Abstract: Aiming at the problem that the pretightening force of highstrength bolts in wind turbine whether to meet the design requirements when they are reused for the second time, based on the ultrasonic measuring technique of the bolts’ pretightening force, a highprecision and portable ultrasonic bolt pretightening force tester was used to test the distribution of pretightening force between hub and pitch bearing installed by torque method when the bolts were used for the first and second time. The deviation between the pretightening force obtained in actual field assembly and by theoretical calculation were compared, and the influence of bolts reused on the pretightening force was discussed. A new technique for measuring and controlling the pretightening force of high strength bolts in wind turbines by ultrasonic method was proposed. The results indicated that the pretightening force obtained from high strength bolts used for the first time is in good agreement with the target value. The pretightening force obtained from reused high strength bolts is 13% lower than the target value in average, the distribution range still meet design requirement, and the highstrength bolt can be reused while keeping the twisting torque unchanged or increasing the twisting torque in an appropriate proportion.
Key words: bolts in wind turbine; pretightening force; torque coefficient; first use; secondary use; ultrasonic bolt pretightening force tester