Choosing Alloys for Food Processing Equipment

## Regulatory Framework Food-contact materials must comply with FDA 21 CFR 174-186, EC 1935/2004, 3-A Sanitary Standards, and EHEDG Guidelines. 300-series stainless steel with Ra less than or equal to 0.8 micrometers is the baseline. ## The Standard: 316L Stainless Steel 316L is the default food processing alloy worldwide. It resists organic acids (citric, acetic, lactic), withstands chloride-based sanitizers at typical use concentrations, achieves the required surface finish by electropolishing, and produces smooth weldable joints. ### When 316L Falls Short 316L can pit in high-chloride brines (>5% NaCl), warm acidified chloride solutions, and aggressive CIP cycles. ## Upgraded Alloys **904L (UNS N08904)**: PREN 36. For warm chloride solutions. Used in mustard production and vinegar processing. **Duplex 2205**: Double yield strength of 316L allows thinner vessels. Resists chloride SCC in warm CIP cycles. **254 SMO (UNS S31254)**: PREN 43. For the most aggressive food processing environments. ## Surface Finish Requirements | Application | Minimum Ra (micrometers) | |-------------|-------------------------| | General food contact | 0.5-0.8 | | Dairy, beverage | 0.4-0.6 | | Pharmaceutical crossover | <0.4 | ## Hygienic Design Principles No crevices or dead legs, self-draining surfaces (minimum 3-degree slope), smooth welds ground flush, sanitary clamp connections instead of threaded fittings, and minimum 6 mm internal radius at corners.