Stainless steel 304 is the usual minimum for product contact parts in food machines. Use 316 or 316L where the product is salty, acidic or rich in chlorides, where cleaning chemicals are aggressive, and for most pharmaceutical contact parts.
Frames and covers that never touch the product can usually be 304, and in some dry, low-hygiene uses, painted mild steel. Your contract should state the grade for each group of parts. If it only says "stainless steel", you may receive a cheaper grade. That can even be a lower-nickel 200-series steel, which looks the same but resists corrosion far less well.
What the difference is
Both are austenitic stainless steels with chromium and nickel. 304 contains roughly 18% chromium and 8% nickel. 316 adds about 2 to 3% molybdenum, which greatly improves resistance to pitting by chlorides such as salt.
The "L" grades, such as 316L, have low carbon, with a maximum of 0.03%. Low carbon reduces the risk of corrosion along welds, so L grades are preferred for welded vessels and pipework.
In European standards, 304 is close to EN 1.4301, 316 to EN 1.4401 and 316L to EN 1.4404.
Where to use which
- Dry products such as grain, pulses, seeds, sugar and most spice powders usually run well on 304.
- Brines, pickles, sauces, tomato products, citrus and other acidic or salty products usually call for 316 or 316L.
- Equipment cleaned with chlorinated or strong acid cleaners is safer in 316 or 316L.
- Pharmaceutical product contact parts are commonly specified in 316L, with measured surface finish.
- Grinding parts such as hammers, pins and blades may be hardened steel for wear life. Confirm they are suitable for food contact in your market.
- Gaskets, seals and hoses must be food-grade materials suited to the product and cleaning method.
How to check you got the right grade
304 and 316 look the same. The difference is in the chemistry, so you need evidence, not appearance.
- Ask for mill test certificates for the sheet, pipe and bar, as explained in material test certificates and EN 10204 3.1.
- Have contact parts checked with a handheld PMI analyser during inspection. It shows whether molybdenum is present.
- Check that welds are ground smooth, cleaned and passivated, and that the stated surface finish has been measured.
- Make sure the machine does not mix grades on contact parts, for example a 316 vessel with 304 fittings.
Who is responsible
Food contact law places duties on the businesses that make and use food contact materials. In the EU, the framework is Regulation (EC) No 1935/2004. Ask the maker for a declaration covering contact materials, and confirm what your market requires with your food safety adviser. For wider design rules, see GMP design for machines.
Next step
We check material certificates and arrange PMI checks on contact parts before a machine ships. To discuss your machine, book a free sourcing review.