Metal Release and Corrosion Resistance of Different Stainless Steel Grades in Simulated Food Contact

• Published in: Corrosion (Houston, Tex.) Vol. 72; no. 6; p. 775
• Main Authors: Mazinanian, N, Herting, G, Wallinder, I Odnevall, Hedberg, Y
• Format: Journal Article
• Language: English
• Published: Houston NACE International 01-06-2016
• Subjects: Acids; Alloys; Austenitic stainless steels; Chloride; Citric acid; Cold; Computer simulation; Corrosion; Corrosion effects; Corrosion resistance; Corrosion resistant steels; Detection; Detection limits; Drinking water; Duplex stainless steels; Exposure; Ferritic stainless steels; Food; Food safety; Foods; Galvanic corrosion; Heat resistant steels; Heavy metals; Investigations; Manganese; Martensitic stainless steels; Metal release; Metals; Molybdenum; Nickel; Open circuit voltage; Passivity; pH effects; Sodium chloride; Spectrum analysis; Stability; Stainless steel; Stainless steels; Surface oxide; Tap water; Time dependence; Water; USA, Texas, Houston; ANE, Europe
• ISSN: 0010-9312; 1938-159X; 1938-159X
• DOI: 10.5006/2057

A new technical guideline has been implemented by the Council of Europe (CoE) to ensure the stability and safety of food contact articles of metals and alloys, using 5 g/L citric acid (pH 2.4) and artificial tap water DIN 10531 (pH 7.5) as food simulants. The objectives of this study were: (i) to quantify the extent of metal release from austenitic (grades AISI 201, 204, 304, and 316L), ferritic (grades AISI 430 and EN 1.4003), and lean duplex stainless steel (grade EN 1.4162) in citric acid (5 g/L, pH 2.4) and in artificial tap water (pH 7.5); (ii) to compare the release of metals to the surface oxide composition, the open circuit potential-time dependence, and the corrosion resistance; and (iii) to elucidate the combined effect of high chloride concentrations (0.5 M NaCl) and citric acid at pH 2.2 and 5.5 on the extent of metal release from AISI 304 with and without prior surface passivation by citric acid. Exposures of all stainless steel grades in citric acid and artificial tap water up to 10 d (at 70 degree C/40 degree C) resulted in lower metal release levels than the specific release limits stipulated within the CoE protocol. For all grades, metals were released at levels close to the detection limits when exposed to artificial tap water, and higher release levels were observed when exposed to citric acid. Increased surface passivation, which resulted in reduced metal release rates with time, took place in citric acid for all grades and test conditions (e.g., repeated exposure at 100 degree C). There was no active corrosion in citric acid at pH 2.4. Fe (in citric acid) and Mn (in all solutions, but mostly tap water) were preferentially released, as compared to their bulk alloy content, from all stainless steel grades. Ni was released to the lowest extent. 0.5 M NaCl induced a very low (close to detection limits) metal release from grade AISI 304 at pH 5.5. When combined with citric acid (5 g/L) and at lower pH (2.2), 0.5 M NaCl induced slightly higher metal release compared to citric acid (pH 2.4) alone for coupons that were not pre-passivated. Pre-passivation in 5 g/L citric acid (pH 2.4) at 70 degree C for 2 h largely reduced this solution dependence. Pre-passivation resulted in an up to 27-fold reduced extent of metal release in solutions containing citric acid and/or NaCl at pH 2.2 to 5.5, and resulted in improved reproducibility among replicate samples.