Fuel tank sealant removal machine

[Andy95W]

Yikes.  Thanks for doing the research, Byron.

[TargetDriver]

If you're referring to us using the Klean products "Aircraft Paint Stripper" in the fuel tanks, no I'm not joking. It dissolves the polysulfides in 30 min, doing what Poly Gone does in 12 hours. 

As for the reaction to aluminum, I've not left it on the metal for than 2 hours typically, rinsing with a thorough Acetone wash, water and dry wipe down, even blowing the seams and joints out with air. 

I am always open to learning and would never claim to know it all, far from that actually, but I have worked extensively  with aluminum for 30 years, having held over 18 AWS weld certifications for aluminum alone. I've prewashed, etched, acid soaked, acid aged, salt solution heat aged and cleaned and ground aluminum with about everything you can think of.  I've built 3 airplanes, two with wet wing tanks and welded fuel cells, and have never ran into enough corrosion produced by an ammonia/methylene based cleaning or wash product left on for the short length of time as we are using to cause any noticeable or measureable amount of damage.

Yes, if it were left on, the corrosion would be noticeable, rapid and destructive. I don't dispute your information in the least, but even .002 is a considerable amount of corrosive wear that would some time to produce unless a hard acidic were used.

A question. Would the sealing of the possibly affected seams basically neutralize the effects of the corrosive reaction you speak of since it wouldn't be an anaerobic reaction? I'm curious, even if this corrosive condition existed. 

 

 

[1524J]

So here's what I found about Klean strip or Methylene Chloride stripper. It does state that it's non-corrosive to common metals under NORMAL exposure times. This is where it could be an issue when trapped between layers of fuel tank structure although the manufacturer seems to be concerned about taping seams due to bleed back stripping of the new finish.

 

I also found this on an aluminum manufactures website on cleaning. I use jet fuel (kerosene) when cleaning an oily belly or cleaning the engine. 

 

[amillet]

Why doesn't Mooney weld our tank seams?

[TargetDriver]

Amillet, I'm sure there's some old money Aerospace Pros lurking here that can answer that but I suspect it was it because of a weight savings and manufacturing effeciency. The fuel tanks in a Mooney are simply the dead air space between the wing ribs and the fore and after spars. They applied the sealer along the wing skin/rib and spar/wing skin joints.  

The Myers has a separate fuel tank that was built and then inserted into the wing. There's a guy that has one in a hangar next to mine and he actually had to pull his fuel tank out and find somebody that had a very small hand and arm to reach in with Poly  and fix a leak but his tank was completely welded and separate from the wing.

Part of the problem with Muniz is when the original Factory assembled the wings they did not put any sealer strips between the skins and the ribs when it was assembled. Correct me if I'm wrong but I believe the newer Mooneys are assembled with a sealant between the skins and the ribs and spars when it's assembled.

[TargetDriver]

Haha. Sorry guys, voice txting stinks. 

Thank you 24J for doing that research. I was pretty confident in my decision but have to admit my heart skipped a beat.

[1524J]

 In the fuel tank stripping procedure forwarded to me several years ago by someone here on Mooneyspace, the IA performing the write up suggests using the "cheapest aerosol stripper" you can find. I never tried using a Methylene Chloride stripper as I had to purchase a minimum quantity of four gallons of SR125A. I think under the circumstances if I were you guys I take extra precaution to flush the fuel tanks, paying special attention to the seams, with generous amount of water. PPG and RPM (SR125A, Polygone) industries both have a cleaner they recommend using post stripping with their products. I tried to find something that would neutralize a Methylene Chloride stripper and since it's a water based solvent, that appears to be the best solution. Keep in mind that anything sandwiched between two pieces of metal can be corrosive over time, even 100LL from what I understand. After stripping and washing I'd recommend using MEK for a final wipe down. 

I'm going to strip and reseal my left tank (five or so years later) but have opted to use 3M SR cutters and radial discs to remove the bulk of the sealant. I'll provide PIREPS as I go.....just as soon as I get up enough gumption to start.

[TargetDriver]

Copy All, especially lots of flushing with water. Having only been a resident of the Kommunist state of Kalifornia for a couple years, I just walked into Home Depot..and Ace Hardware, and Lowes, and...and  trying to just grab some MEK off the shelf and go.. No deal. It's banned in this wonderful place...Cant even have it shipped in after contacting a few places.  If I can find it in Nevada I'll make the 4 hr r/t drive to get some, but for now its acetone and water. Klean Strip does make a "Final Rinse" wash to use after their stripper but I haven't checked it for metal sensitivity. It's made for using on wood.

