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- since 1996 -
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Technical Discussions
langtuteng
Armenia, Joined Nov 2014, 172

langtuteng

Armenia,
Joined Nov 2014
172
15:51 Nov-27-2014
experience of ET

has anyone ever inspect the material Ti? tonight i test the Ti plant with the equipment US-454surface probe SS.75 which was produced by Uniwest company, i found the angle between the signal from the notch on the test block and lift -off was too small. how can i increase this angle? thank you!

    
 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 219

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
219
19:07 Nov-27-2014
Re: experience of ET
In Reply to langtuteng at 15:51 Nov-27-2014 (Opening).

Have you tried changing the operating frequency?

What instrument are you using? Does it have the facility to change X and Y scales independently? You could use that facility to distort the image of the signal to make the apparent angle bigger.

    
 
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langtuteng
Armenia, Joined Nov 2014, 172

langtuteng

Armenia,
Joined Nov 2014
172
07:26 Nov-28-2014
Re: experience of ET
In Reply to Frank Lund at 19:07 Nov-27-2014 .

thank you ,lund.
the instrument i used was UniWest US-454. i changed the test frequence from 200KHz to 700KHz ,meanwhile, i also changed the x scale and y scale. but the angle is still very small.

    
 
 Reply 
 
langtuteng
Armenia, Joined Nov 2014, 172

langtuteng

Armenia,
Joined Nov 2014
172
07:33 Nov-28-2014
Re: experience of ET
In Reply to Frank Lund at 19:07 Nov-27-2014 .

i guess when we use the eddy current to inspect the Ti with the surface probe, due to the conductivity and the magnetic permeability, the angle between the notch from the test block and the lift-off just is small. we can't change it no matter how we change test frequence and the gain ,the x scale and y scale. maybe i was wrong, i'm very appreciate for you help.

    
 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 219

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
219
12:01 Nov-28-2014
Re: experience of ET
In Reply to langtuteng at 07:33 Nov-28-2014 .

The trick is to get the lift-off locus accurately horizontal as it leaves the origin or zero at centre screen with X and Y scalings equal, so that it makes a straight line (typically to 3 o'clock. Then increase the Y gain so that the defect signal goes up a steeper slope and shows a better angle. This relies upon having the lift-off signal horizontal so that it has negligible movement in the Y (defect) direction.

Cheers,
Frank

    
 
 Reply 
 
John Hansen
Director, - Eddy Current Technology
ETher NDE Ltd, United Kingdom, Joined Oct 1999, 73

John Hansen

Director, - Eddy Current Technology
ETher NDE Ltd,
United Kingdom,
Joined Oct 1999
73
12:34 Nov-28-2014
Re: experience of ET
In Reply to langtuteng at 07:26 Nov-28-2014 .

Hi

Here in the UK we would use 2-6MHz for this test. The results at lower frequencies are pretty poor.

6MHz gives a reasonable phase separation and I would generally recommend 12dB higher gain on the vertical axis with the lift off set horizontally

Also your notches need to be narrower than say for Aluminium as the conductivity is so low the contribution from the notch width is much greater than you would get for higher conductivity material.

Hope that makes sense.

Regards

John Hansen www.ethernde.com

    
 
 Reply 
 
langtuteng
Armenia, Joined Nov 2014, 172

langtuteng

Armenia,
Joined Nov 2014
172
14:54 Nov-28-2014
Re: experience of ET
In Reply to Frank Lund at 12:01 Nov-28-2014 .

thanks, lund. when i adjusted the equipment, i rot the degree to make the lift-off locus be horizontal ( 9:00 o'clock). i set the x scale is 0.2v/div and equal to the y scale. i guess maybe the frequence i used is too low.

    
 
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Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 219

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
219
15:16 Nov-28-2014
Re: experience of ET
In Reply to langtuteng at 14:54 Nov-28-2014 .

Now that you have the lift-off horizontal, try increasing the Y sensitivity (say 0.05V/div).

Cheers,
Frank

    
 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 411

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
411
02:17 Dec-03-2014
Re: experience of ET
In Reply to Frank Lund at 15:16 Nov-28-2014 .

Frank,
the change in the 1: 1 ratio between the X component and Y alters the natural shape of the signals. In my basic was presented as deprecated practice.
In this case that is the relationship between the phases, if have to be estimated depths? Plus, starting from phases compressed due to low frequency.
In the end, it does not seem so bad to stay at high frequencies indicated by John.
greetings
mario

    
 
 Reply 
 
John Hansen
Director, - Eddy Current Technology
ETher NDE Ltd, United Kingdom, Joined Oct 1999, 73

John Hansen

Director, - Eddy Current Technology
ETher NDE Ltd,
United Kingdom,
Joined Oct 1999
73
19:06 Dec-03-2014
Re: experience of ET
In Reply to Mario Talarico at 02:17 Dec-03-2014 .

zoom image
Here is a picture of a screen showing a 0.2mm notch and lift off on Titanium at 6Mhz with a standard single element shielded absolute probe. I have 17dB extra gain on the Y axis to make the defect sit up more. The red plot is a timebase plot and you can clearly see there is about 18dB signal to noise.

All the best

John
    
 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 411

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
411
01:22 Dec-07-2014
Re: experience of ET
In Reply to John Hansen at 19:06 Dec-03-2014 .

Hansen,
thanks for your demo: what there is more beautiful than a signal ET !
I note with pleasure a good phase ratio between signal and Lift-off, as well as between signal and noise.
There's more than one way to get something.
greetings
mario

    
 
 Reply 
 
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
14:55 Dec-13-2014
Re: experience of ET
In Reply to langtuteng at 14:54 Nov-28-2014 .

Dear Langtuteng,

If you using low frequency your depth of penetration of eddys will be higher, if you are testing with high frequencies in MHZ your depth will be very less.
The latest equipment's like GE mentor & Olympus Omni scan MX/ECA ,Phasec 600 have the phase angle adjustment option.
Use the same material cal block and adjust the instrument setting to get liftoff indication in horizontal plane and crack signal in 90 degrees to liftoff signal.
The X-Y position of the null point shall be placed on one corner of the screen. The phase or rotation
control shall be adjusted so that when the probe is lifted off the metal surface, the display point travels at 90 deg to the discontinuity depth.

    
 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 219

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
219
16:41 Dec-13-2014
Re: experience of ET
In Reply to JAGAN at 14:55 Dec-13-2014 .

Jagan,

Is that a differential rotation that can be applied separately to the lift-off and defect signals or is it a common rotation that rotates both signals (retaining the angle between them)?

Cheers,
Frank

    
 
 Reply 
 
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
05:31 Dec-14-2014
Re: experience of ET
In Reply to Frank Lund at 16:41 Dec-13-2014 .

Langtuteng,

its common and u need to adjust it for setting lift off signal during calibration.

    
 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 219

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
219
21:39 Dec-14-2014
Re: experience of ET
In Reply to JAGAN at 05:31 Dec-14-2014 .

Jagan,

What about increasing the angle between lift-off signal and defect signal?

That can be very much less than 90 degrees, particularly when inspecting non-ferritic materials. It is the problem that Langtuteng has described.

Cheers,
Frank

    
 
 Reply 
 
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
05:01 Dec-15-2014
Re: experience of ET
In Reply to Frank Lund at 21:39 Dec-14-2014 .

frank,

yes defect signal should be below 90 deg to the lift off signal.
refer ASME sec-V Article-8 mandatory appendix vi & vii for better understanding.

    
 
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