Rubber Mixed Gas Corrosion Testing

Rubber mixed gas corrosion testing evaluates the resistance of rubber materials and finished elastomeric components to simulated industrial atmospheres containing corrosive pollutant gases such as sulfur dioxide, hydrogen sulfide, nitrogen dioxide, and chlorine. Performed in accordance with internationally recognized standards including IEC 60068-2-60, GB/T 2423.51, and ISO 21207, this accelerated environmental test is essential for validating the long-term reliability of seals, gaskets, and insulation materials used in automotive, electrical, petrochemical, and marine applications. Accredited third-party laboratories offer comprehensive mixed gas corrosion testing to support product design, quality control, and regulatory compliance.

Technical Overview

Mixed gas corrosion testing, also known as flowing mixed gas (FMG) testing, is an accelerated laboratory technique that exposes rubber materials and finished products to a controlled atmosphere containing two or more corrosive pollutant gases at very low concentrations, combined with elevated temperature and relative humidity. The test simulates the aggressive air found in industrial zones, petrochemical plants, urban environments, and offshore sites, where combustion products and process emissions continuously attack polymeric materials.

For rubber compounds, corrosive gases such as sulfur dioxide (SO2), hydrogen sulfide (H2S), nitrogen dioxide (NO2), and chlorine (Cl2) dissolve in the moisture film on the material surface to form acidic or oxidizing solutions. These species can degrade the polymer backbone, attack fillers and antidegradants, and disrupt the crosslink network, resulting in surface discoloration, hardening or softening, cracking, loss of elasticity, and corrosion of adjacent metal components in rubber-metal assemblies.

The principal standards governing this test include:

• IEC 60068-2-60 — Environmental testing, Part 2-60: Test Ke, corrosion tests in artificial atmosphere at very low concentration of polluting gas(es)
• GB/T 2423.51 — Chinese national standard for mixed gas corrosion testing of electrical and electronic products, technically aligned with IEC 60068-2-60
• ISO 21207 — Artificial atmospheres, corrosion tests involving alternating exposure to corrosion-promoting gases, neutral salt spray, and drying
• ASTM B845 — Standard guide for mixed flowing gas tests, applicable to assemblies that include elastomeric sealing elements
• ISO 23529 — General procedures for the preparation and conditioning of rubber test pieces used for physical testing

Testing Samples

Standard Test Pieces

Vulcanized rubber compounds are supplied as sheets or plates from which dumbbell specimens are die-cut for tensile testing (ISO 37 or ASTM D412), together with blocks or buttons for hardness measurement (ISO 48 or ASTM D2240) and compression set determination (ISO 815-1). These laboratory-molded pieces allow quantitative comparison of material performance before and after gas exposure.

Finished Rubber Products

Complete commercial components can be tested in their as-delivered condition, including O-rings, gaskets, oil seals, diaphragms, rubber hoses, vibration isolators, protective boots, expansion joints, and cable jackets or sheaths. Testing real products captures the influence of geometry, post-curing, surface treatments, and molding quality on corrosion resistance.

Rubber-Metal Assemblies and Insulating Components

Bonded seals, laminated bushings, connector inserts, and elastomeric insulators are tested to evaluate both polymer degradation and contact corrosion transferred to metallic or conductive parts. This is particularly relevant for electrical products where gas-induced corrosion of contacts must be assessed alongside rubber aging.

All samples should be conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for at least 16 hours prior to testing, in accordance with ISO 23529. Protective coatings or release agents should be removed unless they are part of the evaluated design, and a minimum of three to five specimens per test condition is recommended for statistical validity.

Testing Items

Depending on the product specification and the applicable material or industry standard, mixed gas corrosion testing typically covers the following evaluation items:

• Visual appearance: discoloration, surface cracking, blistering, tackiness, blooming, and efflorescence, rated against defined photographic or descriptive scales
• Hardness change (Shore A) to ISO 48 or ASTM D2240
• Change in tensile strength to ISO 37 or ASTM D412
• Change in elongation at break and in tensile stress at specified strain (100% or 300% modulus)
• Mass change and dimensional or volume change determined gravimetrically
• Compression set after exposure, to ISO 815-1, critical for sealing performance
• Compression stress relaxation to ISO 3384, measuring the loss of sealing force
• Low-temperature flexibility or bend testing after exposure to reveal embrittlement
• Contact corrosion assessment of adjacent metallic parts, expressed as percentage of affected surface area or as an appearance rating
• Retention of electrical properties for insulating rubber, such as volume resistivity and dielectric strength, to IEC 60243

Testing Methods

Test Apparatus and Atmosphere Control

Testing is conducted in an environmental chamber equipped with precision gas dosing and mass-flow control, homogeneous air circulation, accurate temperature and humidity regulation, and continuous or periodic gas concentration monitoring, typically by UV fluorescence, electrochemical, or ion chromatography analyzers. Exhaust gases are neutralized through scrubbers before discharge, and reference metal coupons are often included to verify the corrosivity of the atmosphere within each run.

