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What Is a Salt Spray Test?
Types, Tested Products, Test Procedure and Practical Applications
A salt spray test is an accelerated corrosion test used to evaluate how metals, coatings, plating layers and finished components perform in a controlled salt-laden environment. A salt spray test chamber creates a stable corrosive atmosphere so that corrosion defects can be identified in a much shorter and more repeatable way than natural exposure.
| Main purpose Evaluate corrosion resistance | Common methods NSS, AASS and CASS | Typical equipment Salt spray test chamber |
1. What Is a Salt Spray Test?
A salt spray test exposes a test specimen to a fine mist of salt solution inside a closed chamber. The mist settles on the specimen surface and creates a controlled corrosive environment. The resulting corrosion is then evaluated according to the relevant product standard or specification.
Salt spray testing is mainly used to assess corrosion resistance and to reveal defects such as rust, coating blistering, peeling, cracking and corrosion spreading from damaged areas.
2. Why Is Salt Spray Testing Needed?
A surface can look clean and intact while still having microscopic pores, weak areas or process defects. Salt spray exposure helps manufacturers verify whether a material or protective finish can withstand a specified corrosive environment.
It is especially useful for checking the quality of plating, painting, powder coating, conversion coatings and other corrosion-protection processes.
3. Which Products Are Tested?
| Product / Industry | Typical Test Objects |
| Metal Materials | Carbon steel, stainless steel, aluminum, copper, zinc alloys and metal parts |
| Plated Products | Zinc, nickel, chrome and other electroplated components |
| Coated Products | Painted parts, powder-coated parts and industrial protective coatings |
| Automotive | Fasteners, brackets, wheels, body hardware and coated components |
| Electrical & Electronics | Connectors, terminals, metal housings, switches and brackets |
| Marine & Outdoor | Outdoor hardware, marine components, cabinets and exposed metal structures |
4. Main Types of Salt Spray Testing
ISO 9227:2022 specifies three main salt spray test methods: Neutral Salt Spray (NSS), Acetic Acid Salt Spray (AASS) and Copper-Accelerated Acetic Acid Salt Spray (CASS). The correct method depends on the product, material, coating and applicable specification.
| Test | Full Name | Typical Use |
| NSS | Neutral Salt Spray | General corrosion evaluation of metals, coatings and plating |
| AASS | Acetic Acid Salt Spray | More aggressive testing for selected decorative coatings |
| CASS | Copper-Accelerated Acetic Acid Salt Spray | Higher-corrosivity testing for selected plating and coated aluminum products |
5. How Is a Salt Spray Test Performed?
1. Prepare the specimens. Samples are prepared according to the applicable product standard, including size, quantity, surface condition and positioning.
2. Prepare the test solution. The required salt solution is prepared according to the selected test method.
3. Set test conditions. Temperature, solution properties, spray conditions and test duration are controlled to the required specification.
4. Start salt spraying. The solution is atomized into a fine mist and continuously deposited onto the specimens.
5. Inspect the results. After the specified exposure period, specimens are inspected for corrosion and coating damage.
6. How Long Does a Salt Spray Test Take?
Test duration depends on the product requirement and the applicable specification. Common exposure periods include 24, 48, 72, 96, 168, 240, 480 and 720 hours, but there is no universal test time for all products.
A salt spray duration should not be directly converted into a fixed number of years of outdoor service life. ASTM B117 and ISO 9227 are test methods and do not provide a simple universal lifetime conversion.
7. What Results Are Evaluated?
- Corrosion or rust formation
- White corrosion products on plated or coated surfaces
- Corrosion area or corrosion rating
- Blistering, cracking or peeling of coatings
- Corrosion spreading from a scratch or damaged area
- Overall condition after the specified exposure time
8. What Is the Purpose of the Final Test Result?
Evaluate corrosion resistance. Determine how a material or protective finish performs under the specified artificial corrosion condition.
Verify surface treatment. Check whether plating, painting, powder coating or other protective processes meet requirements.
Compare materials and processes. Support the selection of coatings, materials and manufacturing processes during product development.
Support quality control. Help identify unstable production processes or surface-treatment problems.
Support customer acceptance. Provide test data when corrosion resistance is part of a customer or product requirement.
9. Important Limitations
Salt spray testing is a controlled accelerated corrosion test, not a complete simulation of natural outdoor exposure. Real environments also involve temperature changes, humidity cycles, UV radiation, rain, pollutants, drying and other factors. Therefore, salt spray results should be interpreted together with the product standard, actual service environment and other relevant durability tests.
10. Common Standards
ISO 9227:2022 covers NSS, AASS and CASS salt spray testing methods. ASTM B117 specifies the apparatus, procedures and conditions for operating a salt spray test environment. Product-specific standards may additionally define specimen preparation, exposure time and acceptance criteria.
11. Summary
Salt spray testing is a practical method for evaluating corrosion performance under controlled conditions. It is widely used for metal materials, coatings, electroplated parts, automotive components, electrical products, hardware and outdoor equipment. The most common methods are NSS, AASS and CASS. The final result can support product development, process validation, quality control and customer acceptance, but it should not be treated as a direct prediction of real-world service life.
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