Richard Stratton, Principal at Advanced Coating Solutions, lifts the lid on why traditional insulating materials don’t work and can contribute to corrosion under insulation (CUI).
There are many historical coating/corrosion/temperature differential problems associated with standard areas, wet areas, between machinery spaces (A60) and chiller pipes, and other challenges like freezer spaces below the water line or above engine rooms.
Other difficulties can arise with IMO approvals and testing for fire resistance.
Why new solutions are working and becoming accepted as new spec
Ships have any number of separate challenges, which need to be addressed. Keeping interiors warm and dry has always been a problem; even with steel and aluminium structures that seal off the outside, it’s next to impossible to maintain a dry environment.
The first challenge is keeping humidity from causing condensation to form on cold surfaces. The next challenge is keeping interiors cooler than the outside when operating in hot climates.
Our working experience is mainly based on supporting the Alaska fishing fleet of factory trawler/processors that mainly operates in the Bering Sea.
Even in the summer, the weather would appear to be winter-like, with water temperatures on the surface averaging from 34° F (1° C) in the north to 41° F (5° C) in the south. The period without frosts only lasts for about 80 days in the northern part of the sea, where snow is common even in the summer, and maximum summer temperatures are only 68° F (20° C).
The colds impact on the superstructure chills interiors and causes condensation to form on surfaces. As traditional rock wool insulation is attached to the surfaces with pins, there’s still exposure to air that’s wet enough to deposit moisture on cold surfaces. That moisture eventually leaves surfaces wet enough to dampen the insulation. Another challenge is that insulation is rated when completely dry (0% moisture content). In the real world, just a little moisture changes insulation’s thermal resistance value. For example, according to tests, only 19.5% moisture content causes rock wool to go from its best rated value (0.043 W/mK) to a value of 1.2 W/mK. Since water vapour penetrates all materials with air spaces, those air spaces eventually come into balance with the ambient humidity of the interior. At their worst, spaces may be at over 90% humidity. That means the insulation will eventually be at that level of moisture too, which also means the insulation won’t be working very effectively.
The impact of heat
The heats impact on structures is based on solar heat loading on exteriors, which raises the temperature by as much as 55F/30C on dark steel surfaces. That heat load transfers into the structure and then has to be dissipated via AC. Spaces that are air conditioned tend to cause humid air to condense on the outside of the cold walls or overheads.
Other problem areas on ships are refrigerators, freezers or machinery spaces that have hot equipment operating in them. Chiller lines are also on issue due to the build-up of condensation which freezes and causes the foam wrapping to delaminate.
Freezer spaces are typically located right above bilges. Also, the bilge areas are located right above the water and are rarely insulated. Most freezers use concrete flooring on steel decking above the bilges, and rely on bulkhead and overhead foam for insulation. A majority of freezers allow the frozen product to soften due to the proximity to the water, and still have moisture forming underneath the foam insulation that is under the waterline.
All change
What has changed is that spray-on ceramic-based latex insulation is now used underneath traditional materials, or as a replacement for them. Spray-on insulation coatings keep the traditional materials dry and functioning, and it is less expensive to install – it is also IMO-approved and provides fire resistance. The main reason for using the insulation coating is to control the surface condensation by reflecting the heat back into the spaces. According to several users (Golden Alaska Seafoods, American Seafoods, Trident Seafoods, US Seafoods, Premier Pacific Seafoods, Western Towboat, etc.), the insulation coating has been proven to work. The trial process has taken almost 15 years and has required hands-on exposure to each company’s port and ship engineers.
Ceramic-based insulation is simply a latex-based paint with most of the heavy fillers (titanium dioxide and calcium carbonate) removed and replaced with hollow ceramic micro-beads. Applied via airless spray equipment at a wet film thickness of 300 microns, the micro-beads dry into a tight layer that blocks infra-red bandwidths. These bandwidths are the ones that that happen to be responsible for carrying radiant transferred heat. When multiple layers of insulation are applied and dry to about 250 microns per layer, there are air gaps formed between layers that provide conductive resistance to heat transfer. So, with a relative minimum of mass, at thicknesses varying from 1,000 to 1,500 microns, both radiant and conductive resistance is provided to heat transfer. It is a bit like the thin layers of oxide coatings on glass windows (Low-E windows) that resist heat transfer.
The heat resistance measured by conductivity alone has been measured at about 0.1176 W/mK (at 100°C) per 800 microns/0.8mm dry film thickness (DFT). That conductive value becomes roughly equivalent to the conductive resistance of 50mm of rock wool with 19.5%
