1. 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

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

3. 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

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

5. Case 1 – Laser-EMAT system to the right of the defectx
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

6. 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

7. 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

8. 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

9. 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

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

11. 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

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

13. 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

14. 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