Dry gas corrosion testing is an accelerated reliability test that exposes materials, coatings, and electronic assemblies to controlled concentrations of corrosive gases such as H2S, SO2, NO2, and Cl2 under low-humidity, non-condensing conditions. This article explains the test principles, applicable standards, sample types, test parameters, and evaluation methods used by accredited third-party laboratories to assess corrosion resistance and predict product service life in sulfur-bearing and polluted atmospheres.
Technical Overview
Dry gas corrosion testing is an environmental simulation technique in which specimens are exposed to precisely controlled concentrations of corrosive gases, most commonly hydrogen sulfide (H2S), sulfur dioxide (SO2), nitrogen dioxide (NO2), and chlorine (Cl2), at a stable elevated temperature and low relative humidity. The defining feature of the "dry" condition is that the relative humidity is maintained below the level at which condensation or a continuous adsorbed water film forms on the specimen surface, so degradation proceeds primarily through direct gas-solid chemical reactions rather than classical wet electrochemical corrosion.
Under dry conditions, reactive sulfur-bearing gases attack susceptible metals directly: silver tarnishes rapidly to form silver sulfide (Ag2S), copper forms copper sulfide and oxide layers, and nickel and tin surfaces undergo slow oxidation or sulfidation. Porous or thin noble-metal platings allow gases to penetrate to underlying base metals, leading to corrosion products that can migrate across insulating surfaces and increase contact resistance. Because these reactions are highly accelerated at even ppb-to-ppm gas levels, dry gas exposure provides an efficient method for ranking material compatibility and qualifying protective finishes.
The most widely referenced standards for this type of testing include IEC 60068-2-60 (flowing mixed gas corrosion test), IEC 60068-2-42 (sulfur dioxide test), IEC 60068-2-43 (hydrogen sulfide test), ISO 10062 (corrosion tests in artificial atmospheres at very low concentrations of polluting gases), ASTM B845 and ASTM B827 (mixed flowing gas tests for electrical contacts), and the Chinese national standards GB/T 2423.51, GB/T 2423.19, and GB/T 2423.20. Accredited third-party laboratories perform these tests in specialized chambers with continuous gas concentration monitoring to ensure repeatable, quantifiable results.
Testing Samples
Sample categories span the full range of products and materials that may encounter polluted industrial, urban, or process atmospheres during storage, transport, or service. Specimens should be clean, representative of production quality, and submitted in sufficient quantity to allow both exposed and control evaluations.
Electronic Components and Assemblies
Connectors, relays, switches, printed circuit boards and assembled PCBAs, integrated circuit packages, leadframes, terminals, and cable assemblies are the most frequently tested items, since their long-term signal integrity depends on stable contact resistance and clean insulating surfaces.
Metallic Materials and Plated Finishes
Bare and plated coupons of silver, copper and copper alloys, tin, nickel, zinc, and aluminum are tested to characterize tarnishing rates, plating porosity, and barrier effectiveness. Common finish systems evaluated include gold over nickel, palladium-nickel, pure silver, and immersion silver.
Protective Coatings and Surface Treatments
Conformal coatings (acrylic, silicone, polyurethane, parylene), paints, powder coatings, anodized layers, and chromate or trivalent passivation treatments are qualified by comparing corrosion attack on coated versus uncoated areas.
Complete Equipment and Modules
Telecom modules, sensors, power supplies, automotive electronic control units, and rack-mounted hardware may be tested as complete assemblies to verify that enclosures, gaskets, and venting designs provide adequate protection against gaseous pollutants.
Testing Items
A dry gas corrosion test is defined by a controlled set of environmental parameters and a defined set of measured output characteristics. Typical test parameters and evaluated items include:
- Gas species and concentration: H2S, SO2, NO2, and Cl2, individually or in combination, typically at levels from 10 ppb to 25 ppm depending on the selected method and severity.
- Temperature: commonly 25°C, 30°C, or 40°C, maintained within ±1°C to ±2°C.
- Relative humidity: dry tests are typically run at or below 30% RH, or within a specified non-condensing band such as 50% to 60% RH, depending on the standard and product specification.
- Exposure duration: 4, 7, 10, 14, or 21 days, with extended durations of 28 days or longer for long-life applications.
- Gas flow and uniformity: continuous laminar flow through the chamber with verified spatial uniformity of gas concentration and temperature.
- Post-exposure measurements: surface appearance and corrosion coverage, corrosion film thickness, mass change per unit area, contact resistance change, insulation resistance, and microscopic or surface-chemical analysis of corrosion products.
Testing Methods
Single-Gas Dry Exposure
Specimens are exposed to one corrosive gas, most commonly H2S, at low humidity to evaluate specific failure mechanisms such as silver sulfidation or plating porosity. This approach, covered by methods such as IEC 60068-2-43 and ISO 10062 with dry humidity variants, isolates the effect of a single pollutant and is useful for material screening and plating process qualification.