On using the cutters and radial disks, have you tried a test of doing that?  After opening my outboard access panels I thought " wow, these all look like factory sealants and this will be a snap". Not so. I've since found where someone went over the other bays with multiple layers of sealant... Literally I found sealant that was 1/2 thick in the two inner bays.  It has a rubber-like consistency and I'm not sure how that would work with mechanical stripping action.. it becomes even more pliable when the stripper is applied and wiped away. 

Oh, and did I mention that I found most of the lower cross-drain holes at the base of the ribs filled with sealant...even the small aluminum cross tube between the two main bays was covered over!!  This plane has probably a thousand hours since the last log book entry for tank sealing attempts.  Crazy !  Guys, be very careful when resealing so as NOT to plug those cross drain holes and tube!  Obviously not a plane downer, but it would be sad to run out of fuel and still some in the tanks that you couldn't get to.

[1524J]

Haven't started on the strip/reseal yet but I do have around $1000 invested in cutters, die grinders  and 90 degree drills so if it doesn't work I'll be disappointed. 

The other reason you want the drain holes open is because water can get trapped at the low point in the outer bays. If it comes through the upper holes all at once you may be trying to run the engine on H20 which I heard doesn't work well.

[mooniac15u]

1 hour ago, TargetDriver said:

Copy All, especially lots of flushing with water. Having only been a resident of the Kommunist state of Kalifornia for a couple years, I just walked into Home Depot..and Ace Hardware, and Lowes, and...and  trying to just grab some MEK off the shelf and go.. No deal. It's banned in this wonderful place...Cant even have it shipped in after contacting a few places.  If I can find it in Nevada I'll make the 4 hr r/t drive to get some, but for now its acetone and water. Klean Strip does make a "Final Rinse" wash to use after their stripper but I haven't checked it for metal sensitivity. It's made for using on wood.

On using the cutters and radial disks, have you tried a test of doing that?  After opening my outboard access panels I thought " wow, these all look like factory sealants and this will be a snap". Not so. I've since found where someone went over the other bays with multiple layers of sealant... Literally I found sealant that was 1/2 thick in the two inner bays.  It has a rubber-like consistency and I'm not sure how that would work with mechanical stripping action.. it becomes even more pliable when the stripper is applied and wiped away. 

Oh, and did I mention that I found most of the lower cross-drain holes at the base of the ribs filled with sealant...even the small aluminum cross tube between the two main bays was covered over!!  This plane has probably a thousand hours since the last log book entry for tank sealing attempts.  Crazy !  Guys, be very careful when resealing so as NOT to plug those cross drain holes and tube!  Obviously not a plane downer, but it would be sad to run out of fuel and still some in the tanks that you couldn't get to.

Why do you have a preference for MEK?  Acetone and MEK are chemically very similar and should perform similarly as solvents.

[mooniac15u]

1 hour ago, 1524J said:

 In the fuel tank stripping procedure forwarded to me several years ago by someone here on Mooneyspace, the IA performing the write up suggests using the "cheapest aerosol stripper" you can find. i never tried using a Methylene Chloride stripper as I had to purchase a minimum quantity of four gallons of SR125A. I think under the circumstances if I were you guys I take extra precaution to flush the fuel tanks, paying special attention to the seams, with generous amount of water. PPG and RPM (SR125A, Polygone) industries both have a cleaner they recommend using post stripping with their products. I tried to find something that would neutralize a Methylene Chloride stripper and since it's a water based solvent, that appears to be the best solution. Keep in mind that anything sandwiched between two pieces of metal can be corrosive over time, even 100LL from what I understand. After stripping and washing I'd recommend using MEK for a final wipe down. 

I'm going to strip and reseal my left tank (five or so years later) but have opted to use 3M SR cutters and radial discs to remove the bulk of the sealant. I'll provide PIREPS as I go.....just as soon as I get up enough gumption to start.

Methylene chloride is only partially soluble in water.  I'm not sure a water rinse will be the most effective way to remove it.

[1524J]

41 minutes ago, mooniac15u said:

Why do you have a preference for MEK?  Acetone and MEK are chemically very similar and should perform similarly as solvents.

