Properties of Metals
The important information in this chapter is summarized below.
Corrosion is the natural deterioration of a metal in which metallic atoms leave the
metal or form compounds in the presence of water or gases. General corrosion
may be minimized by the use of corrosion-resistant materials and the addition of
protective coatings and liners.
Galvanic corrosion occurs when dissimilar metals exist at different electrical
potentials in the presence of an electrolyte. Galvanic corrosion may be reduced
by the careful design and selection of materials regarding dissimilar metals and the
use of sacrificial anodes.
Localized corrosion can be especially damaging in the presence of other
destructive forces such as stress, fatigue, and other forms of chemical attack.
Stress-corrosion cracking occurs at grain boundaries under tensile stress. It
propagates as stress opens cracks that are subject to corrosion, ultimately
weakening the metal until failure. Effective means of reducing SCC are 1) proper
design, 2) reducing stress, 3) removing corrosive agents, and 4) avoiding areas of
chloride and hydroxide ion concentration.
Chloride stress corrosion occurs in austinitic stainless steels under tensile stress
in the presence of oxygen, chloride ions, and high temperature. It is controlled by
the removal of oxygen and chloride ions in the environment and the use of low
Problems occurring with the use of inconel include caustic stress corrosion
cracking, wastage, tube denting, pitting and intergranular attack.
resistance to caustic stress corrosion cracking may be improved by heat treating.