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Technical Discussions
RT JEYAKUMAR
NDT Inspector
Singapore, Joined Aug 2002, 10

RT JEYAKUMAR

NDT Inspector
Singapore,
Joined Aug 2002
10
06:15 May-24-2005
SENSITIVITY in UT

As we know sensitivity in UT is half of wavelength., and we know wavelength is v/f., that means, if velosity decreases in the material., will sensitivity increases

Case 1. So, I can put in this way, sensitivity will increase to lower velosity material and decrease for higher velosity material.

Case2. So, sensitivity in shear wave probe is higher than longitudinal wave probe.

Can anyone please kindly explain this confusion.


    
 
 Reply 
 
N.Kuppusamy
Consultant, Level-III
United Testing Co. Pte Ltd, Singapore, Joined Jan 2003, 13

N.Kuppusamy

Consultant, Level-III
United Testing Co. Pte Ltd,
Singapore,
Joined Jan 2003
13
04:52 May-25-2005
Re: SENSITIVITY in UT
Hi,

You are correct. For a given frequency, the sensitivity increases as the velocity decreases for the same size of reflector.

The reflectivity of the defect also plays an important role in the defect detection. Reflectivity is the amount of energy reflected by the defect. Generally it is different for different material.

For a given material, the sensitivity increases as velocity decreases, thus the highest sensitivity is achieved by the surface waves followed by shear waves and compressional waves.

Hope this would clear your doubts.

N.Kuppusamy

----------- Start Original Message -----------
: As we know sensitivity in UT is half of wavelength., and we know wavelength is v/f., that means, if velosity decreases in the material., will sensitivity increases
: Case 1. So, I can put in this way, sensitivity will increase to lower velosity material and decrease for higher velosity material.
: Case2. So, sensitivity in shear wave probe is higher than longitudinal wave probe.
: Can anyoneplease kindly explain this confusion.
------------ End Original Message ------------




    
 
 Reply 
 
Paul A. Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul A. Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
06:57 May-25-2005
Re: SENSITIVITY in UT
Hello,
To continue from the previous response, a reflector has directivity. For a given material wavelength, the reflected sound becomes more directional as the reflector size increases. Similarly, for a given reflector size, the reflected sound becomes more directional as the wavelength decreases. Look at the directivity equations for UT transducers and you will notice directivity is a function of d/lambda (size/wavelength). The directivity of a reflector is identical, except the wavelength is that of the incident sound field.
Paul


----------- Start Original Message -----------
: Hi,
: You are correct. For a given frequency, the sensitivity increases as the velocity decreases for the same size of reflector.
: The reflectivity of the defect also plays an important role in the defect detection. Reflectivity is the amount of energy reflected by the defect. Generally it is different for different material.
: For a given material, the sensitivity increases as velocity decreases, thus the highest sensitivity is achieved by the surface waves followed by shear waves and compressional waves.
: Hope this would clear your doubts.
: N.Kuppusamy
: : As we know sensitivity in UT is half of wavelength., and we know wavelength is v/f., that means, if velosity decreases in the material., will sensitivity increases
: : Case 1. So, I can put in this way, sensitivity will increase to lower velosity material and decrease for higher velosity material.
: : Case2. So, sensitivity in shear wave probe is higher than longitudinal wave probe.
: : Can anyone please kindly explain this confusion.
------------ End Original Message ------------




    
 
 Reply 
 
N.Kuppusamy
Consultant, Level-III
United Testing Co. Pte Ltd, Singapore, Joined Jan 2003, 13

N.Kuppusamy

Consultant, Level-III
United Testing Co. Pte Ltd,
Singapore,
Joined Jan 2003
13
01:12 May-26-2005
Re: SENSITIVITY in UT
Hi,

I approached this problem from the theoritical point of view by keeping all other variables constant except wavelength.

The reflectivity also includes the acoustic impedance mismatch difference.

