liquid coating solution as the regulations refer to the possibility of alternative options by using the term “or equivalent”.

This tantalising alternative option set the team at Safinah thinking, what could be the alternatives that could give an equivalent 15-year target life. The options seem to fall into a number of categories:

1. Alternate epoxy schemes
2. Non-epoxy coatings/linings
3. Physical/Chemical processes
4. No ballast
5. Neutral ballast

The aim of this newsletter is to simply examine these alternatives and to identify possible equivalent technologies that may emerge in the near or distant future.

The system described in the PSPC achieves the target life of 15 years by: 

• Surface preparation
• 2 coat scheme with 2 stripe coats
• Planned maintenance requirements (yet to be defined)

Ballast tanks

Ballast in one form or another has always been required to assure the stability and manoeuvrability of vessels when not carrying cargo. Once solid ballast was replaced by water ballast, because of the improved turnaround efficiency of the vessel, the problems with the presence of ballast tanks emerged.  

In the 1850’s a number of vessel designs were proposed with removable ballast tanks. These were simply bolted to the floor of the hold and removed when cargo capacity was required.

Since then, a variety of concept designs have been drawn up that have included solutions such as “tractor – trailer” sea going ships, LASH ships, and BACAT concepts have all at one time or another been tried, tested or at least emerged on the design boards, but to date no really cost effective alternative to the use of water ballast and hence the need for a ballast tank and the associated coatings has emerged.

Taking each of the above equivalent options in turn:

1.    Alternate epoxy schemes

The two-coat plus two-stripe coat scheme (2 plus 2) has been arrived at as a result of the present capability of:

• Surface preparation technology
• Application technology
• Edge retention capability
• In service experience of owners (tanker operators in particular).

An equivalent may be achieved by removing stripe coats, reducing to one full coat or some combination of these. The implication though is that the technology involved in application needs to be improved and perform consistently to assure the quality of a single coat application. The edge retention problem would need to be resolved and surface preparation quality to remain at least the same.

Looking at these options, it is considered by Safinah unlikely that a solution along this route will find ready acceptance as an equivalent. In theory however there are products from many of the leading Paint Companies that do offer a single coat solution that have the 5-year track record in the field.

A number of systems are in the market offer ease of checking single coat integrity either by a colour change or by the use of luminous pigments. These have been considered for a number of years and have some limited application in practice.

The issue for build yards is clearly one of cycle time, to try and move the blocks through the paint facilities as quickly as possible. Consequently one possible solution is that the scheme applied is a multi-coat scheme as required by the standard but that the first coat is very thin to give adequate coverage and quicker drying. The second coat could then bring the scheme up to the IMO required Dry Film Thickness.

2.    Non-epoxy schemes

Epoxy chemistry has been the back-bone of marine coatings for many years, however of course there are alternative technologies. Some of these other technologies have been used for ballast tanks. Most notably urethanes over the years have had a mixed reputation, but a recent US Navy initiative that recognise the rapid and predictable cure times of these products shows a possible route for their return. In addition these technologies have some serious big raw material suppliers behind them, who would very much like to increase market share in marine.

It is likely that such systems could be considered as equivalent to epoxy systems and would be subject to similar testing regimes for approval (as for epoxy paints) as long as they fall into the category of liquid paints. In addition they would provide yards with a degree of predictability with regards to cycle times and cure time as they can be formulated to cure independent of DFT and temperature in a consistent manner.

3.    Physical/Chemical processes

Anodes

The IMO resolution does not discuss the use of sacrificial anodes. These have long been a part of the standard corrosion protection system in ballast tanks as a chemical process that can aid in the arrest of corrosion.

It is unlikely however that the use of anodes alone or in any format would provide a 15-year target life and hence they will be only used as an assistance technology to other systems (coating or otherwise). Thus it is likely that they will remain a contributor to epoxy based systems and that the IMO resolution will not have any real effect on their use.

Corrosion resistant steels/alternative materials

For many years Nippon Steel and others have supplied corrosion resistant steels and this technology is still being pursued. Nippon Steel recently had a product approved for a 100-year life in land based housing construction. It is possible in the future that alternative materials and structural configurations may provide solutions that require none or very little corrosion protection in the form that we currently thick about. However Safinah do not see these solutions emerging in the short to medium term.

However it could be that a combination of such steels and reduced coatings (say one coat application) could result in an equivalent possibility.

Ballast water treatment systems

Some of the Ballast Water treatment systems operate on a de-oxygenation principle, by stripping oxygen out of the ballast water and further making the ballast tanks inert to a degree by the use of inert gasses of one form or another.

In theory these systems should assist in the arrest of corrosion and there is some evidence to that effect. On that basis it may be acceptable to use such a system in conjunction with a reduced coating specification to achieve the equivalent 15-year target life. Some of these systems have undertaken trials with coatings (Epoxy) and shown positive results.

4.    Non Ballast ships

NOn Ballast Ships (NOBS) have been receiving considerable attention recently and a number of studies are underway in Japan, Europe and the USA. It is readily envisaged how some ship types, such as Cruise and Container ships may be able to operate within a no ballast scenario, but more surprisingly there are also designs for Baulk carriers being proposed. Clearly if vessels could operate without ballast tanks (other than those required for trim), then the implications for the need of ballast tank coatings are considerable, as the double skin tanks would in effect become void spaces, while the number of required ballast tanks for trim would be reduced. These tanks may still need to be coated in accordance to the IMO requirements but the total square metres will be considerably reduced.

5.    Neutral Ballast ships

The elusive solution that was chased by many ship-owners in the late 1970’s was of course having a vessel that could carry cargo on every leg of its voyages. The birth of the OBO or combination carrier, was seen to herald an era where no ballast was required and the earning capability of the vessel could be increased by minimising the need to run in ballast by designing the vessel to carry complimentary cargoes. The death of the “traditional” combination carrier has been slow. Although the vessel design could achieve what was required, the operational efficiency of the vessels left them exposed to fierce competition from specialist carriers.

However, to say that the concept is dead is premature, one could say that in a sense Container vessels are combination carriers, in that the variety of cargo they can carry allows them to run very few legs in Ballast or light condition. The question is whether the future may bring back new options for the transport of bulk cargoes, perhaps in combinations not envisaged before, that would minimise the need for ballast and make the vessels ballast neutral.

If this type of trading solutions were to emerge then the need for ballast tanks could be significantly reduced. There are some ideas at early stages of development but it is too soon to determine their likely success or otherwise.