Acetone evaporates faster than MEK. When cleaning surfaces prior to applying sealant the ideal situation is to wipe with the MEK then wipe again with a clean cloth before it has a chance to dry.

40 minutes ago, mooniac15u said:

Methylene chloride is only partially soluble in water.  I'm not sure a water rinse will be the most effective way to remove it.

That's what the manufacturer recommends....I tried searching for a better solution but came up empty. What's your suggestion?

[mooniac15u]

1 hour ago, 1524J said:

That's what the manufacturer recommends....I tried searching for a better solution but came up empty. What's your suggestion?

It is much more soluble in acetone.  If your main concern is removing all traces of the dichloromethane then rinsing with acetone would probably be effective.  The problem with any solvent rinse is the volume of resulting waste.  I hope you have a plan for disposing of whatever organic waste you generate.

[1524J]

2 hours ago, mooniac15u said:

It is much more soluble in acetone.  If your main concern is removing all traces of the dichloromethane then rinsing with acetone would probably be effective.  The problem with any solvent rinse is the volume of resulting waste.  I hope you have a plan for disposing of whatever organic waste you generate.

Just to be clear and I hope I'm not sounding defensive, I'm just trying to help these guys figure out the best way to clean their fuel tanks in preparation for applying sealant. When I stripped/resealed mine I used SR125A which is a polysulfide stripper similar to polygone. I don't know the chemical makeup of SR125A or polygone other than it appears to take longer to dissolve the sealant....and is very effective as a paint stripper. The Methylene Chloride was brought into question by Byron as to whether they could be doing more harm than good using it as a stripper inside the fuel tank environment. Now that we're to the point where the stripper has been used, what's the best method to mitigate any damage if there a chance the Methylene Chloride stripper could cause corrosion. The manufacturer states to clean with water. Your suggestion sounds like acetone would be better. I use MEK quite often in my work so I'm familiar with it, but my use of MEK is not to neutralize or remove dichloromethane. Simply to provide a good surface for substrate adhesion for the polysulfide.

I had someone send me instructions for stripping and sealing Mooney fuel tanks. It came from an IA who gave his name and phone number at the end the document.  I chose not to use a "store bought" stripper simply because I had more than enough of the good stuff due to minimum quantity ordering. Does this IA know if his methods are good? I don't know. I do know in researching stripping and resealing that a very prominent MSC suggests using MEK to thin the polysulfide if needed. Another well researched paper suggest MEK will chemically change polysulfide and toluene should be used to thin polysulfide. 

This go around I have opted to use 3M SR strippers and radial discs to remove the bulk of the sealant, but I haven't started yet so we'll see how things go. I know this.....the older I get, the more I realize how much I don't know and am always willing to listen to advice from someone who has experience or knowledge, but still take the time to research on my own.....just in case.

[jetdriven]

Ive heard of a few instances where they get paint stripper inside the wheel wells, and a few years later, the spar has corrosion.  Now, they all say they carefully removed all the stripper.  Most recently a pilot of a 1977 M20J here at Ellington. 4 years after a Mena paint job, the spar is corroded and after a 40,000$. wing swap, he is flying again.  Piper's just got hit with a SAIB

SAIB: CE-11-12R1,    because corrosion gets between the rear spar and the wing attach fitting. Corrosion in lap seams is real.  And it is a delayed reaction.

 

Edited April 27, 2016 by jetdriven

[isaacpr7]

Lower recirculating panels complete

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[TargetDriver]

As well as the tank stripping is going, I'd like to pause a moment and take an informal pole.  I guess the only people eligible to take this are those that have actually performed a "strip-n-reseal" of a Mooney fuel tank but I expect that other airplane do-it-yourselfers may be able to play too...

QUESTION:   How many of you can honestly say.... I HATE RIVET HEADS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!      hahaha

[TargetDriver]

Seriously, here's a couple pics from this weekend.  This is the main bay closest to the fuselage. Before and after.  I used Poly Gone gel mostly on the upper corners, which I didn't get a pic of but looks like the rest shown. I found 3 separate layers on sealant in some places, getting as much as 3/8-1/2 thick in the corners!  Not cool !  The stripper seems to work quickest on the second pass, cleaning up the rivet heads and misc brown sealant. Washing it all down with lots of acetone, then water. Just need a final detailing pass to get all the small pieces that are stubborn. I now have 3 bays at this point and one left for a couple final clean up passes.