Regards,
N.Kuppusamy
----------- Start Original Message -----------
: Hello,
: To continue from the previous response, a reflector has directivity. For a given material wavelength, the reflected sound becomes more directional as the reflector size increases. Similarly, for a given reflector size, the reflected sound becomes more directional as the wavelength decreases. Look at the directivity equations for UT transducers and you will notice directivity is a function of d/lambda (size/wavelength). The directivity of a reflector is identical, except the wavelength is that of the incident sound field.
: Paul
:
: : Hi,
: : You are correct. For a given frequency, the sensitivity increases as the velocity decreases for the same size of reflector.
: : The reflectivity of the defect also plays an important role in the defect detection. Reflectivity is the amount of energy reflected by the defect. Generally it is different for different material.
: : For a given material, the sensitivity increases as velocity decreases, thus the highest sensitivity is achieved by the surface waves followed by shear waves and compressional waves.
: : Hope this would clear your doubts.
: : N.Kuppusamy
: : : As we know sensitivity in UT is half of wavelength., and we know wavelength is v/f., that means, if velosity decreases in the material., will sensitivity increases
: : : Case 1. So, I can put in this way, sensitivity will increase to lower velosity material and decrease for higher velosity material.
: : : Case2. So, sensitivity in shear wave probe is higher than longitudinal wave probe.
: : : Can anyone please kindly explain this confusion.
------------ End Original Message ------------




    
 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
09:40 May-26-2005
Re: SENSITIVITY in UT
----------- Start Original Message -----------
: As we know sensitivity in UT is half of wavelength., and we know wavelength is v/f., that means, if velosity decreases in the material., will sensitivity increases
: Case 1. So, I can put in this way, sensitivity will increase to lower velosity material and decrease for higher velosity material.
: Case2. So, sensitivity in shear wave probe is higher than longitudinal wave probe.
: Can anyone please kindly explain this confusion.
------------ End Original Message ------------

Dear Jeyakumar,

There is no confusion. Both of your statements are correct in themselves. Thus, for the same type of waves, i.e. longitudinal, the sensitivity will be better in a material with a lower velocity and thus a shorter wavelength for a given frequency.

For a given material, for a given frequency, shear wave mode of testing will have higher sensitivity since the wavelength of shear waves will be roughly half the longitudinal wavelength.

And combining boththe cases, it is true that for a material with lesser velocity, shear wave mode of testing (assuming that the shear wave velocity is a constant fraction of the longitudinal wave velocity, an assumption not strictly valid), will give higher sensitivity than for a material with higher velocity and tested in longitudinal mode.

As can be seen, there is no confusion.

Best regards,

Swamy





    
 
 Reply 
 
Philippe Rubbers
Engineering
SCM, South Africa, Joined Nov 1998, 21

Philippe Rubbers

Engineering
SCM,
South Africa,
Joined Nov 1998
21
09:18 May-27-2005
Re: SENSITIVITY in UT
Dear Sir

Shear waves are much more sensitive for corner reflectors than long waves, (for equal wavelengths), due to the energy conversion efficiencies, (diffraction and reflection coefficients). An excellent reference book would be:
Krautkramer J. Krautkramer.H Ultrasonic testing of materials. 1968 Ed. George Allen andUnwin.
Tables and curves for these coefficients are found in the appendix.

But your paradox is definitively a point to ponder.

Best regards

----------- Start Original Message -----------
: Hi,
: I approached this problem from the theoritical point of view by keeping all other variables constant except wavelength.
: The reflectivity also includes the acoustic impedance mismatch difference.
: Regards,
: N.Kuppusamy
: : Hello,
: : To continue from the previous response, a reflector has directivity. For a given material wavelength, the reflected sound becomes more directional as the reflector size increases. Similarly, for a given reflector size, the reflected sound becomes more directional as the wavelength decreases. Look at the directivity equations for UT transducers and you will notice directivity is a function of d/lambda (size/wavelength). The directivity of a reflector is identical, except the wavelength is that of the incident sound field.
: : Paul
: :
: : : Hi,
: : : You are correct. For a given frequency, the sensitivity increases as the velocity decreases for the same size of reflector.
: : : The reflectivity of the defect also plays an important role in the defect detection. Reflectivity is the amount of energy reflected by the defect. Generally it is different for different material.
: : : For a given material, the sensitivity increases as velocity decreases, thus the highest sensitivity is achieved by the surface waves followed by shear waves and compressional waves.
: : : Hope this would clear your doubts.
: : : N.Kuppusamy
: : : : As we know sensitivity in UT is half of wavelength., and we know wavelength is v/f., that means, if velosity decreases in the material., will sensitivity increases
: : : : Case 1. So, I can put in this way, sensitivity will increase to lower velosity material and decrease for higher velosity material.
: : : : Case2. So, sensitivity in shear wave probe is higher than longitudinal wave probe.
: : : : Can anyone please kindly explain this confusion.
------------ End Original Message ------------




    
 
 Reply 
 

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