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- since 1996 -
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Technical Discussions
Creed
NDT Inspector,
n.n., Joined Jul 2009, 31

Creed

NDT Inspector,
n.n.,
Joined Jul 2009
31
23:23 Jul-27-2017
PAUT/TOFD testing through coating

Good day everyone.
I have a old question regarding to PAUT/TOFD technical. Can we conduct PAUT/TOFD through coating only for record findings any defects exist on the welds of the in serviced vessels?and How about to comply the welds with PAUT/TOFD through coating?
is there anyone has experience in this concerns, I am very appreciate for any advices.
Thanks

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 755

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
755
17:50 Jul-28-2017
Re: PAUT/TOFD testing through coating
In Reply to Creed at 23:23 Jul-27-2017 (Opening).

The same principles of transfer correction apply. so check the signal loss in pitch catch. I would not feel comfortable using TOFD on coatings because of high gain levels

 
 Reply 
 
George
George
04:21 Jul-29-2017
Re: PAUT/TOFD testing through coating
In Reply to Creed at 23:23 Jul-27-2017 (Opening).

Even on a thin layer of MPI white contrast paint, it is very difficult to get lateral wave in tofd. You need to remove paint. It's my personal experience.

 
 Reply 
 
seyed meeran
NDT Inspector,
heavy engineering and shipbuilding kuwait, India, Joined Feb 2017, 23

seyed meeran

NDT Inspector,
heavy engineering and shipbuilding kuwait,
India,
Joined Feb 2017
23
14:34 Aug-01-2017
Re: PAUT/TOFD testing through coating
In Reply to George at 04:21 Jul-29-2017 .

its not necessary to remove overall paint . i also working in the advanced ut field. my suggestion is to use more couplant to get high resolution peak i also used the glycerine sometimes that is best for getting higher resolution.

 
 Reply 
 
bob
bob
17:45 Aug-01-2017
Re: PAUT/TOFD testing through coating
In Reply to seyed meeran at 14:34 Aug-01-2017 .

Yes more couplant should work that old trick of putting twice as much glycerine between probe and wedge, then pumping the water 3 times faster enabling four times as much water between wedge and scan surface never fails.

 
 Reply 
 
massimo carminati
Consultant, AUT specialist
IMG Ultrasuoni Srl, Italy, Joined Apr 2007, 691

massimo carminati

Consultant, AUT specialist
IMG Ultrasuoni Srl,
Italy,
Joined Apr 2007
691
10:21 Aug-03-2017
Re: PAUT/TOFD testing through coating
In Reply to Creed at 23:23 Jul-27-2017 (Opening).

First thing, make sure you try on the weld itself in the exact testing conditions.
Second, make sure that the painted surface is regular and, if it is the case, smoothen the painting bubbles with sand paper
Third, try with some water the real wetting capability; if water does not wet, add a wetting agent in order to increase superficial tension.
Then painting may reduce LW signal, but may also increase it, it may give a "matching layer" effect.
What you will always experiment, is a degradation of the LW signal in terms of cycles number increase, therefore the LW dead zone will increase compared to unpainted.
Good luck!

 
 Reply 
 
seyed meeran
NDT Inspector,
heavy engineering and shipbuilding kuwait, India, Joined Feb 2017, 23

seyed meeran

NDT Inspector,
heavy engineering and shipbuilding kuwait,
India,
Joined Feb 2017
23
19:47 Aug-03-2017
Re: PAUT/TOFD testing through coating
In Reply to bob at 17:45 Aug-01-2017 .

I accept that water is cheap and best but some times precission material is used in application ...today i have used rust oil but i not know the oil name ..today i used i getting too much of peak with that....i will told oil name later.....

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
22:33 Aug-03-2017
Re: PAUT/TOFD testing through coating
In Reply to massimo carminati at 10:21 Aug-03-2017 .

Massimo, your point about the lateral wave is, I think, critical. My experience with a painted surface was an annoying ringing effect. The pulse leaving the wedge enters the paint and then must refract into the metal (steel?) but at the paint/metal interface there is also results a reflection that then reflects off the wedge so we get multiple entries of the pulse. This has the appearance of multiple lateral waves (greatly increasing the dead zone of the lateral wave).
I saw similar problems on uncoated surfaces when technicians were setting the carbide wear pins on a TOFD probe to be proud of the wedge surface. The increased water-gap had the same effect as paint.
In pulse-echo tests the effect is generally less a problem but can result in an extended pulse ring-time.

 
 Reply 
 

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