B-1 Corrosion & Materials of Construction
Selecting the right pump type and sizing it correctly are critical to the success of any pump application. Equally important is the selection of materials of construction. Choices must be made between metals and/or non-metals for pump components that come into contact with the pumpage. In addition, gaskets and O-ring material selections must be made to assure long leak-free operation of the pump's dynamic and static sealing joints. To assist in proper selection, included in this section is a brief discussion of specific types of corrosion and a general material selection guide.

Corrosion
Corrosion is the destructive attack of a metal by chemical or electra-chemical reaction with its environment. It is important to understand the various types of corrosion and factors affecting corrosion rate to properly select materials.

TYPES OF CORROSION

1. Galvanic corrosion is the electro-chemical action produced when one metal is in electrical contact with another more noble metal, with both being immersed in the same corroding medium called the electrolyte. A galvanic cell is formed and current flows between the two materials. The least noble material called the anode will corrode while the more noble cathode will be protected. It is important that the smaller wearing parts in a pump be of a more noble material than the larger more massive parts, as in an iron pump with bronze or stainless steel trim. Following is a galvanic series listing the more common metals and alloys.