Post on 01-Apr-2015
NON DESTRUCTIVE TESTING
Flaw Detection Flaw Localization Type of Flaw Determination Flaw Dimension Estimation
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
Flaw Localization
•The transducer is scanning until the maximum echo is obtained
- The flaw is exactly below the transducer
• 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
• The transducer position must be changed for obtaining an echo
• If the flaw is perpendicular to the object surface
- Use two transducers
Type of Flaw Determination
• Planar flaw (cracks) more dangerous
• Volume flaw (voids, inclusions) less dangerous
• Change transducer orientation 10o and observe the echo
Flaw Dimension Estimation
• Amplitude Analysis
- 6 db Drop Method
- Comparison Method
- DGS Method
• Time Analysis
- TOFD Method
• Frequency Analysis
- Ultrasonic Spectroscopy
6 dB Drop Method
- Flaw dimension > transducer diameter
Comparison Method
- Flaw dimension < 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
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
DGS graphic for near field
Time of Flight Diffraction (TOFD) Method
- Measure the time propagation of
diffraction waves from the crack tips
221
2 42
1StVd
dStVa 222
2 42
12
V = Wave velocity
d = Crack depth
2S = Transducer distance
2a = Crack dimension
t1, t2 = Time propagation of diffracted waves
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
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.
Steel
T R1
a b
h
c
R2
x yz
Steel
T R1
a b
h
c
R2
x yz
(*)GFqqDh)aE(q)a2DE2(qDh
EDEq2qDaq2ahEDqf2
q)b2a2(bafaq2ah
aq2ahf2aq2ahfbq2bh
aq2ahfbq2bhbq2bhaq2ahf
qcoshcosbh2bhcosah2ahftVyx
cosch2chzcosbh2bhycosah2ahx
22222222
22222222
22
2222222
22222222
22221T
222222
(*)GFqqDh)aE(q)a2DE2(qDh
EDEq2qDaq2ahEDqf2
q)b2a2(bafaq2ah
aq2ahf2aq2ahfbq2bh
aq2ahfbq2bhbq2bhaq2ahf
qcoshcosbh2bhcosah2ahftVyx
cosch2chzcosbh2bhycosah2ahx
22222222
22222222
22
2222222
22222222
22221T
222222
(**)KJqqHh)aI(q)a2HI2(qHh
IHIq2qHaq2ahIHqg2
q)c2a2(cafaq2ah
aq2ahf2aq2ahgcq2ch
aq2ahgcq2chcq2chaq2ahg
qcoshcosch2chcosah2ahgtVzx
cosch2chzcosbh2bhycosah2ahx
22222222
22222222
22
2222222
22222222
22222T
222222
h
qKJqqHh
A
ACBBqCBqAq
KGqJFqHDKJqqHGFqqD
1222
2
2222222
cos2
40
0)()()(
Steel
T R1
a b
h
c
R2
x yz
(**)KJqqHh)aI(q)a2HI2(qHh
IHIq2qHaq2ahIHqg2
q)c2a2(cafaq2ah
aq2ahf2aq2ahgcq2ch
aq2ahgcq2chcq2chaq2ahg
qcoshcosch2chcosah2ahgtVzx
cosch2chzcosbh2bhycosah2ahx
22222222
22222222
22
2222222
22222222
22222T
222222
h
qcosKJqqHh
A2
AC4BBq0CBqAq
0)KG(q)JF(q)HD(KJqqHGFqqD
(**)KJqqHh)aI(q)a2HI2(qHh
IHIq2qHaq2ahIHqg2
q)c2a2(cafaq2ah
(*)GFqqDh)aE(q)a2DE2(qDh
EDEq2qDaq2ahEDqf2
q)b2a2(bafaq2ah
122
22
2222222
22222222
22222222
22
22222222
22222222
22
h
qKJqqHh
A
ACBBqCBqAq
KGqJFqHDKJqqHGFqqD
122
22
2222222
cos
2
40
0)()()(
T(0,50) R1(80,50) R2(100,50)
O(0,0)
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.