National Oilheat Research Alliance 5
While this isn’t always as easy as it sounds,
there are several simple things that can be done
to reduce the accumulation of water in tanks
and help minimize risk of corrosion:
• Make sure all tanks are fully drained
before being installed. Tanks can accumulate
significant amounts of water during storage and
shipment even when plugs are placed in the
tank tappings. Any time a tank is installed with
accumulated water it invites trouble that can
affect the tank’s longevity.
• Keep tanks full during the summer
months. NORA’s research has shown that
when ASTs are left less full over the off season,
condensation is increased. Condensation can
generate about 1 quart of water in tanks that are
left ¼ full during the off season. Topping off
tanks in late spring can help reduce the amount
of water generated by condensation.
• Install tanks inside whenever possible.
Outside ASTs accumulate significantly more
water than inside tanks because they are
subject to wider range of temperature. As
outside tanks are warmed during the day and
then cooled at night, they accumulate more
water from condensation than similar tanks that
are installed inside where temperature changes
are minimal.
In instances where an inside tank cannot
be accommodated, encourage the customer
to consider protecting the outside tank with
an enclosure. Some manufacturers make
integrated tank units designed for outside
installations. In addition to the aesthetic
benefit, the enclosure shades the tank and helps
reduce the impact of wide temperature swings.
• Do not pump the fuel from a tank being
replaced into a new tank. Transferring fuel
from the tank being replaced into the new tank
also transfers existing contaminants from the
old tank into the new tank. This can lead to
premature tank failure, regardless of whether
the tank being replaced is located underground
or above ground. USTs seem to generate less
condensation and have less internal corrosion.
Bacteria usually thrive in warm environments,
such as within an inside tank or an AST
exposed to the summer heat.
Customers often object to disposing of
the fuel in their tank. Try to schedule nonemergency
tank replacements at a time when
the tank being replaced will have less fuel
in it, generally less than ¼ of a tank. This
remaining volume of fuel should be disposed
of properly. When larger volumes of fuel are
present, or the replacement is being performed
on an emergency basis, the use of a temporary
tank on-site is a viable alternative. While a
temporary tank seems expensive in the short-
term, the longer-term benefit of extending the
life of the new tank will prove worthwhile.
• Be vigilant for signs of water in tanks
during service calls and tune-ups. Inspect
the condition of filters, filter canisters, pump
strainers and pump components for the
presence of water and for evidence of water,
such as rust. Evidence of water in the fuel
system can indicate there is an accumulation
of water in the tank. In addition to causing ‘noheat’
conditions, accumulated water can affect
fuel quality and can cause service issues.
Tanks installed with direct fill pipes, such as
USTs or ASTs installed outdoors, can usually
be checked for water using a tank gauge stick
and water indicator paste. Water is heavier
than the fuel and generally settles at the lowest
part of the tank. In assessing an AST, try to
gauge it where the bottom of the tank is at its
lowest point. As stated, condensation is a water
generator for ASTs.
With USTs, water accumulates due to
mechanical failure of components such as fill
caps, fill cap gaskets and vent caps. Less seldom,
a broken or corroded fill or vent pipe may
provide a means of surface water to enter.