technical case study
Stainless Steel in Hydrometallurgy: The Critical Link Between Process Performance and Material Integrity
Stainless steel plays a pivotal role in the success and longevity of hydrometallurgical plants. These operations run at the edge of chemical and mechanical limits, making material performance non- negotiable. The choice of fabrication materials, particularly stainless steels, can reinforce or completely undermine the work of process specialists. This article explores the unique corrosion challenges within hydrometallurgy, explains essential principles of stainless steel selection, and introduces a Life Cycle Costing (LCC) tool to guide cost-effective, long-term material decisions.
Background Stainless steel is a young material, just over 100 years old, and continues to evolve with new grades developed for specific applications. While there are over 200 grades in the stainless steel family, they can be grouped into five distinct categories. For hydrometallurgical plants, the focus is on the more noble or highly alloyed austenitic grades, as well as duplex grades. The basic differences between austenitic (nickel- containing) materials and plain chromium (ferritic) grades highlight why Austenitics are suitable for hydrometallurgical applications. Austenitic stainless steels are both weldable and formable, and contain higher levels of chromium, nitrogen, and molybdenum compared to Ferritics.
While nickel does not directly improve corrosion resistance like chromium does, it allows higher chromium levels to be added, enhancing the passive protective layer. Molybdenum boosts resistance to localised corrosion such as pitting. Nitrogen is added to increase mechanical strength, since carbon levels are restricted in stainless steels. It also plays a key role in resisting pitting and crevice corrosion. However, austenitic grades containing 5 to 20% nickel are prone to stress corrosion cracking. When exposed to elevated temperatures, chlorides, and tensile stress, they may fail unexpectedly due to the formation and propagation of fine hairline cracks. Ferritic grades are not susceptible to stress corrosion cracking, but cannot be effectively welded in thicknesses
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Issue 3 – 2025
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