Corrosion is one of nature's most destructive forces. Not only does it eat away at electrical devices and equipment, it eats away at productivity by causing power interruptions, downtime, and costly repairs. In fact, corrosion costs U.S. businesses, government agencies, and households more than $300 billion a year.
Corrosion is the gradual wearing away of any substance by a chemical, physical, or electrochemical reaction. Electrical systems corrosion usually takes place by means of a natural chemical reaction triggered by metal's inherent tendency to revert to its more stable compound, usually an oxide.
Some metals are more "active," or more likely to enter into a reaction, than others. So-called "Noble" metals, like gold and platinum, are so inactive that corrosion is negligible. Aluminum is active and corrodes quickly, but the thin, transparent layer of oxide that forms actually protects the metal from further corrosion. Iron, however, is extremely reactive. Left unprotected, it will erode, crack, and eventually fail.
The many faces of corrosion
Of the several types of corrosion, the most pervasive in industrial environments is general corrosion, characterized by a uniform thinning of metal across the material's surface. General corrosion is further categorized into galvanic and atmospheric corrosion. Galvanic corrosion occurs when two different metals are electrically connected in the presence of an electrolyte, which is an electrically conductive solution like sodium chloride. A good example of this is corrosion that appears around a steel-to-copper connection when in contact with sea water.
What accounts for more material failures from both a tonnage and cost view, however, is atmospheric corrosion, which can occur when electrical devices and fittings are exposed to the environment around them. The damage done to metal by the oxygen and water in the earth's atmosphere can be significant. Add in industrial pollutants and other contaminants, and it can be even more severe. Such corrosive environments can be found near sea coasts, at industrial sites, in heavily populated urban areas, in some rural locations, and in combinations of any of these. In industrial plants and water treatment facilities, corrosive environments are just as common indoors.
In general, corrosive environments are classified as follows:
- Marine — Sea spray, mist, or fog can carry sodium chloride several miles from the coast, making installations that are a substantial distance from the ocean vulnerable.
- Industrial — Metals can be exposed to a multitude of contaminants in industrial environments, from the sulfur and nitrogen compounds produced by fuel combustion to particles of metal oxides, chlorides, sulfates, and carbon compounds, which are extremely corrosive when combined with oxygen, water, or high humidity.
- Urban — In densely populated areas, emissions from automobiles and heating fuels increase the amount of sulfur and nitrogen oxides in the air.
- Rural — Most people don’t associate corrosion with rural areas, but these environments can contain high levels of ammonia and nitrogen contamination from fertilizers, as well as high concentrations of diesel exhaust.
Three ways to fight corrosion
Since this isn't a perfect world, you can't eliminate corrosion. But you can limit its destructive effects with the following methods:
Control the environment. As much as possible, shelter electrical installations from the weather. In coastal areas, face them away from the water and the prevailing winds from the coast; if you can see the ocean from the site, you can expect severe corrosion. Eliminate industrial contaminants from the air as much as possible, and keep fuel-burning equipment in good repair to minimize emissions.
Choose noncorrosive materials. Depending on your project, you may be able to select electrical devices and fittings made of noncorrosive or corrosion-resistant materials. Nonmetallic control stations, for example, offer unsurpassed resistance to harsh chemicals, while an aluminum conduit body is protected by the thin layer of oxide that forms on its surface.
Specify a protective finish. When your application calls for devices with the high tensile strength and ductility of malleable iron, the best and most cost-effective way to combat corrosion is to choose a coating that effectively seals out water, chemicals, and other contaminants.
The problem with paint
While conventional paint coatings have long been popular, they're simply not effective in resisting corrosion. Paint is hard to apply evenly, so it tends to drip and bubble, miss small crevices, and thin at the edges, leaving these areas more exposed. Paint is also inflexible, making it easy to crack and chip in normal use. Once the coating cracks, the metal corrodes as quickly as it would have if it were completely unprotected.
Epoxy powder coat has proven to be far more effective than conventional paint finishes. It's formed from high-grade epoxy powder applied to devices and fittings electrostatically. Drawn to the metal like a magnet, the powder covers evenly, reaching into the smallest crevices. The powder is then slowly oven baked to cure the coating and ensure a strong bond. The result is a thick, uniform layer of protection that seals out the harshest corrosives, including sulfur oxides, nitrogen oxides, chlorine and chlorides, ammonia and ammonia salts, and hydrogen sulfide
Moreover, epoxy powder coat is extremely durable. And unlike conventional paint, it’s flexible, so it stays intact when the underlying metal expands and contracts during temperature changes and stress fluctuations. Epoxy powder coat also adds value through fewer callbacks and lower operation costs, whie helping to safeguard the environment by virtually eliminating overspray particulates.