Certification |
Leak
rate of 1.717 gph with PD = 95% and PFA = 5%.
The US EPA has not set a minimum detectable leak
rate for aboveground storage tank systems at the time
of this evaluation. |
Leak
Threshold |
0.859
gph.
A tank system should not be declared tight if the test
result indicates a loss or gain that equals or exceeds
this threshold. |
Applicability |
Gasoline,
diesel, jet fuel, fuel oil up to #6.
Other liquids may be tested after consultation with the
manufacturer. |
Tank
Capacity |
AST's
with surface areas from 7,854 to 30,172 sq. ft. and diameter's
from 100 to 196 feet.
Tank must be 20% full. |
Waiting
Time |
Minimum
of 20 minutes. |
Test
Period |
Minimum
of 20 hours.
There must be no delivery, transfer, or dispensing during
test. |
Temperature |
One
Resistance Temperature Detector (RDT) attached to the
bubbler unit. |
System
Features |
This
system uses nitrogen under pressure conveyed to the bottom
of the tank via a hose to generate (bubbler unit) and
release small bubbles at the tank bottom.
The pressure required to produce the bubbles is equal
to the hydrostatic head pressure produced by the fluid
in the tank plus one atmosphere. This pressure is measured
by a pressure transducer.
The measured differential pressure is a direct measurement
of the mass of the fluid in the tank. |
Calibration |
The
differential pressure transducer is benchmark calibrated
by the manufacturer.
Annual calibration is performed by the CBU/SIM unit and returned
to the manufacturer if results fall outside the benchmark
calibration values.
RTDs are calibrated annually.
Barometer is replaced every five years. |
Comments |
Data
set is filtered to extract only night time data to eliminate
the effects of radiant solar heating.
The CBU/SIM control unit is not rated for installation in
areas where an explosive ignition risk may exist.
Method may be applied to steel, concrete, aluminum, or
fiberglass tanks with either fixed or floating roofs.
Bubbler test pressure must not exceed 18 psig. |