Centrifugal pumps are fabricated of almost all the known engineering materials, from simple thermoplastic polymers through metals ranging from cast iron to the various nickel-based alloys to composites and ceramics. The conditions of service and the nature of the pumped liquid finally determine which among this wide range of materials will be the most suitable. A specific choice is based first on past experience with the same liquid or a similar liquid. When past experience is lacking, material properties and known performance must be used. Listings of the materials commonly recommended for various liquids can be readily found in the Standards published by the Hydraulic Institute [1.1], in API-610 [3.1] and in the catalogs and bulletins of pump manufacturers, particularly those who specialize in centrifugal pumps for chemical service, the field that presents the greatest variety of material selection problems. Note, in this connection, that the plant owner is ultimately responsible for the performance of the specified materials, because the precise nature of the pumped liquid is solely under his or her control. It is the pump manufacturer’s responsibility to furnish the specified materials (provided, of course, they are mechanically suitable).