By Paul Dvorak, Editor
Windpower Engineering & Development
A recently introduced handheld device has the ability to monitor and display the elongation, stress, and load on a wind-turbine fastener. Developer Hydratight says its BoltScope Ultra is for applications that call for accurate bolt loads, such as those in the wind, nuclear, other power-generation industries.
It works like this, says Thomas Foley, a technical support specialist with parent company Actuant Corp: An operator pulls up a built-in material menu and identifies the bolt material. This pulls in values for material characteristics such as yield strength, ultrasonic stress factor, and temperature coefficient. The instrument includes a temperature probe to measure bolt temperatures.
The operator places the ultrasonic transducer on one end of the fastener. Triggering the instrument applies a voltage to the transducer, which generates a longitudinal ultrasonic wave that travels the length of the fastener. The wave reflects off the other end and returns to the transducer. This captured signal process is known as “time of flight.”
“Each bolt in a joint requires an initial reference-length reading, known as an L-REF. This is a base, or zero datum because the ‘time-of-flight’ differs on each fastener,” Foley says. A technician would also capture the acoustic velocity in fasteners after tightening. Foley adds that the technology is based on a well-known and reliable pulse-echo measuring technique.
The difference in time-of-flight between the two measurements establishes the resultant fastener stress. That resultant stress is extrapolated to display load, elongation, and strain. Monitored data is presented on an easy-to-read color display and recorded for offline reporting and storage.
A range of automatic settings optimizes signal detection, strength, and stability, Foley says. A simple one-key press optimizes signal stability and strength, eliminating the need for interrogation by the operator.
Using the most recent ultrasonic technology lets the BoltScope Pro and BoltScope Ultra units make it easy to measure fastener load, stress, and elongation, the company states. The display lets users quickly and accurately monitor fastener load before, during, and after tightening. The instrument allows the monitoring of fasteners throughout their life. In addition, field-captured data is easily uploaded for offline reporting, retention, and analysis.
The product comes with essential accessories in a compact carrying case. “We are currently active on a wind-turbine-bolting campaign in which each joint has 128, M72 fasteners,” says Foley.