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interesting info on salt water recoveries

Posted by Tony on Wed Feb 13, 2002 09:17:14 AM

from craig fullers aviation archaeology board


From Larry Webster on 9/17/98

> If you have any good photos I would like to have Wendy (and myself) see
> them because "except for a few cases" she does not believe this. If you
> can prove this her views might change. She also maintains that there is no
> good way to stop the corrosion when brought to the surface. Another key
> point that needs to be argued. I have no experience in this so I can't
> say one way or another. One thing I heard is that if metal is in deep sea
> for a period of time the pressure impregnates the salt water deep inside
> the metal pores which is why it terminally corrodes so fast when brought
> to the surface. If true this would make deep sea recoveries different
> from shallow ones. Any how lets, save this for when we get the debate up
> and running!

Craig,

It disturbs me that Wendy does not believe my (and others) statements on corrosion. The facts prove otherwise. I have been actively studying corrosion in old airframes for 35 years; plus the work I did at Heidelberg regarding corrosion in machinery.

Her background in ship archeology certainly would lead to her beliefs; the malleable irons used in old ships do indeed get impregnated with saline ions, and this should occur more rapidly and intensely as depth increases. Airplanes do not have malleable irons. Aircraft are made of heat treatable high tensile steels and heat treatable hardenable aluminum alloys. I have only studied shallow water aircraft wreckage (less than 150 feet depth) but my work shows that hard anodized (USN) aluminum has very minimal saline impingement, except in areas where defects or stress have caused breakthrough in the surface. Alclad (USAAF) surfaces corrode heavily because of the loss of the Al-0 surface; but again it does not seem to have serious impingement. We checked this out at Quonset and could not effectively measure salt impingement on anodized surfaces because there was almost none there.

The QAM has photos (or had them, we have negatives) for each of the reports we have sent the Navy. The photos do not show much; it is something that has to be seen in person; Wendy is welcome to visit QAM to see this work.

We found, as I had predicted, that corrosion would stop after a few weeks of fresh water baths and an immediate application of ACF-50 or Boeshield T-9. These are common interior treatments for airframes and have saved many an airframe for reuse after an immersion. The wings and fuselage of the F6F have been on display for 4 years with this material on them and there is NO additional corrosion occurring.

Wendy is confused by the chemical reaction that occurs in malleable irons that causes the eventual complete crumbling of such an artifact. That does not happen with aluminum alloys that are used on aircraft. In fact, a thorough drying out of the airframe will stop corrosion; and ACF-50 wicks into lap joints to drive out water.

Steels must be treated with electrolysis; but most aircraft steels are very high tensile or have hardened cases that prevent much impingement. If not treated, though, they do continue to deteriorate at a slow rate. QAM removed almost all the steel from the Hellcat airframe for this separate treatment.

My own backyard has numerous samples of parts and wreckage given to me by fishermen that came from salt water wrecks. The aluminum just stops corroding once the rain has washed the salt away. I have items that have out in the weather for 30 years that have not significantly deteriorated. The steels are another matter!

I do agree that corrosion rates and deterioration vary with aircraft type, location, and how the wreckage is laid out. For example; a wreck with the engine attached to the airframe will corrode at a much lower rate than one with the engine broken free. The magnesium in the engine serves as a sacrificial anode and protects the airframe. I believe this one reason why the QAM survived so well. But every possible salt water recovery should be carefully evaluated before recovery; but non-recovery should not be because corrosion cannot be stopped. That is a false reason.

Larry Webster


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