Transverse Cracks Corner Cracks Pinholes Longitudinal Mid-Face Cracks Star Cracks Sub-Surface Porosity Inter Columnar Cracking Centreline Segregation Spider Cracks Off-Corner Cracks Longitudinal Edge Cracks/Splits Fig. 1. Typical defects found on the surface and inside an as-cast product Electromagnetic Noise Surface Waves Bulk Waves Fig. 2. Comparison signals between the 3 different laser systems

Billet EMAT Lens Laser Plasma Trolley System Fig. 3. The billet being inspected with the Laser-EMAT system using the automated trolley system

Arrival time changes as the EMAT position is moved Voltage/(Arbitrary Units) Time (µs) Fig. 4. Two A-Scans overlapped, showing the change in arrival time when the steel and EMAT have been moved a known distance Fig. 5. Time vs distance graph, where the gradient is the velocity of a Rayleigh wave in steel

Fig. 6. The automatic peak detection algorithm used to calculate the velocity in steel, from twenty different A-Scans

Case 1 – Laser-EMAT system to the right of the defect x Slot Direction of movement Case 1 – Laser-EMAT system to the right of the defect x EMAT Slot LASER Case 2 – The laser and the EMAT are separated by the defect LASER EMAT x Slot Case 3 – Laser-EMAT system to the left of the defect Fig. 7. A side view of a billet with a transverse defect in its middle face. The billet is moving towards the right

Case 1 – Laser and EMAT to the right of the slab Rayleigh Wave Reflected from the Slot Shear (Bulk) Wave Surface Skimming Rayleigh Case 1 – Laser and EMAT to the right of the slab Case 2 – The slab is between the laser and EMAT Case 3 – The laser and EMAT are to the left of the slab Fig. 8. A-Scans for each of the three cases

Fig. 9. B-Scan from the automated trolley system mainly in increments Surface Surface Rayleigh Rayleigh Shear Shear Skimming Skimming Wave Wave (Bulk) (Bulk) Wave Wave Wave Wave This diagonal This diagonal line represents a line represents a Rayleigh wave as Rayleigh wave as it is reflected it is reflected from the slot from the slot CASE 3 CASE 3 CASE 2 CASE 2 Defect Defect This diagonal This diagonal line represents a line represents a Rayleigh wave as Rayleigh wave as it is reflected it is reflected from the slot from the slot CASE 1 CASE 1 These waves are These waves are reflected from the reflected from the billet edge billet edge Fig. 9. B-Scan from the automated trolley system mainly in increments of 2 mm

These waves are reflected Enhanced Rayleigh wave? This is mode-converted or reflected wave from the boundaries. More details can be obtained if long time duration is recorded. These waves are reflected from the billet edge This is mode-converted shear wave This is laser-generated Rayleigh & longitudinal wave refracting at the tip of the crack, and mode-converted into longitudinal and Rayleigh waves. This is mode-converted longitudinal wave This is mode-converted longitudinal wave Defect This is mode-converted or reflected wave from the boundaries. More details can be obtained if long time duration is recorded. Surface skimming. Why isn’t it attenuated more when the slot should completely minimise it? What is with the “X” shape when the slot is present? reflections from the end of the billet Slot reflection I don’t know what the things in the white circles are supposed to be Fig. 10. B-Scan from the automated trolley system, measured in increments of 5 mm

Rayleigh wave enhancement This is a mode-converted Rayleigh wave to surface skimming wave surface skimming wave to Rayleigh wave Fig. 11. Close-up of the region where the defect is

Defect /Arbitrary units) Fig. 12. B-Scan generated when the billet was moved using the trolley system

Prism Convex lens Laser Head Hot Billet Rolls EMAT Holder Fig. 13. Photograph of the hot billet as it passes underneath the laser-EMAT equipment

Defect Very faint reflected waves can be seen Fig. 14. B-Scan of the cold billet moving in the rolling mill

Fig. 15. B-Scan taken at 800 °C, along with the image taken using the Defect /(Arbitrary units) Fig. 15. B-Scan taken at 800 °C, along with the image taken using the thermal imaging camera

Top Thermocouple 5 Top Thermocouple 4 Top Thermocouple 3   Top Thermocouple 2   Top Thermocouple 1     Side Thermocouple 5  Side Thermocouple 4  Side Thermocouple 3 Side Thermocouple 2 Side Thermocouple 1 Fig. 16. Schematic of the billet with embedded thermocouple positions. The FLIR camera was pointed to the side of the billet. The Laser-EMAT equipment measured the top face