ASTM G85 Modified Salt Spray (Fog) Corrosion Testing
The modified salt spray testing is done by ASTM G85 practice that is applicable to metals (non ferrous and ferrous) and coatings (organic and inorganic). The end results are reported as concentration or specific gravity.
TRUSTED BY
- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
ASTM G85 Modified Salt Spray Test – Overview
ASTM G85 is a standardized corrosion testing method that modifies traditional salt spray (fog) testing to better simulate real-world environments. It introduces cyclic conditions, acidified solutions, or alternative electrolytes to evaluate corrosion resistance of metals, coatings, and surface treatments more realistically.
The test is widely used to assess durability under aggressive environmental conditions such as marine, industrial, or polluted atmospheres. It provides improved correlation with field performance compared to conventional salt spray tests by incorporating factors like pH variation and wet-dry cycling.
Scope, Applications, and Benefits
Scope
ASTM G85 defines multiple modified salt spray procedures (Annex A1–A5) that simulate different corrosive environments by altering solution chemistry, pH, and exposure cycles. It enables evaluation of corrosion resistance under more representative service conditions.
The method supports comparative analysis of coatings and materials subjected to complex environmental stresses.
- Simulation of cyclic and acidified salt spray environments
- Evaluation of corrosion resistance under realistic conditions
- Assessment of coatings, platings, and surface treatments
- Measurement of corrosion products and degradation behavior
- Comparison of material performance across test variants
- Standardized accelerated corrosion testing approach
Applications
- Automotive coating and component testing
- Marine and offshore material evaluation
- Aerospace corrosion resistance studies
- Industrial coating and plating validation
- Fasteners and hardware corrosion testing
- Surface treatment performance evaluation
- Research and development of corrosion-resistant materials
Benefits
- Better correlation with real-world environments than ASTM B117
- Simulates complex corrosion conditions (acid rain, pollutants)
- Enables evaluation of multiple environmental scenarios
- Improves coating and material selection decisions
- Supports product durability and lifecycle prediction
- Reduces risk of premature corrosion failure
ASTM G85 Modified Salt Spray Test – Test Process
Sample Preparation
Specimens are cleaned, coated (if applicable), and prepared according to specified dimensions and surface conditions.
1Solution & Chamber Setup
The test chamber is set with the required salt solution, pH, and environmental conditions as per the selected annex method.
2Exposure Cycling
Samples are exposed to controlled fog, drying, and/or humidity cycles to simulate real environmental corrosion conditions.
3Evaluation & Analysis
Corrosion progression is monitored through visual inspection, mass loss, or coating degradation assessment.
4ASTM G85 Modified Salt Spray Test – Technical Specification
| Parameter | Details |
|---|---|
| Standard | ASTM G85 modified salt spray (fog) corrosion test |
| Method | Cyclic or modified salt spray exposure (Annex A1–A5) |
| Measurement Type | Corrosion resistance, coating degradation |
| Sample Type | Metals, coated materials, plated components |
| Loading Type | Salt fog, humidity, drying, and chemical exposure |
| Units | Exposure hours, % corrosion, mass loss (g) |
Instrumentation Used
- Salt spray (fog) test chamber
- Solution preparation system (NaCl, acidified or modified solutions)
- pH control and monitoring equipment
- Temperature and humidity control system
- Spray nozzles and fog generation system
- Specimen racks and holders
- Analytical balance for mass loss measurement
- Visual inspection and imaging tools
Results and Deliverables
- Corrosion rate and severity assessment
- Coating degradation evaluation (blistering, rusting, peeling)
- Time-to-failure or corrosion initiation data
- Mass loss measurements
- Comparative material performance report
- ASTM-compliant corrosion test report
- Quality assurance documentation
- Recommendations for coating or material improvement
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Frequently Asked Questions
The ASTM G85 Modified Salt Spray test is a standardized procedure used to evaluate the corrosion resistance of materials and coatings.
ASTM B117 is limited to testing with salt spray, where a sodium chloride solution of a given purity is sprayed. At the same time, the standard ASTM G85 modification includes tests with acidic salt solutions and cyclic exposure to simulate specific environments.
ASTM G85 introduces cyclic conditions, modified electrolytes, and pH variations that better replicate real environments. Unlike continuous exposure in standard salt spray, it simulates wet-dry cycles and pollutants, improving correlation with actual field corrosion behavior.
Each annex modifies solution chemistry and exposure conditions—such as acidified fog, cyclic drying, or synthetic seawater—allowing simulation of specific environments like industrial pollution, marine exposure, or acid rain conditions.
Lower pH increases solution acidity, accelerating metal dissolution and coating degradation. It also simulates industrial and acid rain environments where corrosion rates are significantly higher.
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