Corrosion question

[Dream to fly]

I have been reading some threads about corrosion and I have a question that may just be a little stupid to some.  Sea planes land in water of all salinity values and there are some as old or older than the mooneys in this forum.  How do they get maintained to stay airworthy and why aren't Mooney aircraft protected the same way? or are they?  I would think that with todays technology we could use chemicals or anodes like on boats to keep it to a minimum. 

[carusoam]

I would suspect that any metals in contact with seawater are at a constant battle with corrosion.  Corrosion is one part and electric system induced electrolysis is the other part.

Protection from electrolysis is usually done by having a piece of sacrificial metal on the important pieces of metal.  Boats usually use zinc to protect the brass and aluminum propellers and drive shafts.

Seaplanes can't have an easy life. They are often the same plane on a set of floats.

The seaplanes with an easy life don't go in salt water.  When they do, they often touch down in a lake before getting put away.

Boss, da plane...  

What gives the idea that seaplanes are better protected than Mooneys?

I like the question.  Let's find an answer if it exists...

Best regards,

-a-

[Yetti]

I believe the Cessna's with the floats package from the factory had additional corrosion protection

[Piloto]

Like on boats and ships, keep painting it. Sea planes have plenty of access panels to easily check for corrosion.

José

Edited April 13, 2017 by Piloto

[carusoam]

The floats continuously have leaks. Saltwater between layers of aluminum must be a challenge. Must be like continuously resealing a fuel tank... checking each rivet.

Best regards,

-a-

[aviatoreb]

I wish my airplane was all titanium.

[Dream to fly]

2 minutes ago, carusoam said:

I would suspect that any metals in contact with seawater are at a constant battle with corrosion.  Corrosion is one part and electric system induced electrolysis is the other part.

Protection from electrolysis is usually done by having a piece of sacrificial metal on the important pieces of metal.  Boats usually use zinc to protect the brass and aluminum propellers and drive shafts.

Seaplanes can't have an easy life. They are often the same plane on a set of floats.

The seaplanes with an easy life don't go in salt water.  When they do, they often touch down in a lake before getting put away.

Boss, da plane...  

What gives the idea that seaplanes are better protected than Mooneys?

I like the question.  Let's find an answer if it exists...

Best regards,

-a-

The plane I bought was originally flown in the central US.  A plane today on this forum spent a long time in the driest of climates.  Both have corrosion to different degrees in different areas both were "properly" protected when built.  If true and the manufacturing process is the same then why are we finding issues?  what is changing?  Is it the electronics we are installing?

[Dream to fly]

Wing spar corrosion baffles me when the plane is in a dessert climate most of its life.  I'd expect heat damage issues.  My plane spent most of its life in Tennessee and Missouri.  the last five years it spent in Florida in McCalpin, 60 miles from and water and hangered with climate control.   Could the original corrosion be from treatment? 

[carusoam]

It's a continuous struggle.  We are finding issues because we look every year.

Some areas are more prone to attack.  The wheel wells get splashed with all kinds of junk.

Some areas don't make much sense.  Like an internal side of a fuel tank.

corrosion does not need water to occur.  It is aided by the presence of moisture.  The presence of salts can also help the corrosion.  Warm weather also helps increase the rate of corrosion.

Some metals are selected for their machinability and strength.  Unfortunately their ability to resist corrosion are not that good.

in the material selection guide that Mooney had in 1965, it probably didn't have a chart wide enough to include a rate of corrosion column fifty years out...  

Even cars were not getting undercoating until the 70s.

Some of the Best protection comes from the surface layers of the Alclad aluminum sheets.  After several decades the thin protective layer may be missing in some locations...drilled through, scratched off, abraided, etc...

One thing to watch for is the rate of corrosion increases after it starts.

The chemistry of corrosion is probably similar to battery chemistry.  We have a really good chemist on board MS.  He may have some insight to this....

PP thoughts only not a mechanic.

Best regards,

-a-

Edited April 13, 2017 by carusoam

[Yetti]

If you read on intergranular corrosion it seems to be bad manufacturing process and then stressing it.  Say lots of hard landings.   The J on the other page had a bad paint prep from the factory.  Or maybe landing/taxi on a salted runway or taxiway

[carusoam]

Wear and tear in the back seats is a place to find some intergranular corrosion.

The combination of people going in and out over the years can remove any protective layers by simple wear. Sand and dirt between the carpet and aluminum is pretty strong.  Any beverages that get consumed can be a hazard to metals.

there is a spar cap right under the kid's feet...covered by an old rug.

Intergranular is a deep corrosion that runs along the granules that make up the metal. Surface corrosion can be cleaned off.  Intergranular needs to be rooted out.

Annual Inspection looking for corrosion is a good practice.  If you find it. Take care of it. Don't wait another year to do something about it.

It doesn't happen all the time.  It usually does give warnings before it gets bad.  Keep both eyes open as you go.

