When installing offshore wind farms, it’s common to use hydraulic bolt tensioners to secure transition pieces to monopiles. However, verifying that proper tension has been achieved in each fastener remains problematic. Recently, Valley Forge & Bolt, a U.S. manufacturer of load indicating fasteners, found a solution to the issue of tension verification in these applications.

Valley Forge’s Maxbolt™ Load Indicating Fasteners contain proprietary technology that measures load directly from within the bolt, then displays it via an easy-to-read tension gauge built into one end. The gauge has graduated lines from zero to 100 to indicate percentage of load.

A wind farm in the Atlantic Ocean is intending to use Maxbolt™ to fasten the wind turbine’s transition piece to the monopile. The monopile is hammered into the ocean floor, and the transition piece is the literal transition point between this monopile support and the body of the wind turbine, making secure fastening vital to future performance.

Wind Farm Valley Forge
Off shore windmills at Middelgrunden just outside Copenhagen, Denmark

“The offshore wind energy market segment is following a trend we see in other energy segments,” said James Brooks, director of engineering at Valley Forge. “They recognize the advantage in using tension-based load indicating fasteners over torque-base bolting, both at installation and for post-installation condition monitoring.”

A hydraulic bolt tensioner is used to begin installation of the Maxbolt™ fasteners, with the tightening process completed manually. After that, technicians are able to see, at a glance, whether proper tension has been achieved simply by reading the gauge. It helps assure that proper load has been achieved before the wind turbine is commissioned.

Maxbolt™ has benefits beyond installation. By their very nature, offshore wind farms are not readily accessible, making maintenance a significant undertaking. Anything that can accelerate the process while maintaining safety is invaluable. The Maxbolt™ tension display makes scheduled maintenance checks more efficient without sacrificing quality. In fact, Maxbolt™ achieves better results in less time, because technicians can quickly see which fasteners are in need of attention.

Maxbolt Valley Forge

This need for ready access to bolt tension information is heightened by the wave loading that is subjected to offshore wind turbines. The continuous impact force from waves creates several issues for wind turbines, including bed erosion and monopile slippage, but also vibration that can loosen bolts. Maxbolt™ provides a means for quickly verifying tension and knowing immediately which bolts are at risk of failure.

Valley Forge also manufactures other load indicating fasteners, which are compatible with remote wireless meters. In the future, these could make it possible to verify bolt load from the mainland. Such a development would further speed maintenance and provide valuable data for planning future maintenance schedules.

“There’s definitely a place for load indicating fasteners in the wind energy market,” said Brooks. “It’s a way to know for sure that you’ve achieved desired tension. It helps ensure the integrity of critical bolted joints, enhances safety and reliability, and reduces maintenance time and costs.”

About Valley Forge & Bolt
Valley Forge & Bolt Mfg. Co. is a domestic manufacturer of patented bolting products for critical applications. These bolts and studs are widely trusted for their unrivaled quality, extraordinary performance, and enduring reliability. Email: POWER@vfbolts.com. Call: 1 (602) 269-5748. On the web: https://www.vfbolts.com/.