Galvanic corrosion on aircraft floats in fresh water?

[BC12D-4-85]

We're having a "big battery" maybe Anode-like thing with floatplanes in Fairbanks. If exposed below the waterline the submerged bare aluminum metal is being eroded and a deposited layer of dry white residue remains when beached and dried after a summer's use. Lots of local chemists have gotten involved (via water quality sampling), and sacrificial zinc plate anodes have apparently not stopped the corrosive process in the fresh water. Tested pH hovers around neutral and dissolved solids are unremarkable I've been told.

The residue can be scrubbed off but what's left is darkened and slightly pitted aluminum in unpainted or treated areas.

After reading the battery and current thread it appears there's some type of galvanic corrosion or big battery event going on. The only other source of opposing charge would be the pond's bottom material or vegetation. The unanswered question is if it takes direct contact between the bottom and float, or can the water carry enough current to start the reaction?

Gary

[aktango58]

Interesting question.

Trollers often have electronic boxes that 'charge' the lines with a specific current; forgot what the 'desired' target is, but supposedly it will repel fish if you are wrong.

I recall putting a multi meter on our lines one time and it was interesting that they created electrical current like you could not believe!

In Juneau the float pond is the most corrosive place to be for float planes. The chemicals used on the runway and other surfaces to de-ice end up in the pond, (that is where all the water collects), and makes quite the aluminum eating cocktail.

Don't just test for PH, test for chemical make up. It might surprise you.

Paint and wax your floats, and keep the scum off of them is the best solution we found.

[BC12D-4-85]

^^^^Yes! The science people did run many water tests (normal limnology qualities) and found nothing beyond the range for Interior Alaskan lakes (I was informed). However, we do have runway chems, deicing chems, and seasonal water bombers scooping up that use wetting agent stuff to make it better. Coated surfaces show no impact. Others suffer. Thanks for the ops from Juneau. PS: my 1320's are painted and show no effects. 'Nuff said.

The troller gizmos are interesting. My buddy R Alan Davis in Sitka would know about this.

Gary

[skywagon8a]

Gary, Is this just on planes kept in the Fairbanks float pond or does it include other local water bodies? My mile long pond is surrounded with homes, some of which are old converted summer cottages on land which is barely above water level. As a result there is seepage from many antique septic systems into the pond. This in addition to a fair amount of motorboat traffic and even some agriculture runoff from cranberry bogs. Seaplanes will get a dirty green/black waterline of an inch or two when left in the water for a season. It doesn't like to clean off, particularly if let to dry. New floats with new paint will develop little holes in the paint down to bare metal all along the waterline in just one season. Old well cured paint will not do the same. Some floats which have been color coated over the original lacquer will form bubbles in the paint. The portion of the float which remains below the wave line isn't effected the same.

Also, we used to keep seaplanes on moorings with a chain between the anchor and buoy. Galvanized chain had a much shorter life than bare chain. It was amazing how the chain deteriorated. Not just from the links rubbing together.

I haven't seen anything resembling salt water corrosion.

[KJC]

We have a cabin on a lake in Ironton Minnesota just east of Brainerd. The area is know as the Cuyuna Iron Range and there were several active open pit mines that were operating there until the 1960s. The entire area is high in iron content. A day of four wheeling will turn all of your clothes and vehicles a nice shade of nearly unremovable rust red. Damn near impossible to wash out. We bought a new pontoon and after even a single season tied to the dock, I noticed the exact same situation you described above. Any chance it’s the iron concentration in the water reacting with aluminum?

[mvivion]

Lake Hood parking has some interesting long term effects on floats. Not sure if anyone has figured that out.

MTV

[stewartb]

I’ve never seen unpainted floats used on an airplane.

Lake Hood water quality is different than it used to be. AIA added runoff control for deicer and the State added a well to supply water to Lake Hood. Now the problem is weed growth. They have a thresher boat to cut the underwater grass. I had 4 sets of floats on Hood through the years. One was painted with Imron and three with float lacquer. No corrosion in my time. Brown staining, yes, but no corrosion.

