Rubber gas corrosion tensile testing evaluates how exposure to corrosive gases such as ozone, sulfur dioxide, hydrogen sulfide, and nitrogen dioxide affects the tensile strength, elongation, and modulus of rubber materials. This combined environmental and mechanical test method is essential for validating the long-term durability of rubber seals, gaskets, hoses, and diaphragms used in automotive, petrochemical, and industrial applications. Accredited third-party laboratories conduct these tests in accordance with internationally recognized standards from ISO, ASTM, IEC, and GB to support material qualification, quality control, and product certification.
Technical Overview
Rubber gas corrosion tensile testing is a combined environmental and mechanical test method designed to quantify the degradation of rubber materials after exposure to corrosive gas atmospheres. The test consists of two sequential stages: first, rubber specimens are exposed to a controlled concentration of corrosive gas, typically while held under a defined tensile strain; second, the exposed specimens undergo tensile testing to measure changes in tensile strength, elongation at break, and tensile stress at specified elongations compared with unexposed control specimens.
The degradation mechanism is well documented in elastomer science. Ozone, even at concentrations as low as a few parts per hundred million (pphm), attacks the carbon-carbon double bonds in unsaturated diene rubbers such as natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). When the rubber surface is held under strain, ozone-induced cracks initiate and propagate perpendicular to the direction of strain, dramatically reducing tensile performance. Acidic industrial gases such as sulfur dioxide (SO2), hydrogen sulfide (H2S), nitrogen dioxide (NO2), and chlorine (Cl2) cause additional chemical damage, including chain scission, secondary crosslinking, filler surface reactions, and extraction of antidegradants, all of which alter the mechanical response of the material.
The test framework draws on complementary international standards:
- ISO 1431-1 and ASTM D1149 define ozone resistance testing under static and dynamic strain conditions.
- IEC 60068-2-60 and GB/T 2423.51 specify mixed flowing gas corrosion tests combining SO2, H2S, NO2, and Cl2.
- IEC 60068-2-42 and GB/T 2423.19 cover sulfur dioxide exposure testing for components.
- ISO 37, ASTM D412, and GB/T 528 specify the tensile property measurement methods applied before and after exposure.
- GB/T 7762 and GB/T 13642 address static and dynamic ozone resistance methods in the Chinese national standard system.
Testing Samples
Standard Dumbbell Specimens
Dumbbell-shaped specimens are die-cut from vulcanized rubber sheets with a preferred thickness of 2.0 ± 0.2 mm. Typical geometries include Type 1 and Type 2 dumbbells per ISO 37 and GB/T 528, or Die C specimens per ASTM D412. A minimum of five specimens per test condition is recommended for both the exposed group and the unexposed control group at each exposure interval.
Cut Specimens from Finished Products
When evaluations must reflect real product performance, specimens may be cut directly from finished items such as hoses, weatherstrips, bellows, and molded seals, provided that a uniform test section can be obtained and the thickness is recorded. Results from such specimens should be identified as product-specific.
Complete Elastomeric Components
O-rings, gaskets, and other sealing elements can be mounted on stretching fixtures or mandrels at a defined elongation during gas exposure to reproduce installed service strain. For tensile evaluation, ring specimens may be tested directly in accordance with the ring test configuration described in ISO 37, or standard dumbbells can be prepared from the same compound for comparative measurement.
All specimens must be free from surface defects, mechanical damage, and molding irregularities. Unless otherwise specified, specimens are conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 16 hours before baseline measurement.
Testing Items
The core test items quantify mechanical property changes caused by corrosive gas attack:
- Tensile strength (MPa) before and after gas exposure
- Elongation at break (%) before and after gas exposure
- Tensile stress at 100%, 200%, or 300% elongation (modulus)
- Percentage retention or percentage change of each tensile property
- Visual crack rating of the exposed surface under magnification, typically at 2x and 7x
- Time to first visible cracking under sustained or dynamic strain
- Hardness change (Shore A) as a supplementary indicator of surface degradation
- Mass and dimensional changes where required by the product specification
The primary acceptance parameters in most specifications are the retention of tensile strength and elongation at break, together with the absence of visible ozone cracking after the specified exposure period.
Testing Methods
Stage 1: Baseline Characterization
Control specimens are tested in tension using a calibrated universal testing machine in accordance with ISO 37, ASTM D412, or GB/T 528. The standard crosshead speed is typically 500 mm/min for Type 1 dumbbells, and the original tensile strength, elongation at break, and modulus values are recorded as the reference baseline.
