TransverseCracks

Corner Cracks

Pinholes

Longitudinal Mid-Face Cracks

Star Cracks

Sub-Surface Porosity

Inter ColumnarCracking Centreline

SegregationSpider Cracks

Off-Corner Cracks

LongitudinalCorner Cracks

Edge Cracks/Splits

Fig. 1. Typical defects found on the surface and inside an as-cast product

Fig. 2. Comparison signals between the 3 different laser systems

Electromagnetic Noise

Surface Waves Bulk Waves

Billet EMAT

Lens

LaserPlasma

TrolleySystem

Fig. 3. The billet being inspected with the Laser-EMAT system using theautomated trolley system

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 aRayleigh wave in steel

Time vs Distance Graph

-0.1200

-0.1000

-0.0800

-0.0600

-0.0400

-0.0200

0.0000

15 20 25 30 35 40 45 50

Time (us)

Dis

tan

ce

(m

)

5 mm

10 mm

5 mm

10 mm

Arrival time changes as the

EMAT position is movedV

olta

ge/(

Arb

itra

ry U

nits

)

Time (µs)

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

LASER

EMAT

x

Slot

x

EMAT

Slot

LASER

LASER

EMAT

x

Slot

Direction of movement

Case 1 – Laser-EMAT system to the right of the defect

Case 2 – The laser and the EMAT are separated by the defect

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

Rayleigh Wave Reflected from the Slot

Shear (Bulk) Wave

SurfaceSkimming

RayleighWave

RayleighWave

Shear (Bulk) Wave

SurfaceSkimming

RayleighWave

Shear (Bulk) Wave

Rayleigh Wave Reflected from the Slot

Rayleigh Wave Reflected from the Slot

Shear (Bulk) Wave

SurfaceSkimming

RayleighWave

Case 1 – Laser and EMAT to the right of the slab

RayleighWave

Shear (Bulk) Wave

Case 2 – The slab is between the laser and EMAT

SurfaceSkimming

RayleighWave

Shear (Bulk) Wave

Rayleigh Wave Reflected from the Slot

Case 3 – The laser and EMAT are to the left of the slab

Fig. 8. A-Scans for each of the three cases

Surface Skimming

Wave

RayleighWave

Shear (Bulk) Wave

CASE 1

CASE 2

CASE 3

This diagonal line represents a Rayleigh wave as it is reflected from the slot

This diagonal line represents a Rayleigh wave as it is reflected from the slot

These waves are reflected from thebillet edge

Defect

Surface Skimming

Wave

RayleighWave

Shear (Bulk) Wave

CASE 1

CASE 2

CASE 3

This diagonal line represents a Rayleigh wave as it is reflected from the slot

This diagonal line represents a Rayleigh wave as it is reflected from the slot

These waves are reflected from thebillet edge

Defect

Fig. 9. B-Scan from the automated trolley system mainly in incrementsof 2 mm

Defect

These waves are reflectedfrom the billet edge

Fig. 10. B-Scan from the automated trolley system, measured in incrementsof 5 mm

reflections from the end of the billetSlot reflection

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?

I don’t know what the things in the white circles are supposed to be

Enhanced Rayleigh 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

This is mode-converted shear wave

This is mode-converted or reflected wave from the boundaries. More details can be obtained if long time duration is recorded.

This is mode-converted or reflected wave from the boundaries. More details can be obtained if long time duration is recorded.

Rayleighwaveenhancement

This is a mode-convertedRayleigh wave to surfaceskimming wave

This is a mode-convertedsurface 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 Convexlens

LaserHead

HotBillet

Rolls

EMATHolder

Fig. 13. Photograph of the hot billet as it passes underneath the laser-EMATequipment

Defect

Very faint reflectedwaves can be seen

Fig. 14. B-Scan of the cold billet moving in the rolling mill

Defect

/(Arbitrary units)

Fig. 15. B-Scan taken at 800 °C, along with the image taken using thethermal imaging camera

TopThermocouple 5

SideThermocouple 1

SideThermocouple 2

SideThermocouple 3

SideThermocouple 4

SideThermocouple 5

TopThermocouple 1

TopThermocouple 3

TopThermocouple 4

TopThermocouple 2

Fig. 16. Schematic of the billet with embedded thermocouple positions.The FLIR camera was pointed to the side of the billet. TheLaser-EMAT equipment measured the top face