Electric utilities routinely use weathering steel (WS) in transmission line structures, capitalizing on corrosion resistance and associated cost savings. The formation of a protective iron-oxide patina on uncoated above-ground WS surfaces depends on the operating environment and exposure conditions. In fact, exposure to common aggressive environments, such as those found in sulfate contaminated industrial areas and chloride-laden coastal areas, may dramatically hinder the corrosion resistance of WS transmission line structures.
To assess the corrosion behavior of WS transmission line poles, field inspections were conducted at five test sites comprising diverse operating environments and pole designs. These sites included three locations in Saskatchewan, Canada, featuring WS poles owned by SaskPower, and two sites in Florida, USA, featuring WS poles owned by Florida Power & Light. The exposure environments include rural, industrial and marine (i.e., chloride-laden) atmospheres. For each WS pole structure inspected, assessment based on visual inspection was paired with a quantitative assessment of atmospheric and soil corrosivity, corrosion rates based on thickness measurements, and corrosion potential measurements. In addition, the microstructure and chemical composition of oxide samples collected from the WS poles were studied by means of scanning electron microscopy and energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), and Mössbauer spectroscopy analysis.
The resulting information, data and evidence offer the means to practically understand the combined impact of the environmental corrosivity parameters examined, together with other factors influencing corrosion behavior (e.g., design and detailing). In particular, it is demonstrated how the results of field inspections and measurements, and laboratory characterization tests, can be used to understand present and future susceptibility to corrosion damage; for example, as a result of the formation of unstable and non-adherent surface oxides. Therefore, this information can be leveraged for diagnosis and prognosis purposes, there by enabling owners to make informed decisions on allocating and prioritizing prevention and remediation resources. To this end, best practices for corrosion assessment, prevention and remediation for WS transmission line poles are discussed, and case-specific recommendations are made for WS poles located in operating environments that feature a representative range of atmospheric corrosivity characteristics.
Atmospheric corrosivity; Cathodic protection; Coatings; Corrosion potential; Energy-dispersive X-ray spectroscopy; Mössbauer spectroscopy; Scanning electron microscopy; Thickness loss; X-ray diffraction analysis; Weathering steel.