Removing urethane efc100 fueltank coating

[Hradec]

HELP!

I'm in the process of replacing my aft stub spar and now a top spar cap. The spar cap repair requires I open up the fueltank. I realized that my tank doesn't have the typical polysulfied sealant. It had an stc in 2002 to install a urethane  coating EFC100. 

How do I remove this stuff? Mechanically?with chemicals? Dynamite?

I did some research apparently it is tough stuff and used in some military  aircraft fuel tanks.

The coating is almost an inch thick in some areas. I am sure my fuel capacity is reduce by multiple gallons because if the thickness of the urethane.

[N201MKTurbo]

https://www.meggitt.com/insights/discover-our-leak-proof-long-life-sealant/

call the tech support number on this website.

[Hradec]

5 hours ago, N201MKTurbo said:

https://www.meggitt.com/insights/discover-our-leak-proof-long-life-sealant/

call the tech support number on this website.

I called them, no answer. I called the company that holds the stc, it has been sold, but they were very familiar with the product, they still use it in the military. Their tech guy was suppose to call me on the removal process. No call yet.

I put samples in mek, acetone, paint stripper and choke and carb cleaner. In almost 2 hrs soaking not much action.

[carusoam]

One sealant remover keeps showing up...

https://mooneyspace.com/search/?q=Sealant remover&updated_after=any&sortby=relevancy&search_and_or=and

Then there is Polygone... that might work also...

https://mooneyspace.com/search/?q="Tank stripper"&updated_after=any&sortby=relevancy

I didn’t take the next step to see what sealants it can remove...

Best regards,

-a-

[N201MKTurbo]

25 minutes ago, Hradec said:

I called them, no answer. I called the company that holds the stc, it has been sold, but they were very familiar with the product, they still use it in the military. Their tech guy was suppose to call me on the removal process. No call yet.

I put samples in mek, acetone, paint stripper and choke and carb cleaner. In almost 2 hrs soaking not much action.

A quick look at removing polyurethane suggests that Vinegar may work. I have no experience with this. 

[N201MKTurbo]

28 minutes ago, Hradec said:

 No call yet.

At work we just bought a $714K motion system that I'm working on. I can't get the vendor to answer the phone or call back either. Nobody's working anymore. Except where I work we are slammed. We are considering turning down $M purchase orders. We are building COVID machines and those folks have huge bucks and want all we can build.

[McMooney]

try searching the web for a urethane solvent

[PT20J]

Sounds nasty. Here's a company that claims to make the stuff -- maybe they can help. https://www.ptipaint.com/products/polyurethane-coating-polyurethane-for-protection-of-integral-fuel-tank-sealing-compound

The Mil Spec (MIL-C-83019) is listed as INACTIVE in Everyspec.com 

 

[Raymond J1]

Typically, polyester urethanes are dissolved in dimethyl formamide as a 18 to 22 % b. w. solution, but dimethyl acetamide maybe used as well or dimethyl sulphoxide. To use THF will lead to lower concentrations. In any case, at ambient temperature only the hydrogen bonds are disrupted, at temperatures > 100°C allophanate or biurete groups from side reactions maybe cleaved, esp. if there are amine impurities in the solvents. Therefore, only highly purified and dried (just before use) solvents should be used.

[Hradec]

1 hour ago, Raymond J said:

Typically, polyester urethanes are dissolved in dimethyl formamide as a 18 to 22 % b. w. solution, but dimethyl acetamide maybe used as well or dimethyl sulphoxide. To use THF will lead to lower concentrations. In any case, at ambient temperature only the hydrogen bonds are disrupted, at temperatures > 100°C allophanate or biurete groups from side reactions maybe cleaved, esp. if there are amine impurities in the solvents. Therefore, only highly purified and dried (just before use) solvents should be used.

Where do I get this stuff and is it safe for aluminum. 

[V1VRV2]

What Raymond said! Best sounding post yet!

[mike_elliott]

Walter Dodge of Kelly Aerospace (wdodge AT Kellyaerospace.com) was involved with the original STC and licensed it to Midwest M20 to apply on Mooney's. He may have some info that could be of help. I am curious, did it develop a leak, or are you just cleaning it up and getting some UL back? Kevin Surrell (RIP) was emphatic that it would never leak back in the day when he was doing this sealant.

