Materials Performance

DEC 2014

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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16 DECEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIAL MATTERS ring deep in the foundation and removed for closer inspection along the entire length of the anchor bolt. If corrosion is found, the sample size for inspection likely will be increased. Currently, the corrosion mitigation strateg y is to replace def icient anchor bolts prior to failure, says Printz; however, he adds, replacing the anchor bolts is a very diff icult, time- consuming process that can be quite costly. One design approach to extend the service life of the anchor bolt assemblies is to increase the rod diameter size so it exceeds the load-bearing requirements and contains extra steel to sacrif ice to corrosion before its load-bearing capacity becomes def icient. To extend the service life of the anchor rod assemblies for wind turbines, Printz advocates the use of anchor rods, hex nuts, and hard washers fabricated from the high-strength, low-carbon, chromium microcomposite steel alloy. This corro- sion-resistant steel, Chro – m X 9120, was developed and patented by MMFX Tech- nologies Corp. and has been used by sev- eral state Departments of Transportation as rebar for concrete applications such as highway bridge decks. According to NACE International member Salem Faza, vice president of engineering and specif i- cation for MMFX, this alloy's composition and manufacturing process were designed to provide a steel with improved corrosion resistance and mechanical properties as compared to conventional CS all-thread bar (e.g., ASTM A1035 3 ) and fasteners (ASTM A29, 4 ASTM F435, 5 ASTM A47, 6 and ASTM A536 7 ). CS comprises a matrix of carbides and ferrites at the grain boundaries that are chemically dissimilar, Faza explains. When exposed to moisture, the carbides and ferrites in CS form microgalvanic cells that initiate galvanic corrosion, a battery-like electrochemical process that occurs between the carbides and the fer- rites and corrodes the steel from within. In contrast, the nanotechnolog y used to manufacture the alloy, which is based on 25 years of research at the University of California, Berk ley, manipulates the The anchor bolts in the pedestal of this foundation are ready to receive the tower fange section. Photo courtesy of Williams Form Engineering. This transmission electron microscope image shows the lath microstructure of the high-strength, low-carbon, chromium microcomposite steel. Photo courtesy of MMFX Technology Corp. Continued f rom page 15

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