Experiencing corrosion on your production equipment or device? But don’t know how it’s forming? Or where it’s coming from? Of course, this can be especially frustrating for those who are already taking precautions.

Is the answer in the parent metal exclusively? Well, what about corrosion resistant coatings? Don’t they all afford equivalent protection?

The answer is, plain and simple: no. Not all corrosion resistant coatings are created equal. Success in one environment does not ensure success in another. In fact, failure to understand the environment can result in lackluster performance. Even catastrophic failure.

We regard the terms corrosion and chemical corrosion as synonymous. When a surface is attacked, it is a chemical (or electrochemical) reaction occurring between the surface and the environment, which results in a negative impact on surface properties or performance. Here are some of their more common manifestations:

So, what are the ideal corrosion resistant coatings? First, recognize these corrosive types and their contributing factors:

Fretting-- visible through pits, grooves, or debris relating to oxidation, occurring at the asperities or \“peaks\” of contact surfaces. An example is vibration, which is the result of load in the presence of repeated relative motion.

Galvanic-- seen by pits, holes, or local oxidation products, the result of dissimilar metal. Here, one metal corrodes faster than it would alone, while the second corrodes slower than it would alone. Often, this is confused with coupled metals exhibiting increased decay based on differences in their electromotive force potentials.

Uniform-- manifested by equal measurable material loss over a larger surface area, which continues until failure. There is often predictability there. And performance is assured, though will diminish over time.

Pitting-- is a localized form. Often difficult to detect, this type is considered more dangerous to design against. Pitting is initiated by local chemical or mechanical damage of protective oxide films or non metallic inclusions, theoretically forming a \“battery\” between an abnormal anode or cathode site.

Other forms, such as ‘Intergranular’, ‘Exfoliation’, ‘Stress’, and ‘Hydrogen Embrittlement’, can also result in localized cracking, severe loss in ductility, and increased residual tensile stresses. Failure in any of these is typically catastrophic.

So what are the best corrosion resistant coatings? Consider the environment. Do you know the service temperature, the corrosive strength, the time of exposure? And how about the corrosive medium. Is it a liquid? A vapor? Both? Under pressure?

Your best coating answers will be found in environmental compatibility. Are materials of the coating inert (non reactive) with the environment? Consider too, surface porosity. Also known as pin holes or holidays, these are microscopic voids reaching through the coating, all the way down to the base metal.

How do you prevent porosity? You don’t really. But you can select materials offering comparatively lower crystallinity, smaller microscopic voids. Your best bet may be to compensate with thickness. More is better. Especially in static environments, non-moving parts, where there are no concerns of coating shear.

Choose, too, a parent metal unlikely to form corrosive products. This will better ensure, in the event of coating permeation, the lower likelihood of coating undermine and loss of adherence.

Can the success of a protective coating be predicted prior to service? Yes. ‘Wet Sponge’ or ‘High Pot’ tests are common and relatively inexpensive ways to assess future performance. Using electricity (under applied voltages) any bare metal spots will quickly be found by an electrical arc discharge.

Here, in the following articles, you will learn about the different types of Teflon, like PFA, FEP, ETFE, and others. You will also read about less known materials, like PVDF or PEEK. Don’t overlook what is being accomplished today in Anodizing, Vapor Deposition, Plating or Thermal Spray. So, you see, there are so many more choices than Epoxy, Phenolic, or Urethane. This is especially important in dynamic environments, where other performance requirements like anti-friction, hardness or wear, are equally critical.

Want to make a better product? Or simply, make your product faster, more reliably, with less scrap? We share your goal for corrosion resistant coatings!

Why Industrial Coatings World?

Because there’s so much more to know! So, where ever your surface engineering takes you, please know we’re here to help. In fact, we’ll get you there faster than you ever imagined. And isn’t that what it’s all about?