[BC12D-4-85]

Sky...it's mainly in the FAI float pond as far as I've seen and was told by others that park elsewhere. We do get some algal growth and brown staining but this is white crusty stuff on the float bottoms and water rudders..even those with zinc plates close by. The aft step cast bracket with the hole on EDO's really gets coated.

KJC...yes we have iron deposits that leech dark iron stained into the pond, especially noticeable after the ice melts in the Spring. Local wells have that problem. But it's been that way since the early 1950's when the pond was dredged. I'v had floats since 1978 there and the last 2-3 years is when the white stuff and corrosion got going.

The chemists are baffled or at least non-committal. The area around the pond has been contaminated with PFAS due to previous airport fire fighting activity. That since stopped but the contamination remains in the flowing water table.

The corrosion scrubs off with some effort, but the surface harm remains on uncoated areas. One interesting thing is there's one docked floatplane that's near but not in contact with the bottom. He still gets the contamination but it's less than his neighbor that's beached. We believe there's some sort of fresh water electrolysis happening so some are making sure zinc anodes are installed on the floats and rudders of exposed metal (note the clip-on the "zinc fish" protection idea in the article). It's also possible the white deposits and surface corrosion are separate effects.

Gary

[MartyC]

What is the aluminum alloy used for these floats?

[RedOwlAirfield]

and keep the scum off of them is the best solution we found.

But if you do that, how will any of us pilots use them?

Joke. Just a joke people. I am both congenitally and anthropologically unable to ignore a good straight line.

I apologize. I'll shut up now and go back to lurking.

[Mr. Ed]

I worked with a guy that had a 75’ aluminum hulled yacht. He was very concerned about corrosion and had some sort of sensor installed that would detect electrical flow/potential/current (whatever it might be called, I’m a non electric stone age guy). When floating through the marina he would monitor this gizmo and make a note of the slip number if there was a spike as he passed by. After docking he would go to that slip and typically find the shore power cord with a section hanging in the water. I have no idea how an insulated electrical cord/cable can impart a current flow to water but he claimed his policing of the marina kept his hull from corroding. Might be a bunch of bunk but, is there any chance some of the folks in your float pond docking area have decorated their docks or beaching areas with electric lighting? Battery tender extension cords in contact with the water?

Does anybody in the pond have composite floats? Any issues with those showing signs of pitted surfaces. If so I would think that indicates something corrosive in the water chemistry.

Just tossing ideas out there. Remember, it’s coming from a stone age guy with no electrical experience so turn down the flame thrower.

[BC12D-4-85]

Mr. Ed thanks for the thoughts and observations. We are still Stone Age in Fairbanks regarding electricity. None available except for a portion of the nearby wheel parking ramp. We light with batteries and heat-power with portable generators! Not even that long since they paved the general aviation parking and roads. Typical Alaskan attitudes. The airport equipment operators and we owners used to oil the gravel roads with drain oil thinned with fuel to keep down the dust. Not anymore of course as the water table is just a few feet below.

Those with either painted or composite floats haven't reported corrosion below the waterline. Just exposed metal surfaces. It may have happened but I also haven't heard of any electrical potential or current sensors being employed. That's a good idea and I'll ask one of the floatplane owners who is a University Chem Professor that would likely know about that tech.

I asked about putting some aluminum pieces similar to float material in the water with and w/o zinc plates and see what happens over the summer. Hasn't happened yet. Might make for a quick school project for some interested class.

Gary

[cammt]

Perhaps multiple issues as mentioned - galvanic corrosion as well as chemical reactions
galvanic often thought of a steel & aluminum issue in salt water. Can be any two metals. A battery is a form of
seawater due to it being conductive (much more so than typical “fresh” water ) only accelerates the reaction.
chemical reactions are often more corrosive at or just above the “liquid” level. You wet the surface with the corrosive chemicals in the tank but have far more available oxygen or other gases above the waterline which often make the reaction more severe.

