Leak testing

What is this method?

Leak testing equipment is a type of nondestructive testing equipment used to measure the escape of liquids, vacuum or gases from sealed components or systems. Some configurations require a separate leak detector or sensor as an input. They are often equipped with various other components such as pumps, calibrators, gages, and cases. A leak is a hole or porosity in an enclosure capable of passing a fluid from the higher-pressure side to the lower pressure side. There are many basic leak test methods and a few variations. The most familiar are dunk testing, pressure decay, mass flow, mass spectrometer and ultrasonic. Dunk testing is still the most popular method, with pressure decay and mass flow rapidly gaining in use. Mass flow is the de facto test method of choice in automotive applications. An exception is pressure decay testing on a brazing fixture.

Why is this method?

Manufacturers that produce parts that contain gas or liquid, need to know if their products include any defects that could allow leakage. Defective products can be costly due to increased warranty claims and potentially endangering consumer safety. A main component of many leak testing methods is the concept of leak flow, which refers to the leakage of a gas or liquid from the product.

When is this method used?

For leaks of air into atmosphere, units are usually expressed as mm3 or cm3 (cc) per second or minute. So, 16.6 mm3/sec = 1 cm3/min. A bubble under water is about 30 – 50 mm3, so 1 bubble per second is about 30 mm3/sec or 2 cm3/min. A standard unit of leakage which takes account of air pressure is the mbarl/sec. (Millibar-litre per second). A leak into atmosphere of 1 mbarl/sec is equivalent to a volume leak of 1000 mm3/sec.

If there is a situation where a no leak application is required, there is only one choice— mass spectrometer—regardless of cost. This application uses helium and hydrogen gases as part of its inspection process. The good news is the leakage may be so microscopic it is rarely detrimental to product performance.

There are various testing techniques which can be applied:
  • under vacuum or under pressure,
  • with different search gas: helium, ammonia, Sulphur hexafluoride,
  • to closed volumes with a value varying of some cubic centimeters to thousand cubic meters.
Roles and responsibilities:

Leak testing now a days is normally done by equipment’s and the equipment’s are made to run in the presence of supervisors and the supervisor must ensure that the leakages in respect of both the gases and the liquids that are flowing in the huge manufacturing pipes and throttles are accurate and periodic check of those with the assistance of leak test equipment’s are to be done.