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Issue Date: November 22, 1995
Revision Date: September 22, 2009
Tanknology
U3 Ullage Test
(Vacuum or Pressure Test)
NON-VOLUMETRIC TANK TIGHTNESS
TEST METHOD (ULLAGE)
| Certification |
Leak rate of 0.1
gph with PD = 100% and PFA = 0%. |
| Leak
Threshold |
A tank system
should not be declared tight when the acoustic signal detected is
different from the baseline.
Baseline is the acoustic signal before tank is pressurized or evacuated. |
| Applicability |
Gasoline, diesel,
aviation fuel, fuel oil #4, waste oil. |
| Tank
Capacity |
Maximum ullage
volume is 16,500 gallons. |
| Waiting
Time |
None between
delivery and testing |
| Test
Period |
A few minutes to
determine background noise and a leak.
Depends on background noise at the site and on the size of the leak.
After the desired pressure has been reached, the tank should be allowed to
settle for 10 minutes.
There must be no dispensing or delivery during test. |
| Test
Pressure |
Vacuum of 1 psi
must be maintained in ullage by a vacuum blower, or total pressure at
bottom of tank of 4 psi must be maintained using nitrogen. |
| Temperature |
Acoustic signal
is independent of product temperature. |
| Groundwater |
Depth to
groundwater in tank excavation backfill must be determined.
If groundwater is above product level, vacuum test should not be
used.
Pressure test may only be used if net pressure can be maintained at a
minimum 1 psi throughout ullage during test.
If this requires more than 5 psi total pressure at tank bottom, the ullage
test must not be used. |
| Comments |
Not evaluated
using manifolded tank systems.
Evaluated using diesel.
Tests only ullage portion of the tank.
Product-filled portion of tank must be tested with an underfill test
method. Microphone was 25 feet away from the leak source during
evaluation.
If background noise is too high, test is inconclusive.
Noise signals are tape recorded (not digitally recorded).
Vacuum test method may not be effective in some tank excavation backfill
(such as clay) because it may plug holes in tank.
If soil is saturated with product, air or water ingress may not be
declared by vacuum test.
A well point in tank excavation backfill may help identify presence of
this condition. |
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Tanknology
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Evaluator:
Ken Wilcox Associates
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11000 North MoPac Expressway, Suite 500
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Tel:
(816) 443-2494
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Austin, TX 78759
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Date of Evaluation:
01/15/93
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Tel: (800) 800-4633
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