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Technical Discussions
Jørgen Lenler
Teacher
FORCE Technology, Denmark, Joined Nov 2010, 3

Jørgen Lenler

Teacher
FORCE Technology,
Denmark,
Joined Nov 2010
3
08:13 Nov-18-2010
Weld testing on paint

I have been asked the question why an indication in a weld found wirth an angle probe on paint has a greater amplitude than the same indication after removal of the paint.
I would think it would be the other way round. It is often 6 to 8 dB difference

Jørgen Lenler

 
 Reply 
 
Nick Welland
Other, Quality and NDT
Aben Technical Services, Australia, Joined Oct 1999, 42

Nick Welland

Other, Quality and NDT
Aben Technical Services,
Australia,
Joined Oct 1999
42
12:17 Nov-18-2010
Re: Weld testing on paint
In Reply to Jørgen Lenler at 08:13 Nov-18-2010 (Opening).

Jørgen,
I have noticed this effect on some occasions. It seems that a very well bonded paint coating improves coupling, but I have not studied the effect with respect to paint thickness, sound velocity in the coating, etc.
Best regards,
Nick

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 897

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
897
16:42 Nov-18-2010
Re: Weld testing on paint
In Reply to Nick Welland at 12:17 Nov-18-2010 .

We have found the same and we think it has to do with the surface finish of the paint.

 
 Reply 
 
Neil Burleigh
Sales
Krautkramer Australia Pty Ltd, Australia, Joined Dec 2002, 159

Neil Burleigh

Sales
Krautkramer Australia Pty Ltd,
Australia,
Joined Dec 2002
159
00:51 Nov-19-2010
Re: Weld testing on paint
In Reply to Jørgen Lenler at 08:13 Nov-18-2010 (Opening).

Hello Gentlemen,
In previous instances we have determined that the acoustic impedance of the paint is similar to the perspex or is between the perspex and the steel and this translates to a transfer gain. Plus yes the surface roughness of the steel plate versus the surface finish of the paint will also bring about a transfer gain.
This same phenomena can also be seen when comparing signal responses from SDH in plated and unplated calibration blocks. The thicker the nickel plated the more pronounced the difference.

Regards
Neil Burleigh

 
 Reply 
 
massimo carminati
massimo carminati
20:21 Nov-19-2010
Re: Weld testing on paint
In Reply to Jørgen Lenler at 08:13 Nov-18-2010 (Opening).

The painting acts like an acoustic matching layer, but its effects is related to coating thickness too.

 
 Reply 
 
Manfred R Richter
Manfred R Richter
00:12 Nov-21-2010
Re: Weld testing on paint
In Reply to Jørgen Lenler at 08:13 Nov-18-2010 (Opening).

Jorgen,
by my experience normally you have better results, but it depends of the what type of paint, how thick and adherence it has.
Best Regards,
Manfred

 
 Reply 
 
aridduan
aridduan
17:27 Feb-15-2011
Re: Weld testing on paint
In Reply to Manfred R Richter at 00:12 Nov-21-2010 .

How about testing the weld using PA without remove paint?Is it same thing will be happen and do we allow to do it with PA without remove paint? Any codes or standard said so or other wise for my reference.

 
 Reply 
 
sadek997
NDT Inspector,
AR, Poland, Joined Feb 2011, 12

sadek997

NDT Inspector,
AR,
Poland,
Joined Feb 2011
12
22:28 Feb-15-2011
Re: Weld testing on paint
In Reply to aridduan at 17:27 Feb-15-2011 .

Every UT standard (differing depending on the part of the world) requires to ensure a constant coupling with the surface. While having only one transducer it is easier to obtain, but You always have to remember that depending on the surface conditions the sound pressure of the beam will be deformated and will differ from the producers assumptions. This beam deformation has to be taken into account during the examination (model reflectors will act differently in such conditions i.e. the maximum amplitude of the wave doesn’t really have to be in the middle part of the beam like it is usually).

The same phenomenon takes place while using PA. The only difference is that You have a greater amount of transducers what causes even more deformation. For instance if you have 16 transducers and 11 of them are attenuated by 3 dB and in the same moment 5 are amplified by 2 dB the result is such that You don’t have any idea how the wave is distributed in the material (angle can change significantly). That’s why commencing PA examination through paint is a sick idea but one can try it on his own skin and find out that miracles in UT happen 

 
 Reply 
 
Lalit Mohan Kothari
Consultant, -
On ..IOCL and BARC(Bhabha Atomic Research Centre).etc, India, Joined Jan 2003, 128

Lalit Mohan Kothari

Consultant, -
On ..IOCL and BARC(Bhabha Atomic Research Centre).etc,
India,
Joined Jan 2003
128
17:36 Feb-16-2011
Re: Weld testing on paint
In Reply to Jørgen Lenler at 08:13 Nov-18-2010 (Opening).

Jorgen,
Cyguns co. can help you better from probe side .
from paint side it is not constant and it is more and more noticed if paint has thick layer.You also can refer ......from my old reply about corrosion....

Thanks & Regard

 
 Reply 
 
aridduan
aridduan
06:32 Feb-22-2011
Re: Weld testing on paint
In Reply to Lalit Mohan Kothari at 17:36 Feb-16-2011 .

Thanks a lot gents for all your information.

 
 Reply 
 

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