In food and pharmaceutical plants, stainless steel alone is not enough. What makes the difference is how it is welded and finished. A weld that leaves a gap, a lap joint or a rough surface becomes a place where residue builds up, bacteria settle in, and cleaning cannot reach.

1. What the standards require

2. Why a polished surface

Roughness is measured as Ra, in micrometres (µm). The lower the number, the smoother the surface. The food industry reference is 0.8 µm Ra or less, recommended by 3-A, EHEDG and the American Meat Institute.

An honest nuance: studies show that going well below 0.8 µm adds little further benefit for bacterial adhesion. Design matters more: no gaps, no crevices, rounded corners. A mirror polish on a poorly sealed weld is useless.

A 2B mill finish is often acceptable, but 3-A asks that it be verified with a profilometer, measuring across the grain.

3. Fully sealed welds

• Continuous welds over the full length: never stitch or skip welds on a sanitary surface.
• No lap joints: two overlapping sheets always leave a gap between them.
• Welds ground and polished to the same finish as the sheet, with no pits or porosity. A crevice in a weld is a defect to be repaired.
• Rounded inside corners, so brushes and wash jets reach everything.

Health Canada even lists "metal surfaces with gaps (e.g. poor welding)" among the places to sample for Listeria in ready-to-eat foods. Biofilms are fought by the mechanical action of cleaning, which does not reach the bottom of a crack.

4. What about pests?

Canadian regulations require plants to protect themselves against pests and not to offer them shelter. In the field we see it often: gaps, open joints and cavities under equipment trap food residue and moisture, which attracts insects and rodents. A closed, smooth construction leaves them no shelter and no food.

5. After welding: remove heat tint and passivate

• The blue or gold colour left by heat (heat tint) weakens corrosion resistance. It must be removed by grinding, pickling or electropolishing; passivation alone does not remove it.
• Passivation (ASTM A967 or A380, with nitric or citric acid) removes free iron from the surface and strengthens the protective layer of stainless steel.
• Acceptable discoloration levels for sanitary tubing are defined in AWS D18.1 and D18.2.

In short

• Aim for 0.8 µm Ra or less on contact surfaces, welds included.
• Require continuous, ground and polished welds, with no lap joints.
• Round inside corners so cleaning reaches everything.
• Remove weld heat tint, then passivate.

We fabricate and repair stainless steel equipment for food and pharmaceutical plants, with sealed, polished TIG welds. Call us at 438-357-8800.

Sources

1. CFIA — Establishment checklist (Safe Food for Canadians Regulations requirements) (French)
2. Health Canada — Good manufacturing practices, GUI-0001 (C.02.004 and C.02.005) (French)
3. Government of Manitoba — Sanitary design of equipment
4. 3-A SSI — Hygienic Design Considerations and Techniques (0.8 µm Ra, continuous welds, radii)
5. Milledge, J.J. — The cleanability of stainless steel used as a food contact surface (University of Southampton)
6. Dixon Sanitary — Surface Finishes, based on ASME BPE (manufacturer sheet)
7. Health Canada — Policy on Listeria monocytogenes in ready-to-eat foods (2023), control measures (French)
8. Virginia — 12VAC5-421-1100 (adopted text of the FDA Food Code)
9. 3-A SSI — Passivation of Stainless Steels (heat tint, ASTM A967 / A380)

Photo: Unsplash. This article provides general information; it does not replace the manufacturer's requirements or your facility's risk assessment.