Risk Mitigation and Condition Assessment of Corrosion in Tower Structures of High Voltage Transmission Lines

The transmission lines traverse through various terrains and climatic condition and are exposed to harsh environmental conditions thereby acting as a catalyst for material degradation. The corrosion at tower footing and stub is a major concern because of its impact on the structural integrity, high cost of rectification, and for system reliability and safety. Our company operates more than 182,000 circuit kilometres of transmission lines. The lines comprise over 290,000 towers and face significant challenges in managing corrosion risks across geographically and environmentally diverse regions. During routine patrolling and inspections, it has been observed that in flood-prone, humid, riverbank, and coastal areas several instances of corrosion at tower chimney, stub, bracing members, etc have been recorded. It has also been noticed that these towers are particularly exposed to prolonged moisture and degraded soil conditions thereby accelerating their deterioration. In such cases, the conventional time based maintenance practices are often insufficient to address such risks effectively across large networks. The paper presents a structured approach for condition assessment and mitigation of tower structure corrosion through the development of a Corrosion Risk Index (CRI) and an associated risk matrix framework. The CRI integrates key corrosion-influencing parameters, including tower vulnerability, environmental exposure, soil condition, coating condition, and asset age. Each parameter is assigned a relative weight and score based on expert judgement, field experience, and analysis of historical inspection data. Subsequently, the CRI values are used to classify towers into low, medium, and high-risk categories. A risk matrix combining risk and impact of corrosion has been developed for defining the inspection schedule and strategies for mitigation. Finally a practical case study of a severely corroded 400 kV transmission tower and subsequent rectification has been demonstrated to strengthen the applicability of the developed model. The

CRI-based risk matrix enables consistent prioritisation of corrosion mitigation measures, reduces subjectivity in inspection based decision making, and optimises allocation of maintenance resources. The proposed research provides a scalable, reliable, and cost-effective solution for condition based asset management which inturn will enhances safety, resilience, and long-term performance of overhead transmission line.