Investigation into the suitability of coating systems on weathered galvanised layer for life extension of electricity transmission towers

This study evaluates the effectiveness of two surface-tolerant coating systems—vinyl-based Paint I and moisture-cured urethane Paint M—for extending the service life of weathered galvanised steel used in electricity transmission towers. The coatings were applied to steel members affected by zinc corrosion products (ZCP) and prepared using high-pressure water cleaning. Performance was assessed through adhesion testing and electrochemical evaluation (REAP). Results showed that Paint M provided superior corrosion resistance due to its highly cross-linked structure but exhibited lower mechanical durability, especially in scratched areas. In contrast, Paint I demonstrated stronger adhesion, particularly on surfaces with residual ZCP. However, high levels of brittle corrosion products reduced adhesion for both coatings. Further testing revealed that coating performance improved significantly on surfaces with less ZCP and lower salt density. A correlation was found between galvanised layer loss, salt density, and adhesion strength, indicating that surfaces with over 52% galvanised loss or salt density above 25 mg/m 2 may not be suitable for coating without additional surface preparation. These findings provide a practical and environmentally viable strategy for prolonging the life of aging transmission towers in remote locations. The study recommends further investigation into the effectiveness of coatings on surfaces with varying ZCP levels (5-50%) and conventional galvanising layer corrosion to better determine their long-term protective capabilities, with detailed findings discussed. • Two coating systems, Panit I (based on vinyl) and Paint M (based on moisture cured urethane), were tested on weathered galvanized steel. • Paint adhesion is significantly reduced by zinc corrosion products (ZCP) present on surfaces. • Paint M provides better corrosion protection, but both paints suffer from adhesion loss on brittle surfaces. • High-pressure water cleaning is not sufficient to remove heavy zinc corrosion products and improve adhesion. For surfaces with low zinc corrosion, high-pressure water cleaning proves to be a cost-effective preparation method. • Further studies are needed to assess coating performance on surfaces with varying levels of zinc corrosion and to determine long-term durability.