NON DESTRUCTIVE TESTING

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NON DESTRUCTIVE TESTING

• Flaw Detection
• Flaw Localization
• Type of Flaw Determination
• Flaw Dimension Estimation

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• Flaw Detection

Face AV Front wall echo (FWE)
Face AR Back wall echo (BWE)
d1 Dimension of first flaw
d2 Dimension of second flaw

CRT Display
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• Flaw Localization

• The transducer is scanning until the maximum echo
  is obtained
• - The flaw is exactly below the transducer

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• If the flaw is not perpendicular to beam wave
  direction
• - The flaw can not be detected by using
  straight beam probe
• - The flaw can only be detected by using angle
  beam probe

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• The transducer position must be changed for
  obtaining an echo

• If the flaw is perpendicular to the object
  surface
• - Use two transducers

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• Type of Flaw Determination
• Planar flaw (cracks)? more dangerous
• Volume flaw (voids, inclusions) ? less dangerous
• Change transducer orientation 10o and observe
  the echo

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• Flaw Dimension Estimation
• Amplitude Analysis
• 6 db Drop Method
• Comparison Method
• DGS Method
• Time Analysis
• - TOFD Method
• Frequency Analysis
• - Ultrasonic Spectroscopy

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• 6 dB Drop Method
• Flaw dimension gt transducer diameter

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• Comparison Method
• Flaw dimension lt transducer diameter
• Using block references with flat bottom hole
  (FBH)
• Flaw dimension is estimated by amplitude
  comparison
• If the amplitude of flaw echo equal to the
  amplitude of FBH
• Flaw dimension ? diameter of FBH

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• Distance Gain Scale (DGS) Method
• D is distance of the flaw
• A is amplitude of the echo
• G is the ratio between flaw dimension and
  transducer diameter

DGS graphic for far field
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DGS graphic for near field
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• Time of Flight Diffraction (TOFD) Method
• Measure the time propagation of
• diffraction waves from the crack tips

V Wave velocity
d Crack depth
2S Transducer distance
2a Crack dimension
t1, t2 Time propagation of diffracted waves
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• TOFD method for oblique crack
• Using tandem transducer
• Measure time propagation for two positions of
  transducer
• Calculate the position of the crack tips
• Estimate the crack depth and orientation

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Problem No. 1 A surface crack is detected in a
steel material. For estimating its dimension (h)
and orientation (?), a tandem system is used
which consists of one transducer as transmitting
transducer (T) and two transducers (R1 and R2) as
receiving transducer. These transducer are
transversal transducers with wave velocity of VT.
The distances between them are a, b and c as
shown at figure below. The time propagation from
T to R1 is t1 whereas the time propagation from T
to R2 is t2. a). Express the crack dimension and
orientation as function of the wave velocity VT
the distances (a, b and c) and the time
propagation (t1 and t2). b). Calculate h and ?,
if VT 3230 m/s, a 40 mm, b 60 mm, c 110
mm, t1 32.275 ?s and t2 47.554 ?s.
c
b
a
T
R1
R2
?
y
x
h
z
Steel
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Assignment No. 1 An oblique crack is detected
inside an aluminum material. For estimating its
dimension (h) and orientation (?), three
transversal transducer with wave velocity of 3100
m/s are used. When these transducers are located
at (0, 50), (80,50) and (100, 50) the time
propagation measured are t1(T-R1) 20.9 ?S,
t2(T-R1) 24.6 ?S t 1(T-R2) 21.8 ?S, t
2(T-R2) 26.1 ?S. a). Design a computer program
using MatLab for estimating the crack dimension
and orientation. b). Calculate h and ? using the
computer program.
T(0,50)
R1(80,50)
R2(100,50)
O(0,0)