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Surface Finishing of Food Grade Stainless Steel Tubes and Fittings

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The characteristics and property of austenitic grade stainless steel has made it the most suitable material to be used in food and pharma processing design. As the internal surface of stainless steel valves, tubes and fittings is the most common contact zone between product and process pipeline, the inner surface finishing is therefore critical.

Dairy tubes or food grade tubes, depending on individual manufacturer, mostly are produced from cold-rolled 2B stainless steel plate, with bright and fine surface. The surface roughness of the 2B thin sheet (0.5 to 4mm thickness) is ranging from 0.1μm to 0.5μm. As recommended in EHEDG Doc.8, large areas of product contact surface should have a surface finish of Ra 0.8μm or better. With current much improved welding technology, most of the food grade tube will not require to be internal ground or polished to achieve Ra 0.8μm. Sometimes, user may prefer inner-polished dairy tube because they are “attracted” by the visual appearance, which is giving the “smoother” impression. Again, depending on individual tube manufacturer and their workers, some polishing techniques may damage the “ready to be used” 2B surface. Wrong speed and too great a pressure may create tiny pits on the surface which can’t be visually seen by user especially when it took place at middle of a standard 6-meter length food grade tube.

Note: Minox recommends EN 10357 tube which is widely use globally in food, beverage and brewery industries. Besides, Minox also supply A270/3A/ASME BPE inner polished tube for food and pharmaceutical industries.

Tube fittings like elbow and tee are generally produced from cut dairy tube, going through some reformation steps such as bending or hot extrusion process, which may damage the original surface of the short tube. As such, surface treatment like polishing would be applied for the inner surface of tube fittings to achieve designated surface finishing in order for sanitary use purpose. Comparatively, to polish a tube fitting either elbow or tee will be easier than polish a tube but still, a strict quality control policy have to be followed to ensure it achieved the requirement to be sanitary grade or for food process use.

All surface that are in contact with the product have an average surface roughness of Ra < 0.8 μm

Note: Minox sanitary stainless steel tube fittings are inspected in high AQL rate to ensure the products received by user is at the higher acceptance level of surface finishing requirement by standard.