My cured Pro-Seal has turned to goo!

[DanH]

Originally Posted by RVDan

I have some work experience (more than 30 yrs) with PS890, PR1422 and PR1440 and never heard of this problem with avgas. Problems from inproper mixing and curing in an environment that was to cold, yes, but not properly mixed and cured.

Builders here have been hearing about it for quite a while. Here's an example...note date on the photo. A Flamemaster rep has also seen this photo.

[RVDan]

Originally Posted by DanH

Builders here have been hearing about it for quite a while. Here's an example...note date on the photo. A Flamemaster rep has also seen this photo.

l'll say it a bit differently. I have not worked withthe Flamemaster product, only the PRC product. Has anyone seen this problem with the PRC product?

[BillL]

Originally Posted by RVDan

l'll say it a bit differently. I have not worked withthe Flamemaster product, only the PRC product. Has anyone seen this problem with the PRC product?

Now we are getting to an investigation, when were (date) the failed tanks made, was it pro-seal or Flame-blah at that time? How long after the units were put into service was the condition found? Was it internal or external or both? Calendar time, not flight hours.

This can begin to tell us the failure rate (or MTBF) in calendar days, etc.

[LettersFromFlyoverCountry]

So is the theory that the leak occurred because the sealant turned to goo.... or the sealant turned to goo because the leak wasn't addressed?

[DanH]

Originally Posted by LettersFromFlyoverCountry

So is the theory that the leak occurred because the sealant turned to goo.... or the sealant turned to goo because the leak wasn't addressed?

Sealant turned to goo because the leak wasn't addressed.

[gmpaul]

Originally Posted by DanH

Sealant turned to goo because the leak wasn't addressed.

Mine was a factory tank in other words a quick build kit. Be sure to check for the blue tell-tail sign of a tiny leak during annual. This will save a lot of grief next year.

[David-aviator]

I've been down this road with quick built tanks that did not leak but showed dozens of blisters at rivets and am not convinced anyone has hit on what is going on with the sealant going goo or blisters that do not show fuel stains or building technique applying the stuff.

What I do know, and it is not conclusive or prove anything for sure, is if you apply enough of the stuff inside the tank at ribs and covers and rivets, the tanks do not leak and the blisters do not appear - at least so far in my history with this stuff.

The RV-7A now owned by Jerry Cochran is not showing blisters to my knowledge (about 6 years,new tanks I built) and neither is the RV-8 (about 2 years). So the message is - use lots of sealant, don't be bashful about it, cover every possible place a fuel can leak out with much of it.

With any luck at all, it won't leak. And don't get all hung up with the cosmetics of how it looks. The worst cosmetic effect is seeing blue on the outside of the tank.

[DanH]

Originally Posted by David-aviator

I've been down this road with quick built tanks that did not leak but showed dozens of blisters at rivets...

Off topic, so just a footnote....the blister problem was/is NOT limited to QB tanks alone. Although much blame was placed on QB's initially, collected data showed blisters were equally common in kit-built tanks.

Returning to sealant reversion....

This from a study conducted for the Navy:



The complete paper is available for download here:

http://oai.dtic.mil/oai/oai?verb=get...fier=ADA087267

There are some interesting clues regarding oxidation of fuels (which apparently leads to sealant reversion) in this paper:

https://web.anl.gov/PCS/acsfuel/prep...08-90_1277.pdf

100LL also has significant quantities of antioxidant added to meet the requirements of long-term storage. This list of approved antioxidants is from the UK 100LL standard; North America and AUS assumed to be similar:



I would suggest a theory ("theory" = an unproven supposition needing work to determine if it is true or false) that when 100LL gets outside the tank (like one of these fuel leaks) the antioxidant evaporates or is combined/dissolved (i.e. all used up), leaving the leaked fuel subject to a high level of peroxide formation. Acid formation may be involved/required per the paper quoted above. The acid contribution seemed to be an unknown at the time of publication (1980).

I am not a chemist, which is why I would like to see a detailed technical explanation from the sealant manufacturer. Failing that, perhaps we can crowd source a qualified individual from our ranks; we have a huge collection of intellect and education lurking on VAF.

[LettersFromFlyoverCountry]

Originally Posted by David-aviator

With any luck at all, it won't leak. And don't get all hung up with the cosmetics of how it looks. The worst cosmetic effect is seeing blue on the outside of the tank.

Heh, I've never understood the obsession with how the inside of the tank looks.

[Breezy]

This thread sparked my interest since I recently observed this on an aircraft that was in service for nearly 10 years. Thing is, the softening was occurring on every sealed joint on both tanks. Even those that showed no staining from leaks. If the softening is the result of the presence of oxygen and gas, well guess what, they are both constantly present. If this is the case proseal is a poor choice.

After looking at the multiple threads on this, I tend to agree with the observation that it appears to be manufacturer specific, especially in occurrences after years in service. I wonder if an informal tally of occurrences would point this out. The difficulty is many aircraft are no longer owned by the builder so identifying the product manufacturer will be difficult. Further complicated by whether or not the builder documented the source of the sealant.

I have inquired with some jet service center techs that regularly use proseal type products on fuel tanks and none have seen this. The common response was "the older it is the harder it gets". The opposite of what is occurring in these threads. Of course these shops are going to be very conscientious regarding MIL-Spec and source to meet certified standards. Experimentals are not held to that.

Maybe we all need to take stock in the old adage: you get what you pay for! There are simply some corners that should not be cut.