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

Abstract

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.

Popular Abstract

Stainless steel is the most widely used material in the food industry. It is hygienic, durable, and mechanically robust, making it the suitable choice for the pipes, tanks, and heat exchangers that process the food we consume every day. However, not all stainless steels are equal, and selecting the wrong grade can have serious consequences for both equipment integrity and food safety. One of the most dangerous threats in these environments is pitting corrosion: a form of localized attack in which microscopic holes form on the metal surface and grow inward, largely invisible to the naked eye. Because pitting develops without obvious external signs, it can go undetected until it causes contamination of the food product, hygiene failures, or even the complete breakdown of processing equipment, with potentially severe economic and environmental consequences.
The challenge is that stainless steel comes in many different grades, each with distinct properties and costs. Selecting a grade that is more resistant than necessary represents an unjustified expense, while selecting one that is too basic for the application introduces unacceptable risk. Striking the right balance has traditionally been done based on experience rather than systematic data, a gap that becomes especially critical when new food products with different chemical compositions are introduced into existing processing lines. This project, carried out in collaboration with Tetra Pak in Lund, Sweden, set out to address exactly that. Three grades widely used in the food industry, 316L, 2205 Duplex, and 254 SMO, were evaluated under conditions representative of real processing environments, including varying salt concentrations, temperatures between 30°C and 90°C, and the presence of acetic acid, a component commonly found in products such as ketchup or vinegar-based sauces.
The results were clear and, in some cases, genuinely unexpected. The most economical grade, 316L, proved unsuitable for demanding conditions. At 90°C, its protective surface layer degrades to such an extent that the addition of salt or acetic acid produces no meaningful further damage, because the material is already critically compromised. For the other two grades, the appropriate choice depends on the specific processing environment. At moderate conditions, 2205 Duplex offers corrosion resistance practically equivalent to 254 SMO at a significantly lower cost, making it a well-justified selection in many scenarios. However, as temperature increases and acetic acid is present, 254 SMO consistently emerges as the more suitable candidate. The most surprising finding of the study was that while acetic acid slightly reduces corrosion resistance in 316L and 2205 Duplex, in 254 SMO the effect is reversed: the acid appears to enhance the resistance of the material to pitting in a significant and consistent way. The mechanism responsible for this behavior remains to be fully understood and represents one of the most interesting open questions for future research.
As a practical outcome, the project developed a set of material selection diagrams that Tetra Pak can use as a decision-making tool. Given a specific combination of temperature, chloride concentration, and acidity, these diagrams indicate which stainless-steel grade is most appropriate, giving engineers a concrete and data-driven foundation for a decision that until now was mostly made based on experience alone.

• author: Krawzoff Ramírez, Carlos
• supervisor: Martin Adell
• organization: Production and Materials Engineering
• course: MMTM05 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Pitting corrosion, Stainless steel selection, Food processing equipment, PREN, 316L, 2205 Duplex, 254 SMO, Transpassive dissolution, CPDP
• other publication id: LUTMDN/(TMMV-5402)/1-59/2026
• language: English
• id: 9245176
• date added to LUP: 2026-06-29 16:36:29
• date last changed: 2026-06-29 16:36:29