R. Mitchells Presentation

Mitchells NDT Inspection Services

Introduction toUltrasonic Testing

Research by Robert Mitchell. Engineering Technician: L.E.P. Registered welding Consultant

M.InstNDT: AINDT.Ex Owner- Director of Mitchells NDT Ltd.

Co-axial cable socket

Matching-element

Damping-medium

Crystal Probe shoe(probe delay)

Housing

workpieceSound pulse

Straight beam probe

Back wall

CrystalPerspex Wedge(probe delay)

Damping mediums

Socket

Probe Housing

workpieceSound pulse

Angle beam probe

Back wall

Probe shoe

10 20 30 40

Near field

Far field

Acoustical axis (central beam)

N = near field length

γ = angle of divergence

Sound field

Defect

Flaw detection

Scatter

Defect

10 20 30 40

Flaw detection

Scatter

10 20 30 40

Flaw detection

Shear wave

Compressional

Defect

Compressional

Poor flaw orientation

Poor defect orientation

Improper flaw location

10 20 30 40

Angle reflection

Angle reflection 10 20 30 40

10 20 30 40

Vertical, near surface flaw

10 155 10 155T R

Tandem technique (top)

10 155 10 155T R

a 2Tandem technique (middle)

10 155 10 155T R

Tandem technique (bottom)

10 20 30 40

Improper flaw orientation

10 20 30 40

Perfect flaw orientation

Sound beam

Flat defect

Reflected sound waves

Flaw detectability with improper flaw orientation

Depth.

Flaw Distance

Defect

Return Echo

Compressional Probe.

Start signal(pulse)

Finish signal(echo)

Transmitter

Transit timemeasurement

Work piece

Sound transitpath

Stop-watch

Principle of transit time measurement

Return echopath

0 2 4 6 8 10

CRT / A-scan display

Un calibrated time base

0 2 4 6 8 10

Work piece

Sound wave starts at crystal

Light point or Initial pulse

transmittertransmitterTransmission

Priciple, transmission pulse

0 2 4 6 8 10

Work piece

Sound wave

TransmitterTransmitter

Priciple, sound wave in the workpiece

0 2 4 6 8 10

Work piece

Priciple, sound pulse at the back wall

0 2 4 6 8 10

work piece

transmittertransmitter

Priciple, sound pulse at the coupling surface

0 2 4 6 8 10

Work piece

ProbeBack wall

Priciple, echo display and 2nd run

2 4 6 8 10

Protecting face or probe shoe

CrystalCompressional

Electricalzero

(initial pulse)

Mechanicalzero

(surface)

Probe delay

Electicalzero

(initial pulse)

Mechanicalzero

(surface)Sound wave

Work piece

Delay(wedge)

Shear wave probe 0 2 4 6 8 10

Probe delay

0 2 4 6 8 10

Work piece

ProbeBack wall

Flawecho

Flaw location and echo display

0 2 4 6 8 10

work piece

Back wallecho

Defectecho

Initial pulse

0 2 4 6 8 10

Work piece

Back wallecho

Flawecho

Initial pulse

0 2 4 6 8 10

flaw echocoveredby initialpulse

Work piece

back wallecho

0 2 4 6 8 10

back wallecho:

without

with flaw

Work piece

0 2 4 6 8 10

Flaw echosequence

Work piece

0 2 4 6 8 10

Dead zone (can be measured)

Dead zone

Work piece

Direction ofosscillation

Direction of propagation

Wave length (can be measured)

Longitudinal wave

Direction ofosscillation

Direction of propagation

wave length (can be measured)

Transverse wave

Medium 1

Medium 2

Reflectedwave

Refractedwave

Incidentwave

Reflection and Refraction

0 2 4 6 8 10

10 20 30 40

TPossible flawlocations

Angle beam probe with both wave types

Perspex

Reflectedwave

Refractedwaves

Incidentwave

α = α1 = 27.5°βT = 33.3°βL = 90°

Longitudinal surface wave

Mitchells NDT Inspection Services T

Perspex

Reflectedwave

Refractedtransverse wave

Incidentwave

α = 36.4°βT = 45°

45° transverse wave in steel

surfacewaveperspex

reflectedwave

incidentwave

α = α2 = 57°βT = 90°

Transverse surface wave

total reflection

perspex

reflectedwave

incidentwave

α > 57°

Total reflection

27,5°

33,3°

90°perspex

Ranges for incident waves

Near surface detectability with angle beam pobes

Receiversocket

Transmittersocket

Damping blocks

Crystal

Acoustical corkbarrier

TR-probe / dual crystal probe

Probe Shoe

0 2 4 6 8 10

Work piece

TR-probe

Probe delay with TR-probes

0 2 4 6 8 10

Cross talkecho

flawecho

TR-probe

Cross talk at high gain

0 2 4 6 8 10

0 100 mm50

steel, L

Range calibration

5 10 15

Calibration block 1 with angle beam probes

100mm85mm90mm

5mmIndex point

5 10 15

0 2 4 6 8 10

100 mm

1st echo from circular section

5 10 15

0 2 4 6 8 10

100 mm 200 mm 300 mm

Echo sequence from 100 mm radius

s = 25 mms = 100 mms = 175 mmetc.

this wave will be absorbed !

25 mm radius of calibration block 2

s = 50 mms = 125 mms = 200 mmetc.

50 mm radius of calibration block 2

5 10 15

0 2 4 6 8 10

0 100 mmsteel

100 mm range calibration on K2

Test piece Discontinuity

Sound path

0 2 4 6 8 10

s = k•Rs = sound pathk = scale factorR = screen reading

Flaw loaction

flaw location

Sound entry point projectionpoint

a = s•sin ßd = s•cos ß

ßa = surface distance

ß = probe angled = depth

S = sound path

Flaw triangle

Snells law

Flaw location with angle beam probes

work piece reflector

Index point -Front edge of probe

a = surface distance from index pointa' = reduced surface distancex = x-value = distance:

Flaw location with angle beam probes

apparent flaw location

sd = apparent depth

Flaw location with an angle beam probe on a plate

apparent flaw location

real flaw location

d' = apparent depthd = real depthT = work piece thickness

a = s • sinβd‘ = s • cosβd = 2T - d

Flaw location with an angle beam probe on a plate

Large defects parallel to the scanning surface

Scanning the edge of the defect 6 db drop

Flaw echo drops to 50% of its maximum value

"half value" positions

delaminationprobe positionwith echo amplitudereduced to 50 % = 6db drop

Determination of the defect area

0 2 4 6 8 100 2 4 6 8 10 0 2 4 6 8 10

IP BER IP BER IP BER

Flaw sizes and echo amplitudes

0 2 4 6 8 10

IP BER

Flaw distances and echo amplitudes

0 500100 200 300 400

4 mm3 mm

Distance amplitude curves on the CRT screen

0 2 4 6 8 10

IP BEF

instrument gain: G = 34 dB

Defect evaluation by comparison - 1

0 2 4 6 8 10

IP BER

instrument gain: 34 dB

0 2 4 6 8 10

IP BERE

+ 8 dB

instrument gain: 42 dB

0 2 4 6 8 10

10 20 30 40 10 20 30 40 10 20 30 40 10 20 30 40

Position

Distance amplitude curve (DAC)

0 2 4 6 8 10 0 2 4 6 8 10

time corrected gainDAC

DAC and TCG

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