304 or 316L Stainless Steel for Hygienic Process Equipment

The Practical Difference

316L contains molybdenum, which improves resistance to pitting and crevice corrosion from chlorides. The L means low carbon, which reduces carbide precipitation at the weld heat affected zone and so reduces the risk of intergranular corrosion after welding. 304 is perfectly adequate for many food and beverage duties and costs less.

When 316L Is the Right Call

Choose 316L where chlorides are present, which includes brine, many cleaning chemicals, seawater cooled circuits and coastal wash-down environments. Choose it for pharmaceutical duty, for purified water systems, and wherever the component will be welded into a line and then has to be validated.

When 304 Is Enough

304 handles neutral food product, potable water, and standard caustic CIP at normal concentrations. Structural and non-contact items such as pipe supports are usually specified in 304 unless the environment is corrosive.

Mixing Grades in One Line

It is common and usually fine, but keep the grade consistent within any section that sees the same media. What causes problems is a 304 component in an otherwise 316L chloride-bearing line, because that one item becomes the corrosion site.

Evidencing the Grade

Material certificates to EN 10204 3.1 are available on request. Ask for them at the order stage rather than after delivery, because the certificate has to follow the specific material batch used for your parts.