Cathodic Protection
What is the electrochemical goal of cathodic protection?
To shift the protected structure's potential in the electronegative direction so anodic metal dissolution is suppressed and the corrosion current is redirected to the anode system.
What are the two main types of cathodic protection?
Galvanic CP uses a more active sacrificial metal; impressed current CP (ICCP) uses an external DC source and a more durable anode system.
Where does cathodic protection actually work?
Only where the metal is in contact with an electrolyte such as water, soil, or concrete pore solution; it is not effective in dry air exposure.
Cathodic protection (CP) is an electrochemical corrosion-control method that makes the target metal the cathode by supplying DC current from an external anode or attaching a sacrificial anode. It reduces corrosion only where the metal contacts an electrolyte such as soil, seawater, concrete, or process water, not in dry atmospheric service.
On a CNC-heavy industrial site, cathodic protection matters less for cutting tools and more for the embedded steel and iron assets around the machine: subframes, pits, tank floors, dock hardware, buried piping, and marine-related fixtures that sit in wet or conductive environments. The system forces protective DC current through the electrolyte so the protected structure stays at a more negative potential and corrosion is suppressed. Two standard implementations exist: galvanic CP uses zinc, aluminum, or magnesium anodes that corrode preferentially, while impressed current CP uses a rectifier and durable anodes to drive current. Coatings remain essential because they reduce current demand and let CP focus on holidays, welds, edges, and damage points. On the floor, verification means measuring structure-to-electrolyte potential against a reference electrode, commonly aiming for about -0.85 V relative to a saturated copper/copper sulfate electrode, with IR drop considered. CP is a system, not a coating substitute.
No electrolyte, no CP: Bolting sacrificial anodes to a mostly dry machine frame or tooling base creates no sustained circuit because continuous electrolyte contact is missing, so exposed areas keep corroding.
Electrical isolation breaks the circuit: Paint build-up, nonconductive gaskets, isolating bushings, or poor bonding between structure and anode prevents current flow, leaving the protected metal underprotected while nearby areas corrode faster.
Wrong potential or overprotection: Underdesigned systems miss the protection criterion, while overdriven ICCP can cause coating disbondment, hydrogen damage on susceptible steels, and accelerated anode consumption.