Heat Exchanger Coatings
Another significant cost driver is heat exchanger coatings for corrosion protection or for cosmetic purposes. Coating for corrosion protection is most common on aluminum heat exchangers, since aluminum corrodes more easily than other metals. There are several types of heat exchanger coatings to minimize corrosion: chemical conversion coating, anodization, e-coating, and painting.
One of the most widely used coating options is chemical conversion coating or chromate conversion coating, also known as "Chem Film", that minimizes surface oxidation. Most government and commercial heat exchanger engineering specifications require that aluminum be chemical conversion coated (per military standard MIL-DTL-5541F, previously MIL-C-5541E).
In addition to Chem Film, another option that can be used to protect aluminum is anodization. Anodizing minimizes corrosion and abrasion by modifying the crystal structure close to the metal surface. It produces a harder part with even greater corrosion protection. However, it is not a common coating and it's more expensive than chemical conversion coating.
A third coating method that provides corrosion protection is called an e-coat, also known as electrodeposition or electrocoating. A DC charge is applied to a metal part immersed in a bath of oppositely charged paint particles. The paint particles are drawn to the metal part and paint is deposited on the part, forming an even, continuous film over the entire surface. It is the most expensive type of heat exchanger corrosion protection.
Heat exchangers may also be coated with paint for corrosion protection or cosmetic purposes. For example, copper heat exchangers are sometimes painted for aesthetics since uncoated copper may change color over time. For epoxy paint applications, the cost per heat exchanger can range from $10-$200 per heat exchanger. The cost of the paint application will depend not only on the coating itself, but also on the amount of surface area to be coated. Weigh the value of the added corrosion resistance or improved appearance against cost to determine to opt for coating or painting. How long do you want your heat exchanger to last? Will your heat exchanger be visible and how important to your end users is heat exchanger appearance? The appearance of a heat exchanger on equipment in a hospital is likely to be more important than the appearance of a heat exchanger on equipment in a factory.