|
Certification |
Leak
rate of 0.005 gph as vapor with PD = 100% and PFA =
0%. |
|
Leak Threshold |
A tank
system should not be declared tight when the change in helium concentration
in the interstitial space over time exceeds the method’s preset threshold. |
|
Applicability |
Method tests under pressure
the primary containment of secondarily contained tanks, piping and other
components.
The primary and secondary components of the system under test
must be dry, containing no liquid. |
|
Tank Capacity |
Not
limited by capacity. |
|
Test Period |
Minimum 10 minutes for piping and 20 minutes for tanks.
Test period varies
in accordance with iota software and test procedures, and is a function of
several factors, including interstitial volume, flow rate, diffusion rate,
and the concentration of helium in the component being tested. |
|
Waiting Time |
No
waiting period is required between adding helium to the primary containment
and starting the test. |
|
Dosage |
Helium
dosage varies depending on the component being tested.
In all cases, 100%
industrial helium is used as prescribed in the manufacturer's test
procedures. |
|
Sampling Points |
Sampling is performed by circulating air through the interstitial space
between the primary and secondary walls of the component(s) being tested and
measuring the He levels in the circulated air.
|
|
Groundwater |
Groundwater level is not determined and does not impact the test.
Flow meter
is used to verify that the interstitial space is dry and has sufficient air
movement. |
|
Detector |
Helium
is measured by the helium detector, which supplies data to the iota system
for analysis and pass/fail determination.
Third-party evaluation was
conducted using the Varian models PHD-04 and 979 detectors, but evaluator
indicates that any helium detector meeting at least the following
performance standards can be used: |
|
|
Minimum Detectable Concentration:
Smallest Detectable Leak:
Response Time:
Background Suppression: |
2 ppm
5 x 10-6 atm-cc/sec
< 2 seconds
Automatic |
|
Calibration |
Helium
detector performs an auto calibration on start up and must be checked
monthly and, if necessary, calibrated in accordance with manufacturer’s
instructions. |
|
Comments |
This method is intended
primarily for use on new installations before product has been added to the
system.
The interstitial volume of
the components being tested must be entered manually, or the iota software
can calculate volume based on piping type/length or sump dimensions entered
by the tester.
Third-party evaluation
included tests to show that the method can find leaks on a variety of UST
system components, including double-wall piping, double-wall USTs, and
primary components contained within tank top/under dispenser sumps.
This method is only able to
test double-walled tanks that have 2 interstitial access ports on opposite
ends of the tank and have a dry primary and interstitial space.
The method was evaluated on
a 32 foot long tank with access ports spaced 28 feet apart. |
