Meaning
Electro-chemical conditions occur when the applied electrical potential to a metal structure exceeds the level required for corrosion prevention. Excessive current in cathodic protection overpolarization leads to secondary chemical reactions that can degrade the structural integrity of the asset. The boundary of protection is crossed when the negative potential reaches a point where the electrolyte, usually water, begins to dissociate.
Hydrogen Risk
Atomic hydrogen evolves at the metal surface when the potential becomes too negative. This cathodic protection overpolarization allows hydrogen atoms to penetrate the steel lattice and cause brittle failure or cracking. High strength steels are particularly vulnerable to this form of embrittlement.
Coating Damage
High alkalinity levels at the metal-coating interface result from the excessive current. These conditions cause cathodic protection overpolarization to weaken the adhesive bonds of epoxy or polyethylene layers. Disbondment occurs as gas bubbles form underneath the protective film and push it away from the substrate.
Operational Threshold
Control systems must maintain a voltage window that prevents metal loss without reaching the level of dissociation. A cathodic protection overpolarization event usually stems from a faulty transformer rectifier or an incorrect reference electrode reading. Frequent audits of groundbed outputs prevent these settings from drifting into the hazardous zone.
