Salt Spray Test

Neutral Salt Spray · Acetic Acid Salt Spray · CASS · Cyclic Corrosion · Standard Selection Guide ISO/IEC 17025 Accredited Testing Where Applicable | Salt Spray and Corrosion Testing Capability | Automotive Materials Testing Malaysia Salt spray testing is one of the most widely specified corrosion tests in automotive manufacturing. It provides a controlled, accelerated corrosive environment that allows coatings, platings, and surface treatments to be evaluated against defined acceptance criteria within days rather than years. What is less straightforward is which standard to test to, because several different standards govern salt spray testing, and they are not all equivalent. For automotive manufacturers and component suppliers in Malaysia and Southeast Asia working across Japanese, European, American, and global supply chains, knowing the difference between ISO 9227, ASTM B117, JASO M609, and DIN 50021 is practical knowledge that prevents mistakes at the specification stage and avoids retesting when a submission is rejected for referencing the wrong standard. What Is a Salt Spray Test A salt spray test, also called a salt fog test, exposes a specimen to a continuously atomised salt solution inside a controlled chamber under defined temperature conditions. The purpose is to accelerate the corrosion processes that would develop over much longer periods under real environmental exposure, allowing manufacturers to evaluate corrosion protection performance in a practical timeframe. The result of a salt spray test is an assessment of the specimen’s condition after a defined exposure period, typically evaluated by visual inspection for corrosion products, blistering, coating breakdown, and corrosion creep from any scribed lines cut into the coating before exposure. The result is compared against the acceptance criteria defined in the applicable specification. Salt spray testing does not directly simulate specific years of real-world service life. Test hours should not be converted to service years. The test is a comparative and qualification tool, not a life prediction method. ISO 9227, The International Standard ISO 9227 is the primary international standard for salt spray corrosion testing. It defines three test atmospheres, each suited to different material and coating types.   Atmosphere Abbreviation Test conditions Typical application Neutral Salt Spray NSS 5% NaCl solution, 35°C General corrosion testing for metallic materials with or without corrosion protection Acetic Acid Salt Spray AASS 5% NaCl with acetic acid, 35°C Decorative coatings, anodised aluminium, specific plating systems where specified Copper Accelerated Acetic Acid Salt Spray CASS 5% NaCl with acetic acid and copper chloride, 50°C Decorative copper-nickel-chromium or nickel-chromium coating systems where specified   ISO 9227 is referenced by European OEM specifications and most global OEM material standards. It is the standard most commonly encountered by automotive suppliers in Malaysia serving European or broadly international supply chains. The NSS atmosphere is by far the most widely used. AASS and CASS are applied only when the applicable specification specifically calls for them. Using AASS or CASS when NSS is required, or vice versa, is a test method non-conformance that invalidates the result. ISO 9227:2022 Revision The most recent revision of ISO 9227 was published in 2022, updating the previous 2017 version. The 2022 revision clarifies requirements for chamber calibration, fog collection measurement, and specimen positioning, but the fundamental test conditions for NSS, AASS, and CASS remain unchanged. Laboratories accredited to ISO/IEC 17025 should ensure their procedures reference the current version unless the customer specification explicitly names an earlier edition. ASTM B117, The American Standard ASTM B117 is published by ASTM International and is titled Standard Practice for Operating Salt Spray (Fog) Apparatus. It specifies the neutral salt spray atmosphere using a 5% sodium chloride solution at 35°C, which is directly comparable to the NSS atmosphere defined in ISO 9227. The important distinction is that ASTM B117 covers only the neutral salt spray atmosphere. It does not include AASS or CASS equivalents within the same standard. When a North American OEM specification references ASTM B117, it is specifying neutral salt spray only. For automotive suppliers in Malaysia receiving drawings from North American OEMs or their Tier-1 suppliers, ASTM B117 is the corrosion test reference most commonly encountered. The underlying test conditions match ISO 9227 NSS, but the report must reference the correct standard as named in the specification. ASTM B117 vs ISO 9227 NSS: Key Parameters Parameter ASTM B117 ISO 9227 NSS Salt solution 5% NaCl by mass 50 ± 5 g/L (approximately 5%) Temperature 35 ± 2°C 35 ± 2°C Solution pH 6.5 – 7.2 6.5 – 7.2 Fog collection rate 1 – 2 mL per 80 cm² per hour 1 – 2 mL per 80 cm² per hour Chamber volume Not specified Minimum 0.4 m³ recommended   The test conditions are functionally equivalent for neutral salt spray. The report must reference the standard named in the specification, even though the underlying conditions match. Related Standard: ASTM G85 While ASTM B117 covers neutral salt spray only, ASTM G85 (Standard Practice for Modified Salt Spray Testing) defines additional corrosive environments including acetic acid salt spray and copper-accelerated tests that are broadly comparable to ISO 9227 AASS and CASS. Some North American OEM specifications reference ASTM G85 annexes rather than ASTM B117 when acidic or accelerated atmospheres are required. JASO M609, The Japanese Automotive Standard JASO M609 is published by the Society of Automotive Engineers of Japan (JSAE) and defines a cyclic corrosion test method widely used by Japanese OEMs including Toyota, Honda, and Nissan. Unlike ISO 9227 and ASTM B117, which specify continuous salt spray exposure, JASO M609 defines a cyclic test protocol that alternates between salt spray exposure, drying at elevated temperature, and humid conditions. This cyclic approach is designed to better represent the wet-dry cycle experienced by vehicle components in real service conditions, particularly in the Japanese and East Asian markets where vehicle corrosion performance was historically a key quality differentiator. JASO M609 is not a direct substitute for ISO 9227 NSS or ASTM B117. Continuous salt spray and cyclic corrosion produce different corrosion morphologies and cannot be directly compared in terms of hours of exposure. Suppliers serving Japanese OEM supply chains in Malaysia should confirm whether JASO M609 or a derivative