Question...  There are vertical and diagonal "L" braces riveted to the ribs. They do not intersect with the wing skins but are only riveted to the ribs. Why do we apply sealant and sealer to this seams and rivets?  They only lead to the fuel tank bay next to it. What does it matter if there's no seal between them.  Is it because of the possible corrosion that could develop from the fuel itself?  If that's the case, why isn't there corrosion on the flat bare aluminum?  You can see one of them in the 3rd pic.

 

[isaacpr7]

Seriously, here's a couple pics from this weekend.  This is the main bay closest to the fuselage. Before and after.  I used Poly Gone gel mostly on the upper corners, which I didn't get a pic of but looks like the rest shown. I found 3 separate layers on sealant in some places, getting as much as 3/8-1/2 thick in the corners!  Not cool !  The stripper seems to work quickest on the second pass, cleaning up the rivet heads and misc brown sealant. Washing it all down with lots of acetone, then water. Just need a final detailing pass to get all the small pieces that are stubborn. I now have 3 bays at this point and one left for a couple final clean up passes.

Question...  There are vertical and diagonal "L" braces riveted to the ribs. They do not intersect with the wing skins but are only riveted to the ribs. Why do we apply sealant and sealer to this seams and rivets?  They only lead to the fuel tank bay next to it. What does it matter if there's no seal between them.  Is it because of the possible corrosion that could develop from the fuel itself?  If that's the case, why isn't there corrosion on the flat bare aluminum?  You can see one of them in the 3rd pic.

 

I'm no expert by any means but from what I've read, the aluminum used has an alclad coating which prevents corrosion but it is only a thin layer. When said aluminum is drilled in order to install rivets and bolts the thin coat is compromised. If water or fuel ends up between the rivets, then corrosion can form such as inside a battery where the fluid is used as a conductor.

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[isaacpr7]

OMG!!!!! Finally got it clean enough to lay the first coat of sealant. What a PIA for a first timer but if I had to do it again it would be way easier since I learned a few things as I went along. I'd like to offer a PIREP on the extrusion gun. That thing is amazing! Without it, I would have gone through a few cans of sealant because they would have dried out on me since I've never used the product before. I used the small 2.5 oz cartridge and the size was perfect for maneuvering the gun inside the tank bays. Once you get the hang of how much the trigger needs to be pressed and how fast you should move the gun it's on an popping The only drawback is having to refill the cartridge every few seams but it's still faster than using a spatula and there is a 6 oz cartridge available that you can use. I'm glad I bought the one without the pistol grip because it allowed me to maneuver inside the tank freely and in any direction without hitting anything.

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[isaacpr7]

Checked up on the first coat after 24 hrs and it dried to a nice rubber consistency. What I had before stripping the tank was more like cheap bubble gum, which is why it took for ever to remove. I think it must have been a very old product or one that was not mixed properly. I didn't want to risk mixing the batch improperly so I mixed the entire can all at once and it worked out perfectly.

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[isaacpr7]

Second coat went down a lot smoother. Now waiting for it to dry so I can apply the final (red) protective coat. Here are some pics; however, they were taken prior to cleanup.

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[isaacpr7]

Right wing is finally 100% complete. I will be posting the times I logged during the entire reseal process once I add everything up. When I use the recirculating machine on the left tank I will post those times as well; however, that won't happen until I get back from my next deployment. Right now I just want to fly her

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[orionflt]

Have you started the left tank with the machine? Wonder how it is going. I went to go flying today and my sump would not seal (it is the original 1961 unremovable version) I popped my tank lid to see if I could make it seal and found some of the sealant around it bubbling . Looks like I am about to start dripping and resealing. How much poly gone did you use on the right wing?

 

Brian

[isaacpr7]

Have you started the left tank with the machine? Wonder how it is going. I went to go flying today and my sump would not seal (it is the original 1961 unremovable version) I popped my tank lid to see if I could make it seal and found some of the sealant around it bubbling . Looks like I am about to start dripping and resealing. How much poly gone did you use on the right wing?

 

Brian

The left wing I will start next year with the machine. Right now I just want to spend some time with the family before deploying again. I nearly used the entire tub of polygone gel. I believe there was only a quarter of the tub left but the sealant in my tank was like cheap bubble gum and was a PIA to remove. I am still in the middle of moving but soon I will add up the times and post how long it took me to do one tank.

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