With the life expectancy of a modern LNG carrier in the order of 30-plus years it is clear that corrosion protection plays a key role.

As with other vessel types, the water ballast tanks are the critical areas in terms of corrosion protection, especially considering the restricted access, tight sailing schedules and repair costs.
A correct choice of ballast tank coating is not only a matter of corrosion protection but also long-term economic necessity.
The result of this choice should not only combine factors such as resistance to wet/dry and hot/cold seawater cycling but also, just as important, fit shipyard procedures as the final coating result is a combination of intrinsic performance characteristics and correct application.
“SigmaPrime - a pure epoxy system from Sigma Coatings - seems to fit both these requirements, providing long term anti-corrosive performance as well as being suited to modern high-speed production methods,” a Sigma spokesman said. “With over 12 million sq m either applied or specified since its introduction in 2000 it has fast become the coating of choice for many shipowners and shipyards.”
The anti-corrosion properties of SigmaPrime are not in doubt, as can be seen by a number of SigmaPrime vessels currently in service, observed the spokesman.
Sigma Coatings has also invested in independent testing at the Det Norske Veritas (DNV) laboratories in Bergen, resulting in SigmaPrime being awarded the highest rating (B1) for ballast tank coatings on both shop-primed and mechanically pretreated surfaces. This B1 rating is recognised by the ship classification arm of DNV for Type Approval as an anticorrosive coating suitable for use in ballast tanks.
Performance at service is not the only requirement of a ballast tank coating - before it can perform it has to be applied. Currently, the key coating issue at newbuildings is the application of elevated coating film thicknesses. It is a widely held belief that the more paint the better, but unfortunately this is very often not the case. As the speed of shipbuilding increases, the consequences of too little paint being applied are severe. This has led to a trend of elevated film thickness, particularly in complex and difficult-to-reach areas such as double-bottom tanks. In the worst cases this can result in cracking of the coating providing a breach in the anticorrosive barrier and the onset of corrosion.
With this in mind SigmaPrime, which is typically specified at 2 x 150 microns in the ballast tanks, is crack resistant at up to 2,000 microns, nearly seven times the specification thickness.
“In practice, the user-friendly nature and easy application characteristics of SigmaPrime mean applicators can easily control applied film thickness and that excessive film thickness is not often reached but the crack resistance builds in extra safety for both applicator and operator,” said the spokesman.
“Long-term coating performance is a combination of many factors but correct coating choice and application at newbuildings are by far the most important. SigmaPrime provides suitability to current shipyard procedures as well as long-term performance in service.”