Overview
An impressed current cathodic protection (ICCP) system is a control loop: a power supply drives current from anodes to the structure, and a reference electrode tells the controller whether the structure is at the target potential. Because it is a system of interacting parts, it fails in characteristic ways — and most of those failures announce themselves in the data long before they become a loss of protection, if someone is looking.
The engineering principle
ICCP holds the structure at a set potential by adjusting output against a reference. Every element of that loop can fail: the reference can drift and mislead the controller; the anodes can degrade or become electrically insulated; the cables and connections can develop resistance or break; and the rectifier or control electronics can fault. Because the controller trusts its inputs, a fault upstream of it — a drifting reference in particular — can cause the system to confidently do the wrong thing.
The recurring failure modes
Reference electrode drift is the most consequential because it corrupts the control signal: the controller holds the structure at what it believes is the target, but the real potential is off, leading to quiet under- or over-protection. Anode-related failures include physical consumption, mechanical damage, and the build-up of surface films — including calcareous deposits in seawater — that increase circuit resistance and reduce output. Cable and connection faults, from corroded terminations to damaged insulation, add resistance or break continuity so that current no longer reaches part of the structure. And rectifier or control-panel faults — loss of output, a stuck setting, or a tripped supply — stop protection outright.
- Reference electrode drift — corrupts the control signal; the loop holds the wrong potential.
- Anode consumption, damage or films (including calcareous build-up) — reduced or lost output.
- Cable, termination and continuity faults — current no longer reaches the structure.
- Rectifier / control faults or power loss — protection stops or is stuck at a wrong setting.
- Over-protection — excessive negative potential, which can have its own consequences on some materials and coatings.
Common mistakes
Trusting the panel readout without independent verification of the reference; treating the rectifier output as proof of protection (it proves current is flowing, not that the structure is protected); leaving the system without a realistic inspection interval so that a slow drift or a growing resistance is only discovered when protection is already lost; and responding to a symptom (turning up the output) without diagnosing the cause (a failing reference or a broken connection).
Inspection and verification
The defence against all of these is periodic inspection at an interval matched to the asset's risk: independent potential survey to confirm the structure — not just the panel — is protected, cross-checking permanent references against a calibrated portable reference, inspecting anodes and connections, and logging rectifier output to spot trends. Most ICCP failures are gradual, so trend data catches them while they are still cheap to fix.
How CCME-MCPS can help
CCME-MCPS inspects, surveys and maintains ICCP systems, and designs inspection regimes that catch these failure modes early rather than at loss of protection. Where a system is already misbehaving, diagnosis focuses on the control loop as a whole rather than the most visible symptom.
Important note
This article explains general cathodic-protection engineering principles for education. It is not a design, and it is not guidance for any specific structure — every real system must be engineered to the applicable standards and the specific conditions of the asset. Standards are referred to by name only.