Wind turbine OEMs provide plenty of guidelines and instructions for tightening the bolts on their equipment. Each bolt gets a prescribed torque or tension. Bolts that fasten tower flanges, for instance, are often tightened to 2065 ft-lb. while foundation bolts are assigned a particular tension. Tension and torque, of course, call for different tools.
“We see specs for both tension on some turbine towers and torque on others. Whatever the characteristic, it depends on the OEM,” says Aztec Bolting sales engineer Adrian Keith (bolting.com).
Foundation bolts most often require applying a load with a tensioner. Briefly, the tensioner works like this: A worker hand tightens a nut on the bolt then places a socket around the nut. A bridge sits around the nut to support a hydraulic cylinder. Lastly, a puller screws onto at least three threads at the end of the bolt and until it contacts the piston on the hydraulic cylinder. The cylinder is energized by a pump which pulls the bolt to a prescribed tension. “It’s fairly accurate. The nut is then further tightened by hand, or with a short rod called a tommy bar. It does not take much effort. Then releasing the pressure lets the nut and bolt carry the load,” says Keith.
Most other places on the tower call for a torque and that requires a torque wrench. It can be manually applied with a long bar and some sort of indicator, but up tower, that method is dangerous. A hydraulic torque wrench makes more sense. The accompanying cutaway shows some internal detail in a design from Enerpac. In it, a hydraulic piston moves a ratcheting device about 20° maximum at a time. A worker would hit a spring-loaded switch to start the pump motor and monitor a pressure gage until it reads the pressure equivalent to a prescribed torque.
“In addition to loads, equipment dependability is extremely important,” adds Keith. “One thing we hear a lot is that an expensive crane is waiting because hydraulic tools are down. So a malfunctioning $5,000 pump, for example, could be delaying the work of a crane that costs $40,000 a day. The pump’s cost gets lost in the zeros.”
The hydraulic equipment is all heavily used and heavily loaded so it’s going to fail sometime. “Be prepared for it,” says Keith. Most often, he adds, a device’s seals fail from wear and then they can’t generate a required pressure, so keep a replacement set readily available.
Filed Under: Components, Construction, Safety