What’s Cathodic Protection?

rustin’ things, by Clay Junell on Flickr

What is your job?

This is a question that I often receive (starting from my wife and children). How to find a simple answer?

I see myself as a populizer, a person who tries to find simple ways of communicating complex technical or scientific concepts or ideas.

To understand what’s Cathodic Protection, it is necessary to understand in the first place WHY do we need Cathodic Protection.

Well: do you know that the oldest metallic artifacts on Earth are of extra-terrestrial origin?

No: stop imagining green humanoids; I simply said that they arrived here from outside our Planet, in asteroids or comets.

Why? Because pure metals are really rare on Earth: they react with the environment, giving birth to oxides (what we call Rust, related to Iron).

But how it is possible? We use metals daily!

Yes: during Bronze Age and Iron Age we discovered Metallurgy: we take metal ores and we purify them.

So what’s the problem? The problem is that Nature is lazy: it always tends to minimize the use of energy (in scientific terms this is called Law of Entropy).

So what? Well: we put energy in, to purify metals; Nature take energy out, by returning our metals to the oxidized state: this category of phenomena is called Corrosion (in scientific terms Oxidation and Reduction Reactions).

How can we stop Corrosion? Good question: corrosion happens when the metal is in contact with the environment; if we isolate the metal from the environment, no corrosion happens; the ancient inhabitants of the Mediterranean coasts discovered this some millennia ago: a coating on your metal stops the Corrosion.

Wow! So we solved our problem! Wait: how about Cathodic Protection? OK: you’re really smart! There is another issue: coatings aren’t perfect; they have holidays; humidity, water, soil enter inside them and Corrosion starts, concentrated in a smaller surface and sometimes faster.

Ok: time for this Cathodic Protection thing, uh? Right! An engineer called Daly discovered that it is possible to use Nature Laziness (read: Corrosion) to our advantage: give it an object simpler to corrode and it will corrode it, instead of our precious metal.

Now I understand why you used the term Protection, but tell me about Cathodic. Well: it is electronic terminology; to defend my precious metal, I have to make it more electrically negative than my sacrificial object; the scientific term for this is Cathodic (incidentally the sacrificial object is called an anode).

I start to understand: we put another object near the one we want to protect. Well: it isn’t so simple. They need to be connected, to establish an electric circuit: electrons will flow between the two objects through the connection, ions will flow inside the medium (the scientific term is electrolyte) and we will have oxidation reactions and reduction reactions.

What’s the goal of Cathodic Protection? We protect some parts of metal that have a big value for us (pipelines, bridges, rebars inside reinforced concrete, tanks, …), sacrificing scrap metal (the anodes).

So: what do you do for a living? As I said, I try to make complex things simple. We have a lot of Cathodic Protection Systems to protect our assets (Corrosion costs 6 to 7% of GDP, trillions of dollars per year!!!). These Systems, as every human product, are subject to failure and when they fail, our assets are no more protected. So we have to monitor if they are working. In the past, we periodically sent someone to check this. Nowadays we can use Measure Instruments that continually check and periodically send back data through Communication Networks; they are called Remote Monitoring Units (RMUs). I’m involved since more than 20 years in designing these monitoring systems (the RMUs and the software that manages data transmission and data processing) and in presenting them to the market. During these years I’ve traveled to more than 30 Countries around the World to do this.