Types of Iron Rust

Generalized Corrosion/Rust

• Generalized corrosion is a type of rust that spreads out evenly across the entire surface of the iron or alloy. Generalized corrosion typically occurs in shallow layers, and does not penetrate far beyond the surface. It is fairly easy to treat and remove, and is the least damaging of all types of corrosion or rust. Generalized corrosion typically occurs in an environment with a low corrosion rate or with a form of corrosion control.

Pitting Corrosion/Rust

• Pitting rust, also called "deposit corrosion," is a type of rust that occurs only at small localized areas, where it penetrates deeper into the metal surface, creating a pockmarked or "pitted" surface. Pitting corrosion typically occurs separately from generalized rust, and occurs as a result of surface deposits, improper protective surface, pre-existing imperfections, or another initiating mechanism.

Galvanic Corrosion

• Galvanic corrosion is a type of rust that occurs as a result of an electrochemical reaction. This type of rust typically occurs when other metals are present, as the metals operate like the poles of a battery. For instance, galvanic corrosion is common in iron or steel pipes that have been connected to copper tubing; the steel or iron acts as an anode while the copper or brass acts as a cathode. The electrochemical reaction between the two causes galvanic corrosion, an aggressive and localized form of oxidization (rust).

Green Rust

• Green rust is a type of rust that occurs when iron reacts with chlorine ions in an environment with low oxygen. This results in the formation of a series of iron hydroxides, which are green in color, resulting in the colloquial name "green rust." This type of rust typically occurs in seawater, which is high in chlorine content without an excess of dissolved oxygen; for example, reinforcement bars that are located underwater in the ocean often accumulate thick layers of green rust.