A full chemical analysis is needed

note: every electrical cord / line has losses. If this were not true you would not need a 10/3 for a good 100ft cord vs a 14/3 for 25ft for same current.
think about next time you use a clamp on multimeter to measure the field created by current.
A cord in the water could create a differential - local or distance would be a function of source (power available) and loss (how conductive is the surrounding water per ~lineal foot)
Mentioned boat owner probably had pretty sensitive equipment to detect as he went but - but there is plenty of precedence.
Ask the navy submarine force.
Recall the extensive efforts by the military to degauss airplanes all the way up to include B-52s on a large wooden platform.
Air currents over a parked aircraft can create a charge let alone one which just landed from a flight in the right conditions.

Back to: a good chemical analysis of multiple samples with temperatures and O2 levels

russ

[BC12D-4-85]

Thanks Russ. I had a copy of a couple of surface water quality tests (similar to this) that was done but my Mac lost all e-mails from 1/18 to 4/22 last year. The folks involved wrote that nothing exceptional was discovered that might lead to corrosion. The water table is contaminated with fire fighting PFAS. There test wells all over the airport with remediation. They had to install domestic water supplies for homeowners affected by the pollution. Maybe those compounds are the source of the corrosion? I don't know.

Gary

[gbflyer]

I always understood magnesium anodes were used in fresh water, zinc in salt water.

[BC12D-4-85]

Thanks gb for the info...I've passed on the magnesium info for freshwater to my floatplane buds. Amazon is one source of them. Learning something here every day.

Gary

[stewartb]

Do a little google search and there’s info about sacrificial anodes in clean fresh water and polluted fresh water. When polluted the anode of choice is aluminum. And that’s for aluminum boats.

[BC12D-4-85]

The aluminum anode is interesting....but I guess I'd wonder how it would give up material before many square feet of bare aluminum alloy nearby?

Here's one opinion (https://performancemetals.com/pages/...-aluminum-boat) but they show magnesium is still less "noble" - lower voltage potential - than aluminum. And another that says magnesium is preferred> https://www.boatus.com/expert-advice...al-anodes-work

I'm no expert just learning about this, and it may be that the fresh water's conductivity is a critical factor.

Gary

[MartyC]

Gary, If possible, the "white residue" should be analyzed for any oxidizing elements, it would help to identify a possible source. Was chlorine detected in the water test sample?

Is there any chance the floats in question were in seawater? If so, corrosion could have started there and would continue whenever re-wetted.

Microbial corrosion typically occurs with a biofilm coating on the surface. Since the vegetation is on the lake bottom and not on the floats, I don’t think the bottom vegetation is a contributing factor.

If the float skins are 2024 Al, then corrosion is more apt to occur since 2XXX aluminum alloys have poor corrosion resistance. The poor corrosion characteristics for 2XXX alloys are mitigated by cladding with a high purity aluminum alloy such as 1100 or 3003. As mentioned previously, an adherent painted or coated surface will protect against corrosion unless the surface is scraped, dented, etc. Aerocets are anti-corrosive as well.

KJC mentioned the mining runoff. It’s iron oxide; probably very small particulates. It stains everything, but I don’t think it’s a contributor to the corrosion since it is in a stable oxide form.

gbflyer mentioned zinc (Zn) anodes for sea water and magnesium (Mg) anodes for freshwater. From what I’ve read the reason for not using Mg in seawater is because it is much more reactive in seawater. Simply, they would corrode faster and need replacement more often. Therefore, using Zn anodes in seawater provides the necessary protection, but they are replaced less frequently.