Stage 2: Corrosive Gas Exposure
For ozone exposure per ISO 1431-1, ASTM D1149, or GB/T 7762, specimens are mounted at a specified static elongation, commonly 20%, and placed in an ozone chamber at a standard concentration of 50 ± 5 pphm, a temperature of 40 ± 2 °C, and near-atmospheric pressure with controlled gas exchange. Common exposure durations include 72, 96, and 168 hours, with higher concentrations up to 200 pphm used for accelerated screening. For mixed gas corrosion testing per IEC 60068-2-60 or GB/T 2423.51, specimens are exposed to a flowing gas mixture containing low parts-per-billion levels of SO2, H2S, NO2, and Cl2 at 25 °C and 70% to 75% relative humidity for 4 to 21 days. Dynamic strain test methods, in which specimens are cyclically strained during exposure, are applied when the service condition involves repeated flexing.
Stage 3: Post-Exposure Tensile Testing
After exposure, specimens are removed from the chamber and allowed to rest under standard laboratory conditions, generally for 16 to 96 hours but not more than 96 hours, before tensile testing. The same tensile method, grip separation, and crosshead speed used for the baseline measurement are applied to ensure comparability. Exposed surfaces are inspected under magnification before testing to record crack initiation and severity.
Data Evaluation
Property retention is calculated as the measured value after exposure divided by the mean value of the control specimens, multiplied by 100. Typical acceptance criteria in automotive and industrial specifications require tensile strength retention and elongation retention of at least 70% to 80%, with no cracking visible at the specified magnification. The test report documents the gas type and concentration, temperature, humidity, strain condition, exposure duration, median results for each group, retention values, and crack ratings.
Applications
Rubber gas corrosion tensile testing is applied across industries where elastomeric components face corrosive atmospheres during service:
- Automotive engineering: qualification of engine bay hoses, fuel system seals, door and window weatherstrips, and suspension bushings exposed to ozone, NOx from exhaust, and under-hood chemical atmospheres.
- Petrochemical and oil and gas: validation of seal rings, gaskets, and diaphragms exposed to sour gas streams containing hydrogen sulfide and sulfur compounds.
- Electrical and electronics: evaluation of cable jackets, connector seals, and insulating elastomers intended for industrial atmospheres containing SO2 and NOx, aligned with IEC environmental test frameworks.
- Water treatment and chemical processing: assessment of seals and membranes in chlorine- and ozone-bearing environments.
- Rail, mining, and tunneling: verification of rubber components exposed to polluted tunnel air and diesel exhaust byproducts.
- Material development: comparative ranking of polymer compounds, antiozonant packages, and EPDM, CR, NBR, and FKM formulations during formulation optimization.
Test data support new material introduction, supplier qualification, periodic production audits, failure analysis, and compliance demonstrations for OEM specifications and international certification programs.
FAQ
Which corrosive gases are most commonly used in this test?
Ozone is the most frequently applied gas because it causes rapid surface cracking in unsaturated rubbers. Mixed gas tests per IEC 60068-2-60 additionally use sulfur dioxide, hydrogen sulfide, nitrogen dioxide, and chlorine to simulate polluted industrial atmospheres and their effects on both the rubber surface and the tensile properties.
How long does a typical test take?
A standard ozone exposure with tensile evaluation typically runs 72 to 168 hours of chamber exposure plus baseline and post-exposure tensile testing, so the complete program usually takes about one to two weeks. Mixed gas corrosion programs of 4 to 21 days may extend the overall schedule to three to four weeks.
What results are considered acceptable?
Acceptance limits are set by the product specification, but common criteria require tensile strength and elongation at break retention of at least 70% to 80% of the control values, with no visible cracks on the strained surface at the magnification specified in the standard.
How does this test differ from heat aging tensile testing?
Heat aging per ISO 188 or ASTM D573 evaluates bulk thermal oxidative degradation at elevated temperature, whereas gas corrosion testing evaluates the specific chemical attack of ozone or acidic gases, which is concentrated at the surface and strongly accelerated by tensile strain. The two methods are complementary and are often run together in full qualification programs.
Do ozone-resistant rubbers still require this test?
Yes. Saturated elastomers such as EPDM exhibit excellent ozone resistance, but gas corrosion tensile testing is still used to verify compound quality, antidegradant dispersion, and resistance to mixed industrial gases, and it provides documented evidence for material qualification files.