Production Leak Detection Systems

Up Effect of Leak Meth. Amount of Leak Meth Traditional Methods

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FTI Production Leak Detection:

FTI prides itself on developing leak detection systems at the leading edge of technology.  FTI offers various methods of leak detection, including pressure change, and Mass Spectrometry related methods.  In addition, FTI offers the traditional forms of leak detection; Sniffing, and Immersion (bubble testing).  

FTI will examine the details of your application, and precisely match the method that is appropriate.  

Leak Testing Overview:

What is a Leak?

A leak is a flow of material, either out of an orifice, or through a material (permeation).  It is an admission or release of a material. 

A crack in a brazed joint, a cut O-ring or a thin walled area of a molded container all result in leaks. 

What is Leak Testing?

In general, leak testing is the measurement of the amount of media leaking through material over time.  There are many methods used to measure the amount of released material, and various media are used as the tracing agents (depending on the measurement method used).  Each method carries with it different characteristics that make one method more favorable than another for a specific application.  Examples of these characteristics are economics, accuracy, tolerance to environmental conditions, leak rate specification, production rate, equipment component limitations, etc.  Most leak detection methods do NOT locate the leak in a part, they simply quantify  the rate at which a part leaks.  Other methods are used to locate leaks on a part.

More about Leaks: 

EVERYTHING LEAKS.  A product may exhibit an extremely small leak rate, but it will still leak.  All materials have cracks, crevices, or holes, of some dimension (possibly microscopic).  These may have been created during the manufacturing process, due to wear, fatigue, stress, or just due to the porosity of the material.  

The big question is HOW MUCH does something leak?  How much is safe?  How much is the industry or governmental standard?  How much is allowable, while still satisfying your customer's needs?

Leak Rate Specifications:

Leak rates are defined as the mass of tracer media escaping over a given time, at a given pressure.  

A leak rate is fully specified if the following three parameters are known or can be calculated: 

bulletMass flow rate "Q" (includes Mass and Time components)
bulletAt pressure "p"

A typical leak rate in the air conditioning industry would be 1.8 x 10-5 std. cc/sec Helium at 300 psi, or 0.1 oz. Freon/year at 300 psi.  

There are two basic set of constraints effecting leak testing machines: natural constraints and equipment constraints.

Natural constraints can include the amount of pressure change inside the part due to leaks, the effect of part geometry on the detection of leaks, the temperature effects, humidity and many other factors. 

Equipment constraints can consist of the resolution and range of measuring equipment, allowable pressures and feasible volumes.  Currently, high production measurable leak rate specifications range between 100 to 10-9 std. cc/sec.

How do we measure leaks?

Leak measurement is available in three types:  

bullet Effect of the Leak Methods
bullet Amount of the Leak Methods
bulletTraditional Leak Testing Methods. 

The following table summarizes the methods.

Click on the links below to learn more about each group of methods:

Effect of leak methods

Amount of leak methods

Traditional methods

bulletPressure Decay
bulletPressure Differential
bulletPressure Increase
bulletVacuum Decay
bulletMass Flow
bulletHard Vacuum Inside/Out
bulletHard Vacuum Outside/In
bulletCarrier Gas

What is the difference between Effect of the Leak and Amount of the Leak?

To demonstrate the difference between Effect of the Leak and Amount of the Leak testing methods, we will use a swimming pool example.  

Imagine the water level of the swimming pool (height).  If we were to use a 0.4 cc spoon to remove 10 spoonfuls of water from a 100 ft. long by 30 ft. wide and 9 ft. deep swimming pool (representing a leak from a product), the Effect of the Leak method would attempt to measure the change in the level (height) of the swimming pool due to the removal of the water.  

Amount of the Leak method would attempt to measure the volume of the spoonfuls of water removed.  In the case of the swimming pool example, it would make sense to use the Amount of the Leak method because the volume of the spoonfuls is much easier to measure.  The measurement would be more accurate, and more repeatable.  

To illustrate the difficulty in obtaining an accurate Effect of the Leak measurement in our pool example, we calculate that the environmental effect of temperature on the water level of the pool from an increase in the temperature of 1 degree C would raise the height of the water level 0.026 in.  Taking out 10 spoonfuls of water would only lower the height 0.00000063 in.  Not only would we have difficulty accurately measuring such a small number, but the environmental effects would falsify the test.