SO 9227 is a globally recognised international standard that specifies the apparatus, reagents, and procedure for conducting accelerated corrosion tests on metallic materials, both with and without protective coatings. The primary purpose of the standard is not to predict the real-world lifespan of a material, but to serve as a quality control check to assess the uniformity and integrity of protective coatings and to detect defects or pores.
The core of the standard involves placing test specimens in a controlled, enclosed chamber and exposing them to a continuous, atomised salt solution (a salt fog) at a constant, elevated temperature. This creates a highly corrosive environment that accelerates the corrosion process.
ISO 9227 outlines three distinct types of salt spray tests, which vary in their chemical composition and aggressiveness:
- Neutral Salt Spray (NSS) Test: This is the most common and fundamental method. It uses a neutral pH solution of 5% sodium chloride. The NSS test is widely applicable to metals and their alloys, metallic coatings (like zinc and chrome plating), conversion coatings, anodic oxide coatings, and organic coatings (paint, powder coat) on metallic surfaces. The typical chamber temperature is 35°C.
