Leak testing is a critical procedure used by inspectors to determine whether an object or system is operating within specified leak limits. This method helps identify any defects that could lead to the escape of liquids or gases, ensuring the integrity and safety of the components being tested.

Leaks occur when there's a flaw—such as a crack, hole, or weak seal—in a container or system, allowing its contents to escape. Leak testing uses pressure to detect these flaws, making it an essential part of regular maintenance and quality control procedures. By identifying and addressing leaks early, companies can prevent failures, reduce waste, and improve overall product reliability.

Leak testing is commonly applied to objects and systems designed to hold or transport liquids or gases. It plays a vital role in industries where even the smallest leak can have serious consequences, such as in medical devices, automotive parts, or food packaging.

As a non-destructive testing (NDT) method, leak testing allows inspectors to evaluate the condition of an object without causing damage. This makes it ideal for routine checks and long-term monitoring of equipment. Non-destructive methods are widely preferred because they preserve the integrity of the tested item while still providing valuable insights into its performance.

[Non-destructive leak testing is just one of many NDT techniques. Discover more about NDT in this detailed guide.]

What Is Leak Testing?

Leak testing involves using pressure to detect defects that may be causing leaks in an object. The principle behind this method is simple: when a substance leaks out of a container, it moves from an area of high pressure to low pressure. Leak testing exploits this natural flow by applying controlled pressure to the system and monitoring the movement of the substance to locate the leak.

This technique is most effective when testing closed systems, where the presence of a leak would significantly affect internal pressure. The success of a leak test depends on the material and design of the object being tested. Different materials respond differently to pressure, which can influence the accuracy and effectiveness of the test.

During a leak test, inspectors look for various types of defects, including:

• Cracks
• Holes
• Weak seals
• Other imperfections that might allow gas or liquid to escape

Leak testing is widely used across multiple industries, such as:

• Automotive
• Consumer goods
• Medical devices
• Packaging
• Sealed electronics

Advances in Leak Testing

Recent technological advancements have significantly improved the accuracy and efficiency of leak testing. Innovations in sensors, valves, and data processing have made it possible to detect even the smallest leaks with greater precision. These improvements have not only increased the speed of testing but also enhanced the ability of engineers to monitor and maintain systems in real time.

The integration of the Internet of Things (IoT) has revolutionized how leak testing data is collected and shared. With remote access capabilities, inspectors can now monitor systems from anywhere, ensuring timely responses to potential issues. This connectivity also enables better collaboration between teams, leading to faster decision-making and more efficient maintenance strategies.

Leak Testing Methods

There are several common methods used in leak testing, each suited for different applications:

• Burst: Applies increasing pressure until the device fails, useful for determining structural limits.
• Chamber: Used for sealed systems without direct access for pressure introduction.
• Pressure Crack: Detects small leaks using a downstream sensor.
• Pressure/Vacuum: Compares pressure between the test object and a reference volume to identify leaks.
• Pressure Decay: Measures pressure changes under positive pressure to detect leaks.
• Vacuum Decay: Identifies leaks under negative pressure conditions.
• Occlusion: Detects obstructions in gas flow paths.

Most leak tests operate at low pressures, typically at least 15 psi or 25% of the design pressure, whichever is lower. This ensures safety while still being effective in detecting leaks.

Key Considerations for Leak Testing

While leak testing is a powerful tool, it comes with unique challenges. Inspectors must take several factors into account to ensure accurate results and avoid unnecessary damage to the tested object.

Acceptable Leak Rate

Knowing the acceptable leak rate is crucial. Not all leaks require immediate action—some may be monitored or ignored if they fall within safe limits. Industry standards often define these thresholds, helping inspectors make informed decisions.

Manufacturing Considerations

Understanding the original purpose of a system or component is important. Some items are designed to be completely sealed, while others are meant to allow controlled flow. This distinction affects how leak testing is performed and interpreted.

Material Considerations

The material properties of the object being tested play a significant role. Brittle or highly flexible materials may react unpredictably under pressure, so testing procedures should be adjusted accordingly.

Medium Considerations

The type of substance being held by the object also influences the testing process. Gases and liquids behave differently under pressure, and their molecular size determines what kind of defect can cause a leak. Choosing the right pressure range is essential to avoid false readings or damage.

Leak Testing Equipment

A variety of tools are used in leak testing, depending on the method and application. Here are some of the most common devices:

Air LeakAGE Inspection Devices

Photo credit: Zaxis

Air leak testing devices provide real-time data to inspectors, supporting a wide range of testing methods. They are especially useful for vacuum decay, pressure decay, and other pressure-based tests.

Compact Pressure Decay Leak Tester

Photo credit: Zaxis

This compact device reduces connection volume, improving test sensitivity and reducing testing time. It’s ideal for use in tight spaces or during production line inspections.

Large Display Leak Tester

Photo credit: Zaxis

Larger models like the Zaxis 7i offer enhanced features such as larger screens, higher capacity, and faster testing speeds, making them suitable for complex or large-scale operations.

Leak Standard

Photo credit: Zaxis

Leak standards help calibrate testing equipment and ensure consistency in measurements. They are used to simulate leaks or compare different testing systems for accuracy.

Leak Testing Standards and Codes

Leak testing is governed by a number of international and industry-specific standards. These codes help ensure that testing is conducted consistently and effectively across different sectors.

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