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Technical Discussions
LANRE ALAPINI
NDT Inspector,
NDT TRAINING AND TESTING CENTRE HOUSTON TEXAS USA, Nigeria, Joined Nov 2008, 3

LANRE ALAPINI

NDT Inspector,
NDT TRAINING AND TESTING CENTRE HOUSTON TEXAS USA,
Nigeria,
Joined Nov 2008
3
06:27 Dec-09-2008
flaw checking

can any body explain the term lack of back wall reflection


    
 
 Reply 
 
James Boaden
Sales,
Midas NDT Systems Ltd., United Kingdom, Joined Jun 2002, 6

James Boaden

Sales,
Midas NDT Systems Ltd.,
United Kingdom,
Joined Jun 2002
6
07:00 Dec-09-2008
Re: flaw checking
----------- Start Original Message -----------
: can any body explain the term lack of back wall reflection
------------ End Original Message ------------

Using ultrasonics, a signal is generated that reflects back from the back surface of a component (when generated outside the component some sound reflects off the front surface and some penetrates, this then reflects off the back surface).

You should always get reflections from the back surface unless something stops the sound reaching it. Lack of back wall reflection dictates that a defect has stopped the sound reaching the back surface and the area of lack of back surface will be the same as the planar area of the defect.


    
 
 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
07:36 Dec-09-2008
Re: flaw checking
----------- Start Original Message -----------
: can any body explain the term lack of back wall reflection
------------ End Original Message ------------

Lack of back wall reflection or echo means that the transducer is not receiving the ultrasound signal reflected from the back surface (opposite side of the test object). This can happen due to one or more of the following reasons:

It is assumed that the instrument and the probe are working and that the range has been calibrated properly.

Very rough surface resulting in poor coupling

Highly curved surface resulting in sound not entering the test object

Lack of parallelism between the test surface and the back surface, for example a wedge

Sintered material with lot of porosity.

We had some interesting experiences while testing hot rolled austenitic stainless steel plates and tungsten-copper blocks. If any one is interested, I will share. Or I may submit a short case study like paper.

Swamy
NDT Guru





    
 
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