Corrosion and metal release characterization of stainless steel 316L weld zones in whey protein solution

Sadegh Varmaziar,Yolanda S Hedberg,Masoud Atapour

doi:10.1038/s41529-022-00231-7

Sadegh Varmaziar, Yolanda S Hedberg + Show 1 more

Open Access

https://doi.org/10.1038/s41529-022-00231-7

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Abstract

Stainless steel ASTM 316 L is often used in the food industry as contact material with protein-rich dairy products. It has to be welded at some locations for many of these contact materials. This study aimed at i) determining any combined effects of the presence of whey protein (WP) and welding-induced weaknesses on corrosion and metal release, and ii) determining the appropriate welding procedure and filler metal (316 L, 309 L, 312). All weld metals (WMs) showed a higher pitting corrosion susceptibility as compared to the base metal (BM). Under induced friction (stirring), WP significantly enhanced the metal release from all materials, which was accelerated between 1 and 3 days of exposure. Post-imaging indicated pits. 312-WM released significantly higher amounts of metals as compared to the BM and the other WMs. This study indicated that the presence of WP, friction, and weldment-induced corrosion susceptibilities could synergistically cause metal release and corrosion of food contact materials.

Highlights

Non-corroding, cleanable, and safe materials for the production, transportation, and storage of food and beverages are vital for the achievement of food security and improved nutrition[1], which are sustainability goals of the United Nations
The microstructure of the base metal (BM) 316 L consisted of equiaxed austenitic grains with some annealing twins, as expected[18,32], Fig. 1a, while a varying fraction of ferritic phases is found for the weld metal (WM), Fig. 1b–d
The varying δ to γ ratios in the WMs can be understood from the solidification modes, which are influenced by their Creq ∕ Nieq ratio, see Supplementary equations 1–6 in the supplementary methods

Summary

Introduction

Non-corroding, cleanable, and safe materials for the production, transportation, and storage of food and beverages are vital for the achievement of food security and improved nutrition[1], which are sustainability goals of the United Nations. Stainless steels are frequently used in the food industry due to their corrosion resistance, mechanical properties, and appropriate lifetime[2]. Among all stainless steel grades, AISI 316 L is a popular grade in dairy industries[4,5]. It is an austenitic (face-centered cubic, non-ferromagnetic) grade with about 16–18 wt.% chromium (Cr), which is responsible for the formation of a thin (1–3 nm), passive surface oxide[6]. It contains about 10 wt.% nickel (Ni), which is not present in its surface oxide, but enriched beneath the oxide[6–8]. It contains about 2.5 wt.% molybdenum (Mo), which is responsible for its high resistance against localized corrosion (pitting or crevice corrosion)[9]

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