Standard Test Conditions

IEC 60068-2-60 defines several severity methods. Typical conditions widely applied to rubber components include:

• Method 1 (two-gas atmosphere): hydrogen sulfide at 10–15 ppb and sulfur dioxide at 25–35 ppb, at approximately 25 °C and 75% relative humidity
• Method 2 (three-gas atmosphere): hydrogen sulfide at 10–15 ppb, nitrogen dioxide at 200–300 ppb, and chlorine at 10–20 ppb, at approximately 30 °C and 70% relative humidity
• Alternative severity methods covering additional three-gas and four-gas combinations at comparable or elevated concentrations, selected according to the service environment being simulated

Exposure durations are commonly 4, 7, 10, 14, or 21 days, with longer durations used to accelerate lifetime estimation for harsh-service products. ISO 21207 provides a more severe cyclic alternative that alternates gas exposure with neutral salt spray and drying phases for components exposed to combined gaseous and saline atmospheres.

Test Procedure

• Verify sample identification, cleanliness, and conditioning history, then record baseline appearance, dimensions, mass, and mechanical properties
• Load specimens into the chamber with adequate spacing so that all surfaces are uniformly exposed to the flowing gas mixture
• Stabilize temperature and humidity, then introduce the certified gas mixture at the specified concentrations and flow rate for the chosen duration
• Perform intermediate inspections where required by the specification without interrupting the exposure profile
• After exposure, allow samples to recover under standard laboratory conditions, then repeat all measurements and destructive mechanical tests
• Calculate percentage changes against baseline values and compare them with the acceptance criteria defined by the product or material standard

Evaluation Criteria

Acceptance limits are set by the relevant product specification, but common qualification thresholds for sealing rubber include a tensile strength change of no more than 25–30%, an elongation change of no more than 40%, a hardness change within approximately ±10 Shore A units, no visible cracking or corrosive deposits that impair function, and a compression set consistent with the sealing design requirement.

Applications

Mixed gas corrosion testing is applied across industries where rubber components must survive polluted or chemically aggressive atmospheres over long service lives:

• Automotive: engine bay seals, fuel and brake system components, exhaust hangers, and electric vehicle battery pack gaskets exposed to sulfur-bearing gases
• Electrical and electronics: connector sealing inserts, enclosure gaskets, cable jackets, and insulating bushings for switchgear and control equipment
• Petrochemical and chemical processing: pipeline flange gaskets, valve seats, pump seals, and diaphragm materials in SO2- and H2S-rich process streams
• Power generation and transmission: transformer gaskets, insulator components, and cable accessories in industrial air quality zones
• Marine and offshore: hatch seals, O-rings, and dampers exposed to humid air combined with industrial emissions
• Rail transit, mining, and defense platforms requiring verified durability in severe environmental categories

Test results support material selection, supplier qualification, design verification, failure analysis, and evidence packages for product certification and tenders.

FAQ

What is rubber mixed gas corrosion testing?

It is an accelerated environmental test in which rubber materials or finished products are exposed to a controlled atmosphere containing multiple corrosive gases at parts-per-billion levels, together with controlled temperature and humidity, in order to evaluate degradation resistance and predict service life in polluted environments.

Which gases are used, and at what concentrations?

The standard gases are sulfur dioxide, hydrogen sulfide, nitrogen dioxide, and chlorine, typically at concentrations between 10 and 300 ppb depending on the severity method, with ozone resistance covered separately under ISO 1431 or ASTM D1149 where required.

How long does a typical test take?

Most exposures run for 4 to 21 days depending on the chosen standard, severity method, and product specification. Additional time is needed for baseline measurements, post-exposure conditioning, and mechanical testing, so a complete evaluation usually requires two to four weeks.

What sample quantity and size are required?

For compound evaluation, standard tensile dumbbells plus hardness and compression set pieces are required, generally three to five specimens per condition. Finished products such as O-rings or gaskets can usually be tested as supplied, and the laboratory can advise on the minimum quantity during test planning.

How is test quality assured?

Reputable accredited third-party laboratories operate under ISO/IEC 17025 quality systems, use certified gas mixtures traceable to national measurement standards, verify chamber corrosivity with reference coupons, and calibrate temperature, humidity, and gas analysis instrumentation at defined intervals.