The most commonly specified requirement in food, beverage, and dairy equipment procurement is "contact surface Ra ≤ 0.8 μm." This is correct, but it is only theentry-level line: a tank that meets Ra but has weld depressions will still fail cleaning validation (CIP).
One-Sentence Verdict
Use 316L (not 304), control contact surface Ra within 0.8 μm, grind welds flush and acid-pickle/passivate, and design without dead corners.Only when all four are met simultaneously can it be considered "cleanable"; meeting Ra alone is the most common half-finished job.
What the Two Systems Require
- 3-A Sanitary Standards: The U.S. dairy/food equipment system, which sets an explicit upper limit on contact surface roughness (commonly Ra ≤ 0.8 μm) and includes clauses oncleanability, absence of dead corners, and connection methods;
- EHEDG: The European hygienic engineering system, which also uses Ra ≤ 0.8 μm as a common baseline but places greater emphasis oncleaning validation(cleanability) and design details: slope, drainage, no threaded connections, seal types.
The common ground between the two is important:they govern not "how shiny it is" but "how clean it gets."Ra is the means; cleaning validation is the end.
Why Ra Is Not Enough
Ra is thearithmetic mean deviationof the profile — it averages out a deep pit and a wavy area. As a result, you get:
- Overall Ra 0.6 μm passes, but there is a 0.3 mm pit at the weld root → product accumulation, bacterial growth;
- Polishing direction perpendicular to product flow → microscopic "interception grooves," harder to clean than a surface with the same Ra but aligned with flow;
- Weld heat tint not removed → missing passive film, pitting corrosion even if Ra meets spec.
In addition to Ra, actual acceptance should also check:presence of visible pits/scratches, whether welds are ground flush with the base metal, whether post-weld acid pickling or electropolishing is performed, and whether polishing lines run in the direction of product flow.
How to Achieve This in Practice
- Mechanical polishing: Typically achieves Ra 0.4–0.8 μm, lower cost, controllable line direction;
- Electropolishing (EP): Achieves Ra 0.2–0.4 μm, with a chromium-enriched surface (thicker, more uniform passive film), commonly used in pharmaceutical and high-cleanliness applications;
- Weld treatment: Grind flush with base metal, then acid-pickle/passivate or perform localized electropolishing; untreated post-weld seams are the most widespread nonconformity in this industry;
- Material: Cleaning agents are mostly chlorinated alkaline/acidic; 316L is the minimum. 304 will eventually show rust spots under frequent CIP.
Common Pitfalls
- Only spot-checking Ra without inspecting welds and dead corners — audits look at structure and cleaning results;
- Using carbon steel tools to grind welds, causing iron contamination and local rust spots, misdiagnosed as "wrong material";
- Using 2B sheet directly as food-grade: 2B is a rolled surface; although Ra is low, it has waviness, and weld issues remain the same;
- Procurement only specifies "food-grade 316L" without stating the Ra upper limit, polishing method, and weld treatment requirements, making it impossible to judge upon delivery;
- Ignoring gasket and seal materials — seals are often the source of cleaning dead corners.
For food/pharmaceutical equipment, tell us your contact surface requirements (Ra upper limit, polishing method, whether electropolishing is needed), cleaning method, and applicable standards. We can control surface and weld treatment per drawing and provide batch material certificates and surface inspection records.
