Why do we measure galvanic currents?
Monday, 26th February 2018
Hevasure is a unique company in many ways. Not only does our ‘HVAC monitoring’ system include up to 9 different sensors, enabling us to determine key system parameters and prevailing conditions at all times, but we incorporate two completely novel devices. One of these is our galvanic current sensor. Please allow me to explain how this works and why we feel it is such a useful tool in our corrosion prevention service.
Galvanic currents are generated between different metals in a system; i.e. between the more noble metal (cathode) and the more active metal (anode). In a typical commercial system, the steel components act as the anode and can start to dissolve (corrode) if the conditions are not benign. If for instance, dissolved oxygen finds its way into the system water, the resulting cathodic current will cause the anodic reaction to occur. Therefore, by measuring the presence and magnitude of this current, we can determine whether or not the steel in the system is corroding and the approximate rate of the corrosion processes. Indirectly, it also gives us a low cost way of determining dissolved oxygen.
What is even more interesting is the effect of inhibitors on galvanic currents. The purpose of commercial inhibitors is to reduce or kill galvanic currents. They do this by preventing the cathodic or anodic reactions taking place. Most common commercial inhibitors (e.g. ones containing molybdenum) are anodic and work by passivating the anodic metal surfaces. Under certain circumstances, for instance when they are too dilute or the metal surface is covered with debris, the inhibitor does not work effectively and the steel is vulnerable to corrosion when oxygen enters the system. Therefore, by continuously monitoring the galvanic currents we tell if the inhibitor has become ineffective. When we combine all our sensors together we get a complete picture of conditions within a system and can tell whether or not corrosion is likely to occur before any serious damage is done.
Finally, I mentioned in the first paragraph that we have developed 2 novel devices. The second one is our crevice corrosion sensor – more on this next time.