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Peening - The mechanical working of metal by light hammering with a round nose hammer. Peening has the effect of stretching the surface of the metal and this relieves contractual stresses. Physical Properties - The qualities of a material which are inherent characteristics of the material such as thermal conductivity, electrical conductivity, coefficient of expansion, density and color. Parameters - The welding settings on a welding machine such as voltage and amperage, normally read on a volt meter and an amp meter. It may also include things as travel speed, electrode size, torch angle, electrode extension and weld joint position and preparation. Partial Joint Penetration - A condition in the root of a groove weld when the weld metal does not extend through the joint thickness. By design this is acceptable and not a defect, because it will carry the load for which it was intended. Plasma - The electrically charged, heated ionized gas which conducts welding current in a welding arc. Plug Welding - A weld made by filling (or partially filling) a hole in one member of a joint, fusing that member to another member. Pool - The weld pool is the liquid state of a weld prior to its becoming solid weld metal. It indicates no limit to depth as the nonstandard term puddle tends to note a shallower depth. Porosity - A cavity type discontinuity formed by gas entrapment during solidification. Positioner - A device which moves the weldment when a stationary arc is used. Positioners include turning rolls, head and tail stocks and turntables. Pounds Per Square Inch (psi) - A measurement equal to a mass or weight applied to one square inch of surface area. Primary Power - Often referred to as the input line voltage and amperage available to the welding machine from the shop’s main power line. Often expressed in watts or kilowatts (kw), primary input power is AC and may be single- or three-phase. Welding machines with the capability of accepting more than one primary input voltage and amperage must be properly connected for the incoming primary power being used. Puddle - More properly referred to as molten weld pool, the weld puddle is the liquid state of a weld prior to its becoming solid weld metal. Pulsing - Varying the current from a high peak amperage level to a lower background amperage level at regular intervals. Pulse controls also adjust for the number of pulses per second and the percent of time spent at the peak amperage level. Pulsing is used to control heat input and allow for improved weld profile. Purging - Cleaning, purifying or removing something from a container. Such as applying shielding gas to the inside of a piping structure prior to welding it with the GTAW process. Partial Pressure – In any gas mixture the total pressure is equal to the sum of the pressures (partial) which each gas would exert were it alone in the volume occupied by the mixture. Parts Per Million (ppm) – A convenient means for expressing low concentrations. As applied to gases, ppm stands for moles per million moles. ppm by weight is expressed as pounds per million pounds. Ppm by volume is usually expressed in cubic feet per million cubic feet. Permissible Exposure Limits (PEL) –See “Exposure Limit.” Physical Hazard – Descriptive of a chemical for which there is scientifically valid evidence that it is a combustible liquid, a compressed gas, explosive, flammable, an organic peroxide, an oxidizer, pyrophoric, unstable reactive or water reactive. Poison – A substance that in relatively small doses has an action, when it is ingested by, injected into, inhaled or absorbed by, or applied to a living organism, that either destroys life or impairs seriously the function of one or more organs or tissues. Polymerization – A chemical reaction, usually carried out with a catalyst, heat or light, and often under high pressure, in which a large number of relatively simple molecules combine to form a chain-like macromolecule. Proof Pressure – A test pressure applied to control devices to verify structural integrity. No deformation or excessive leakage is permitted at this pressure and the control device must function normally subsequent to this test. Normal industry standard is 1.5 times (150%) of working pressure. See also “Burst Pressure” and “Maximum Operating Pressure.” Pyrophoric – The ability of a chemical to ignite spontaneously in air at a temperature of 130 degrees F or below. Pyrophoric Gas – A gas that can spontaneously self-ignite when exposed to normal atmospheric conditions.
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