Flow Control: Technology information & new products for fluid handling engineers

8/12/2009

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GLOSSARY OF TERMS: Leak Detection

ADSORPTION: Refers to the condensation of gas or vapor on the surface of a solid.

AMBIENT AIR: Air to which the sensing element is normally exposed.

BURST TEST: The burst test method requires the filling of a container with liquid or part and pressurizing it until it bursts, thus establishing its tolerances. This is usually a destructive test.

FLOODING: In leak detection, a system under leak test that becomes so filled with a tracer gas that it is not possible to continue the leak test. In gas detection, a sensor flooding occurs when a gas concentration at the sensor exceeds its stoichiometric mixture. The signal from the sensor reverts to zero because the mixture in the air is too gas-rich to burn.

HYDROSTATIC: Leak testing method whereby components are internally pressurizing with water. Not to be confused with a burst test.

IMMERSION: A leak testing method where an object is immersed in a liquid and a leak in indicated by the escape of air in the form of bubbles. Particularly useful for odd-shaped objects.

LEAK: Technically, 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. Leaks are often conceived of being simply a round hole; however, this is almost never the case. A leak normally has an involved geometry sometimes extending quite a distance from beginning to end. As a result, leakage repair may require locating both the start and end of the leak.

PERMEATION: A type of leak through a barrier that has no hole or discrete passage.

QUANTITATIVE: In leak measurement, overall leakage measurement for a complete component or system, but with no location.

SENSITIVITY: In terms of leak testing, the smallest leak rate that the technique used (instrument, equipment, system, method, etc.) is capable of detecting under a specified set of conditions (pressure, temperature, etc.)

SOAP SOLUTION: A primitive form of bubble leak testing since replaced by synthetic solutions, such as thin-film leak testing. Soap and water has low sensitivity and tends to obscure small leaks by foaming when applied.

STANDARD: In leak testing, a device that permits a tracer gas to be introduced into a leak detector or leak testing system at a known rate to facilitate calibration of the leak detector.

STOICHIOMETRIC: The exact percentage of two or more substances which will react completely with each other leaving no unreacted residue. For example, a 7 percent mixture of methane by volume in air will react completely with the oxygen present leaving only CO2 and H2O as residue. If the methane concentration here is less than 7 percent, there would be oxygen left over. If the methane concentration were greater than 7 percent, there would be methane left over.

THIN FILM TEST: A leak test using a solution that bubbles upon finding a leak.

TRACER DYE: A dye, usually red or fluorescent, which when added to a fluid (water, oil etc) will visually show the path the fluid is traveling and, therefore, reveal a leak if there is one.

TRACER GAS: A gas, which passing through a leak can then be detected by a specific leak detector and thus disclose the presence of a leak.

ULTRASONIC: A leak detector that translates inaudible ultrasonic frequencies into a variety of recognizable sounds and meter readings.

This glossary of terms and definitions was contributed by American Gas & Chemical Co. (www.amgas.com), a supplier of detectors and monitors for leak and gas testing.

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