A well-designed sealing performance determination scheme is essential for verifying the leak-tightness, reliability, and service life of seals, gaskets, valves, packaging, and enclosures across automotive, pharmaceutical, oil and gas, and electronics industries. This technical article outlines how to structure a complete sealing test plan, covering sample categories, measurable performance parameters, internationally recognized test methods such as pressure decay, vacuum decay, and helium leak detection, and the relevant ISO, IEC, ASTM, EN, and GB standards. Accredited third-party laboratories routinely apply these schemes to support product development, quality control, and regulatory compliance.
Technical Overview
Sealing performance determination refers to the systematic evaluation of a component or assembly's ability to prevent the unintended passage of gases, liquids, or particulate contaminants across a sealing interface. A testing scheme design translates this objective into a documented plan that defines the test object, the performance parameters to be measured, the test media, pressure and temperature conditions, the instrumentation and method to be used, the acceptance criteria, and the reporting format.
A robust scheme is typically structured around four pillars. First, the functional requirement must be quantified, for example as a maximum allowable leak rate in Pa·m³/s, mbar·L/s, or sccm. Second, the test method must be matched to the required sensitivity, since pressure decay techniques typically resolve leak rates down to approximately 10⁻³ mbar·L/s, whereas helium mass spectrometry can reach 10⁻⁹ mbar·L/s or lower. Third, the environmental conditions, including temperature cycling, vibration, and differential pressure, must reflect the intended service environment. Fourth, the acceptance criteria must be traceable to product specifications or recognized standards.
The scheme design process should also incorporate statistical considerations, such as the number of samples per batch, the sequence of non-destructive and destructive tests, and the treatment of borderline results. Where certification is required, testing is commonly performed by accredited third-party laboratories operating under ISO/IEC 17025 management systems.
- Define the sealing function and failure mode to be evaluated
- Select measurable parameters such as leak rate, pressure drop, or water ingress
- Match the detection method to the required sensitivity threshold
- Specify test media, pressures, temperatures, and dwell times
- Establish traceable acceptance criteria and reporting requirements
Testing Samples
Elastomeric Seals and O-Rings
O-rings, grommets, lip seals, and molded rubber seals are tested for leak tightness, compression set, and stress relaxation. Typical materials include NBR, EPDM, FKM, silicone, and PTFE compounds. Dimensional verification per ISO 3601-1 and material characterization are usually performed before leak testing to isolate geometric from material effects.
Flat Gaskets and Flange Joints
Metallic, semi-metallic, and non-metallic gaskets used in bolted flange connections are evaluated for sealing performance under controlled gasket stress. Test schemes reference standards such as EN 13555, which defines the PQR characteristics (leak rate as a function of gasket stress and internal pressure), and ASTM F37 for sealability of gasket materials.
Industrial Valves
Gate, globe, ball, butterfly, plug, check, and safety valves are tested for shell tightness and seat tightness. Scheme design references ISO 5208, API 598 equivalents, and GB/T 13927, with additional fugitive emission testing of stem seals per ISO 15848-1 and ISO 15848-2.
Flexible and Rigid Packaging
Pharmaceutical blister packs, vials, sachets, pouches, and sterile barrier systems are tested for seal integrity using deterministic methods such as vacuum decay and helium leak detection, or probabilistic methods such as dye ingress and microbial challenge. Relevant standards include ASTM F2338, ASTM F2096, ASTM F3029, and ISO 11607 for terminally sterilized packaging.
Electrical Enclosures and Connectors
Enclosures, cable glands, connectors, and lighting fixtures are tested against the IP code system defined in IEC 60529, including dust ingress (IP5X, IP6X) and water ingress (IPX1 through IPX8). Automotive connectors may additionally be evaluated under USCAR-2 style performance specifications.
Building Components
Windows, doors, curtain walls, and ventilation assemblies are assessed for air permeability using ASTM E283, EN 1026, or GB/T 7106, often combined with watertightness and wind load resistance to form a complete envelope performance scheme.
Testing Items
The measurable outputs of a sealing performance scheme depend on the product class, but the core parameters are summarized below.
- Leak rate determination, expressed in mbar·L/s, Pa·m³/s, sccm, or cm³/min
- Pressure decay rate over a defined stabilization and measurement interval
- Seat and shell tightness of valves at 1.1 to 1.5 times rated pressure
- Fugitive emission concentration, typically measured as methane or helium leakage in ppmv at stem and body joints
- Water ingress behavior under immersion, spray, or jet exposure per IPX ratings
- Dust ingress classification for enclosure testing
- Air permeability of building components at defined pressure differentials
- Seal integrity of packages under vacuum, internal pressure, or trace gas conditions
- Compression set and stress relaxation after thermal or oxidative aging
- Cyclic durability, including pressure cycling, thermal cycling, and mechanical flexing
Testing Methods
Pressure Decay Method
The test part is pressurized with dry air or nitrogen, isolated from the source, and the internal pressure is monitored over time. A pressure drop beyond the calculated threshold indicates leakage. The method is fast, fully automated, and non-destructive, making it suitable for 100 percent production line testing. Temperature drift must be compensated because a one-degree change can mimic a small leak. Scheme design should define fill pressure, stabilization time, measurement time, and the resolution of the transducer.
