Since the late 1940s’, austenitic grade of stainless steel has been widely used for food and pharma processing design, mainly due to it’s corrosion resistance level, strength, formability, machinability, weldability and most importantly, cleanability.
The EHEDG (European Hygienic Engineering Design Group) Guidelines, Doc.8: Hygienic Equipment Design Criteria highlighted the prevention of the microbial contamination of food products as the guideline’s fundamental objective. If equipment and process pipeline is of poor hygienic design, or produced not according to requirement, it will be difficult to clean. The property of austenitic stainless steel helps to create a smooth, easy to clean and non-absorbent surface for long period of time to resist accumulation of bio-films that present hygiene hazard.
As such, food grade or sanitary grade stainless steel valves and fittings must be inert both to the product and to detergents and disinfectants under the conditions of intended use. At the same time, they must also be corrosion resistant, non-toxic, mechanically stable, and their surface finish must not be adversely affected.
Most of the sanitary grade stainless steel valves, tubes and fittings are produced from two classic austenitic types, 304/304L (4301/4307) and 316L (4404).
Heavy welded section on grade 304 may require post-weld heat treatment (annealing) for maximum corrosion resistance. To reduce the risk of chromium carbide formation during welding process, low carbon series (0.03% max) of stainless steel, 304L or 316L are the solution.
Note: In Minox, all of our food grade stainless steel tube is produced from low carbon series, 304L (4307) and 316L (4404), and 90% of Minox sanitary valves, welding union (SMS, DIN, Tri Clamp, IDF, RJT, DS, Hygienic and Aseptic Flange and etc.) and weld end tube fittings (elbow, tee and reducer) are also produced with the same series. It has since helped users to reduce significantly on the risk of intergranular corrosion after the welding process.
Good TIG weld for hygienic requirement.
Intergranular corrosion caused by bad welding.