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26 DECEMBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 12 FEATURE ARTICLE chemistry (i.e., the presence of moisture and corrosive ions), its level of electrical resistivity, stray currents, and the nature and surface areas of grounding materials. Accelerated underground corrosion can also take place in the absence of oxygen due to the presence of bacteria or acidic soils. Other factors are also associated with corrosion of a galvanized steel structure, Zamanzadeh notes, such as improper galva- nizing thickness, excessive brittleness of the intermetallic alloy layer, general galvanizing failure, poor substrate surface preparation (especially if it was previously coated), stor- age conditions, installation damage, and unsuitable protective topcoat selection for the in-service soil or atmospheric exposure conditions. Because deterioration of the protective zinc coating can lead to damage of the underlying CS structure, corrosion is a con- cern for galvanized transmission and distri- bution assets since it can lead to weakening of the structure, and then failure or col- lapse, says Gilpin-Jackson. A corrosion risk assessment can determine the environ- ment's corrosivity and the associated corro- sion risk to galvanized steel structures. When evaluating transmission and distri- bution infrastructure for corrosion, individ- ual assets should be assessed in order of their structural priority. Existing corrosion damage noted in the assessments should consider, among other criteria, the struc- ture's age, location, past history, its impor- tance in the power system, future plans for the structure, and the safety and financial consequences if the structure fails. Assessing for In-Ground Corrosion A significant portion of corrosion miti- gation activities for transmission and dis- tribution structures is focused on the embedded portion of poles and towers, notes Gilpin-Jackson, since the assets' foundations are critical to their stability and continuing service. Because founda- tions for existing structures are buried and out of sight, they could be deteriorating and close to causing a structural col- lapse—without any traditional inspector being aware of the problem. Zamanzadeh adds that determining corrosion risk in the structure's deep burial area (~6 to 8 ft [1.8 to 2.4 m] underground) is often missed due to lack of knowledge about corrosion risk assessment. "It is often the case that utility inspectors perform only minimal Corrosion of a galvanized steel pole. Photo courtesy of BC Hydro Transmission. Mehrooz Zamanzadeh conducts a below-grade corrosion assessment of a buried tower leg. Photo courtesy of Mehrooz Zamanzadeh and BC Hydro Transmission. Zamanzadeh emphasizes, however, that the galvanizing on structures will corrode over time. The rate that the thickness of the zinc coating will diminish and the length of the remaining service life of the galvaniz- ing—and the structure itself—are contin- gent on the active corrosivity of the environ- ment. Several factors are associated with the corrosion rate of galvanized structures, such as the in-service atmospheric condi- tions to which the aboveground portion of the structure is exposed, and the soil envi- ronment where the structure's foundation is buried. Atmospheric environments considered corrosive include marine environments with salt-laden air, and industrial environ- ments, which can produce acid rain as a result of industrial activity. In soil, corrosion activity can be accelerated by the soil's