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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Page 17 of 100

15 NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS PERFORMANCE DECEMBER 2014 Information on corrosion control and prevention any where from 25 to 35 ft (7 to 10 m) deep, resembles a concrete tube that is hollow in the center and backf illed with earth. The anchor bolts for the tower f lange are located around the perimeter of the con- crete tube. The industry's main corrosion con- cern is specif ically related to the anchor bolts that secure the tower to the con- crete foundation, says Printz. Because any ty pe of corrosion can cause a reduc- tion in cross-sectional area, whether localized or around the entire rod diam- eter, this loss of area can cause the anchor bolt to rupture and fail while it is under load. While massive failures from anchor bolt corrosion have not been reported, wind turbine foundations have been experiencing corrosion issues that have resulted in the replacement of anchor rods before the end of the wind turbines' designed service life, which is generally 20 to 30 years. The PVC sleeve provides a layer of pro- tection to the embedded rods from corro- sion mechanisms that can affect steel in concrete; however, anchor rod corrosion ty pically is initiated by the presence of air, water, and contaminants such as salts or sulfates from the surrounding soil that have inf iltrated the anchor bolt assembly from the top, notes Printz. This can hap- pen during the construction process or during the service life of the tower struc- ture, particularly if the protective PP caps are not tightly secured to the tower f lange anchorage assembly. Because there is the potential for fail- ure when the anchor bolts corrode, many wind turbine owners have established an extensive maintenance program to ensure the anchor bolts are unaffected by corrosion, he says. Maintenance and cor- rosion monitoring practices vary depend- ing on the owner, but ty pically the anchor bolts are inspected for corrosion every three to f ive years. This is done by remov- ing the PP anchor bolt cap and examining the hex nut and bolt extension above the tower f lange on a percentage of the bolts (~10% for a foundation). If they show signs of signif icant surface oxidation, the bolts may be unthreaded from the embedment The pedestal reinforcing steel, embedment rings, and tower anchor bolts for this foundation are in place. Photo courtesy of Williams Form Engineering. Continued on page 16

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