Atmospheric Corrosion of Copper-Brass and Aluminum Heat Exchangers
While many people have strong feelings about whether a copper-brass or an aluminum heat exchanger cools better, rarely is there a clear understanding about their resistance to regular corrosion in the atmosphere. They are very different in this matter, so read on to understand just what those differences are.
Regardless of how much care and attention to detail you take with maintenance on parts, some corrosion is inevitable. In this article we’ll take a look at the factors that contribute to atmospheric corrosion.
Corrosion in the Atmosphere
Needless to say, components are almost always exposed to the atmosphere; however, copper-brass and aluminum have very different susceptibilities to this kind of corrosion. Atmospheric corrosion occurs due to pollutants and moisture in the air. This can be accelerated in heavily polluted environments, such as industrial businesses or heavy urban settings. Some protection is provided by both metals as they form an oxide layer, a thin layer of corrosion, when first exposed to the atmosphere; however, this layer is very different between the two.
Aluminum Oxide Layer
The layer formed on aluminum is extremely strong yet very thin. It is clear in color, so you don’t notice it. This layer protects the aluminum from additional corrosion and is self-healing. If the layer is scratched off or damaged, it reforms almost immediately. Besides being remarkably strong, aluminum’s oxide layer is also impermeable to fluids. This makes aluminum especially resistant to corrosion when compared to all other metals. In fact, aluminum is added to many different alloys to help increase their corrosion resistance.
Copper-Brass Oxide Layer
When copper-brass fully forms its oxide layer it is greenish in color, like the Statue of Liberty (an all copper statue). While it does provide some protection, it does not form as quickly as aluminum’s layer nor is it as strong. This is partly why copper-brass heat exchangers, such as radiators or charge air coolers, are painted. That paint helps to protect the component from deterioration, but it can also interfere with the heat transfer process. As you can see from the photos of the copper-brass heat exchanger below, metal deterioration can be rampant and complete.
This copper-brass heat exchanger core has been completely lost to corrosion. Many of the fins have deteriorated to nothing. Needless to say, the cooling ability of this radiator has been reduced to zero. Move your cursor over each image for a closer view.
Pollutant Accelerated Corrosion
As we mentioned before, pollutants in the air can cause accelerated corrosion. Copper-brass tends to be more susceptible to this due to its relatively weaker oxide layer which can be damaged from contaminated runoff from rain or high humidity. Aluminum will be adversely affected as well, just not to the same degree thanks to how rapidly the oxide layer reforms. As an example, we have a customer needing radiators for a fertilizer plant that had numerous copper-brass heat exchangers installed. Those coolers had to be replaced every few months due to the rapid corrosion they experienced. This customer asked us to build an aluminum radiator to test out and see how well it would perform. It was custom built to match the dimensions of their existing radiators, and it has lasted over a year now with no problems. Our customer now has us building aluminum radiators to replace the remaining copper-brass.
Other Environmental Considerations
Some environments are just hostile to any type of metal. These aren’t necessarily “atmospheric” type environments, but we wanted to mention them as extreme situations. In particular, marine (or saltwater) environments are notoriously destructive on metals. Other extreme environments include high humidity, high temperature, and acidic type environments. In these type conditions, the corrosion process can be severely accelerated. You will want to look at taking additional steps to protect your equipment. Some of these steps may include:
- Adding protective paint
- Washing the equipment to remove a build up of contaminants
- Installing sacrificial anodes, blocks of metal that will take the brunt of the corrosion (if possible)
The bottom line is, aluminum is much more resistant to atmospheric corrosion than copper-brass. Aluminum’s protective layer is so strong and resilient that it surpasses most other metals in resisting deterioration. It even outperforms copper-brass in heavy pollutant, industrial environments. As always, care should be taken in extreme environments where additional protection for the metal components is required.