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Technical Discussions
gowrishankar
R & D, scientist
ISRO, India, Joined Nov 2008, 34

gowrishankar

R & D, scientist
ISRO,
India,
Joined Nov 2008
34
01:43 Jan-27-2006
ultrasonic testing of Al. alloys

sir,
In ultrasonic testing, We happend to come across (UT -NORMAL BEAM INSPECTION ) some flaw like indication which is below DAC Level more or less in the middle of screen,when we test Cylindrical shaped aluminum forgings.
AND interestingly it is vanishing if we rub the bottom face or the other side of the forging with oil layer. what may be the reason? this case was repeated in several Al. forgings like AA2219,7020 etc
please provide me the answer.


 
 Reply 
 
Buddy
Buddy
01:52 Jan-27-2006
Re: ultrasonic testing of Al. alloys
Try turning down your pulse rep rate.


----------- Start Original Message -----------
: sir,
: In ultrasonic testing, We happend to come across (UT -NORMAL BEAM INSPECTION ) some flaw like indication which is below DAC Level more or less in the middle of screen,when we test Cylindrical shaped aluminum forgings.
: AND interestingly it is vanishing if we rub the bottom face or the other side of the forging with oil layer. what may be the reason? this case was repeated in several Al. forgings like AA2219,7020 etc
: please provide me the answer.
------------ End Original Message ------------




 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 528

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
528
05:59 Jan-27-2006
Re: ultrasonic testing of Al. alloys
Assuming you have calibrated the depth of the forging to be roughly across the screen, I.e. what you mean is that this indication is appearing as if it was in the middle of the part,(which it obviously isn't) then it seems that this is a 'ghost' echo, that is sound from a previous pulse is still bouncing around in the material.

Reducing the Instrument PRF (i.e. increasing the time between pulses so that the sound has time to die away) should eliminate it

Good luck
Joe

----------- Start Original Message -----------
: sir,
: In ultrasonic testing, We happend to come across (UT -NORMAL BEAM INSPECTION ) some flaw like indication which is below DAC Level more or less in the middle of screen,when we test Cylindrical shaped aluminum forgings.
: AND interestingly it is vanishing if we rub the bottom face or the other side of the forging with oil layer. what may be the reason? this case was repeated in several Al. forgings like AA2219,7020 etc
: please provide me the answer.
------------ End Original Message ------------




 
 Reply 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 183

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
183
06:29 Jan-27-2006
Re: ultrasonic testing of Al. alloys
reply by Udo Schlengermann:

I make a guess:
If your probe is not suited very well for the diameter of the test object, e.g. the probe diameter is too large for the given curvature, the probe has not full contact to the object. The probe may generate surface waves that travel circumferentially.
If you wet the surface or press your wet fingers to the object you damp the surface waves.
Please check, and use a probe of smaller diameter or with matched contact surface.

Kind regards
Udo Schlengermann
GE Inspection Technologies GmbH
Huerth, Germany

----------- Start Original Message -----------
: Assuming you have calibrated the depth of the forging to be roughly across the screen, I.e. what you mean is that this indication is appearing as if it was in the middle of the part,(which it obviously isn't) then it seems that this is a 'ghost' echo, that is sound from a previous pulse is still bouncing around in the material.
: Reducing the Instrument PRF (i.e. increasing the time between pulses so that the sound has time to die away) should eliminate it
: Good luck
: Joe
: : sir,
: : In ultrasonic testing, We happend to come across (UT -NORMAL BEAM INSPECTION ) some flaw like indication which is below DAC Level more or less in the middle of screen,when we test Cylindrical shaped aluminum forgings.
: : AND interestingly it is vanishing if we rub the bottom face or the other side of the forging with oil layer. what may be the reason? this case was repeated in several Al. forgings like AA2219,7020 etc
: : please provide me the answer.
------------ End Original Message ------------




 
 Reply 
 
John D.
John D.
02:06 Jan-29-2006
Re: ultrasonic testing of Al. alloys
----------- Start Original Message -----------
: sir,
: In ultrasonic testing, We happend to come across (UT -NORMAL BEAM INSPECTION ) some flaw like indication which is below DAC Level more or less in the middle of screen,when we test Cylindrical shaped aluminum forgings.
: AND interestingly it is vanishing if we rub the bottom face or the other side of the forging with oil layer. what may be the reason? this case was repeated in several Al. forgings like AA2219,7020 etc
: please provide me the answer.
------------ End Original Message ------------

All the answers given are correct. We used to see those indications when examining long studs. You have alot of mode conversion in long pieces such as studs and cylinders from the beam spread alone. They are in fact "ghost indications" resulting from the mode conversion that takes place along the side of the cylinders. The search unit is trying to talk and listen at the same time. As Joe stated, if you adjust your Pulse rep rate, they should dissappear.


 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
00:04 Jan-29-2006
Re: ultrasonic testing of Al. alloys
Dear Sir,

In the past three decades of UT of forgings, I have come across many such mysterious echoes and all were explained. In the case that you have refered, it is essential to know the forging dimensions, probe details like diameter, frequency etc., to understand the source of the echo.

P V SASTRY

----------- Start Original Message -----------
: sir,
: In ultrasonic testing, We happend to come across (UT -NORMAL BEAM INSPECTION ) some flaw like indication which is below DAC Level more or less in the middle of screen,when we test Cylindrical shaped aluminum forgings.
: AND interestingly it is vanishing if we rub the bottom face or the other side of the forging with oil layer. what may be the reason? this case was repeated in several Al. forgings like AA2219,7020 etc
: please provide me the answer.
------------ End Original Message ------------




 
 Reply 
 

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