Gas corrosion resistance evaluation is a critical reliability testing process that assesses how materials, coatings, and electronic components withstand corrosive industrial atmospheres containing gases such as hydrogen sulfide, sulfur dioxide, nitrogen dioxide, and chlorine. This comprehensive guide covers internationally recognized testing standards, including IEC 60068-2-60, ASTM B845, and GB/T 2423.51, along with sample requirements, test methods, and evaluation criteria used by accredited third-party laboratories worldwide.
Technical Overview
Gas corrosion resistance evaluation, also known as mixed flowing gas (MFG) testing or industrial atmosphere corrosion testing, is a laboratory simulation technique used to determine the susceptibility of materials, protective coatings, and electronic assemblies to corrosion in environments contaminated with corrosive gases. Industrial facilities, petrochemical plants, wastewater treatment stations, paper mills, and urban environments contain trace concentrations of gases such as hydrogen sulfide (H2S), sulfur dioxide (SO2), nitrogen dioxide (NO2), and chlorine (Cl2). When combined with elevated temperature and humidity, these gases can cause rapid degradation of metallic surfaces, contact finishes, and solder joints, leading to electrical failures and shortened service life.
The evaluation exposes test specimens to precisely controlled concentrations of corrosive gases under defined conditions of temperature and relative humidity, replicating years of field exposure within days or weeks. Common test durations range from 4 to 21 days, depending on the severity class required by the product specification. The resulting corrosion products—typically sulfides, oxides, and chlorides—are analyzed to quantify corrosion film growth, contact resistance drift, and morphological changes. This testing supports product design validation, material selection, qualification of protective coatings, and compliance with industry standards published by ISO, IEC, ASTM, EN, JIS, and GB.
Governing Standards
- IEC 60068-2-60 – Environmental testing, Flowing mixed gas corrosion test (Method 1 through Method 4)
- IEC 60068-2-42 – Test Kc: Sulfur dioxide test for contacts and connections
- IEC 60068-2-43 – Test Kd: Hydrogen sulfide test for contacts and connections
- IEC 60068-2-49 – Guidance for Tests Kc and Kd
- ASTM B845 – Standard Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
- ASTM B809 – Standard Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor
- ISO 10062 – Corrosion tests in artificial atmosphere at very low concentrations of polluting gas(es)
- ISO 6988 – Metallic and other non-organic coatings, sulfur dioxide test
- GB/T 2423.51 – Environmental testing for electric and electronic products, flowing mixed gas corrosion test
- GB/T 19745 – Corrosion tests in artificial polluted atmosphere
- EIA-364-65A – Mixed Flowing Gas Corrosion Test for electrical connectors
- Telcordia GR-63-CORE – Network Equipment-Building System (NEBS) requirements, airborne contaminant test methods
Testing Samples
Electronic Components and Assemblies
Printed circuit boards (PCBs), integrated circuits, connectors, relays, switches, and soldered assemblies are among the most frequently tested items. These components rely on thin metallic finishes and stable contact interfaces, making them particularly vulnerable to corrosive gas attack. Specimens should be submitted in their final manufactured condition, complete with all platings, conformal coatings, and surface treatments, without additional cleaning that could remove protective films or contamination layers.
Metallic Materials and Coatings
Bare metals, galvanized steels, anodized aluminum alloys, electroplated finishes (silver, gold, nickel, tin, copper), conversion coatings, and organic coatings such as paints and powder coatings can be evaluated for corrosion film formation and adhesion degradation. Coupon-style specimens with defined surface area and known initial mass enable quantitative gravimetric analysis after exposure.
Finished Products and Sub-assemblies
Complete products including telecommunication equipment, data center hardware, automotive electronics modules, industrial control cabinets, and consumer devices may be tested in operating, powered, or unpowered states. Product-level testing captures the combined effects of material interactions, enclosure design, and airflow patterns on corrosion behavior.
Sample Preparation Requirements
- Specimens must be clean, dry, and free from fingerprints, oils, and packaging residues before exposure
- Minimum sample dimensions should permit mounting on non-reactive fixtures without contact between adjacent specimens
- Duplicate or triplicate samples are recommended to ensure statistical validity of results
- Reference control coupons (typically copper or silver) are included to monitor chamber corrosivity per ASTM B845 monitoring requirements
- Client-supplied acceptance criteria or product specifications should accompany the samples when applicable
Testing Items
Gas corrosion resistance evaluation encompasses several measurable parameters that characterize both the extent of corrosion and its functional impact on the test item. The selection of test items depends on the material type, product application, and applicable specification.
- Corrosion film thickness and mass gain – quantified by gravimetric measurement and coulometric reduction analysis
- Contact resistance – measured before and after exposure to detect increases caused by corrosion films on contact surfaces
- Visual appearance and corrosion morphology – documented through photography and rating of discoloration, tarnish, pitting, and crevice attack
- Corrosion product identification – performed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD)
- Coating porosity – assessed per ASTM B809 or electrographic methods to reveal pore sites that allow substrate attack
- Solderability and wire bondability – evaluated after exposure for electronic assembly materials
- Insulation resistance and dielectric performance – measured on assemblies where corrosion products may create leakage paths
- Porosity of platings on copper alloy substrates – determined via sulfur vapor exposure techniques
Testing Methods
Mixed Flowing Gas (MFG) Testing
Mixed flowing gas testing per IEC 60068-2-60 and ASTM B845 is the most widely applied method. Specimens are placed in a chamber through which humidified air containing controlled concentrations of multiple corrosive gases continuously flows. The standard defines four test methods with escalating severity, covering environments from light industrial to harsh chemical processing conditions. Typical exposure durations are 4, 7, 10, or 21 days. Chamber corrosivity is verified using copper and silver coupon monitoring to ensure the exposure meets the specified reactivity class.