Mr. Ed mentioned stray currents at a marina dock. I've attached an illustration explaining what happens.

stewartb mentioned aluminum anodes for aluminum boats. I looked at the links in your last post Gary, and it appears the aluminum anodes or Navalloy, has a composition of aluminum (95%) and zinc (5%). I read boat hulls are made mostly from a 5XXX series, a strong, non-heat treatable and weldable alloy with good anti-corrosion characteristics. A bare aluminum hull would have a good aluminum oxide coating for corrosion protection and therefore the Navalloy anodes would work well. My guess Mg anodes would work just fine too.

I’m curious if anyone has used Navalloy anodes on their floats.

I grabbed these attachments off the internet for illustration purposes.

[BC12D-4-85]

MartyC,

Thank you for the extended reply and helpful suggestions. I agree the white powdery material should be analyzed. It may have been done, but one of the prime movers of this has left the floatpond for some reason. I'll suggest that to those still affected. The floats in question have been 90%+ in fresh water. It's a long way from Fairbanks to the ocean.

Microbial corrosion was my first suggestion to the group (I was a fish biologist, and you know what they feel like plus where they live). Typically the floats have a good covering of green stuff by August in Fairbanks. I would brush them off as it affects performance in September when hunting season starts. Whether or not a new type of underwater growth has emerged is likely undocumented.

Painted floats experience the microbial but only corrosion on exposed areas like the lower water rudders and keel skeg that get scraped by bottom material like gravels. There's not much for typical sand on beaches here...it'll take a few more thousand years for that to develop if ever.

Iron oxide in part of the water table at times, mainly in local shallow wells and during winter when the aquifer that flows under Fairbanks gets reduced in volume. During Summer the water table rises several feet due to nearby river discharge from melting snow and ice fields, with some rain added by Fall.

I suspect most that used added anodes have zinc based attached. Local boat shops also service ocean fish boats so likely would stock them. We're going to try some magnesium "Fish" this summer to see if that helps. In the end it's simply a matter of owner interest and concerns about float performance that might drive any remedial action. Most just want to fly and not deal with aluminum corrosion.

Gary

[MartyC]

Gary,

I'm always happy to assist with metal/material issues if able. I should add, seawater (chlorine) pitting corrosion in aluminum is an autocatalytic process. The same thing with cars and salt use on roads. Once it starts, it will continue. Sealing is about the only way to prevent, stop and inhibit pitting corrosion. I look at anodic protection as a method for slowing corrosion.

You are right about gravel, pretty rough on floats. I used to park my 180 with 2960's on a ramp at Crane Lake, MN and the floats would have a nasty coating at the end of the season, tough to clean off. We now have a hangar and take the plane out at the end of the day and clean them up before putting it away.

As you point out, it becomes an owner choice for taking action. A little regular maintenance goes a long way.

MartyC

[BC12D-4-85]

I mentioned a link in #14 the potential for PFAS contamination and interaction with the floatplanes. Also: https://dec.alaska.gov/spar/csp/site...-airport-pfas/ I don't know if those chems cause corrosion.

Also, we are visited by water bombers (CL-415's and several AT-802F Fire Boss amphibs) that scoop water from the float pond to dampen forest fires. I suppose it's possible their use of any chemicals to enhance the wetting and performance properties of their load can get washed off the hulls and into the pond water. That's not every year, but it's been more frequent.

Other than those nothing's changed much in the 49 years I've been there except the recent corrosion issues.

Gary

[Utah 12 Driver]

"Those with either painted or composite floats haven't reported corrosion below the waterline. Just exposed metal surfaces."

FWIW dept

Gary, I am far from being an expert in this area but there has to be a Marine Eletrician near by, I would reach out to them and get them to test any current that maybe in the water around your plane. It happens at boat docks a lot especially those with older wiring. I had a problem with my boat not being properly grounded after returning from the Bahamas, the guys cleaning the bottom reported having some current in the water while cleaning my boat. I was able to get an old boat electrician out to the boat and he found the issue within 45 mins. I use the "fish" until I could deal with the root issue.

