ASTM B117 vs ISO 9227: Choosing the Right Salt Spray Test Standard for Your Industry

Two primary standards dominate salt spray testing worldwide: ASTM B117 and ISO 9227. Understanding their similarities, differences, and appropriate applications is essential for manufacturers seeking compliance and meaningful test results.

Overview of ASTM B117

ASTM B117 specifies the apparatus, procedure, and conditions for operating neutral salt spray (fog) testing. It is widely used in North America, particularly in automotive and general industrial applications. The standard focuses on a 5% sodium chloride solution at neutral pH and 35°C.

Overview of ISO 9227

ISO 9227 is the international standard and defines three test methods:

• NSS (Neutral Salt Spray) — Similar to ASTM B117

• AASS (Acetic Acid Salt Spray) — More aggressive acidic environment

• CASS (Copper-Accelerated Acetic Acid Salt Spray) — Highly aggressive, used for decorative coatings and certain plated finishes

Key Differences and Selection Guidance

While the basic NSS methods are comparable, ISO 9227 offers additional aggressive variants useful for specific materials. ASTM B117 is often preferred for its simplicity and long history in automotive specifications. For zinc and zinc-alloy coatings, CASS testing under ISO 9227 can accelerate failure modes more aggressively.

Practical Recommendations

Choose ASTM B117 when specifications explicitly require it or for general comparative testing. Select ISO 9227 when international compliance or more aggressive conditions are needed. In many cases, performing both NSS and CASS provides complementary data.

Modern salt spray test chambers designed to meet both standards offer the flexibility required by global supply chains.