National Oilheat Research Alliance 15
Tanks manufactured of 10 gauge steel meet
UL 58 criteria for underground installations,
however, NORA recommends 7-gauge sti-P3,
ACT-100® or fiberglass tanks.
sti-P3
sti-P3 tanks are steel tanks protected with a
factory installed corrosion protection system
designed by the Steel Tank Institute. They
carry a standard 10 year warranty (an optional
30 year warranty is available) against failure
due to corrosion.
These tanks feature a three part protection
system:
• an exterior polyurethane, fiberglass reinforced
plastic (FRP) or coal tar dielectric
coating
• factory installed electrical isolation
bushings in the tank fittings
• sacrificial anodes designed to provide
protection of exposed steel in the event
of an isolated coating failure
sti-P3 tanks are available in single and
double wall configuration. Double wall models
allow for leak monitoring by means as simple
as manual gauging of the interstice through the
access tube when it is extended to grade.
The sacrificial anode protection needs to be
ACT-100 tank
tested at installation and periodically thereafter.
Owners of sti-P3 tanks should contact a tank
inspection service provider or certified cathodic
protection tester for the testing.
ACT-100
The ACT-100 uses an advanced multicomponent
fiberglass reinforced plastic (FRP)
coating applied directly to the exterior of the
steel tank shell to provide corrosion protection.
Since the 100 mil, high impact, abrasion resistant
coating is significantly thicker than the
coating of a sti-P3, the tanks are not equipped
with sacrificial anodes.
ACT-100 tanks are also available in single
or double wall configuration.
ACT-100-U
The ACT-100-U is another version of a
coated steel tank. In this case, a 70 mil coating
of urethane is used to isolate the steel from
the electro chemical mechanisms of corrosion.
Like the ACT-100, the tank is not equipped
with sacrificial anodes and is reliant on the
superior coating for corrosion protection. The
urethane is thinner and softer than the FRP
coating of the ACT-100, a protective material
is installed beneath the tank to cushion it on
the backfill. The ACT-100-U is also available
in both single wall and double wall configurations.
In Ground Fiberglass Tanks
Fiberglass reinforced plastic (FRP) tanks are
available in the U.S. for underground installation.
FRP tanks do not rust because they are
made of corrosion-resistant materials eliminating
the possibility of leakage due to either
sti-P3 tank internal or external rusting.