Issue Date: April 28, 2005
MassTech
International, Ltd.
MassTech 002 Ullage Test System (Pressure or
Vacuum Test)
NON-VOLUMETRIC
TANK TIGHTNESS TEST METHOD (ULLAGE)
Certification
|
Leak
rate of 0.1 gph with PD = 100% and PFA = 0%.
|
Leak
Threshold
|
Tank
ullage should not be declared tight when a predetermined
threshold is exceeded. This threshold may be modified
by the results of the static test.
|
Applicability
|
Gasoline,
diesel, aviation fuel, fuel oil #4, waste oil. Empty tanks
may also be tested.Tanks containing other liquids may
be tested after consultation with the manufacturer.
Tests only ullage portion of the tank.
Product-filled portion of the tank must be tested using
an underfill test method.
|
Tank
Capacity
|
Maximum
ullage volume is 30,000 gallons.
|
Waiting
Time
|
2.38
hours with tank filled to 5%
1.5 hours with tank filled to 50%
0.27 hours with tank filled to 95%
The wait time may be shortened by the technician when
steady state conditions are reached earlier.
|
Test
Period
|
Total
collection time is 2.63 hours with tank filled to 5%
Total collection time is 1.75 hours with tank filled to
50%
Total collection time is 0.52 hours with tank filled to
95%
The 25-minute static test in which the tank is sealed
but not pressurized may be shortened by the technician
when steady state conditions are reached earlier.
Test data is acquired by computer and forwarded electronically
to an analysis center where proprietary software is used
to assist in the determination of the tank condition.
|
Test
Pressure
|
A
nominal pressure or vacuum of 1.5 psig must be maintained
in the ullage.
|
Temperature
|
Method
is sensitive to temperature, atmospheric pressure and
other environmental fluctuations. These are empirically
modeled during the static test.
|
Groundwater
|
Depth
to groundwater in tank excavation backfill must be determined.If
groundwater is above tank bottom, a water sensor must
be located at the bottom of the tank or the test must
be conducted in conjunction with the standard MassTech
wet test.
|
Comments
|
Vacuum
test method may not be effective in some tank excavation
backfill (such as clay) because it may plug holes in tank.
If free product is present in tank excavation backfill,
a leak in the free product zone may not be detected by
a vacuum test method.
A well point or observation well in the tank excavation
backfill may help determine backfill material, water level
in tank excavation backfill, and free product.Operators
must be trained and certified by the manufacturer.
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