Welding Glossary O

O.D. Outside diameter, the exterior width of a pipe, tube or any round object, measured at its widest point.
Off time In resistance welding, the time between repeat cycles, when the electrodes are off the work.
Ohmeter An instrument for measuring the resistance to the flow of electricity through a circuit.
Ohms The unit of measure for resistance to the flow of electricity through a circuit.
Open arc An arc that is open, unaltered or shielded by a constricting nozzle.Also, a visible arc.
Open-Circuit Voltage (OCV) With an open circuit, no current flows. The voltage is impressed upon the circuit so that when the circuit is complete, current will flow immediately.OCV is the voltage in a welding machine circuit when it is on but the arc is not on.
Operator controls In robotics, the controls used by an operator to start a programmed operation.
Organic Originating in once-living matter; animal or plant, not mineral.
Organic fluxes Fluxes that contain carbon.They are corrosive during the welding operation, but become non-corrosive when the welding is complete and can be washed away with water.
Orifice The opening through which wire, gases or a plasma arc passes.A precise hole that may be in a regulator, torch or torch tip.
Orifice gas The gas that surrounds the electrode in plasma arc welding and cutting.It becomes ionized in the arc to form the plasma.
Orthographic projection A method of developing a mechanical drawing, based on viewing an object as if it were in a transparent cube.
Oscillating Moving back and forth in an uninterrupted manner.
Oscilloscope An instrument that shows electrical impulses on a calibrated screen.
OSHA The Occupational Safety and Health Administration, the federal agency responsible for safety in the workplace.
Other side The area of the welding symbol above the horizontal reference line.Also, the side of the welding joint opposite the side touched by the welding symbol arrow.
Outfit Refers to all the welding equipment needed to make a weld.
Out of position weld Welds made in the vertical, horizontal or overhead positions.
Outside corner weld Fusing two pieces of metal together, with the fusion taking place on the under part of the seam.
Overhead position A weld made on the underside of the joint with the face of the weld in a horizontal plane.
Overheating Applying excessive heat, and thus, damaging the properties of the metal.When the original properties cannot be restored, the damage is referred to as burning.
Overlap Extension of the weld face metal beyond the toe of the weld.
Oxidation The process of oxygen combining with elements to form oxides.
Oxidation resistance The ability of a material to resist the formation of oxides.Metal oxides occur when oxygen is combined with metal.
Oxide A chemical compound resulting from a combination of oxygen with other elements.
Oxygen A gas formed of the element oxygen.When it very actively supports combustion it is called burning, when it slowly combines with a substance it is called oxidation, as in rusting of iron.
Oxygen arc cutting under water A process that uses the arc from a hollow electrode to heat the metal, and pressurized oxygen flowing through the electrode to make the cut.