Best regards,

-a-

[Dream to fly]

Just now, carusoam said:

Wear and tear in the back seats is a place to find some intergranular corrosion.

The combination of people going in and out over the years can remove any protective layers by simple wear. Sand and dirt between the carpet and aluminum is pretty strong.  Any beverages that get consumed can be a hazard to metals.

there is a spar cap right under the kid's feet...covered by an old rug.

Intergranular is a deep corrosion that runs along the granules that make up the metal. Surface corrosion can be cleaned off.  Intergranular needs to be rooted out.

Annual Inspection looking for corrosion is a good practice.  If you find it. Take care of it. Don't wait another year to do something about it.

It doesn't happen all the time.  It usually does give warnings before it gets bad.  Keep both eyes open as you go.

Best regards,

-a-

I use a process to protect automotive aluminum called bright dipping.  I wonder if this can be done to our planes.  Forgetting for a minute that the FAA might have a cow or worse.  Also would using a media blaster to remove corrosion be an acceptable method to remove it especially in tight spaces?  Walnut shell is used on the new aluminum body fords to reduce warping and pitting that actually causes corrosion to start. 

[carusoam]

We have a few sources of maintenance procedures available...

The maintenance manual has all the approved methods.  Our mechanics are trained at their arts and sciences...

Most shops have bead blasters in them... they use...?

All of this is way outside my PP experience.

In other areas, not aviation, I have used glass Beads, blasting aluminum.  It shortens the part's life time pretty well...

Do you have a link for the bright dipping material?

Somebody with an A&P background might give some insight.

Best regards,

-a-

Edited April 13, 2017 by carusoam

[Dream to fly]

9 minutes ago, carusoam said:

We have a few sources of maintenance procedures available...

The maintenance manual has all the approved methods.  Our mechanics are trained at their arts and sciences...

Most shops have bead blasters in them... they use...?

All of this is way outside my PP experience.

In other areas, not aviation, I have used glass Beads, blasting aluminum.  It shortens the part's life time pretty well...

Do you have a link for the brigh dipping material?

Somebody with an A&P background might give some insight.

Best regards,

-a-

http://www.delsplating.com/

[carusoam]

One of the challenges we have run into is the simple polymer coating of control yokes.

I believe the FAA had put a stop for a while to plastic coating of metal parts. (Powder coating) The combination of the heat process that could damage the part and the polymer thickness that could hide a crack made it a challenge.

So even a really well known coating idea can run into some challenges until it can be well proven.

The experimental plane area is full of some good ideas that don't have this particular FAA challenge.

Best regards,

-a-

[Yetti]

Much like avionics the FAA keeps things old and not changing much.  Not as much was known about aluminum and how it would do over the 40 year lifespan.  Coatings have improved over the last 40 years.  The FAA has not moved forward at the same pace.

[rbridges]

7 hours ago, carusoam said:

One of the challenges we have run into is the simple polymer coating of control yokes.

I believe the FAA had put a stop for a while to plastic coating of metal parts. (Powder coating) The combination of the heat process that could damage the part and the polymer thickness that could hide a crack made it a challenge.

So even a really well known coating idea can run into some challenges until it can be well proven.

The experimental plane area is full of some good ideas that don't have this particular FAA challenge.

Best regards,

-a-

is powder coating not allowed on the yokes?  I didn't realize that.

[Browncbr1]

I would think sacrificial anodes would help

[mooniac15u]

10 hours ago, Yetti said:

If you read on intergranular corrosion it seems to be bad manufacturing process and then stressing it.  Say lots of hard landings.   The J on the other page had a bad paint prep from the factory.  Or maybe landing/taxi on a salted runway or taxiway

The FAA prohibits the use of chloride salts for deicing aircraft operational areas. https://www.faa.gov/documentLibrary/media/Advisory_Circular/150-5200-30D.pdf

4.6.2 Landside Chemicals.

The most effective landside chemicals used for deicing/anti-icing in terms of both cost and freezing point depression are from the chloride family, e.g., sodium chloride (rock salt), calcium chloride, and lithium chloride. However, these chemicals are known to be corrosive to aircraft and therefore are prohibited for use on aircraft operational areas.

 

 

 

[mooniac15u]

10 hours ago, carusoam said:

It's a continuous struggle.  We are finding issues because we look every year.

Some areas are more prone to attack.  The wheel wells get splashed with all kinds of junk.

Some areas don't make much sense.  Like an internal side of a fuel tank.

corrosion does not need water to occur.  It is aided by the presence of moisture.  The presence of salts can also help the corrosion.  Warm weather also helps increase the rate of corrosion.

Some metals are selected for their machinability and strength.  Unfortunately their ability to resist corrosion are not that good.

in the material selection guide that Mooney had in 1965, it probably didn't have a chart wide enough to include a rate of corrosion column fifty years out...  

Even cars were not getting undercoating until the 70s.

