Opinions on some surface corrosion...

[Gregg Brightwell]

Ok guys, I am trying to remember back from A&P School about corrosion....I cannot recall which type of corrosion this is... (pic below).


Again, I bought my wing kit 2nd hand in April 2010. Little had been done, so inspection of all parts was easy. I knew that it only came with 3 skins. (2 bottom outboard, and one top outboard.) All 3 skins were stored leaning against a wall in a metal shop on a concrete floor. Bottom line, all 3 outboard skins have some of the white powdery corrosion shown above. I HAVE looked at my AC43-13, and can't find what I am looking for there. I HAVE also done a search for corrosion here, and found one issue similar. I have taken a scotchbrite wheel in a dotco, and can fairly easily clean it off. Under the whitish powder, it is pitted a bit. (Again though, I can clean it ALL off with the dotco) I think I can clean it up, alodine it, and then prime. If this is a bad idea, tell me, just be nice about it. Lastly, out of curiousity, how much 'coverage' of this corrosion would be grounds for rejection of a skin?

[chaskuss]

Gregg,
General rule is that you should remove all pitting and blend [bevel] the area where you had to remove the metal. If you have to remove more than 10% of the material thickness [ie .0025" on a .025" skin] the part should be scrapped, due to weakening of the material. Be sure to prime any area where you break through the Alclad layer [about .0005" thick]
Charlie
PS The 90% rule is not absolute. If you have to go further, contact Vans to see if it will be a problem. Their decision will depend on the area and the part.

[Sparky]

I'm no expert, but since you asked, I believe that type of corrosion is called filiform corrosion. I could be wrong.

[Rick_A]

I believe this is uniform surface corrosion that is progressing towards pitting

I would agree that it does look something like filiform, but filiform is normally found under a paint when the metal was not properly treated prior to painting.