Without proper grounding you are just a giant Battery sucking up loose current from somewhere in the water around or under the pond. It's a common problem in marinas.

Good Luck

[BC12D-4-85]

"there has to be a Marine Electrician near by, I would reach out to them and get them to test any current that maybe in the water around your plane"

None within hundreds of miles from Fairbanks that we are aware of. But, the question is a great one. Given I'm surrounded by A&P's plus People of the Trades on floats, how would I use a common multimeter (Klein MM-700) to test for current or electrolysis? Voltage or current from the plane to ?

Gary

[supercub83a]

I would think you would have to be plugged into (engine heaters in the fall??) to a common ground to get a stray current corrosion problem. In boats with AC and DC systems, the two systems have to share a common ground for safety. This effectively connects the AC green wire to the negative terminal of the battery to the shore power ground. Stray DC current from one boat will then take the path of least resistance back to the negative terminal of its own battery (or negative to positive, see electron flow discussion haha). All of the boats metal underwater parts must also be grounded to the common ground. The path of least resistance may then be through a neighboring boats propellor to their common ground to the shore power ground and then to the neighboring boats common ground setting up an anode/cathode condition between the underwater exit and entry points of the two boats. I actually was unaware this could happen in fresh water so there is probably a lot more I don’t understand. They do make DC current blockers that can go into an AC ground to prevent this too. A lot of saltwater boats have this just incase a neighbor has a leaky DC system. Of course this doesnt help you if its your DC system thats leaking and everything isnt bonded correctly but with an airplane i dont see how you could have the airframe/engine/battery not electrically bonded.

Again, not the gospel here, Im no marine electrician and I live a long ways from the ocean (Fairbanks) but I have pretended to be a marine electrician a few times at sea and Ive stayed at a holiday Inn on occasion!


Sent from my iPhone using SuperCub.Org

[BC12D-4-85]

Thank you ^^^^ for this post. Maybe next summer we can get together and share what you've learned at the Holiday Inn! I'm not affected yet by corrosion as my Taylorcraft's 1320's painted. But others at the FAI pond are. Jim Dodson started this because his C-185 EDO's (Tommy Kushida's old plane) got white powdery corrosion upon removal in the Fall. Others looked and found some on their bare metal. There was lots of correspondence between us'ins (like the airport advisory group - not a member) and them's like the airport and university chems. Some water was sampled then nothing definitive was resolved. Pitch forks and torches are still ready for deployment.

I'm at FP 188 so stop by anytime for a visit. Maybe we can put your skills to use now I know there's a marine sparky closer than Valdez.

Thanks again, Gary

[MartyC]

Gary,

I scanned through the links in posts #14 and #22. It appears to me the concentration levels of the compounds in question are in parts per trillion (ppt) and those concentrations are probably too low for causing corrosion of anything. If these materials were really corrosive, I would think the water bombers would experience excessive corrosion in short order.

In addition, from what I read lately, PFOS (Perfluorooctane Sulfonic Acid) and PFOA (Perfluorooctanoic Acid) are very similar to PTFE (Polytetrafluoroethylene) otherwise known as DuPont's creation, Teflon. These are very stable compounds, referred to as "forever" chemicals or compounds because they are very stable, strong chemically bonded compounds and they do not break down easily over time. These compounds may present some environmental hazards and toxicity in water, however, I do not believe they would not be corrosive.

MartyC

[BC12D-4-85]

Thanks MartyC for the very helpful analysis. My organic chem is 56 yrs old and well buried. We were told similar...nothing to see here so move on re the "P's" plus water bombers.

I can see doing some experiments this coming summer. Get a piece of float aluminum (or use wet floats) and a sacrificial anode then measure current potential plus visible corrosion/films over time. But like most tasks, the labor may soon outweigh any benefit (hey, let's just go fishing and wash it off)....then someone would offer "what would we do about it?" If a clip-on magnesium fish would help that's simple enough for even the least motivated among us.

Gary