Passivation of austenitic stainless steels for the purpose of manufacturing and handling beer

Technical Session 12: Engineering Session
Harvey Claussen, The Zythos Project LLC, Portland, OR, USA

ABSTRACT: Creating and maintaining a suitable non-reactive surface for brewery vessels requires an understanding of the nature of austenitic stainless steels. The selection of the appropriate chemical and electrochemical system for passivation is critical. All of this can be brought into perspective for the brewer. An example is the composition of the surface during passivation of molybdenum containing austenitic stainless steels such as Avesta AB with 3.6 a/o Mo and Sandvik AB with 1.7 a/o Mo in 0.1M HCl + 0.4M NaCl. Low levels of chlorides can seriously alter the nature of the seemingly inert coating. The alloys exposed to certain electrolytes under polarization can develop varying corrosion potentials, as well as active and passive potentials. Electrochemical polarization can vary depending on the initial voltaic potential, as well as the rate of an increasing potential. Ni and Fe cations can be present to varying degrees in the oxide. An enrichment of Ni by 10 a/o may also develop on the surface of the metallic phase. At the passive region, the film formed on the alloy can be chromium oxide. Bringing all of the passivation technology together can be daunting, so the presentation focuses on a simplified approach to the understanding of passivation technology.

Harvey Claussen received a B.S. degree in chemical engineering from the University of Washington in Seattle. He has been involved with the design, construction, and operation of fine chemical, agricultural, and food facilities since 1961. He first entered the brewing world in 1984, siting and designing microbreweries. In addition, Harvey enjoys home brewing when time permits. He and his associates founded The Zythos Project LLC, a beer think tank, in 2011.