Corrosion Glossary - O

Occluded cell: an electrochemical cell created at a localized site on a metal surface which has been partially obstructed from the bulk environment.
Oil burner: a burner for firing oil.
Oil paint: a paint that contains drying oil, oil varnish or oil-modified resin as the film-forming ingredient. The term isincorrectly used to refer to any paint soluble by organic solvents.
Oleoresin: a natural plant product that contains oil and resins, e.g. turpentine.
Open-circuit potential: the potential of an electrode measured with respect to a reference electrode or another electrode when no current flows to or from it.
Operating pressure: the pressure at the top of a pressure vessel at which it normally operates. It cannot exceed the maximum allowable working pressure (Stamped Pressure).
Orange peel: a surface bumpiness or waviness that resembles the skin of an orange. Orange peel is often caused by poor leveling and is a common defect in both spray and roll applied coatings.
Organic matter: substances of or derived from plant or animal matter. Organic matter is characterized by its carbon-hydrogen structure.
ORP: for an electrode that gives a measure of the Oxidation Reduction Potential more commonly known as REDOX potential.
Osmosis: a process of diffusion of a solvent such as water through a semi-permeable membrane which will transmit the solvent but impede most dissolved substances. The normal flow of solvent is from the dilute solution to the concentrated solution in an attempt to bring the solutions on both sides of the membrane to equilibrium.
Overpressure: minimum operating pressure of a hot water boiler sufficient to prevent the water from steaming.
Overspray: sprayed paint that misses the area being painted and falls upon the surrounding surface. Can cause gloss loss with gloss paints or mottling with flats paints.
Overvoltage: the change in potential of an electrode from its equilibrium or steady state value when current is applied. (See overpotential)
Oxidation: loss of electrons by a constituent of a chemical reaction. (Also refers to the corrosion of a metal that is exposed to an oxidizing gas at elevated temperatures.
Oxidized surface (on steel): surface having a thin, tightly adhering, oxidized skin (from straw to blue in color), extending in from the edge of a coil or sheet.
Oxidizing agent: a compound that causes oxidation, thereby itself being reduced.
Oxidizing atmosphere: an atmosphere which tends to promote the oxidation of materials.
Oxygen: gas used to support combustion of fuel gases in combustion thermal spray processes. Achieves much higher flame temperatures than using air. (see dissolved oxygen)
Oxygen attack: corrosion or pitting in a boiler caused by oxygen.
Oxygen concentration cell: a galvanic cell resulting from difference in oxygen concentration between two locations; see differential aeration cell.
Ozone: a powerfully oxidizing allotropic form of the element oxygen. The ozone molecule contains three atoms (O₃).

Link to glossary of corrosion and materials maintenance terms