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Leak Testing Methods - A Non-Destructive Testing Technique 

Leak testing is a non-destructive testing method that ndt inspectors utilize to determine whether a substance or system works with a determined leak limit. Leaks come up when there is the presence of a flaw, such as a crack, hole, or some other type of flaw in a substance, enabling whatever gas or liquid it contains to pour out. Leak testing utilizes pressure to recognize all these deformities to deal with them as part of normal maintenance procedures. 

As a whole, leak testing is performed on materials that reserve or shift liquid or gasses. Leak testing is one of the most utilized examination methods. It is a non-destructive testing method; inspectors can execute it without permanently causing any harm to the object. 

What Is Meant By Leak Testing?

Leak testing is a widespread non-destructive testing used by inspectors to identify the existence of defects in a material that is the reason for leaks. When elements come out of the container, they flow from where the pressure is increased to where it is low. Leak testing tends to leverage this phenomenon by utilizing pressure to produce flow towards the lower pressure, that is, the location of leaks, while strictly monitoring the flow. 

Leak testing must be performed when inspecting for flaws within an enclosed system. The success of this non-destructive testing completely relies on the object being tested. This is so because different objects and materials might respond differently to the high pressure generally utilized in leak testing to push a gas or liquid out of a defect. In leak testing materials, ndt inspectors will examine for deficiencies like holes, weak seals, cracks, or any other imperfections. Leak testing is commonly utilized in various industries as a part of their maintenance procedures, such as packaging, consumer goods, sealed electronics, automotive, medical devices, etc. 

Also Read, Pipe Line Isometric Drawings

Methods Of Leak Testing 

Here are a few common leak testing methods that you must know: 

a) Burst

This specific method utilizes either a non-destructive or destructive test that ramps pressure to find the juncture at which the device will burst open. 

b) Pressure Crack 

This is used to observe "weeping" in valves accompanied by a downstream sensor monitor. 

c) Chamber

This method is utilized to recognize defects that result in leaks in a sealed environment, similar to a package or device, that was not developed with an opening to enable the curtain-raiser of pressure for leak testing. 

d) Pressure Decay 

This leak testing utilizes the pressure change of a material or system under positive pressure to determine defects that result in leaks. 

e) Pressure / Vacuum 

This method utilizes the pressurization of a test material and a reference volume. If there is a leak, the difference between the two will improve. (This procedure is completely automatic in nature).

f) Occlusion 

It helps identify the obstructions in a gas's flow path to recognize deformities causing leaks. 

g) Vacuum Decay

It utilizes the pressure change of a material or system under negative pressure to recognize defects that result in leaks. 

Leak Testing Considerations You Must Know 

A leakage inspection needs inspectors to input pressure into an object in order to recognize leaks, and it has some unique considerations as a non-destructive method. 

Here is an outline of the things that you must keep in mind: 

1) Acceptable Leak Rate 

It is essential for ndt inspectors & maintenance personnel to understand the acceptable leak rate for a material or system while performing a leak examination. However, all leaks need maintenance; some might require better monitoring or even zero action. Various industries generally have guidelines describing acceptable leak rates for numerous substances and products. 

2) Material Considerations 

The material that the entity is made out of, its material will create an impact on the leak test, and it must be taken into consideration. Suppose a substance is excessively brittle or malleable. In that case, these characteristics will directly relate to how the introduction of pressure will change the object, resulting in it changing or expanding the shape in some other way that must be considered when scheduling a leak test. 

3) Manufacturing Considerations 

Before executing a leak test, it is crucial to consider the function for which a part, system, or material was originally constructed. The target use case for a given material might require manufacturers to have developed it in such a way that it will be able to either allow or retain liquids to pass through. 

4) Medium Considerations

The material an object is created to retain must be considered when scheduling a leak test. Various substances have different sizes of molecules. While performing a leak test, it is important to be aware of the size of the defect that may be acceptable and the size that would be huge enough to enable a certain gas or liquid to escape. A relevant consideration is — pressure because different types of substances will truly respond in different ways to different ranges of pressure. An extremely high-pressure range could possibly cause damage to the object which is being tested. At the same time, a pressure range that is extremely low might return inconclusive outcomes. 

Further Reading, Acceptance Criteria for Liquid Penetrant Testing

Leak Testing Standards And Codes 

Leak testing is generally utilized for code-based examinations, and there will be leak testing standards in most countries that use these tests for examinations. 

Here are some of the most widespread testing codes: 

ASME (AMERICAN SOCIETY OF MECHANICAL ENGINEERS)

ASME B31.3: Pressure Testing and Leak Testing Requirements for Process Piping

ASTM (AMERICAN SOCIETY FOR TESTING AND MATERIALS)

ASTM E432-91(2017)e1: Standard Guide for Selection of a Leak Testing Method

ASTM E493 / E493M - 11(2017): Standard Practice for Leaks Using the Mass Spectrometer Leak Detector in the Inside-Out Testing Mode

ASTM E499 / E499M - 11(2017): Standard Practice for Leaks Using the Mass Spectrometer Leak Detector in the Detector Probe Mode

ASTM E1003 - 13(2018): Standard Practice for Hydrostatic Leak Testing

ASTM A1047 / A1047M - 05(2019): Standard Test Method for Pneumatic Leak Testing of Tubing

ASTM E1603/E1603M-11(2017) Standard Practice for Leakage Measurement Using the Mass Spectrometer Leak Detector or Residual Gas Analyzer in the Hood Mode

ASTM F2164 - 21: Standard Practice for Field Leak Testing of Polyethylene (PE) and Crosslinked Polyethylene (PEX) Pressure Piping Systems Using Hydrostatic Pressure

ASTM F2786 - 16(2021): Standard Practice for Field Leak Testing of Polyethylene (PE) Pressure Piping Systems Using Gaseous Testing Media Under Pressure (Pneumatic Leak Testing)

ASTM E2930 - 13(2021): Standard Practice for Pressure Decay Leak Test Method

ASTM WK76995: New Practice for Field Leak Testing of Polyamide-12 (PA12) Pressure Piping Systems Using Gaseous Testing Media Under Pressure (Pneumatic Leak Testing)

ISO (INTERNATIONAL ORGANIZATION FOR STANDARDIZATION)

ISO 20484:2017(en): Non-destructive testing — Leak testing — Vocabulary

ISO 20485:2017(en): Non-destructive testing — Leak testing — Tracer gas method

ISO 20486:2017(en): Non-destructive testing — Leak testing — Calibration of reference leaks for gasses

ISO 27895:2009(en): Vacuum technology — Valves — Leak test

Conclusion 

This was all about the leak testing method; I hope this article has served its purpose well in explaining different areas related to leak testing. For more such articles based on different types of nondestructive testing methods, visit OnestopNDT. Also, you can reach out to us for any further queries.