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The Critical Role of Corrosion and Coating Inspections in Transmission Tower Asset Management

Executive Summary

Steel transmission towers form the backbone of power delivery infrastructure. As these towers age, corrosion emerges as a silent yet severe threat, especially at ground level and in high-exposure environments. Proactive corrosion and coating inspections are pivotal for assessing tower condition, guiding maintenance, and avoiding costly replacements. This white paper explores inspection methodologies and strategic mitigation approaches that prioritize safety, cost-efficiency, and infrastructure resilience.

1. Introduction
Across North America and beyond, transmission towers are aging, with many nearing or exceeding their design lifespans. Corrosive factors such as moisture, industrial pollutants, and airborne chlorides exacerbate degradation. Corrosion may remain hidden until it threatens structural integrity—making timely inspections essential for grid reliability and capital forecasting.

2. Anatomy of Tower Corrosion
Corrosion typically initiates where towers meet the ground, driven by oxygen, moisture, and contaminants attacking compromised galvanizing layers. Damage may include:

  • Surface rust and pitting

  • Section loss in leg and bracing members

  • Degraded anchor bolts

  • Compromised coatings allowing moisture ingress

3. Inspection Strategies: Coating and Corrosion Assessment
Visual Inspection
  • Surface-level check for visible signs of rust, discoloration, flaking coatings

  • Limited effectiveness for hidden/subsurface degradation

Corrosion Inspection Techniques
  • Ground-level excavation to inspect buried legs

  • Ultrasonic thickness measurements to detect steel loss

  • Soil resistivity testing to map high-risk environments

  • Section loss quantification using calibrated probes

Coating Inspection Techniques
  • Adhesion tests (pull-off strength) to assess coating bond

  • DFT (dry film thickness) readings for compliance

  • Chalk testing to detect degradation

  • Gloss and color comparison for aging assessment

Inspection Type
Key Focus Areas
Common Tools Used
  • Corrosion Inspection: Steel loss, underground damage — UT meters, soil probes, visual inspection

  • Coating Inspection: Adhesion, film thickness, failure — Pull-off testers, DFT gauges, microscopes

4. Mitigation Options Based on Inspection Data
Depending on condition severity:

  • Steel repair: Bracing, leg splices, bolt replacement

  • Surface prep and recoating: High-performance zinc-rich or epoxy systems

  • Cathodic protection: Sacrificial anode or impressed current systems

  • Full replacement: When cost of repair exceeds value

5. Lifecycle Planning and Risk-Based Asset Management
Integrating inspections into lifecycle planning empowers utilities to:

  • Anticipate failure before structural compromise

  • Allocate capital with precision

  • Extend asset life with minimum disruption

  • Align with industry standards (e.g., ISO 55000, IEEE 951)

Routine condition monitoring feeds predictive models that help prioritize towers with the highest criticality and degradation rates.

6. Conclusion
Corrosion is an inevitable but manageable threat. By investing in reliable inspection methodologies—both for steel and protective coatings—utilities can extend tower lifespan, reduce unplanned outages, and ensure public safety. Effective asset stewardship begins with seeing inspections not just as checks, but as core tools for informed decision-making.