Corrosion+in+the+Context+of+the+Brewery+Process

=Corrosion in the Context of the Brewery Process=

Before beginning a detailed chemical analysis of the corrosion mechanisms, it is important to identify where, in the context of the brewery process, corrosion is likely to occur. Even before tanks are shipped to the brewery, they may be exposed to corrosive substances during the manufacturing and transport process.

At the plant, disinfectants, used to clean the various metal pipes, help maintain a high standard for hygiene, but there may be associated corrosion problems. Corrosion only occurs under "exceptionally harmful circumstances" [1]. According to the technical staff at the Wild Rose Brewery, such circumstances only occur due to the misuse of a cleaning agent [2]. However, NACE claims that these circumstances often occur, especially when there are rapid thermal changes (which provide a thermodynamic force that causes tank implosions), or if CIP acid is trapped on dirty surfaces (which causes pitting corrosion) [1]. The discrepancy between the two sources incites a need for critical analysis. It is our conclusion that NACE's world-renowned report is more reputable than the information provided by the technical workers at Wild Rose Brewery. Although these workers are adept when it comes to the brew-making process, they are not experts on the process of corrosion. Furthermore, the brewery workers are biased, aiming to protect their company's reputation by diminishing the significance of corrosion problems at their brewery. NACE, on the other hand, conisists of disinterested, multidisciplinary experts drawing on experiences from various locations.

Under these harmful circumstances, the cleaning agent will oxidize the metal [1]; in other words, the cleaning agent will act as an oxidizing agent, as described by the following reduction half-reaction:

OCl - +H 2 0 + 2e- <> Cl - +2OH - (E 0 = 0.89 V)

Although this reaction shows hypochlorite as the oxidizing cleaning agent, other cleaning agents could be used and include peracetic acid, hydrogen peroxide and chlorine dioxide. Hypochlorite is also an important inhibitor of bacterial corrosion; it kills the bacteria before they can contribute to corrosive damage. This is why this process is not affected by microbiological organisms.

The oxidation half-reaction of a brewery-related metal, such as iron, would be:

Fe (s) <> Fe 2+ (aq) + 2e - (E 0 =0.44 V)

Note, once again, that the overall reaction potential is 1.33 V, which denotes that this reaction spontaneously occurs.  Corrosion also occurs in other parts of the brewing process, including the carbon dioxide recovery plant, where carbon dioxide, created during the fermentation process, is recovered. In this plant, corrosion often affects the gas side of the stainless steel piping, compressor and valve casings. It is usually caused by processed water, treated with chlorine dioxide at the brewery, entering the system as aerosols [1]. The chlorine dioxide acts as an oxidizing agent, undergoing the following reaction:

ClO 2 - + 2H 2 O +4e - <> Cl - + 4OH - (E 0 =0.76 V)

This spontaneous reaction causes corrosion in the carbon dioxide recovery plant.

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 [1] H.C Aller, B. Bertelsen, P. Cheepsujjayan, J.E. Franstan, K.U. Hattesen, T. Mathiesen. 2008. “Common Corrosion Problems in the Brewery Sector.” NACE Corrosion; 2008 March; New Orleans, Los Angeles.

[2] Wild Rose Brewery (personal correspondance)