For desalination pump applications, what materials are used when in direct contact with salt water?
A primary concern in selecting materials for seawater applications is resistance to corrosion. Flowing saltwater can be corrosive but it can be worse if it sits stagnant in tight clearances. This type of corrosion is referred to as crevice corrosion. Stainless steels and some other alloys rely on an oxide coating to generate a corrosive-resistant film.
Pump designs that have tight crevices or fits do not permit the continued replenishment of this oxide film and may corrode in these areas, even though the material is basically compatible with the liquid being pumped. Certain liquids, such as seawater and halide salt solutions, are more likely to promote crevice corrosion.
For seawater applications, and increasingly important when the pump is operated intermittently or not washed out, higher-alloyed materials are often required. High alloy metals have relatively high amounts of chromium and nickel.
For more information on pump materials of construction, refer to “ANSI/HI 9.1-9.5 Pumps - General Guidelines” at pumps.org.