Overview
ISO 20485:2017 - Non‑destructive testing - Leak testing - Tracer gas method defines standardized techniques for detecting leaks by using a tracer gas and tracer‑gas‑specific detectors. The standard covers principles of detection, apparatus, object preparation, detailed Group A and Group B test techniques (tracer gas flowing into or out of the object), calibration and setup procedures, and test reporting. It applies where leak detection is required without destructive inspection of the component.
Key topics and technical requirements
- Principles of detection: Create a partial pressure difference across the test boundary so tracer gas passes through any leak and is revealed by chemical or physical detection. Chemical methods rely on visible reactions (colour change); physical methods use sensors that give an electrical signal proportional to tracer partial pressure.
- Detector types: Examples include mass spectrometers (helium), electron‑capture/alkali ion diodes (halogens/SF6), Pirani gauges (thermal conductivity differences), and photometers (absorption/emission band‑pass).
- Group A techniques (tracer flows into object): Evacuate or pressure‑test the item and apply tracer gas externally (total, partial, local vacuum techniques). Total technique can quantify leak rate; partial/local techniques are for localization.
- Group B techniques (tracer flows out of object): Fill the object with tracer gas and sample externally (vacuum box, accumulation, sniffing, bombing, vacuum chamber, carrier gas). Includes chemical methods such as ammonia with colour‑change reagents.
- Apparatus and calibration: Required equipment includes leak detectors, calibrated leaks (see ISO 20486), pressure/temperature gauges, tracer gas or certified mixtures, vacuum/purge systems, enclosures/hoods, sampling probes and data recording. Detectors must be adjusted and verified with calibrated leaks and background signals recorded.
- Object preparation & testing procedure: Clean, degrease and dry parts; seal irrelevant openings; avoid porous/plastic materials that cause virtual leaks. Reference/test conditions and system response times must be recorded and stated in the test report.
Practical applications and users
ISO 20485 is used by:
- NDT technicians and leak test specialists
- Quality and production engineers in aerospace, automotive, HVAC, valves, pressure vessels, and vacuum equipment manufacturing
- Research labs and service providers offering helium or tracer gas leak detection
It supports both leak localization and quantitative leakage-rate verification when non‑destructive integrity assessment is required.
Related standards
- ISO 20484 - Leak testing vocabulary (terms and definitions referenced)
- ISO 20486 - Calibrated leaks (referenced for calibration and traceability)
Keywords: ISO 20485, tracer gas method, leak testing, non‑destructive testing, helium leak detection, vacuum technique, sniffing test, vacuum box, bombing technique, calibrated leaks.
