Corrosion protection for coils and static evaporators

In general, all components of a refrigeration system that is used in or for a potentially corrosive environment must be adequately protected from the time of manufacture. In the case of commercial refrigeration, we are talking about supermarket refrigerated cabinets and counters, under-counter cabinets in the Horeca sector, and cold rooms or cold rooms in the distribution or food industry. The risk of corrosion can come from the area in which it is located or the type of product to be refrigerated.

In particular, corrosion in a coil or static evaporator causes the separation between the tube and the fin and therefore the heat transfer between one and the other disappears; on the other hand, the tube is degraded and refrigerant gas leaks can occur.

The most common situations in which corrosion can occur in commercial refrigeration are:

• Exposure to moisture, for example in areas near the coast or unprotected liquid storage.
• Saline environments, either by being a work area near the sea or in the conservation of products with high salt content as is the conservation of fish.
• Contacts with acids, for example in bread and pastry dough fermentation processes. In this process, microorganisms metabolize nutrients and produce organic acids, gases, and alcohol that can be corrosive to metals. Another example of contact with acids is the preservation of some fruits, e.g. apples.

Protective coatings to prevent corrosion in evaporators

In general, evaporators can be protected by means of an integral cataphoresis treatment, a tin bath, or paint. We would like to focus on the latter system since there are different solutions for painting. In general, the advantage of using paint as a means of protection is its cost compared to a tin bath or cataphoresis. All the methods indicated reduce heat transmission because none of them is specially designed for this purpose. This is where a paint specifically designed for the protection of heat exchangers can save on the manufacturing costs of the evaporator without a significant reduction in its properties. Good thermal conductivity will save energy costs in the installation throughout the useful life of the heat exchanger.

In commercial refrigeration it is also important to ensure that the anti-corrosion treatment of the heat exchanger is compatible with the food environment and has the appropriate certifications. It is not necessary that it can be in direct contact with food, but it is necessary that it does not release any substance that could alter or contaminate it.

At Sereva we protect the evaporator coils by applying a solution based on polyurethane impregnated with aluminum. This is the KL10K coating system manufactured by AQUA AERO composed of polyurethane binders impregnated with a metallic component with high elongation properties, aluminum pigmentation added to establish heat transfer, chemical resistance, and UV blocking properties. Corrosion resistance reaches more than 10 000 hours (ASTM B117) and G85 3000 hours: chemical resistance is excellent. It also withstands temperatures up to 120°max and -40°C minimum. It has been tested up to 180°C, which also allows it to be used in extreme conditions such as climatic chambers.

Attached is the following comparison between various paint solutions:

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Corrosion protection of the remaining evaporator components

The described paint protection is applied to the whole heat exchanger block, i.e. coil, fins and headers. In case of using a casing or in the case of a forced draft evaporator, the casing, screws and other metal parts can be made of stainless steel.