Mixed Flowing Gas Exposure
Multi-gas tests expose specimens to a controlled mixture of two to four corrosive gases, following IEC 60068-2-60, ASTM B845, or GB/T 2423.51. The gases act synergistically, producing corrosion films and migration behavior closer to real polluted environments. A dry variant of the mixed gas method uses reduced relative humidity to evaluate products intended for dry climates, data centers, or sealed enclosures.
Test Procedure
The standard workflow followed by accredited third-party laboratories includes the following steps:
- Cleaning and marking of specimens, followed by preconditioning in a controlled ambient for stabilization.
- Mounting of specimens on inert, non-metallic fixtures with adequate spacing and, where required, a defined tilt angle to avoid contact and cross-contamination.
- Chamber stabilization at the specified temperature, humidity, and gas concentration, verified by calibrated gas analyzers before specimens are introduced.
- Continuous exposure with real-time monitoring and periodic recording of temperature, humidity, and gas concentrations, plus chamber gas change rates of typically three to five volumes per hour.
- Recovery of specimens in clean ambient conditions before evaluation begins.
Post-Test Evaluation and Acceptance Criteria
Evaluation combines visual and magnified inspection, gravimetric measurement of mass change, electrical measurement of contact and insulation resistance, and analytical techniques such as scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) or X-ray photoelectron spectroscopy (XPS) to identify corrosion products. Common acceptance criteria include no corrosion whiskers or bridging, contact resistance increase within specified limits (for example, a few milliohms of change), corrosion film thickness below a defined limit, and no visible attack beyond a defined percentage of the surface area.
Applications
Dry gas corrosion testing supports reliability engineering, qualification, and failure analysis across many industries in which gaseous pollutants degrade materials or electronics:
- Telecommunications and data center hardware, where low-humidity sulfur environments can drive silver sulfide corrosion and whisker growth on immersion silver circuit boards.
- Automotive electronics, including engine-compartment and under-body modules exposed to sulfur compounds and combustion gases.
- Industrial process control and petrochemical plant instrumentation located near SO2 and H2S sources.
- Aerospace and defense equipment subjected to polluted ground atmospheres during storage and operation.
- Consumer electronics reliability demonstration and warranty risk reduction for products sold into industrializing urban environments.
- Materials research and development, plating line qualification, conformal coating selection, and supplier finish comparisons.
- Failure analysis, where laboratory gas exposure is used to reproduce field corrosion mechanisms and confirm root cause.
FAQ
What is the difference between dry gas corrosion testing and conventional mixed flowing gas testing?
Conventional mixed flowing gas tests such as those in IEC 60068-2-60 and ASTM B845 are usually run at 70% to 75% RH, where thin adsorbed moisture layers accelerate electrochemical corrosion. Dry gas corrosion testing keeps humidity at or below roughly 30% to 60% RH without condensation, so the dominant mechanism is direct chemical reaction between the gas and the surface, which better represents dry climates, sealed enclosures, and data center environments.
Which gases are used and at what concentrations?
The most common gases are H2S, SO2, NO2, and Cl2. In multi-gas methods, individual gas concentrations typically range from 10 ppb to 500 ppb. Single-gas screening tests may use higher levels, for example 10 to 15 ppm H2S or up to 25 ppm SO2, depending on the selected standard and the severity required.
How long does a dry gas corrosion test take?
Typical durations are 4, 7, 10, 14, or 21 days, with 28-day or longer exposures used for high-reliability applications. The required duration depends on the product specification, the expected service environment, and the acceptance criteria agreed with the client or defined in the applicable standard.
How should specimens be prepared for testing?
Specimens must be clean and free of fingerprints, flux residues, and protective oils unless those contaminants are part of the evaluation. They should be representative of production parts, mounted on inert fixtures without metal contact, and accompanied by unexposed control samples whenever electrical or gravimetric comparison is required.
How are test results interpreted?
Results are assessed against product-specific acceptance criteria covering corrosion appearance, film thickness, mass change, contact resistance increase, insulation resistance, and the presence of conductive corrosion product migration or whiskers. A qualified pass indicates the material or product should resist gaseous corrosion for its intended service life; failures guide selection of more resistant finishes, barrier coatings, or enclosure designs.
Which standards govern dry gas corrosion testing?
The principal references are IEC 60068-2-60, IEC 60068-2-42, IEC 60068-2-43, ISO 10062, ASTM B845, ASTM B827, GB/T 2423.51, GB/T 2423.19, and GB/T 2423.20. Test plans should always state the governing standard, severity level, gas concentrations, humidity, temperature, and duration so that results are comparable between laboratories and test campaigns.