Experiencing cathodic protection system issues? Discover the top reasons CP systems fail and how to fix them. Includes guidance on diagnostics, repairs, and when to call a specialist.
Cathodic protection (CP) systems are essential for preserving the integrity of metallic structures that are buried or submerged, such as pipelines, tanks, jetties, offshore platforms, and reinforced concrete. When these systems are performing correctly, they offer long-term defence against corrosion, reducing operational risks and maintenance costs. However, when CP systems fail or underperform, the consequences can be significant, from leaks and contamination to structural failures.
This guide examines the most common causes of CP system failure and outlines practical steps for identifying and rectifying these problems. Whether you are managing a pipeline, marine asset, or industrial facility, understanding the root causes of CP issues is key to maintaining asset integrity.
Common Causes of CP System Failure
1. Insufficient Current Output
Cathodic protection systems must deliver enough current to polarise the entire structure to protective potential that meets corrosion-control criteria, ensuring corrosion is effectively mitigated. A shortfall in current output is one of the most frequent problems and can result from:
- Faulty transformer rectifier (TR) units
- Faulty electrical connections or broken continuity cables
- Anodes reaching the end of their service life
- Inadequate system design for the structure’s size, coating condition, or environment
Troubleshooting steps:
- Use a multimeter or data logger to measure the TR outputs (voltage and current). Test under varying load conditions to confirm the TR can maintain its rated output.
- Inspect key electrical connections and bonds for corrosion, breaks, or loose joints
- Evaluate Groundbed conditions. Measure groundbed resistance-to-earth and compare to commissioning records. Increased resistance indicates anode depletion, backfill drying out, or cable degradation.
- Conduct a current output test and compare it against design specifications. Perform detailed potential surveys (e.g., ON/OFF, close interval survey) to identify areas not receiving adequate polarization.
- Assess whether the structure’s coating has deteriorated, increasing the required current
Upgrading TR units, repairing faulty wiring, or adding new anodes may be necessary to restore performance.
2. Coating Degradation and Increased Current Demand
Protective coatings reduce the surface area requiring cathodic protection. When the coating degrades, more bare metal is exposed, increasing the current demand. If the CP system is not designed for this increased demand, parts of the structure may become unprotected.
Inspection and fixes:
- Conduct Close Interval Potential Survey (CIPS) and Direct Current Voltage Gradient (DCVG) surveys to identify coating defects and assess the effectiveness of the CP system. Compare the new survey data with previous baseline surveys to detect changes in polarization levels, new coating holidays, increased current demand, or progressive deterioration.
- Review historical data for trends indicating coating deterioration
- Recalculate system requirements and add anodes or adjust TR output as needed
3. Anode Depletion or Incorrect Type
All anodes, whether sacrificial or impressed current, have a finite service life. Once consumed beyond a certain point, they cannot deliver the necessary protective current.
Signs and solutions:
- Increased anode groundbed resistance. A key indicator of anode depletion. Compare measured resistance-to-earth with commissioning or historical records.
- Maximum TR current output decreases even when the voltage is raised
When anodes deteriorate, the TR reaches a point where additional voltage no longer produces additional current. - Flattened TR output curve. Recording current output at different rectifier voltage settings reveals whether the groundbed can respond to higher drive voltage. A depleted or incorrect anode will show minimal current increase.
- Higher current demand than the anode bed can supply. The rectifier may be operating at or near maximum voltage without achieving protective potentials.
- For sacrificial systems: significant loss of anode mass or complete consumption.
As the remaining anode material decreases, the effective surface area is reduced and the anode-to-electrolyte resistance increases. This leads to lower current output and inadequate protection. Sacrificial anodes typically require replacement once they are consumed beyond 70–80% of their original mass.
Replacing the anodes with correctly specified units and verifying all electrical connections can restore adequate protection. Corrpro Europe manufactures zinc, aluminium, magnesium, and silicon-iron, MMO anodes suitable for a wide range of cathodic protection applications.
4. Loss of Electrical Continuity
To protect a metallic structure using CP, all parts of the structure must be electrically continuous. Disruptions can occur due to physical damage, poor installation, or corrosion at joints.
Assessment methods:
- Conduct ON/OFF potential surveys along different sections of the structure to identify electrically isolated areas.
- Temporarily switch the CP system off and measure the structure-to-electrolyte potential at multiple test posts.
- Compare ON and OFF potentials to detect discontinuities or poorly bonded sections.
- Analyse differences across areas to pinpoint joints or sections with high resistance.
- Compare bond and jumper currents with historical data to identify open or high-resistance connections that may not be immediately apparent from potentials alone.
- Inspect electrical bonds and jumper wires for corrosion, looseness, or damage that could interrupt continuity.
Once identified, restore electrical continuity through repairs or supplemental bonding can reinstate effective protection.
5. Stray Current and Interference Issues
CP systems can be affected by stray currents originating from adjacent electrical systems, railways, or neighbouring CP systems. These unwanted currents can accelerate corrosion or cause erratic CP readings.
Diagnostic and mitigation steps:
- Carry out data logging and AC/DC interference surveys
- Use data modelling to simulate current paths and interference zones
- Install AC mitigation systems, monitoring devices, earthing, decoupling devices, drainage points, or bond systems
Corrpro Europe has experience delivering interference studies and mitigation designs for complex energy corridor environments.
When to Troubleshoot Internally vs Call in Experts
Routine inspections and basic maintenance can be carried out internally by qualified site personnel. However, complex CP failures, particularly those involving interference or system redesign, require specialist input.
Typical In-house task:
- Verify test station readings against baseline levels
- Log TR output and potential values
- Inspect visible system components such as bonds, posts, and cables
- Maintain a record of performance data over time
Engage Corrpro Europe if:
- Potential readings are consistently outside acceptable criteria
- CP performance drops despite no visible system faults
- There is suspected AC/DC interference or electrical isolation issues
- Major changes have occurred in environmental or structural conditions
Corrpro Europe’s ICorr- and NACE-certified engineers provide detailed diagnostics, system evaluations, and full repair and retrofit capabilities.
Survey and Monitoring Tools to Diagnose CP Problems
Professional diagnostic surveys can uncover hidden problems and help validate system effectiveness:
- Close Interval Potential Survey (CIPS): Measures structure-to-soil potential at close intervals to detect unprotected zones
- DC Voltage Gradient (DCVG): Locates and assesses coating faults that increase current demand
- Current Attenuation Survey: Identifies how far current travels along the structure and highlights weak protection zones
- Soil Resistivity Survey: Evaluates site conditions to support system redesign, especially for groundbed performance
- Remote Monitoring: Allows real-time data tracking and early warning of system anomalies
- Client Specific CP Audits can help to identify and solve hidden issues
These methods provide actionable insights to inform system optimisation, repair, or redesign strategies.
Restore Protection and Minimise Downtime
When cathodic protection systems underperform, the risk to your infrastructure increases. Left unresolved, corrosion can escalate, leading to leaks, outages, environmental damage, or expensive remediation. Timely diagnosis and intervention are essential.
Corrpro Europe offers:
- CP system health checks and audits
- Replacement of TR units, anodes, and cabling
- Comprehensive diagnostic survey packages
With over five decades of technical leadership and manufacturing strength, Corrpro Europe provides dependable CP solutions tailored to your asset type, location, and regulatory environment.
Contact us today to book a CP system health check or request emergency support. Let our engineering specialists ensure your cathodic protection system is operating at full effectiveness.
