Strategies and tools for corrosion prevention for cable systems

The Main Findings and Conclusions are:

a. Galvanic (Electrochemical) Corrosion

• Occurs when two dissimilar metals (e.g., copper and aluminium) are in contact with an electrolyte (e.g., moisture).
• The more anodic metal (aluminium) corrodes faster while the cathodic metal (copper) remains protected.
• Common in cable terminations and joints where multiple metals interact.

b. Chemical and Atmospheric Corrosion

• Caused by exposure to acidic or alkaline substances in the environment.
• Pollution, industrial gases (e.g., sulphur dioxide), and saltwater accelerate corrosion.
• Leads to oxidation and degradation of metallic sheaths and armour.

c. Fretting Corrosion

• Results from mechanical vibration and friction between cable components.
• Common in cable joints where micro-movements wear away protective coatings, exposing metals to oxidation.

d. AC Corrosion

• Induced by alternating current leakage, leading to material degradation over time.
• More common in buried cables near high-voltage transmission lines.

e. DC Corrosion (Stray Current Corrosion)

• Occurs when direct current leaks from nearby infrastructure (e.g., railways, cathodic protection systems).
• Leads to rapid metal dissolution and structural weakening.

f. Localised Corrosion (Pitting and Crevice Corrosion)

• Small-scale, highly concentrated attacks on the metal surface.
• Pitting corrosion leads to deep holes, severely weakening metal components.
• Common in submerged and underground cables.

g. Biological Corrosion (Microbially Induced Corrosion – MIC)

• Bacteria and fungi can accelerate corrosion by producing acidic by-products.
• Occurs mainly in wet or buried cable installations.

Inspection & Monitoring Techniques

To detect and mitigate corrosion, the report recommends multiple inspection and monitoring techniques.

a. Visual Inspection

• Used to identify general corrosion, pitting, and damage on exposed cables.
• Limited effectiveness for buried or submerged cables.

b. Hydrogen Gas Detection

• Corrosion of metallic sheaths releases hydrogen gas, which can be detected to assess corrosion levels.
• Particularly useful for monitoring lead sheaths and steel components in underground cables.

c. Time Domain Reflectometry (TDR) & Frequency Domain Reflectometry (FDR)

• Detects changes in electrical impedance along the cable, helping locate corroded sections.
• Used in conjunction with other monitoring techniques for a comprehensive analysis.

d. Oversheath Testing

• Applies a test voltage between the metal screen and ground to check for sheath integrity.
• Helps identify breaches that allow moisture ingress, a key factor in corrosion.

e. Neutral Resistance Measurement

• Assesses the conductivity of the cable's neutral wires to detect potential corrosion-related resistance changes.

Preventive Strategies for Corrosion Mitigation

a. Material Selection

• Use of corrosion-resistant metals like stainless steel, galvanised steel, and aluminium alloys.
• Avoiding dissimilar metal contacts (e.g., using bimetallic connectors where copper and aluminium meet).

b. Protective Coatings & Sheaths

• Polyethylene, bitumen, and PVC coatings for moisture protection.
• Special coatings for subsea cables to prevent saltwater-induced corrosion.

c. Cathodic Protection

• Impressed Current Cathodic Protection (ICCP): Uses an external power source to apply a protective current, reducing corrosion.
• Sacrificial Anodes: Zinc or magnesium anodes corrode instead of the main cable components.

d. Water Blocking Measures

• Radial Water Blocking: Using metallic or polymeric sheaths to prevent water penetration.
• Longitudinal Water Blocking: Incorporating water-blocking powders, gels, and tapes within the cable structure.

e. Design and Installation Improvements

• Ensuring proper drainage in underground installations to prevent water pooling.
• Avoiding mechanical stress that could lead to microcracks, accelerating corrosion.
• Proper sealing of joints and terminations to prevent moisture ingress.

Industry Recommendations & Future Outlook

The report emphasises the need for industry-wide standardisation and improved data collection.

a. Standardisation of Corrosion Prevention Practices

• Develop clear guidelines for material selection, installation, and maintenance.
• Implement uniform testing methods for corrosion detection.

b. Improved Data Collection & Failure Analysis

• Mandatory documentation of corrosion-related failures to enable trend analysis.
• Development of centralised databases to track ageing and failing cable systems.

c. Enhanced Training for Installers and Inspectors

• Increase awareness of corrosion risks among engineers and maintenance personnel.
• Training programs for best practices in corrosion prevention and monitoring.

d. Research & Development in Corrosion-Resistant Materials

• Explore new alloys and coatings with superior corrosion resistance.
• Development of self-repairing or corrosion-inhibiting materials for cable systems.

In chapter 7 we give recommendations to the B1 RAG, for collections of failure data in order to get a better picture how much damage is caused by corrosion.
In chapter 8 the brochures gives field examples of recent corrosion failures

Conclusion

Corrosion poses a significant threat to the reliability and longevity of high-voltage cable systems. The report underscores the importance of:

• Early detection and monitoring using advanced inspection techniques.
• Material and design improvements to enhance corrosion resistance.
• Industry-wide standardisation to ensure best practices.
• Proactive maintenance to prevent failures before they occur.

By implementing these strategies, the service life of high-voltage cables can be significantly extended, reducing costly failures and maintenance.