Issue Date:  September 1, 2023

 

Think Tank Petroleum Service, LLC

Think Tank - Tank Tightness Tester

NON-VOLUMETRIC TANK TIGHTNESS TEST METHOD (VACUUM)

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 signal before a vacuum is placed on the tank, or when water ingress is detected by the water sensor.

Applicability

Gasoline, diesel, aviation fuel, fuel oil #4, fuel oil #6, solvents, and waste oil.

Tank Capacity

Maximum of 30,000 gallons. 
Evaluated at product levels between 9%* and 95% full. 
Maximum of 30,000 gallons per tank for manifolded tank systems with microphone, water sensor and pressure monitoring gauges in each tank.

Waiting Time

None between delivery and testing.

Test Period

When groundwater level in tank excavation backfill is below bottom of tank: 
A few minutes to determine background noise and at least 30 seconds to run the test after desired vacuum is reached. 
When groundwater level in tank excavation backfill is above bottom of tank or when the groundwater level in the tank excavation backfill has not been determined:
The time it takes for water ingress to increase the water level in the tank to allow the water sensor to detect the "minimum detectable change in water level" (see "Water Sensor" section below).
Test period based on water ingress is dependent on tank size.
Before starting test, water sensor must be calibrated to "minimum detectable water level" (see "Water Sensor" section below) according to manufacturer's instructions.
There must be no dispensing or delivery during test.

Test Pressure

Pressure differential across tank wall at bottom of tank must be at least 1 psi or up to 3.7 psi.  Pressure differential across tank wall is equal to the absolute value of vacuum applied to tank, plus groundwater pressure on tank, minus pressure of liquid in tank.

Temperature

Acoustic signal is independent of product temperature.

Water Sensor

Conductivity water sensor must be used to detect water ingress and must be calibrated for every test when groundwater level in tank excavation backfill is above bottom of tank or when the groundwater level in the tank excavation backfill has not been determined.
Minimum detectable water level is less than 0.125 inch. 
Minimum detectable change in water level is 0.125 inch. 
Minimum water level in tank must be adjusted to at least 0.125 inch (sensor's minimum detectable water level) before calibrating sensor and starting test.
Groundwater Groundwater level in tank excavation backfill must be determined by observation well or soil probe in tank excavation backfill.
If groundwater level in tank excavation backfill is above bottom of tank or the groundwater level in the tank excavation backfill has not been determined, water sensor must be used and test time extended to ensure water ingress detection during test.
Method should not be used to test tanks containing fuel higher than a 10% ethanol content if the water table is above bottom of the tank.
Comments Microphone was 25 ft away from leak source during evaluation. 
*Although not evaluated on empty tanks a third-party acoustics specialist has certified that the measured acoustic signal of a 0.1 gph leak would be detected in an empty tank.
Test may be inconclusive if there is high background noise. 
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. 
An observation well or soil probe in tank excavation backfill may help determine backfill material, water level in tank excavation backfill, and free product.
Requires annual tester certification for operator and equipment by the manufacturer.
Operator hearing test should be within normal range, 0 to 20 decibels for annual exam. More than 4 psi pressure differential across the tank wall at any location in the tank could damage tank.

 

Think Tank Petroleum Service, LLC Evaluator:  Ken Wilcox Associates
P.O. Box 1729 Tel:  (816) 443-2494
Travelers Rest, SC 29690 Date of Evaluation:  02/10/2023
Tel:  (864) 370-0637  
   
   

 

 

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