From Principles of Corrosion Engineering and Corrosion Control



It is a form of localized corrosion of a metal surface where small areas corrode preferentially leading to the formation of cavities or pits, and the bulk of the surface remains unattacked. Metals which form passive films, such as aluminum and steels, are more susceptible to this form of corrosion. It is the most insidious form of corrosion. It causes failure by penetration with only a small percent weight-loss of the entire structure. It is a major type of failure in chemical processing industry. The destructive nature of pitting is illustrated by the fact that usually the entire system must be replaced.


Generally, the most conducive environment for pitting is the marine environment. Ions, such as Cl -, Br - and I -, in appreciable concentrations tend to cause pitting of steel. Thiosulfate ions also induce pitting of steels.

Aluminum also pits in an environment that cause the pitting of steel. If traces of Cu 2+ are present in water, or Fe +3 ions are in water, copper or iron would be deposited on aluminum metal surface and pitting would be initiated. Oxidizing metal ions with chloride, such as cupric, ferric and mercuric, cause severe pitting. Presence of dust or dirt particles in water may also lead to pitting corrosion in copper pipes transporting seawater. With soft water, pitting in copper occurs in the hottest part of the system, whereas with hard waters, pitting occurs in the coldest...

Products & Services
Passivates are chemicals used to reduce surface reactivity to protect a metal against corrosion. Depositing an inert coating or forming a coherent oxide layer can also passivate a surface.
Chemical Water Treatment Equipment
Chemical water treatment equipment mitigates the formation of scale, calcium carbonate deposits, in process water systems such as cooling towers, boilers and heat exchangers by controlled chemical addition and system monitoring.
Oil Additives and Fluid Additives
Oil additives and fluid additives are chemical substances that are added to oils and industrial fluids to impart or improve certain properties. They are used with lubricants, coolants, thermal oils, greases, metal working fluids, and other application-specific fluids.
Wafer Chucks
Wafer chucks are used to handle semiconductor wafers during wafer processing applications. Common work clamping technologies include vacuum and electrostatic.
Deaerators are used to remove dissolved, corrosive gases from boiler feed water. They heat incoming makeup water for injection into the boiler, and return the condensate to a temperature which minimizes the solubility of these gases.

Topics of Interest

4.7 INTERGRANULAR CORROSION Intergranular corrosion refers to preferential corrosion along the grain boundaries. Grains are crystals usually on a microscopic scale, that constitute the microstructure...

Salt spray corrosion pits are a common site of fatigue crack initiation in aluminum alloy aircraft components. Salt corrosion pitting occurs during exposure to the marine atmosphere and results in...

4 Stainless Steel Stainless steel is the name given to a range of steels that include elements other than iron and carbon, which passivate the metal against corrosion. Typically, the passivating...

Corrosion related fatigue in aluminum structural alloys and fretting damage in high strength steels are primary failure mechanisms that reduce the structural integrity of aging aircraft. A chemically...

Conventional approaches to mitigate corrosion related failure mechanisms in aircraft usually involve isolation from the corrosive environment via protective coatings, alloy substitution, or...