Vacuum Decay Method
The sample is placed in a test chamber connected to a vacuum source, and chamber pressure is monitored for a rise indicative of package or component leakage. Conforming to ASTM F2338, this deterministic method is widely used for pharmaceutical packaging integrity and can detect defects in the micron range depending on package format.
Bubble Emission and Immersion Tests
For qualitative assessment, the sample is submerged while internally pressurized or placed under vacuum, and escaping gas streams are observed as bubble chains. ASTM F2096 describes internal pressurization for packages, while water bath dunk tests are commonly used for castings, welds, and hose assemblies. These methods are inexpensive and localize the leak path, although sensitivity is limited to approximately 10⁻³ to 10⁻⁴ mbar·L/s.
Helium Mass Spectrometry
Helium leak detection offers the highest sensitivity among industrial methods, reaching 10⁻⁹ to 10⁻¹² mbar·L/s. Two configurations are used: the vacuum method, where the evacuated test object is charged with helium and connected to a mass spectrometer, and the sniffing method, where a probe detects helium escaping from a pressurized part. Helium techniques are specified for critical components such as hermetic enclosures, refrigerant circuits, vacuum systems, and nuclear and aerospace hardware.
Tracer Gas and Flow Measurement
Alternative tracer gases such as hydrogen-nitrogen mixtures or SF6-free insulating gases can be detected with dedicated sensors. For larger enclosures and building components, direct airflow measurement at controlled pressure differentials per ASTM E283 or EN 1026 quantifies air leakage as a volumetric flow rate rather than a discrete leak rate.
Environmental and Combined Testing
Sealing performance is strongly temperature dependent because elastomer modulus, gas viscosity, and clearances change with temperature. Advanced schemes combine leak testing with thermal cycling per IEC 60068-2-14, damp heat per IEC 60068-2-78, or vibration per IEC 60068-2-6, then re-measure tightness to detect degradation. Long-term schemes may include accelerated aging of seal materials and subsequent compression set measurement per ASTM D395 or ISO 815.
Typical Scheme Sequence
- Incoming inspection: dimensional and material verification of seals and gaskets
- Baseline leak measurement at ambient temperature
- Environmental conditioning or mechanical cycling as applicable
- Post-conditioning leak measurement to quantify degradation
- Data analysis against acceptance criteria and issue of test report
Applications
Sealing performance schemes are applied across virtually every engineered industry, with typical use cases including the following.
- Automotive: fuel system components, coolant circuits, brake modules, battery packs, headlamps, and sensor housings
- Medical and pharmaceutical: sterile barrier systems, pre-filled syringes, vials, infusion sets, and implantable device enclosures
- Oil and gas: valve fugitive emission compliance, flanged joints, wellhead equipment, and pipeline pigging interfaces
- Aerospace: hermetic connectors, hydraulic fittings, fuel tanks, and pressure vessel welds
- Electronics and lighting: IP-rated enclosures, underwater cameras, connectors, and power supplies
- HVAC and refrigeration: compressor shells, evaporator and condenser circuits, and heat pump assemblies
- Construction: window and curtain wall air permeability, waterproofing membranes, and expansion joints
- Packaging and food: modified atmosphere packs, retort pouches, and can seam integrity
FAQ
How is the allowable leak rate determined in a scheme design?
The acceptance limit is derived from the functional consequence of leakage, such as allowable product loss over shelf life, ingress of moisture or contaminants, or emission regulatory limits. For valve fugitive emissions, ISO 15848 defines leak rate classes such as AH, BM, and related designations; for packaging, the limit is often tied to the sterile barrier requirement verified by method suitability studies.
Which leak test method should be chosen?
Method selection balances sensitivity, cycle time, cost, and whether the test must be non-destructive. Pressure and vacuum decay suit production screening; bubble tests suit localization and low-cost verification; helium mass spectrometry suits high-sensitivity requirements; and airflow measurement suits large building components.
What test pressure should be applied?
Unless a standard specifies otherwise, valve shell and seat tests are commonly conducted at 1.1 to 1.5 times the rated pressure with water, while air tests for enclosures and packages use the maximum expected service differential pressure. The scheme must never exceed proof pressure limits that could damage the specimen.
Why do temperature and stabilization time matter?
Gas pressure readings are temperature dependent, and sealing materials relax after pressurization. Adequate fill and stabilization periods prevent false failures. Climate-controlled test areas and temperature compensation algorithms are recommended for tight acceptance windows.
How many samples are required?
For design verification, a typical scheme uses three to five units per configuration for destructive tests and larger statistical samples for production validation. For routine manufacturing control, 100 percent testing with pressure decay is common because the method is non-destructive and fast.
Can a sealing test scheme support certification?
Yes. When executed by accredited third-party laboratories, results can support IP code marking, valve type approval, packaging system validation, and compliance demonstrations to ISO, IEC, ASTM, EN, and GB requirements for regulatory submission or customer acceptance.