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 the entry threshold: a tank that meets Ra but has weld depressions will still fail cleaning validation (CIP).
Quick Verdict
Material 316L (not 304), contact surface Ra controlled within 0.8 μm, welds ground flush and acid-pickled/passivated, no dead corners in the structure. Only when all four are met simultaneously can it be considered "cleanable"; meeting Ra alone is the most common half-finished condition.
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 on cleanability, absence of dead corners, and connection methods;
- EHEDG: The European hygienic engineering system, which likewise uses Ra ≤ 0.8 μm as a common baseline but places greater emphasis on cleaning validation (cleanability) and design details: slope, drainage, no threaded connections, seal design.
The common ground between the two is important: they are not concerned with "how bright it is polished," but with "how clean it can be washed." Ra is the means; cleaning validation is the end.
Why Ra Is Not Enough
Ra is the arithmetic mean deviation of the profile — it averages out a deep pit and a wavy area. As a result:
- 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 → microscopically forms "interception grooves," making it harder to clean than a surface with the same Ra but parallel to flow;
- Weld heat tint not removed → missing passive film, pitting occurs even if Ra meets the limit.
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 the polishing pattern direction follows the product flow.
How Processes Meet This Requirement
- Mechanical polishing: routinely achieves Ra 0.4–0.8 μm, lower cost, controllable pattern direction;
- Electropolishing (EP): achieves Ra 0.2–0.4 μm, with a chromium-rich 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 local electropolishing; untreated post-weld seams are the most widespread nonconformity in this industry;
- Material: cleaning agents are mostly chlorinated alkaline/acidic, so 316L is the minimum; 304 will eventually show rust spots under frequent CIP.
Common Pitfalls
- Only sampling 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, which are misjudged 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 actual 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-specific material certificates and surface inspection records.
