Looking through the email archives, there seem to be some
misunderstanding on what the tank is made of. It is polyethylene (PE).
It is definitely not PTFE (Teflon) or nylon as some had suggested. I
don't know why polyethylene was chosen, but my guess is it is the
rotomolding process itself. The majority of rotomolding is done with
polyethylene so that may have been the most cost-effective choice.
Weather it is LDPE (Low density polyethylene) or HDPE, neither one is
great with gasoline. Assuming it is LDPE, the attached chart lists it
as "Limited Compatibility" at 20C and "Not Satisfactory" at 60C.
Granted, liquids don't heat up quickly, but over a full hot summer
week, 40C may not be unrealistic. It would be interesting to examine
if the tank failures have come mostly from warmer climates.
There have also been discussions about inadequate support of the tank
that could lead to tank failures. This is true, but polyethylene
should only yield under stress, not crack. Cracking is more indicative
of a brittle material. My tank has been sitting on the shelf for over
12 years and when I was drilling out the bosses this week, it felt
waxy and ductile, not hard and brittle. So it is not the age of the
tank that makes it brittle. It is the exposure to gasoline. All of
this points to the importance of a good barrier coating, and probably
even more important in hot climates.
I was also told by Fluoroseal that automotive level coating is
generally not done in Europe. Not knowing the level of coating is the
main reason I am pursuing a second coating on my tank.
On Mon, Nov 4, 2013 at 9:09 PM, Pete <peterz@zutrasoft.com> wrote:
> I had used the same company to fluorinate my circa 2001 tank to the highe
st "automotive level", and it did indeed come back with a much different "
frosty" finish. So although I cannot attest to its effectiveness as it stil
l :-( does not have fuel in it, the treatment surely did change the surfa
ce texture, so it must have penetrated more than the reported factory treat
ment. This is the same company that treats automotive fuel tanks to meet ev
aporative emissions standards, as well as at lower levels for items such a
s shampoo bottles etc. I did carefully clean my tank and cobra with naphth
a, and wrapped and sealed them in poly inside a shipping crate to keep them
clean and as a result I did not have any "burning" issues from the treatme
nt. I followed the company's advise and made *all* finish cuts to the open
ings prior to treatment. To not do so (as per the factory tanks) negates th
e surface treatment as the fuel migrates into the material via the untreate
d cuts and subse!
> quently swells and suffers long term embrittlement. I had gone it alone
at the time as I could not find any other takers - hopefully Andrew will h
ave better luck. I figured the cost is well worth the high likelihood that
I will avoid the tank swelling and cracking others have had over the long t
erm, with the resultant hacking in of a replacement down the road.
>
> I am contemplating piggy-backing on this order to treat a small LDPE moto
rcycle fuel tank I had purchased, but need to first verify with that mfg if
this tank's "x-linked PE" is compatible. They did not treat their tanks a
s they do not need to meet (off road) emissions std's, but experience has s
hown me that these tanks do smell up a garage.
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