Applicability Analysis of Inspection and Monitoring Technologies in Wind Turbine Towers

Table 1

Summary of nondestructive testing technologies.

Nondestructive testing technologies	Principle	Advantages	Limitations	Applications in wind turbine tower
Ultrasonic phased array detection	A set of independent wafers inducing ultrasonic waves independently, and deflection of an acoustic beam is realized by delay technique	Suitable for detection of structures that are difficult to access, accurate localization of defects, high sensitivity of detection	Poor repeatable accuracy, difficult to calculate the flaws quantitatively	Detection of welding seam
TOFD detection	Huygens principle	High defect detection rate, accurate location and quantified calculation of flaws	Blind spots of detection in the surface, probe cannot be placed at the continuous weld between flange and the tower	Detection of welding seam
Magnetic memory	Magnetic memory properties of ferromagnetic materials	Improvement of detection rate, reduction of the detection cost	Magnetic memory signal is weak and may be influenced by many factors	Detection of welding seam and flanges
Acoustic emission	Elastic waves are released from the flaws of material	No external energy is needed, less affected by the environment. The dynamic tracking of flaws	Mixture of mechanical and environmental noise with AE signals	Monitoring during its whole life cycle
Fiber Bragg grating	The selection of a grating for a particular light	High sensitivity, strong anti-EMI capability	Sensitive to temperature of the environment	Deformation monitoring
Piezoelectric impedance	Piezoelectric effect	No external excitation is required, sensitive to small changes of measured structural parameters	Easily affected by environmental factors and the stability of detection needs to be improved	Detection of flange bolt looseness