Frequently Asked Questions
Q.Why use Helium leak detection?
A.

Helium Leak detection is a tried and tested method of leak detection which has been used in industry for over 60 years.

The concentration of helium by volume in the earth's atmosphere is only 5.2 parts per million. Because of this very low background value, helium is an excellent tracer gas.

Helium is the second lightest element in the periodic table and, being a light gas, it can penetrate small leaks rapidly.

Helium is an inert gas, non-flammable and readily available.


Q.Is Helium an expensive gas to use?
A.

Through the continuous improvement and development of testing and calibration methods, Ovec AET Micro leak detectors' usage of helium is very low.

On average, customers report that a system running 24/7 requires one standard helium bottle per month. As the system runs on balloon grade helium, this represents excellent value for money.


Q.What is a micro leak?
A.

Micro Leak has been adopted by the canning industry to describe very small leaks down to 1 x 10-6 cc/sec .

Explanation:

Micro is a prefix denoting a factor of 10-6 (one millionth)

Since leak openings often have irregular shapes, leaks are sized by the leakage flow rate, as in volume of gas leaked per time, rather than the size of the opening.

The two most common leakage rate units are:

  1. mbar litre per second
  2. atmospheric cubic centimetre per second.

As 1 mbar l /sec = .987 atm cc/sec these are, for all intents and purposes, the same.

Example: A micro leak of 3 x 10-6 atm cc/sec means that 0.000003 cubic centimetres of gas will flow though the hole in 1 second = 94.608 cubic centimetre of gas in 1 year.

For further explanation see our KEY LEAK DETECTION FACTS


Q.Why do I want to find micro leaks?
A.

All sealed components leak, however the level of acceptable leakage is the critical factor in maintaining the working life of the component.

The acceptable standard leak rate used in can End production is <3x10-6 atm cc/sec. This has been determined to ensure that an acceptable level of gas will remain in the can at the end of its shelf life.

Please see our LEAK DETECTION REPORT for further details


Q.What are the advantages of helium leak detection over pressure and light testing?
A.

The main advantage of helium leak detection is that it is in the region of 1000 times more sensitive than light detection. This is summarised in the table below:


SUMMARY OF DETECTABLE LEAK RATES
PRESSURE DROP/RISE

1x10-2 cc/sec

Shelf life for 33cl can
1 hour

 

LIGHT DETECTION TEST

 

1x10-3 cc/sec

Shelf life for 33cl can
10 hours

 

BUBBLE TESTING

 

1x10-5 cc/sec

Shelf life for 33cl can
6 weeks

 

DYE PENETRATION

 

1x10-6 cc/sec

HELIUM MASS SPECTROMETER

1x10-6 cc/sec

Shelf life for 33cl can
15 months

For further details of the principles of leak detection please download and have a look at our SLIDESHOW at your leisure.


Q.Should we have On or Off-line micro leak detection?
A.

Although the test methods and sensitivity are the same for both on and off-line systems, there are advantages and disadvantages for each sampling method.

Offline Advantages

One system can test samples from several presses
Can be used to test test different size Ends
Can be used for 100% defective batch inspection
Automatic samplers available - AES

Offline Disadvantages

Time delay between manufacture and testing can result in several hours' production of defective Ends.
Labour costs associated with sample collection

Online Advantages

Automatic testing of up to 1.5% (1.5% from a 3 lane press running at 650 s/m = 1755 ends/Hr or approx 3 bags/hr).
24 hr testing.
Press can be stopped as soon as a reject End is detected.
Optional manual feed unit available, allowing batch testing when necessary.

Online Disadvantages

Initial outlay. One system required per press.
It is not unusual for End plants to have both on and off-line systems on site. Please contact us to discuss your specific requirements.


Q.Do I require sample leaks to calibrate an Ovec AET Micro Leak Detector?
A.

No, these are not required for any Ovec micro leak detector. Each system is self calibrating, after a user definable number of cycles, through the use of calibrated reference leaks.


 

 

 

 


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