What is Welding Air Leakage Test?

A welding air leakage test (also called a pressure decay test or leak test) is a non-destructive testing (NDT) method used to detect leaks in welded joints by pressurizing the component with air (or another gas) and monitoring for pressure drops or visible/heard leaks.

Methods for Welding Air Leakage Testing

Bubble Test (Soap Solution Test)

Apply a soapy water solution to the welded area.

Pressurize the component with low-pressure air (typically 1–5 psi).

Bubbles form at leak points.

Pros: Simple, low-cost, effective for small parts.

Cons: Manual inspection, not suitable for high-pressure systems.

Pressure Decay Test

Seal the welded component and pressurize it to a specified level.

Monitor pressure drop over time using a gauge or sensor.

A significant drop indicates a leak.

Pros: Quantitative, good for closed systems.

Cons: Requires calibration, sensitive to temperature changes.

Vacuum Leak Test

Evacuate air from the component and check for pressure rise.

Alternatively, use a vacuum box with soap solution on the outside.

Pros: Effective for large structures (e.g., tanks, pipelines).

Cons: Requires vacuum equipment.

Ultrasonic Leak Detection

Use an ultrasonic detector to pick up high-frequency sounds from escaping air.

Pros: Detects tiny leaks, no need for liquid solutions.

Cons: Requires skilled operation, background noise interference.

Helium Leak Testing (Mass Spectrometry)

Pressurize the component with helium and use a detector to locate leaks.

Pros: Extremely sensitive (detects very small leaks). Cons: Expensive, requires specialized equipment.

• Standards & Acceptance Criteria
• ASME BPVC Section V: Covers leak testing standards for pressure vessels.
• ISO 9978: For leak detection in radioactive systems.
• AWS D1.1: Specifies acceptance criteria for welded structures.
• Acceptable Leak Rates depend on application (e.g., HVAC vs. high-pressure gas lines).
• Best Practices
• ✔ Clean surfaces before testing (oil, dirt can mask leaks).
• ✔ Use appropriate pressure (avoid over-pressurizing thin materials).
• ✔ Document results for quality control.