Fig. 1. Eddy current thermography principle

Fig. 2. Hollow copper tube

Fig. 3. (a) Toroidal coils; (b) Core-type coils; (c) Helmholtz coils

Fig. 4. Small-bore pipe model of pressure vessels

Fig. 5. Excitation coil model

Fig. 6. Coil adaptation diagram

Fig. 7. Defect model included

Fig. 8. Temperature distribution map

Fig. 9. Temperature curve above the defect

Fig. 10. Intersecting lines

Fig. 11. Coil movement trajectory

Fig. 12. (a) Weld surface temperature distribution when the coil moves to defect 1; (b) The coil moves to the weld surface temperature distribution between defects 1 and 2; (c) Weld surface temperature distribution when the coil moves to defect 2; (d) The coil moves to the weld surface temperature distribution between defects 2 and 3; (e) Weld surface temperature distribution when the coil moves to defect 3

Fig. 13. Experimental simulation system

Fig. 14. Engineering drawings

Fig. 15. Experimental setup

Fig. 16. 8 mm defect temperature distribution image

Fig. 17. 4 mm defect temperature distribution image

Fig. 18. Three-dimensional reconstruction of the temperature field

Fig. 19. 4 mm defect raw thermal imaging grayscale map; (b) Image processing diagram