Helium Leak Testing with Mass Spectrometer Detection

Helium leak testing detects leaks between one thousand and one million times smaller than pressure decay methods can resolve. The helium atom is small enough to pass through paths that hold back other gases, and mass spectrometer detection responds to helium alone, so moisture, process residues and atmospheric conditions produce no false indications. itmad provides helium leak testing by sniffing, hard vacuum and integral hood methods, detecting leak rates as low as 1×10⁻¹² mbar·l·s⁻¹ and locating leaks precisely. itmad operates across the Middle East, Asia and Europe. Last reviewed: October 2026.

Sensitivity

The hard vacuum technique resolves leak rates as low as 1×10⁻¹² mbar·l·s⁻¹, and sniffing detects to around 1×10⁻⁶ mbar·l·s⁻¹. For scale, a leak of one cubic millimetre per second is roughly 1×10⁻³ mbar·l·s⁻¹, several orders of magnitude larger than what this method finds.

Methods

In helium sniffing, the component is pressurised with helium and a hand-held sniffer probe is scanned across weld seams, flanges, seals and valve packing, which suits large assemblies, pipelines and anything that cannot be placed in a vacuum chamber. In the hard vacuum or vacuum spray method, the component is evacuated and helium is sprayed on the outside, and helium entering through a leak path reaches the mass spectrometer connected to the evacuated system. It gives the highest sensitivity available and suits pressure vessels and sealed assemblies.

The integral hood under pressure method pressurises the object with helium and encloses it in a collection hood, where escaping helium accumulates and the detector measures the total leak rate, which is used where a whole-item figure is needed and not a location. A bombing test is used for hermetically sealed components with an internal cavity: the item is held in a helium pressure chamber for an extended period so that helium penetrates any leak path, and is then moved to a vacuum chamber where escaping helium is measured, for sealed electronics, semiconductor packages, ampoules and small pressure-tight assemblies that cannot be connected to a detector directly.

The integral hood under vacuum method evacuates the object and surrounds it with a helium-filled hood, giving a cumulative total leak rate suited to small closed vessels, medical devices and semiconductor components. Bubble leak testing, by direct pressure or vacuum box, wets the surface with a surfactant solution and applies a pressure differential so that bubbles form at a through-wall defect. It is far less sensitive than helium, but fast, low cost and suited to large weld seams and tank floors, where the leak sizes of interest are well within its range.

Where it applies

In oil and gas, helium testing is used on pipelines, pressure vessels, valve assemblies, flanges and wellhead components; in power generation on boilers, condensers, steam turbines and heat exchangers; and in marine and offshore work on vessels, rigs, subsea equipment and offshore containers. It is used on reactors, storage tanks and process pipework in chemical and petrochemical plants, on closed vessels, vacuum chambers and production line verification in manufacturing, on hydraulic and fuel system components and sealed enclosures in aerospace and defence, and on engine components, fuel tanks, heat exchangers and HVAC in automotive.

Why helium rather than pressure decay

Helium detects leaks orders of magnitude smaller, and it is selective to helium, so there are no false positives from moisture or other gases. It locates the leak precisely and does not merely confirm that one exists, and it is dry and temperature-independent, so no drying is needed before return to service. It gives quantified, reproducible leak rates suitable for an audit trail, and it finds micro-leaks early, before they develop into failures.

Standards applied

ASME Boiler and Pressure Vessel Code Section V, Article 10, covers leak testing, including the detector probe, tracer probe and hood techniques, with acceptance to the relevant construction code section. ASTM E498 covers leak testing using the mass spectrometer leak detector in the tracer probe mode, ASTM E499 the detector probe mode and ASTM E493 the inside-out testing mode, and ISO 20485 covers the tracer gas method for non-destructive leak testing. Client, project and manufacturer specifications apply where they set a tighter acceptance threshold.

Calibration and reference leaks

A leak rate figure is only meaningful if the instrument was calibrated against a known standard at the time of the test. The detector is calibrated with a certified reference leak before testing begins and verified again on completion, so that any drift during the test is identified and not assumed absent. Response time and background helium level are established before measurement, since residual helium in the working area would otherwise mask or exaggerate a leak.

Acceptance criteria

The code or specification governing the item sets acceptance, not the test method. Pressure equipment built to ASME normally carries an acceptance threshold stated in the construction code, while process and pipeline work is more often governed by a client specification. Where no criterion has been specified, itmad says so before testing and does not apply a default, because a leak rate reported against the wrong threshold is worse than no test.

Preparation and limitations

Surfaces must be clean and dry at the test location, as oil, water and residues will temporarily seal a leak path and reopen in service. Components previously exposed to helium retain background gas that must be allowed to dissipate before a valid test, and very large volumes take longer to evacuate and to reach a stable background, which affects scheduling on shutdown work. Where a leak is intermittent or opens only at operating temperature or pressure, a test at ambient conditions may not reveal it.

Safety

Helium is non-toxic, non-flammable and chemically inert. Because bottled helium is an asphyxiant, the work is carried out with appropriate ventilation and confined space controls where required.

What the client receives

A report identifying the item tested, the method applied and the test parameters, with the measured leak rate and the acceptance threshold applied, the location of each leak found, the instrument calibration traceability and a pass or fail result against the specification.

Frequently asked questions

What is helium leak testing used for?

Detecting and locating leaks in pressurised systems, vacuum systems, sealed components and pipelines, wherever an undetected leak would create a safety, environmental or quality risk. Mass spectrometer detection resolves leak rates as low as 1×10⁻¹² mbar·l·s⁻¹.

Which helium leak testing methods does itmad use?

Helium sniffing, hard vacuum or vacuum spray, integral hood under pressure and under vacuum, the bombing test for hermetically sealed components, and bubble leak testing. The choice depends on the component and the sensitivity required.

How sensitive is helium leak testing?

The hard vacuum technique resolves leak rates as low as 1×10⁻¹² mbar·l·s⁻¹, and sniffing detects to around 1×10⁻⁶ mbar·l·s⁻¹. That is up to a million times more sensitive than pressure decay methods.

Which standards apply?

ASME Section V Article 10, ASTM E498, E499 and E493 for the mass spectrometer modes, and ISO 20485 for the tracer gas method. Client and manufacturer specifications apply where they set a tighter threshold.

Is helium leak testing safe?

Helium is non-toxic, non-flammable and chemically inert, but bottled helium is an asphyxiant. The work is therefore carried out with appropriate ventilation and confined space controls where required.

Why is helium preferred to pressure decay?

It detects far smaller leaks, gives no false positives from moisture or other gases, locates the leak precisely, and needs no drying before return to service. It also gives quantified, reproducible leak rates for an audit trail.