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If there is a leak or seep where sealant is always being exposed to evaporating fuel, the sealant will become soft. If you want to know the chemistry explanation you will have to contact the sealant manufacturer, but they will tell you the same thing |
Thanks everybody. It seems like this is a normal phenomenon and maybe not the result of an improper mix ratio. Who knew?
I'm in the middle of cleaning up all the soft stuff and fuel and should have ample amounts of new sealant in place in the interior of the tank in the next day or two. I'll also lop some more on externally just for good measure. Thanks again! |
So I presume the takeaway here is : See a leak? Drop everything and fix the leak?
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There are a lot of variants of "Proseal". At least 3 different manufacturers and 2 or 3 varieties for each manufacturer. What stuff are you using on the fuel tanks?
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http://standards.sae.org/air4275/ ![]() Quote:
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Since I have seen it numerous times (once a very mild case on my own airplane), and the word that someone at Flame Master acknowledged it can happen, that has always been enough information for me. They way I look at it... I don't need to know why.... I just need to know to always be inspecting for fuel leakage, and then fix it as soon as it is detected. |
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BTW, oxidation is a maybe, but I soaked a cured sealant sample in 3% hydrogen peroxide nearly 4 years without softening. It did eat the metal can. And I recently examined a softened polysulfide sealant sample taken from inside a tank. It wasn't fully reverted (more like not very sticky week-old chewing gum, or old-fashioned window glass glazing putty), but certainly not normal-as-cured. The owner removed the rivets and easily peeled the skin off the ribs. Samples from the top of the tank (vapor/splash exposure) and the bottom of the tank (submerged exposure) were similar. Samples of the same sealant from outside the tank (zero fuel contact) were solid/normal. Built circa 2005, sealant brand unknown; checking now. Postscript: Sealant was Chem Seal (Flamemaster) 3204-B....same stuff common to RVs. |
Maybe it just a coincidence, but everytime I've seen this it was with the flamemaster stuff.
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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. |
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