Chapter 12 - Metallurgy

Abstract

Corrosion is the major consideration when selecting pump material. Corrosion problems occur mostly in pumps that use fluids with high sodium chloride content. There are different types of metal corrosions, such as general uniform corrosion, galvanic corrosion, pitting, crevice corrosion, erosion corrosion, cavitation corrosion, stress corrosion, and vibration crack corrosion. Metals exposed to oxygen form a covering layer, also called a passive layer, of oxide, which protects the metal from corrosion. General uniform corrosion can be prevented easily by using the correct metallurgy, such as stainless steel or nickel alloy steels. The various types of stainless steel make up the largest group of metals capable of forming thick passive layers. Local corrosion may occur in standby pumps in aggressive services. To maintain the passive film, the metal needs a constant supply of oxygen. Flooding of these pumps with fresh water when on standby is a possible solution. This chapter provides a list of some common materials that are used in the pump industry: cast iron, ferritic steel, martensitic stainless steel, nickel alloys, and copper alloys.