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27 NACE INTERNATIONAL: VOL. 55, NO. 12 MATERIALS PERFORMANCE DECEMBER 2016 Assessing Galvanized Steel Power Transmission Poles and Towers for Corrosion testing, such as visual inspection and coat- ing thickness measurements, to a depth of 2.5 ft (0.8 m) below grade. Unfortunately, these practices fall short in determining the condition of deep buried structures where accelerated corrosion may be tak- ing place. We were recently involved in a case with a collapsed tower due to acceler- ated corrosion in deep burial that could have been avoided if adequate corrosion risk assessment procedures were in place," he comments. Below-ground corrosion risk is primar- ily contingent on the amount of moisture and corrosive ions in the soil or outside interference. For example, when the soil is dry, its resistivity is generally high enough to inhibit corrosion; however, when mois- ture conditions change at a site, soil resis- tivity can be altered and corrosion may accelerate. Although galvanizing steel has considerable resistance to corrosion when buried, corrosion attack can be initiated in soils that are reducing, acidic, or contain large amounts of corrosive, water-soluble salts. Generally, terrain with lower resistiv- ity and reducing properties promote higher corrosion rates; however, it is important to define the corrosivity of the environment to determine the type of corrosion mitigation required and how often maintenance is needed, Zamanzadeh says. To determine the corrosiveness of a soil, different soil characteristics and relevant attributes of the physical environment should be considered. This type of assess- ment combines corrosion and materials science, metallurgy, and electrochemistry, and correlates them with the structure's design features; and then quantitatively determines the environment's physical characteristics so a multi-faceted, risk- based corrosion assessment can be done. Assessments include testing the soil envi- ronment to rate its corrosiveness; conduct- ing visual and physical condition inspec- tions of buried structural components at a shallow depth; and electrochemically test- ing the interaction between the soil and steel (i.e., potential values and soil resistiv- ity) to predict structural corrosion at deep burial depths. The test results can be used to assign a below-grade corrosion risk rating or condi- tion assessment value to each structure, which takes the structure's age, size, design, function, and importance into consider- ation. The ratings then can facilitate the Localized corrosion in a deeply buried foundation structure is caused by microbiologically influenced corrosion (MIC). Photo courtesy of Mehrooz Zamanzadeh and BC Hydro Transmission. Below-grade, deeply buried portions of power utility towers are subject to accelerated corrosion. Photo courtesy of Mehrooz Zamanzadeh and BC Hydro Transmission. development of suitable remediation and mitigation procedures. Zamanzadeh notes that the confidence level of the risk assess- ment, which indicates the ability of the technique used to produce reliable corro- sion risk data, depends on the scope of the evaluation performed. Geographic information system (GIS) data with geological records that summa- rize soil parameters can be used to conduct a desk study (pre-assessment). Soil data collected should include classification, resistivity, corrosivity, and pH. Because the accuracy and reliability of this assessment