Glossary 877 Physical testing: Examination of a material to fi nd out its physical properties. Physics principles: Underlying principles that govern how matter and energy interact. Pickling: A method of removing surface oxides from metals by chemical or electrochemical reaction. Pickling solution: A solution that removes any scale and rust from the surfaces of parts. Pierce: To produce a relatively small hole (in comparison to the size of the metal surface) through a steel plate. Pig iron: Hot iron that has been poured into molds and allowed to cool and solidify. Pilot arc: A nontransferred arc in plasma arc cutting used to initially ionize the plasma gas. Pinch force: Electrical force that causes the globule or droplet at the tip of an electrode to separate from the rest of the electrode. Pipe: A hollow cylinder with relatively thick walls. Pitch: Center-to-center distance of welds. Pitch dimension: Indicates the distance from the center of one weld segment to the center of the next on intermittent welds. Plain carbon steel: Alloy of iron and carbon. Plasma: Temporary physical condition of a gas after it has been exposed to and has reacted to an extremely high temperature. The gas becomes ionized. Plasma arc cutting (PAC): A metal cutting process that uses an electric arc and fast fl owing ionized gases. Plasma arc welding (PAW): A welding process in which an arc is used to generate plasma in the torch. The plasma is forced through a constricting nozzle to heat the weld area. Plasma gas: Superheated ionized gas. Plasma spraying (PSP): Thermal spraying process that uses a nontransferred plasma arc to melt and propel the surfacing material onto the base. Plastic welding: Process in which heated air softens and fuses synthetic plastic materials. Plasticity: Ability of a metal to bend without breaking (rupturing). Plasticize: The process of generating heat in a material to soften it and make it fl ow without melting. Platen: A smooth, extremely fl at surface that is built so it will not warp. Usually made of iron or granite, a platen is used to check measurements and to arrange parts for large assemblies. In resistance welding, a large, gener- ally fl at surface through which current fl ows and to which projection welding dies are attached. Plug weld: A weld made through and in a round hole that has been cut into one piece of metal that is lapped over another piece. Polarity: The direction of fl ow of electrons in a closed direct current welding circuit. Porosity: Gas pockets or voids in a metal. Positioner: A device used to hold a weldment and move it or rotate it into the best position for welding. It may be moved manually or automatically. Positive-pressure torch: Commonly used oxyfuel gas welding torch that normally operates at a pressure of 1 psig to 10 psig (6.9kPa to 69kPa), depending on the torch tip size. Postfl ow: The timed fl ow of shielding gas after the arc is extinguished. Its purpose is to protect the hot electrode and weld area from oxidation. Postheating: Application of heat to a metal after a welding or cutting operation has been performed. Postweld heat treatment: Heating a weldment after welding. Powdered metal: Metal processing method in which the metal to be used is reduced to a fi ne powder, then forced under high pressure into a heated steel mold. Powder metallurgy: The art and technology of producing powdered metal and of utilizing it in the production of parts. Powered air purifi er: A device, worn by a welder, that has a motorized blower and fi lters to remove harmful or toxic particles and chemicals from the recirculated air. Precipitation-hardening stainless steels: Stainless steels that develop their strength through heat treatment processes. Prefl ow: The fl ow of shielding gas that begins before the arc is struck. Preheating: Application of heat to a metal before a welding or cutting operation has been performed. Preheating furnace: Used to heat metal gradually to the correct preheat temperature before the necessary welding is performed. Pressure regulator: A mechanism installed between the cylinder and the torch lines to reduce and stabilize gas pressure. Print: A copy of a drawing or plan. Previously referred to as a blueprint. Procedure qualifi cation record (PQR): A nonstandard term. See Welding procedure qualifi cation record (WPQR). Procedure specifi cations: Limiting instructions, written by a manufacturer or contractor, that explain how welding will be done. Process anneal: A type of annealing that is usually performed on low-carbon steels. The steel is heated but remains below the A1 critical temperature. It is held at this temperature long enough for softening to occur, then is air-cooled. Processes: Methods or means of performing an action. Program: A series of movements, actions, times, pressures, welding sequences, and other variables that must occur during an automatic welding procedure. Usually placed into a computer memory. Projection welding (PW): A type of resistance welding in which current fl ow is concentrated at predetermined points by projections, embossments, or intersections. Psia: Pounds per square inch atmospheric. Psig: Pounds per square inch gauge. PSW guns: Portable spot welding machines. Also called gun welders or gun welding machines. Puddle: A nonstandard term. See Weld pool. Pulsed arc: Electronically controlled current that provides a period of high welding current and a period of lower current. Pulsed arc welding: A welding arc in which the current is interrupted or pulsed as the welding arc progresses. GMAW-P and GTAW-P are two pulsed arc processes.