Preventing+corrosion

=Methods of Preventing Corrosion =  Corrosion prevention in the brewing industry is a fairly straight-forward process. Solvents and disinfectants are easily run through the system to remove any build up or provide added corrosion protection.

Preventing Pitting and Crevice Corrosion
Pitting corrosion can be prevented by control of the alloy’s environment. The most common place to prevent pitting is in the welding stage of the stainless steel [3]. It is important that the surface of the stainless steel is of good quality and that welding is performed correctly. This ensures that the steel is exposed to oxygen uniformly, and weaknesses do not occur in heated zones [3]. By specifying standards for welding and choosing a steel grade that is corrosion-resistant, pitting can be greatly reduced [1].Any scratches or tool marks on the steel should be buffered out as well, as these areas are susceptible to localized corrosion, such as pivoting [3]. This should then be followed by pickling and passivation [3]. Pickling is when the metal is dipped in an acid to remove any leftover particles of the grinded metal [3].

Passivation is the formation of a hard surface film that is non-reactive and which inhibits corrosion. With stainless steel, this is achieved by promoting oxidation of the steel, and then converting the steel to a metalophospate with phosphoric acid [3].

Preventing Intergranular Corrosion
There are several ways to reduce susceptibility to intergranular corrosion. These include:

The use of high temperatures, upwards of 1050*C, is an effective treatment because it precipates carbides; subsequent rapid cooling prevents their reformation.
 * 1) Treatment at High Temperatures**

Although it adds an extra cost, the reduction of carbon content of steel will significantly decrease the susceptibility to intergranular corrosion. This is because high carbon content is correlated with intergranular corrosion of steel.
 * 2) Reduction of Carbon Content**

Elements such as Ti and Cb have higher affinity for carbon, compared to chromium, meaning that carbon will not diffuse across grain boundaries; instead of reacting with chromium, the carbon already present at the boundary will react with Ti or Cb, instead of with Cr.
 * 3) Addition of Titanium or Columbian (Niobium)**

Preventing Corrosion due to Disinfection
To avoid corrosion due to disinfection, breweries usually have to develop cleaning methods that rely on short but frequent contact times [1]. This ensures that the disinfection is done, but the temperature gradient, or thermodynamic driving force between the metal surface and the disinfectant, is never given enough time to become so great that it causes more corrosion. A typically cleaning method involves many water flushes plus an alkaline and acidic rinse cycle [1]. The process generally uses an oxidizing agent like hypchlorite, chlorine dioxide, or peracetic acid [1]. Disinfection of the system also helps to control bacterial corrosion in the system. After disinfection it is important to properly rinse the system so that product quality and safety is maintained.

Preventing Corrosion in the Carbon Dioxide Recovery Plant
In the carbon dioxide recovery plant, filters are installed to treat the processed water entering the inlet to the water scrubber. This prevents chlorine dioxide from entering the facility and acting as a reducing agent that oxidizes the metal [1].

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References
  [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] J. Bushman. 2002. “Corrosion and cathodic protection theory.” [Online]. Bushman & Associates inc. Medina, OH. Available: [], [Accessed Nov. 29, 2009]. 

[3] Mathiesen T, Frantsen JE. 2009. Corrosion aspects for stainless steel surfaces in the brewery, dairy and pharmaceutical sectors. Paper 095373, NACE corrosion.