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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14 DECEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIAL MATTERS Service life of wind turbine foundations extended with corrosion- resistant microcomposite steel W ind turbines today have the capacity to generate a sizeable amount of the world's electricity. Global wind energy capacity reported for the end of 2013 was reported to be 318,105 MW, 1 including 91,000 MW of capacity in China and 61,000 MW in the United States—with Texas alone contributing an installed ca- pacity of 12,755 MW. 2 To help the wind en- ergy industry protect wind turbine foun- dations from corrosion and prolong their service life, Williams Form Engineering (Belmont, Michigan), in partnership with MMFX Technologies Corp. (Irvine, Califor- nia), has developed anchor bolt assemblies fabricated from a low-carbon, chromium microcomposite steel that incorporates high strength and corrosion resistance. the lower embedment ring, and covered with a poly vinyl chloride (PVC) sleeve that extends to the top surface of the con- crete so the rod doesn't bond with the concrete and is free to elongate when the anchor bolt is tensioned. The portion of the anchor rod above the upper embedment ring protrudes from the concrete pedestal and is used for attaching the tower f lange to the pedestal with an anchorage assembly consisting of a hex nut and hard washer that bear directly on the tower f lange. This above- grade anchorage assembly is ty pically covered with a high-impact poly propy- lene (PP) cap f illed with corrosion-inhib- iting grease. Printz comments that wind turbine foundations utilize many anchor bolt conf igurations, but the most com- mon arrangements use 140 or 144 bolts per foundation. Ty pical anchor rods used are Grade 75, #10 (1-1/4 in [32 mm]) and #11 (1-3/8 in [36 mm]), and Grade 150 KSI, 1-1/4 and 1-3/8 in, all-thread bar. Several foundation designs are uti- lized when constructing onshore wind turbines, says Printz. A spread footing foundation comprises a large mass of reinforced concrete (which resists the shear and overturning moments) with a concrete pedestal (~9-ft [2.7-m] tall) in the center. A rock anchor-supported foun- dation utilizes an outer ring of ground anchors that are bonded with grout to the rock below the foundation; and the pedes- tal, with the anchor bolt conf iguration that secures the turbine tower, is installed within the ring of rock anchors. Once the pedestal concrete is poured and cured, the ground anchors on top of the concrete foundation are tensioned and locked. A deep foundation, which can be Anchor bolts, a key component in wind turbine foundations, are the ele- ments that secure the steel turbine tower to the concrete foundation. Anchor bolts are also used as ground anchors to pro- vide overturning and shear resistance for the foundation. According to Tom Printz, vice president—engineering with Wil- liams Form Engineering, anchor bolts are embedded deep in the concrete founda- tion and extend to the surface of the con- crete. When used to connect the turbine tower to the concrete foundation, the anchor rods ty pically join two carbon steel (CS) embedment rings to form a cylindrical cage that is incorporated into a steel-reinforced pedestal before the con- crete foundation is poured. Each anchor rod is threaded into a hex nut underneath A construction crew works on setting this spread footing foundation's reinforcing steel and positioning the embedment ring and anchor bolts for the turbine tower fange. Photo courtesy of Williams Form Engineering.

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