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midsidenode (Mining) (OP)
3 Jan 08 14:46
We have an item made from aluminum (6061-T6) that needs a dye penetrant inspection. The problem is that the person that prepared the part for inspection stripped all the coatings off using media blasting. As a result, it is not possible to perform the inspection properly because of all the impacted residue. Can anyone tell me how we can now clean the surfaces in preparation for penetrant?

thanks
CoryPad (Materials)
3 Jan 08 14:50
Sanding, ultrasonic cleaning, both

Regards,

Cory

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Helpful Member!  metengr (Materials)
3 Jan 08 15:24
Are you sure this is impacted residue and not residual coating material?
stanweld (Materials)
3 Jan 08 15:35
You may be able to use acid etching methods.

Helicopterjunky (Materials)
3 Jan 08 16:16
This seems like an easy question but could be quite complicated depending on what you have and what blast media
was used and at what pressures.  If you truly have impacted media such as glass or steel you will need to remove around .0015/.002" of material from the surface of the part to perform viable liquid penetrant inspection.  This could be done mechanically or chemically or a combination of both. Please tell some more about the part and details of the blasting..media...pressure.  Also about the part, machinement, weldment, casting.....Also specify if the part is tight tolerance, as removing material will invariably change size.
sreid (Electrical)
3 Jan 08 18:29
Possibly a wire brush.
Kwan (Aerospace)
4 Jan 08 23:24
stanweld has the right answer.  you want to etch the surface after any machining or media blasting.  work to the surface can smear the aluminum into the crack and lead to non-indication from dye pen.

you might consided eddy current surface scan which may be more reliable to dye pen.  Think of dye pen as a visible indicaton of a crack (it just enhances the visible inspection).  Look into eddy current inspection methods.
marclar (Mechanical)
24 Jan 08 13:30
i have the same problem with a piece of support equipment.  the item in question in a aluminum weldment that is used for a lifting fixture.  it was mistakenly blasted with melamine 12/20 @ 40 psi before ndi.  i assume that under these conditions the media has impacted any cracks that may be present.

if the fixture is proofloaded, will any cracks open back up and allow a valid dye penetrant test?
metengr (Materials)
24 Jan 08 13:38
marclar;
Unfortunately, the answer is possible, and not a definitive yes. I would not rely on a proof test to validate a liquid penetrant examination of a welded component.

If the NDT was specified or required prior to proof loading and after, you need to prepare the surface for liquid penetrant testing by using one of the methods mentioned above to assure proper technique was followed both before and after. Do you have a procedure for conducting liquid penetrant testing? If not, you are at great risk of missing surface flaws.
marclar (Mechanical)
24 Jan 08 14:53
metengr, thanks for the response.  Yes, we have liquid penetrant test procedures and certified technicians.  This specific item does not require regular proof loading, only liquid penetrant testing.  It will pass the required inspection with proof load testing in lieu of NDI or visual.  I was just curious whether a single proof loading would reveal any cracks that were hidden in the blasting process.  I agree with you in that it may or may not.  Technically, the item can be re-deployed upon successfully proof loading until the next 52 week inspection.

The main problem is that since this item doesn't require regular proof loading, we have no fixture to perform the proof load.  Therefore, we either get creative, pay for a fixture to be fabricated, or pay for an acid dip.
Kwan (Aerospace)
24 Jan 08 22:15
If it's a local inspection you can use a brush acid etch.  But again, consider using eddy current to really be sure you are crack free.

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