Involve Test and Control Inc'

1
Air Leak Test Methodology

• Involve Test and Control Inc.

2
NON-DESTRUCTIVE TESTING IS A NECESSITY

• Modern non-destructive leak testing is used by
  manufacturers to
• Ensure product integrity and reliability.
• Prevent failures and accidents.
• Ensure customer satisfaction and maintain
  reputation.
• Maintain a uniform level of quality.
• Aid in product design improvements.
• Control the manufacturing process.
• Lower manufacturing and warranty costs.

3
BUBBLE UNDERWATER LEAK TESTING

• Of all leak testing methods this is the easiest
  to understand.
• The part is pressurized while underwater. Are air
  bubbles escaping from the part? If yes, the part
  is leaking.
• Unless specific techniques are used internal
  leakage (one passage to another) can not be
  detected visually.
• It also identifies the approximate location of
  any external part leakage.
• It is very easy to miss seeing bubbles underwater
  especially when part leakage is very slight.
• Usually not practical for production leak
  testing. It does not produce a quantitative leak
  test result.

4
PRESSURE DECAY LEAK TESTING

• This method is also easy to understand and it
  does indicate the magnitude of part leakage.
• The part is pressurized to a given test air
  pressure (FILL).
• After reaching test air pressure, the air
  pressure supply is shut-off (STABILIZATION).
• The leak rate is calculated indirectly using a
  formula based on the internal volume of the part
  and a pressure drop over time (TEST).
• To produce a measurable drop in pressure, more
  time is required to sense small leakage in large
  volume parts.
• An acceptable method for measuring part leakage
  if there is sufficient time (FILL STABILIZATION
  TEST).

5
DIFFERENTIAL PRESSURE LEAK TESTING

• This method is similar to Pressure Decay leak
  testing except the leak rate is calculated
  indirectly after measuring the difference in air
  pressure between a fixed and identical reference
  test volume and air pressure in the
  part-under-test.
• If the part is not leaking, air pressure inside
  the part equals air pressure inside the reference
  test volume (no difference no leakage).
• If the part leaks, the air pressure will be lower
  inside the part when compared to the air pressure
  inside the reference test volume (some difference
  some leakage).
• As with Pressure Decay leak testing, there must
  be sufficient time to sense a pressure drop
  between the part-under-test and the reference
  test volume (sensitivity).
• An acceptable method if there is sufficient time
  (FILL STABILIZATION TEST).

6
MASS FLOW LEAK TESTING

• The part-under-test is pressurized and the leak
  rate is measured directly.
• When test air pressure is reached, air flow is
  directed through a mass flow transducer. A mass
  flow transducer is a device that generates a
  voltage output in relationship to the amount of
  air flowing through it.
• If the part is leaking, air flows through the
  mass flow transducer and into the part replacing
  any air that is flowing out (leakage).
• The leak rate is measured directly when air
  flowing into the part equals the air flowing out
  of the part.
• An acceptable method for quickly measuring low to
  high leak or flow rates.

7
LAMINAR FLOW LEAK TESTING

• Like Differential Pressure leak testing, the
  difference in air pressure between the part-
  under-test and the test air pressure is measured
  to calculate the leak rate. However, laminar flow
  leak testing directly measures the leak rate and
  does not require a reference test volume.
• Similar to Mass Flow leak testing air flows into
  the part through a Laminar Flow Element (LFE) at
  the same rate that it flows out of the part.
• If the part is leaking, air pressure after the
  LFE is lower than air pressure before the LFE.
• Once the leak rate becomes fully stabilized, air
  is flowing into the part at the same rate it is
  flowing (leaking) out of the part. Once the air
  pressure differential stops increasing actual
  part leakage is produced.

8
ACCELERATED LAMINAR FLOW
Settle
Fill
Since the difference A at time point a is
proportional to difference B at time point b,
part leakage can be measured at time point a
accurately with repeatable results.
A
Flow curve for leak
Flow Through LFE
B
Flow curve for no-leak
Fully Stabilized
b
a
Time

• Air pressure differential across the LFE is
  proportional to the air pressure difference
  across the LFE before and after full
  stabilization. Therefore, the leak rate can be
  measured accurately before full stabilization.
  Hence the term accelerated testing.

9
ACCELERATED MASS FLOW
Settle
Fill
Since the difference A at time point a is
proportional to difference B at time point b,
part leakage can be measured at time point a
accurately with repeatable results.
A
Flow Through Transducer
Flow curve for leak
B
Flow curve for no-leak
Fully Stabilized
b
a
Time

• Gas flowing into the part-under-test during
  (SETTLE) is proportional to gas flowing out of
  the part after full stabilization. Therefore, the
  leak rate can be accurately measured before full
  stabilization. Hence the term accelerated
  testing. Accelerated testing is achieved when
  (FILL) is sufficiently shortened to permit
  forward flow into the part-under-test at the
  start of (SETTLE).