Materials Performance

OCT 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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30 OCTOBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 10 CATHODIC PROTECTION E The durability of power transmission foundations not only satisfies stability and safety issues but also plays a sig- nificant role in reliability of overhead power lines by acting as part of the grounding system. Following a brief description of corrosion and cathodic protection of steel in concrete, a novel approach is presented regard- ing corrosion assessment and ca- thodic prevention of foundations for electric transmission towers in the Persian Gulf region. Electric transmission tower foundations E ission Electric transmission tower foundations E tower foundations have a great impact on the stability and E ve have a great impact on the stability and E a great impact on the stability and p e r f o r m a n c e o f t h e t o w e r s . Wi t h o u t E r f o r m a n c e p e r f o r m a n c e o f t h e t o w e r s . Wi t h o u t E o f t h e t o w e r s . Wi t h o u t having sound and safe foundations, these E i having sound and safe foundations, these E d having sound and safe foundations, these E nd having sound and safe foundations, these E safe foundations, these structures cannot perform the functions E uctures structures cannot perform the functions E cannot structures cannot perform the functions E perform the functions for which they are designed. Reinforcing E which they are designed. Reinforcing steel bars (rebar) in concrete foundations E el bars (rebar) in concrete foundations for power transmission towers also act as E mission for power transmission towers also act as E towers also act as th e th e g roun d el e c E g roun d th e g roun d el e c E el e c th e g roun d el e c E tro d e s durin g current faults. 1 Corrosion assessment, lifetime estima- tion, and corrosion protection of concrete structures are very important issues in cor- rosive areas. As an example, Iran operates more than 125,908 km of overhead power transmission and subtransmission lines (>63 kV ). 2 Approximately 19% of these high-voltage lines are located in corrosive coastline environments (Figure 1). Around 17% of these high-voltage lines are more than 30 years old . 3 Operation of power Applying Cathodic Prevention to Electric Transmission Tower Foundations Hadi Beirami and m aryam e H tes H amzade H , Shahid Bahonar University of Kerman, Kerman, Iran transmission lines is controlled by regional electric power companies. One of the com- panies, Hormozgan Regional Electric Co., spends more than US $400,000 annually to repair and rehabilitate nearly 1,000 cor- roded tower foundations. 4 Corrosion and Cathodic Protection of Steel in Concrete When chlorides reach the steel surfaces inside reinforced concrete structures, active corrosion leads to the formation of expan- sive corrosion products, resulting in cracks of the concrete cover. It takes only a small amount of corrosion metal loss (e.g., ~0.1 mm) at the rebar surface to create corrosion products sufficient to generate internal stresses that crack the concrete (Figure 2). 5 Cathodic protection (CP) is the most effective method of controlling ongoing corrosion in reinforced concrete struc- tures. By applying cathodic polarization, the corrosion potential is shifted to the region of immunity in the Pourbaix dia- gram ; and corrosion is stopped from a practical point of view. 6 The application of CP to a reinforced concrete structure transforms the environ- ment around the steel reinforcement over a period of time. The metal surface becomes negatively polarized, thus repelling chlo- rides; oxygen and water are consumed; and hydroxyl ions are generated at the metal surface. The hydroxyl alkalinity restores the pH at the metal surface, inducing passivity of the metal. 7

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