ISO 20486:2017

Overview

ISO 20486:2017 - "Non-destructive testing - Leak testing - Calibration of reference leaks for gases" specifies how to calibrate reference gas leaks used to set and verify leak detectors. The standard describes comparison and direct (volumetric) calibration methods so routine reference leaks become traceable to primary standards. It emphasizes calibration for helium (preferable because a mass spectrometer leak detector - MSLD - can selectively measure it) and defines procedures, uncertainty influences, labeling, reporting and handling of reference leaks.

Key topics

• Scope and purpose: Calibration methods for reference leaks used in everyday leak testing; establishing traceability to primary standards.
• Calibration approaches:
  • Comparison methods (A, As, B, Bs) - preferred for helium and suited to leaks with reservoirs and leakage rates below about 10−7 Pa·m3/s.
  • Volumetric / direct methods (C, D, E, F, G) - direct flow, under-water, gas meter, pressure-change in known volume, and volume-change at constant pressure.
• Leak classification:
  • Permeation leaks (reservoir type): good long‑term stability; significant temperature coefficient (~3.5 %/K).
  • Conductance leaks (capillary, aperture/orifice, compressed powder): capillary leaks have low temperature coefficient (~0.3 %/K) but are easily blocked.
• Reference conditions and nominal leakage rates: Recommended reference conditions (e.g., ambient temperature 20 °C, atmospheric exhaust pressure 1000 mbar, vacuum exhaust <100 mbar) and requirement to use nominal leakage rates for comparisons.
• Measurement and evaluation: Setup, sequence, uncertainty contributions, and evaluation formulas for each method are covered.
• Practical topics: Preparation of leaks/apparatus, temperature accommodation, reporting, labelling and handling of reference leaks.

Applications and users

ISO 20486:2017 is used by:

• Calibration laboratories establishing traceable reference leaks
• NDT and leak testing service providers setting or checking leak detectors
• Manufacturers of leak detectors and reference leak devices
• Quality and metrology engineers in aerospace, automotive, semiconductor, vacuum systems and refrigeration industries

Practical benefits include ensuring detector calibration traceability, reducing measurement uncertainty, harmonizing calibration practice (especially for helium MSLD use), and providing clear reporting and labeling rules for reference leaks.

Related standards

• ISO 20484 - Non-destructive testing - Leak testing - Vocabulary (MSLD definition and terminology used by ISO 20486)

Keywords: ISO 20486:2017, leak testing, calibration of reference leaks, non-destructive testing, helium, MSLD, reference leak calibration, volumetric calibration, comparison methods, traceability, measurement uncertainty.