ASTM B117 Salt Spray (Fog) Testing
ASTM B117 is a standard test method that determines the corrosive effects of salt on metallic items. The standard is most commonly used for accelerated corrosion testing services. This procedure creates a controlled corrosive environment that is used to generate data on the relative corrosion resistance for metal and coated metal test specimens exposed in specific test chambers. Corrosive resistance of different metals is compared, and corrosion creep along with coating adhesion are determined. The results are reported as concentration or specific gravity. Read more about ASTM B117 below.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM B117 describes a standardized method for testing the corrosion resistance of metals and their protective coatings by exposing the test samples to a continuous salt-spray (fog) inside a controlled chamber. In its basic form, a salty solution, typically 5% sodium chloride with a pH that is strictly controlled, accelerates the corrosive behavior.
It is a widely used method for estimating the probable service life of metals and coatings under the most unfavorable conditions. This technique also provides a uniform basis for comparing corrosion performance for metals, coatings, and treatments to streamline product improvement, quality control, and performance verification.
Scope, Applications, and Benefits
Scope
ASTM B117 outlines procedures for creating and maintaining a controlled salt fog environment to evaluate corrosion resistance.
It evaluates:
- General corrosion resistance of metals and coatings
- Coating adhesion and corrosion creep
- Relative performance of different surface treatments
The method relies on controlled chamber conditions to ensure repeatable and comparable results across laboratories and industries.
Applications
- Evaluating corrosion resistance of automotive components
- Testing aerospace and defense materials
- Assessing protective coatings, paints, and platings
- Comparing material performance for infrastructure and transport applications
- Supporting R&D for corrosion-resistant materials and coatings
Benefits
- Accelerates corrosion testing under standardized conditions
- Enables comparison of different materials and coatings
- Supports material selection for corrosive environments
- Aids in quality control and product qualification
- Helps predict long-term durability and service performance
Test Process
Specimen Preparation
Test specimens are cleaned and prepared according to material specifications and positioned at defined angles within the chamber.
1Salt Fog Generation
A salt solution (typically 5% NaCl) is atomized using compressed air to create a continuous corrosive fog at ~100% relative humidity.
2Exposure
Specimens are exposed continuously for a specified duration as defined by the relevant product or material specification.
3Post-Test Evaluation
Specimens are removed, gently rinsed to remove salt deposits, dried, and examined for corrosion, blistering, or coating failure.
4Technical Specifications
| Parameter | Details |
|---|---|
| Test Principle | Continuous exposure to salt spray (fog) in a controlled chamber |
| Salt Solution | Typically 5% NaCl (range may vary by specification) |
| pH Range | 6.5 – 7.2 |
| Relative Humidity | Approximately 100% |
| Sample Types | Metals, coated metals, plated components |
| Exposure Duration | Defined by product or material specification |
| Measured Output | Visual corrosion, rust formation, coating degradation |
Instrumentation Used for Testing
- Salt spray (fog) test chamber (bench-top or walk-in)
- Atomizing spray nozzles and compressed air system
- Humidifying tower with heated deionized water
- pH meter and salinity measurement instruments
- Temperature and humidity monitoring systems
Results and Deliverables
- Visual assessment of corrosion and coating degradation
- Time-to-failure or corrosion onset data
- Comparative corrosion performance between materials or coatings
- Documentation of test conditions and exposure duration
- Suitability assessment for material selection and quality compliance
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Read Case StudyFrequently Asked Questions
Your samples are exposed to a continuous indirect spray of salt water solution called fog or mist. The salt spray testing solution is prepared by dissolving pure sodium chloride into pure water, in a 5% sodium chloride ratio to 95% water, by weight.
It entails a 24-hour spray of a 5% salt solution at a temperature generally kept around 35°Celsius. After 24 hours, the unit is removed and allowed to dry for another 24 hours. Then, it goes back into the chamber and is subjected to the 5% salt spray, or salt fog, for another 24 hours.
Salt spray testing is an accelerated corrosion test that produces a corrosive attack on coated samples to evaluate (mostly comparatively) the suitability of the coating for use as a protective finish.
The salt solution is a solution of 5% (in weight) of NaCl (more than sea water, which is only 1.8% to a maximum of 3%).
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