Fig. 1. Finite element model of inner wall defect of thick pipe

Fig. 2. Images of ultrasonic transmission at different moments. (a) 9×10^-6 s; (b) 14×10^-6 s; (c) 18×10^-6 s; (d) 24×10^-6 s

Fig. 3. Laser ultrasonic detection device

Fig. 4. Distribution of sound field in different propagation process. (a) Piezoelectric probe excites ultrasonic longitudinal wave on thick-walled tube; (b) longitudinal wave is reflected when it encounters inner wall; (c) creeping wave is formed by mode conversion of longitudinal wave on internal wall; (d) creeping wave propagates along inner wall

Fig. 5. Detection device of creeping wave probe

Fig. 6. Detection signal of the trial-produced probe. (a) No load of probe; (b) probe is attached to non-defective steel tube; (c) probe is directly above crack; (d) probe and crack are at position of 90°; (e) probe and crack are at position of 180°; (f) probe and crack are at position of 270°