Helium Leak Testing (HLT)

Helium Leak Testing is a highly sensitive non-destructive testing (NDT) method used to detect and measure very small leaks in pressure systems, vacuum systems, and sealed components. It is widely used in industries where leak-tightness is critical, such as aerospace, nuclear, semiconductor, and medical device manufacturing.

Overview

Helium Leak Testing uses helium gas as a tracer because of its small atomic size, inert nature, and low natural background presence in the atmosphere. Helium is introduced into or around the test object, and a mass spectrometer leak detector is used to sense and quantify any escaping helium. This method can detect leaks as small as 10-9 mbar·L/s, making it one of the most sensitive leak detection techniques.

Apparatus and Working

Apparatus

  • Helium gas supply: High-purity helium cylinders.
  • Mass spectrometer leak detector: Sensitive instrument tuned to helium.
  • Vacuum pumps: To evacuate the test object or detector system.
  • Test connections: Valves, hoses, and fittings for pressurization or sniffing.
  • Sniffer probe: For detecting helium escaping into the atmosphere.

Working Methods

  1. Vacuum method: The test object is evacuated and surrounded by helium; any helium entering is detected by the mass spectrometer.
  2. Sniffer method: The object is pressurized with helium, and a probe is used externally to detect escaping helium.
  3. Accumulation method: The object is placed in a chamber; helium escaping accumulates and is measured over time.

Principle

Helium Leak Testing is based on the principle of using helium as a tracer gas. Due to its small atomic size and inertness, helium can pass through extremely small openings. A mass spectrometer tuned to helium detects its presence with very high sensitivity. The amount of helium detected corresponds to the leak rate, allowing both qualitative (leak location) and quantitative (leak size) assessment.

Advantages and Disadvantages

Advantages

  • Extremely high sensitivity (detects very small leaks).
  • Helium is inert, non-toxic, and safe to use.
  • Provides both leak location and leak rate measurement.
  • Applicable to complex systems and sealed components.
  • Widely accepted in critical industries (aerospace, nuclear, medical).

Disadvantages

  • Equipment is expensive and requires skilled operators.
  • Test setup can be time-consuming.
  • Not suitable for very large leaks (detector may saturate).
  • Helium supply can be costly and limited in some regions.

Applications

  • Aerospace: Testing of fuel systems, hydraulic lines, and spacecraft components.
  • Nuclear industry: Leak testing of reactor components and containment systems.
  • Semiconductor manufacturing: Ensuring vacuum integrity in process chambers.
  • Medical devices: Testing pacemakers, catheters, and sealed implants.
  • Refrigeration and HVAC: Detecting leaks in compressors, condensers, and piping.

Welding Defects Detectable by Helium Leak Test

  • Porosity (open to surface): Gas pores that allow helium to escape.
  • Cracks: Surface-breaking or through-thickness cracks that leak under pressure.
  • Lack of fusion (surface-reaching): Imperfect bonding that creates leak paths.
  • Incomplete penetration: Root defects that extend through the weld thickness.
  • Pinholes and blowholes: Small openings in weld metal that connect to the surface.