Corrosion, Defined.

So. What exactly is corrosion?

A simple question with an awful lot of depth behind it. We promised in our first post to keep things short and informative around here, so let’s answer that simple question as simply as possible.

Corrosion, as defined by Everett Collier in his essential The Boatowner’s Guide to Corrosion, is “the deterioration of a metal or alloy by chemical or electrochemical reaction with its environment”. Now, there are several ways in which corrosion might occur. For our purposes, the three most pressing and relevant forms are simple, galvanic, and electrolytic corrosion. Let’s define those a bit more here before diving in with our next few posts.

Simple Corrosion plays out in a single piece of metal (pure or alloyed). Everyone’s familiar with this idea, even if they’ve never been near a boat.

Galvanic Corrosion is a reaction of dissimilar metals in contact with one another in a common electrolyte. What’s an electrolyte?  The ABYC defines it as an aqueous solution – such as seawater – that can conduct electricity, facilitating ion flow. What’s an ion? Don’t worry, we’ll get there.

Electrolytic Corrosion occurs when current is introduced to a galvanic cell. Easily the most misunderstood type of corrosion out there (for example: this is not the same process as electrolysis). Capable of sudden, dramatic damage.

Next, we’ll explore these types of corrosion in more detail. We’ll also get into poultice corrosion [turning again to the ABYC for a definition: “corrosion (typically in aluminum) caused by oxygen deprivation”]. Corrosion has an appropriately fearsome reputation. But it's important to know right away that it can be observed, tested, and corrected. In order to learn how to do that, we’ll need to commit to the practice of thinking like a scientist. More on that next week.