Single-Gas Exposure Tests
Tests Kc (SO2) and Kd (H2S) per IEC 60068-2-42 and IEC 60068-2-43 expose contacts and connections to a single pollutant gas under warm, humid conditions. These tests are particularly suited to evaluating silver and copper alloy contacts, where silver sulfide film growth is the dominant failure mechanism. ISO 6988 provides an analogous sulfur dioxide test for metallic and inorganic coatings, widely referenced in EN and JIS-aligned specifications.
Typical Test Conditions
- Test gases: H2S (10–100 ppb), SO2 (100–500 ppb), NO2 (200–500 ppb), Cl2 (10–50 ppb), depending on the severity class
- Temperature: 25 °C, 30 °C, or 40 °C maintained within ±1 °C
- Relative humidity: 70–75% RH maintained within tight tolerance, as humidity critically governs corrosion kinetics
- Gas flow rate and chamber volume exchange rates controlled to ensure uniform concentration distribution
- Duration: commonly 4, 7, 10, 14, or 21 days of continuous exposure
Post-Exposure Evaluation Procedure
Following exposure, specimens undergo conditioning in a controlled environment before measurement. Gravimetric analysis determines mass change attributable to corrosion film formation. Contact resistance is measured at specified normal forces to quantify interface degradation. Microscopic examination, supported by SEM-EDS elemental mapping, identifies corrosion product composition and distribution. The final report compares measured values against acceptance criteria and assigns a corrosion severity classification based on observed degradation.
Applications
Gas corrosion resistance evaluation serves a broad range of industries where equipment reliability in corrosive atmospheres is essential for safety, uptime, and lifecycle cost control.
- Telecommunications and data centers – qualification of servers, routers, optical modules, and passive infrastructure against airborne contaminants in urban and coastal facilities, aligned with Telcordia GR-63-CORE requirements
- Automotive electronics – validation of engine control units, sensors, and wiring systems exposed to exhaust-derived pollutants and road salt environments
- Industrial automation – reliability assessment of PLCs, control cabinets, and instrumentation installed in chemical plants, refineries, and smelters
- Rail transit and infrastructure – evaluation of onboard and trackside equipment exposed to tunnel and underground atmospheres
- Petrochemical and power generation – material selection and coating qualification for equipment in H2S-rich sour gas environments
- Consumer electronics – assurance of connector and plating durability for products used in high-humidity, polluted urban environments
- Metallurgy and plating industries – development and quality control of precious metal and sacrificial coating systems
- Military and aerospace – environmental qualification of mission-critical hardware under severe atmospheric contaminant profiles
FAQ
What is the difference between salt spray testing and gas corrosion testing?
Salt spray testing (such as neutral salt spray per ISO 9227 or ASTM B117) simulates marine and road-deicing chloride environments using an electrolytic fog, and it primarily drives electrochemical corrosion. Gas corrosion testing exposes specimens to trace concentrations of gaseous pollutants such as H2S and SO2 under controlled humidity, producing thin-film chemical corrosion on contacts, platings, and precision surfaces. The two methods address distinct failure mechanisms and are often both required for comprehensive qualification.
How is the required test severity class selected?
Severity class selection is based on the intended service environment classification, product specification, or contractual requirements. IEC 60068-2-60 Methods 1–4 and the exposure classes within ASTM B845 correspond to progressively harsher pollutant concentrations and humidity levels. Manufacturers of equipment destined for telecom central offices typically apply milder classes, while equipment for chemical plants or offshore installations requires the most severe exposure profiles.
How long does a typical gas corrosion test take?
Chamber exposure durations commonly range from 4 to 21 days depending on the standard and severity class. Including pre-test conditioning, coupon monitoring, and post-exposure analysis, a complete evaluation typically requires two to five weeks. Accelerated equivalence estimates relate the exposure to several years of service in moderate industrial atmospheres.
Why are copper and silver coupons monitored during the test?
Copper and silver coupons act as reactivity monitors that quantify the actual corrosivity of the chamber atmosphere, expressed as film thickness growth in angstroms per the framework defined in ASTM B845 and related instrumentation standards. Because gas concentration sensors may drift and chamber dynamics vary, coupon-based verification provides direct evidence that the exposure achieved the specified corrosivity class, ensuring test validity and inter-laboratory comparability.
Can powered or operating equipment be tested?
Yes. Many specifications, particularly for telecom and data center hardware, require the device under test to remain powered and functional during exposure. Operating conditions can influence local temperature, humidity, and pollutant deposition, so powered testing provides a more realistic assessment of in-service corrosion behavior. The chamber must be equipped with appropriate electrical feedthroughs and safety provisions.
What acceptance criteria are typically applied?
Acceptance criteria are defined by the product specification and may include limits on contact resistance increase, absence of visible corrosion products on specified surfaces, maximum allowable mass gain, minimum remaining solderability, and functional performance after exposure. When no explicit criteria exist, test reports present measured values against the severity class framework of the applied standard so that engineering judgment can be exercised.