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Technical Discussions
carlo
NDT Inspector
aerospace, Canada, Joined Jan 2010, 3

carlo

NDT Inspector
aerospace,
Canada,
Joined Jan 2010
3
06:49 Jan-11-2010
Penetrant Inspection

We prepare parts by etching(alkali etch) prior to penetrant inspection. We are currently experiencing indications coming out from our 2000 series aluminum parts. After doing the approved written procedure it bleeds back but when we look at it under white light and 10x magnification, I can hardly see any unacceptable discontinuity base on the specifications. Is this acceptable or not?
The indications are all over the surface of the parts under black light. Is there any suggestions or inputs with the significance and how to make proper evaluation? Is there any one who experienced the same thing as what we are experiencing?
Thank you.
Carlo

 
 Reply 
 
anjafo79
NDT Inspector
Norway, Joined Aug 2009, 204

anjafo79

NDT Inspector
Norway,
Joined Aug 2009
204
09:00 Jan-12-2010
Re: Penetrant Inspection
In Reply to carlo at 06:49 Jan-11-2010 (Opening).

sounds like heat induced stress cracks on the surface to me but thats a guess.

not sure if the etching would do anything to your material.

bleed out is telling you something is there, you have to distinguish what it is and check the accept criteria. maybe send one in for micro-analysis or post a picture here.

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 893

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
893
16:07 Jan-12-2010
Re: Penetrant Inspection
In Reply to anjafo79 at 09:00 Jan-12-2010 .

Carlo,

If you have access to one, why don't you try Eddy Current with a 500kHz absolute pencil probe. You maybe able to get a depth from those indications as well.

 
 Reply 
 
carlo
NDT Inspector
aerospace, Canada, Joined Jan 2010, 3

carlo

NDT Inspector
aerospace,
Canada,
Joined Jan 2010
3
20:14 Jan-12-2010
Re: Penetrant Inspection
In Reply to anjafo79 at 09:00 Jan-12-2010 .

We send out two sections of the part for metallurgical analysis. They examine the part by Stereomicroscopic examination, Fluorescent penetrant exam, Scanning Electron microscopy and Metallographic examination and found out that these "stars at night" type indications that we saw confirmed the presence of superficial surface indications and these are shallow etch pits. What is the effect of these indications on the part? The maximun depth was measured at 20 microns. The microstructure consisted of Aluminum alpha grains w/ a dispersion of non-metallic incluson(AlCu-FeMn) Thank you to your responses. I appreciate it really.

 
 Reply 
 
David Forsyth
R & D
TRI/Austin, USA, Joined Nov 2001, 41

David Forsyth

R & D
TRI/Austin,
USA,
Joined Nov 2001
41
22:49 Jan-14-2010
Re: Penetrant Inspection
In Reply to carlo at 20:14 Jan-12-2010 .

Effect of etch pits depends on how part is used. If it is used in a manner that includes mechanical loads, fatigue cracks will happily nucleate at these pits.

Post-etch alodyne/anodize or some sort of coating should be used to get corrosion resistance if that is a concern.

So if you are making pots and pans with no warranty, who cares. If you are making aerospace structures, then you have work to do!

 
 Reply 
 
Carlo
NDT Inspector
aerospace, Canada, Joined Jan 2010, 3

Carlo

NDT Inspector
aerospace,
Canada,
Joined Jan 2010
3
08:02 Jan-16-2010
Re: Penetrant Inspection
In Reply to David Forsyth at 22:49 Jan-14-2010 .

If not for metallurgical analysis we will not find out that it is etch pits. How can you evaluate this if you are inspecting it. They bleed back so tiny but all over the surface under black light but under magnifiaction 10x, you cannot distinguish these as pits or whatever, no metallurgical analysis yet, what would be your decision? who should be responsible in distinguishing these? Is it the NDT Inspector? I am just new in this career as level 2 and want to know who should be responsible. Me, I put them on-hold because i am not sure what it is. Is it the right thing to do? Any advise is highly appreciated. Thank you.
(We are anodizing these parts in-house)

 
 Reply 
 

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