Piping and Valves

Piping materials: The most commonly used piping materials for biotechnology plants, in order of usage, are stainless steel, thermoplastics (polypropylene, polyethylene, polyvinyl-dine fluoride), carbon steel, copper, iron, glass, and lined pipe (glass and plastic liners).

The guiding document for engineering, design and installation of Water for Injection (WFI) and other sterile systems is CGMP-LVP (Current Good Manufacturing Practice-Large Volume Parenterals, Part 212.49 of Subpart C, Water and Other Liquid Handling Systems), which was issued by the Food and Drug Administration (FDA) in 1976 as a performance specification, in the absence of a code (198). This document specifically mentions stainless steel as the material of construction for WFI and by inference, sterile services.

In sterile fermentation processes, a great deal of attention is necessary for the layout of lines and the construction of joints. Lines for sterile air and lines for transferring sterile mash are the subject of special care during installation to prevent the formation of pockets where liquid can collect. Adequate slopes, continuous in one direction, have to be given in what would be normally horizontal lines. Loops in lines are best excluded, but if unavoidable have to be provided with drain points so that residual mash and steam condensate can be removed. For purposes of sterilization, steam is introduced wherever possible at the highest point or points in the system, with the steam condensate removed from the lowest points.

Valves used on sterile lines have given cause for thought for a considerable time. For robust industrial processes such as alcohol fermentation, or even for yeast cultivation, the use of the standard type of gate valve is normally acceptable. However, for fermentation systems more prone to contamination, the use of a standard valve has obvious shortcomings. The introduction of a diaphragm capable of standing up to steam for longer periods into the valve has encouraged a gradual changeover to the use of the diaphragm type of valve. Presently, with a diaphragm life of 3-4 months, the use of this type of valve for aseptic applications is justified.

Drain valve: The best drain valve available is a flush mounted diaphragm valve. Designs that include a coupling connected directly to the tank should not be used for any aseptic application. There is no way to keep such a valve clean or free of solids buildup.

Sight Glass: Circular-type sight glasses with sanitary clamp mountings are generally used. These are easy to clean and to replace. The long, rectangular types are much more expensive, and require special modifications to make them self draining.

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