Official Answer
Answer
In pharmaceutical manufacturing, wave springs must be free of all organic contaminants and have a robust passive oxide layer to prevent leaching of metallic ions. Vapor degreasing using chlorinated or fluorinated solvents removes residual oils from the coiling process. This is followed by passivation according to ASTM A967, typically using a nitric or citric acid bath. Passivation dissolves free iron from the surface and enhances the chromium-to-iron ratio in the surface film, significantly improving corrosion resistance. For 316 stainless, citric acid is often preferred for environmental reasons and its ability to effectively chelate iron without attacking the base alloy, ensuring the spring meets FDA requirements for cleanliness.