Some of the Best protection comes from the surface layers of the Alclad aluminum sheets.  After several decades the thin protective layer may be missing in some locations...drilled through, scratched off, abraided, etc...

One thing to watch for is the rate of corrosion increases after it starts.

The chemistry of corrosion is probably similar to battery chemistry.  We have a really good chemist on board MS.  He may have some insight to this....

PP thoughts only not a mechanic.

Best regards,

-a-

Battery chemistry and corrosion are both electrochemical oxidation processes.  In batteries you have both oxidation and reduction occurring inside the battery with the resulting electron flow being available to power things.  In rechargeable batteries the process is reversible.  For metallic corrosion there are a lot of different processes that can be involved.  We tend to think of water as being the culprit but it is usually just a medium for electolytes.  Oxygen is the key to oxidation but it is much harder to eliminate oxygen than water.

Aluminum and salt water is a special case.  Aluminum metal tends to oxidize at the surface and form a thin layer of aluminum oxide that prevents further oxidation.  The chloride ions in salt water can break down the oxide layer and lead to additional oxidation of the aluminum.

Galvanic corrosion is what we tend to call bimetallic corrosion.  With two different metals in contact you can create an anode/cathode situation.  Add a little water with electrolyte and you get a little battery.  This whole process can be influenced if you add an electric current (think electroplating).  Does grounding electrical devices through the airframe induce electrolytic corrosion?  I don't really know but it seems possible.

[Shadrach]

11 hours ago, Dream to fly said:

The plane I bought was originally flown in the central US.  A plane today on this forum spent a long time in the driest of climates.  Both have corrosion to different degrees in different areas both were "properly" protected when built.  If true and the manufacturing process is the same then why are we finding issues?  what is changing?  Is it the electronics we are installing?

Given a screw driver and enough time, I bet I could find corrosion of some sort on almost any airframe beyond 10 years old.  The best thing to do is keep the plane clean, hangared, and free of chemicals that might facilitate corrosion.  Research the properties and look at the MSDS of a product before you use it as a cleaner or degreaser.  If you have kids, no soda in the cockpit...softdrinks are not good to metals of any kind.  

The aircraft you refer to in the other thread may or may not have corrosion in the area photographed.  Folks are understandably wary of corrosion in airframes.  Inspections are the key.  Caught early, many problems can be mitigated with little cost.   Many aircraft go long periods of time without a super thorough airframe inspection other's get one yearly.  What you don't know may or may not kill you, but eventually it's going to get your wallet.  

We don't tear the interior out every year, but that is because we stripped it down to its skin on the inside in 2011. At that time we painted the inner skins with zinc chromate. We also stripped and painted the cage with zinc chromate epoxy.  Every time we have removed the interior since it looks just as it did the day after all this preventative mx was performed. Unless our operating environment changes, I am confident this airframe will last long enough for my yet to be born grandkids to fly it (my son is 15 months old).

[carusoam]

3 hours ago, rbridges said:

is powder coating not allowed on the yokes?  I didn't realize that.

For a period of time, it was not an approved process...

Keep in mind my 65C yokes had a plastic coating from the factory that would chip and fall off revealing corrosion underneath...

Sweat is probably one of the more corrosive liquids that will commonly contact the planes parts.

Some plastic coatings are not oxygen barriers at all. Some aren't moisture barriers either....

I believe the resistance to using these types of coatings was they do a nice job of hiding corrosion more than preventing corrosion...

PP ideas only. Not a mechanic.

Best regards,

-a-

[MBDiagMan]

For those fortunate enough to keep their plane in a dry climate, all this is almost a non issue.  My plane has always been hangared.  For a few years in Dodge City, Kansas, but almost all of thatime has been in ahangar in Kerrville where it was built.  As a result an old gentleman who spent years working at Mooney did the prebuy and told me that plane was amazingly corrosion free.  It is difficult to beat keeping  it dry.

[Yetti]

Most aluminun on sail boats is anodized. Planes are not so lucky

Powder coating is not plastic coating. It is a different method of applying epoxy coating. Like spray painting without the acetone and spray.

[carusoam]

Might be a phraseology thing...

Are we talking about the process used or the polymer that is being used...?

Epoxy is a plastic.  Having something epoxy coated leaves it covered in plastic.

Painting is typically using a solvent based polymer coating.  Requiring the solvent to dry out.  Same thing for dip coating...  our 60’s yokes probably got dip coated...

Some epoxy coatings use a chemical reaction to polymerize the liquid chemicals that make the finished epoxy coating. Some Epoxy floor coverings use this technique.

Powder coating uses a dry powder form and electrostatic spraying gun.   The fine dust is attracted to an electrically grounded part.  Then off to the oven to finish the process...

The advantage of the powder coating process is it can use a very tough, high molecular weight, polymer and get it uniformly in place on the part.

Polymer coatings and their processes have really developed a lot over time.

All coatings struggle when there is drilling and bending involved.

Best regards,

-a-