Japanese OEM protocol is specified before selecting a test method. JASO M609:2024 Update JASO M609 was comprehensively revised in 2024, replacing the 1991 version that had been in use for over three decades. The 2024 revision defines three test methods: Method A for cosmetic corrosion evaluation, Method B for perforation corrosion assessment, and Method C for combined evaluation. The cyclic protocol typically alternates between salt spray, controlled drying at elevated temperature, and high-humidity conditioning over a repeating cycle. Because the 2024 revision is a major update, suppliers should confirm with Japanese OEMs which version applies to their programme. DIN 50021, The German Standard and Its Relationship to ISO 9227 DIN 50021 is a German standard that historically specified salt spray testing before the equivalent ISO standard was established. It is now largely superseded by ISO 9227 for most applications, and most German OEM specifications that previously referenced DIN 50021 have transitioned to ISO 9227. Where DIN 50021 still appears in older component drawings or legacy specifications that have not been updated, it is generally treated as equivalent to ISO 9227 NSS for the neutral salt spray atmosphere. However, if a specification explicitly references DIN 50021, the laboratory should document the applicable standard correctly on the test report. Substituting ISO 9227 without confirming equivalence with the customer is not recommended. How to Choose the Right Standard The correct standard for a salt spray test is always determined by the component drawing, material specification, or OEM quality requirement, not by the laboratory or the supplier. The decision tree is straightforward.   If the specification references ISO 9227, identify which atmosphere is required: NSS, AASS, or CASS If the specification references ASTM B117, the test is neutral salt spray to the American standard If the specification references JASO M609 or a Japanese OEM cyclic protocol, the test is a cyclic corrosion test, not continuous salt spray If the specification references DIN 50021, confirm with the customer whether ISO 9227 NSS is accepted as equivalent before testing For suppliers in Malaysia receiving components from multiple OEM relationships, it is common to encounter two or more of these standards across different programmes. Each specification must be addressed individually. Do not assume that meeting one standard automatically satisfies another. What the Standards Have in Common Despite their differences in origin, scope, and test atmosphere, all four standards share certain fundamental characteristics. Test duration is defined by the specification.
Exposure periods ranging from 96 hours for basic coating qualification to 1,000 hours or more for demanding exterior and underbody applications are all valid, depending on what the specification requires. Acceptance criteria are defined by the specification.
Results are interpreted against a specific pass or fail criterion, whether that is maximum corrosion creep from a scribe line, maximum percentage of surface showing corrosion, or a visual rating against a defined photographic standard. Specimen preparation and positioning affect results.
All four standards specify requirements for cleaning before testing, positioning in the chamber (typically at 15 to 30 degrees from vertical), and handling to prevent contamination. Deviations can invalidate the test result. Test reports must state key parameters.
All four standards require the report to state the standard used, the test atmosphere, the exposure duration, and the chamber conditions, alongside the specimen description, inspection observations, and pass or fail conclusion. Frequently Asked Questions What is the difference between ISO 9227 and ASTM B117?
ISO 9227 defines three test atmospheres: NSS, AASS, and CASS. ASTM B117 covers neutral salt spray only. The NSS conditions in both standards are equivalent in terms of salt concentration and test temperature. The report must reference the standard named in the specification. What is JASO M609 and how does it differ from ISO 9227?
JASO M609 is a Japanese automotive cyclic corrosion test that alternates between salt spray, drying, and humidity phases. ISO 9227 specifies continuous salt spray exposure. The two methods produce different corrosion patterns and are not interchangeable. Cyclic corrosion test results and continuous salt spray results should not be compared directly. Is DIN 50021 still used in automotive specifications in Malaysia?
DIN 50021 appears occasionally in older drawings and legacy specifications that have not been updated to reference ISO 9227. For most practical purposes it is treated as equivalent to ISO 9227 NSS, but confirm equivalence with the customer before substituting one for the other on a test report. How many hours of salt spray testing does my component need?
The required exposure duration is defined by the component specification, not by the laboratory. Basic coating qualification tests may run from 96 to 240 hours. More demanding exterior or underbody requirements typically specify 500 to 1,000 hours or more. Confirm the required duration with the specification before testing begins. Can salt spray test hours be converted into years of service life?
No. Salt spray testing is an accelerated comparative method, not a direct simulation of field exposure. The relationship between test hours and service life depends on the specific coating, the operating environment, and other factors that salt spray testing does not replicate. What acceptance criteria are commonly used for salt spray testing in automotive applications? Acceptance criteria are defined by the component specification. Common criteria include maximum corrosion creep from a scribed line (typically 1 mm to 5 mm), maximum percentage surface corrosion (often 5% to 10% for exterior components), or rating against photographic standards such as ISO 10289 or ASTM D1654. Basic coating qualification tests typically run 96 to 240 hours. Exterior body panels and trim commonly require 500 to 1,000 hours. Underbody and chassis components may specify 1,000 hours or more. Next Steps See our full Materials and Environmental Testing services for automotive corrosion testing Read our detailed guide on ISO 9227 vs ASTM B117 salt spray testing Read our guide on accelerated aging and environmental simulation testing: /blog/accelerated-aging-environmental-simulation/ Contact our team for a corrosion testing quotation or technical discussion   ISO/IEC 17025 Accredited Testing Where Applicable | Salt Spray and Cyclic Corrosion Testing | Automotive Corrosion Testing Malaysia