Corrosion Protection of Steel Lattice Transmission Towers

Corrosion mitigation project for BC Hydro

The Applied Materials Department managed a project to implement corrosion mitigation—in the form of sacrificial anode cathodic protection (SACP) systems—to 145 towers with ground conditions considered corrosive to buried grillage. With age and exposure to environmental conditions, critical load-bearing members of steel lattice transmission towers are susceptible to corrosion. For the above-ground tower structures, zinc galvanizing provides a very effective corrosion barrier by forming a stable protective patina (surface oxide layer) in reaction to the environment and sacrifices itself to protect the steel substrate. However, for the tower legs buried below the earth, galvanizing is not always able to form this patina. In these cases, industry practice is to use galvanizing in combination with SACP systems. The systems attach sacrificial anodes—pieces of metal more electrically active than the tower steel—to the base metal. Because the anodes are more active, the corrosive
current exits from them rather than the steel tower, thus protecting the steel while sacrificing the anode. To mitigate impending corrosion attack, the Applied Materials Department oversaw the installation of SACP systems to the separate legs of the 145 towers. Following installation, crews conducted structure-to-soil potential measurement to ensure the installations met industry-accepted criteria to be considered cathodically protected.