[Hradec]

4 hours ago, mike_elliott said:

Walter Dodge of Kelly Aerospace (wdodge AT Kellyaerospace.com) was involved with the original STC and licensed it to Midwest M20 to apply on Mooney's. He may have some info that could be of help. I am curious, did it develop a leak, or are you just cleaning it up and getting some UL back? Kevin Surrell (RIP) was emphatic that it would never leak back in the day when he was doing this sealant.

No leaks, pulled the skin back to do an upper spar cap. I have to remove the stuff to rivet it back together, clean it up and reseal

[mooniac15u]

6 hours ago, Hradec said:

Where do I get this stuff and is it safe for aluminum. 

I'm pretty sure Raymond just copy/pasted that from the internet.

https://www.researchgate.net/post/How-do-I-dissolve-a-polyester-urethane-resin-after-it-has-hardened

 

[mooniac15u]

I'm more of an organic/medicinal chemist so I haven't done any polymer chemistry in a long time but I seem to recall that crosslinked polyurethanes are extremely solvent stable.  You probably won't be able to get it to actually dissolve.  You may be able to get it to swell and separate from the metal with something like methylene chloride.

[Prior owner]

Whatever you decide to use to remove that sealant, my only advice would be to mechanically remove as much as you possibly can, prior to introducing a chemical stripper into the tank... it will easily cut the job in half as far as effort and time. Try the 3M SR Cutting heads.

https://multimedia.3m.com/mws/media/177797O/3mtm-sr-cutter.pdf
 

 

 

[N201MKTurbo]

https://www.stonermolding.com/store/shop-online/polyurethane/product/B505PLSTON01/b505-polyoff-polyurethane/cp_/polyurethane/mold-cleaner

Maybe this would work?

They make a few versions. It says it is safe on aluminum.

[N201MKTurbo]

1,2-dimethyl imidazole seems to be the hot ticket.

[Raymond J1]

9 hours ago, Hradec said:

Où puis-je trouver ce produit et est-ce sans danger pour l'aluminium? 

You can find ready-made strippers based on DMF, but you have to choose on which medium they are suitable because the concentration of DMF is variable. For example, removers for woodwork, those for metals or concrete contain the most. Depending on this concentration, they will be more or less effective. Prefer gel cleaners with at least 20% DMF, which must be applied in a thick layer after "offloading"(?, I don't the exact terme in English) the polyurethane with acetone. Work at at least 12-15°C. DMF is water soluble. Boiling point high enough, there is little danger to the product itself. On the other hand, vapors are more dangerous (for high concentrations), consider using cold lights to illuminate your work in the tank. Use rubber gloves. The DMF can be bought pure in cans or barrels, in this case it is from a professional.

Edited December 18, 2020 by Raymond J

[Raymond J1]

3 hours ago, mooniac15u said:

Je suis presque sûr que Raymond vient de copier / coller cela à partir d'Internet.

https://www.researchgate.net/post/How-do-I-dissolve-a-polyester-urethane-resin-after-it-has-hardened

 

Yes, because I had the same question for my tanks and that's what guided me to the choice of a solvent.

[Mooneymite]

As an aside, I guess we all need to note that various repairs, like this aft spar repair, involve breaching the sealed fuel tanks on our wet wing Mooneys.  Perhaps this is a good case where a bladder installation would make such repairs simpler/cheaper?

[mooniac15u]

Polyurethanes are a class of polymers that can contain different levels of crosslinking and branching.  What may work for one specific polyurethane may not be effective for others.  The level of crosslinking in the tank sealant material will determine how effective any of these solvents are.  Even DMF may just cause it to soften and swell but that may be enough to remove it.  Heat may help but be careful with any heat sources in an enclosed space with solvents.

[Hradec]

1 hour ago, Raymond J said:

Yes, because I had the same question for my tanks and that's what guided me to the choice of a solvent.

You had the same stc applied to your tanks with the urethane?

[Gary0747]

 

5 hours ago, mooniac15u said:

You may be able to get it to swell and separate from the metal with something like methylene chloride.

 

I would strongly recommend not using any chlorinated solvents around aluminum especially where they might get into cracks and seams.  Over time they can degrade to form HCl. 

[mooniac15u]

34 minutes ago, Gary0747 said:

 

 

I would strongly recommend not using any chlorinated solvents around aluminum especially where they might get into cracks and seams.  Over time they can degrade to form HCl. 

Methylene chloride is fairly volatile and doesn't leave a residue.  It has a lower boiling point than acetone.  There is little reason to be concerned about long term effects on aluminum.  Of course you are unlikely to be able to buy any unless you work in a lab so it's probably a moot point either way.