Product contact surfaces must be finished to a degree of surface roughness that is smooth enough to enable them to be easily cleaned and disinfected. The surface finish must have a roughness area Ra as low as practicable and without cracks, pits or cavities where water or soil might remain. Surface roughness Ra can be defined as the arithmetic average value of the departure of the profile above and below the mean line throughout the specified sampling length. A surface finish of roughness Ra # 0.8 pm is considered as acceptable for closed equipment used for handling liquid food and normally cleaned in-place. A roughness Ra exceeding 0.8 pm may be acceptable if test results have demonstrated that the required cleanability can be achieved through other design features or more intensive cleaning methods.


A wide range of tanks is used in the food industry, which can be classified either as storage tanks or process vessels. The function of storage tanks is purely storage of raw materials and intermediate or final products at different stages of the production process. Process vessels can include mixing, blending, heating, cooling, separation, and fermentation operations. Process vessels are more complex in design than plain storage tanks because of the presence of various internal components. However, the design criteria are the same for all types of tank.

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