Selection of Stainless-Steel Grades for Food Processing based on Pitting Corrosion

Sammanfattning

Selecting the right stainless-steel (SS) grade for food processing equipment is a critical decision, since processing environments vary widely and a grade that performs well under one set of conditions may be inadequate under another. The following study evaluates the pitting corrosion resistance of three grades commonly used in the food industry, 316L, 2205 DSS and 254 SMO, under varying chloride concentration, temperature and acetic acid content, with the aim of developing a grade selection matrix for Tetra Pak when introducing new food solution products. The results confirmed a clear pitting resistance hierarchy (254 SMO > 2205 DSS > 316L), with temperature as the most damaging factor, revealing that at 90°C the passive oxide layer of 316L is thermally saturated to the point where further changes in chloride or acid content have negligible additional effect. The most unexpected finding was that acetic acid consistently increased pitting potential in 254 SMO while slightly reducing it in the other two grades, suggesting an inhibitory interaction with this alloy that strengthens its advantage under aggressive conditions. Phenomena such as transpassive dissolution was frequently observed in 2205 DSS and 254 SMO under less aggressive conditions, and crevice corrosion was clearly present in 316L but ambiguous and far less pronounced in the higher-alloy grades. The pitting engineering diagrams developed from these results show promise as a practical selection tool for new food products at Tetra Pak. As a pilot study, the adaptation of welded 254 SMO samples to the experimental setup produced meaningful results that establish a basis for their future integration into the selection matrix.