872 Modern Welding Hydrogen embrittlement: A low-ductility condition that occurs in metals due to absorption of hydrogen. Hydrostatically: Using water under pressure. Hydrostatic pressure testing: Application of pressure to a closed pressure vessel or pipe in order to prove fi tness for service. Hyperbaric welding: See Dry welding. Hypereutectoid steels: Steels that have a higher carbon content than the eutectoid composition. Hypoeutectic cast irons: Cast irons that have less carbon than the eutectic composition. Hypoeutectoid steels: Steels that contain less carbon than the eutectoid composition. I Ignition temperature: The lowest temperature in a normal atmosphere at which a given material will ignite sponta- neously without any external spark or fl ame. Ignitron tubes: Devices used as contactors in older welding controllers. Impact energy: The amount of energy that must be exerted to fracture a part. The measurement is usually made in an Izod or Charpy test. Impact strength: Material’s ability to resist shock. Impact test: Careful measurement of how materials behave under heavy loading, such as bending, tension, or torsion. Charpy or Izod tests, for example, measure energy absorbed in breaking a specimen. Impact wear: Constant impacts of a part with hard mate- rials, which tend to change the original dimensions of a part by pounding it out of shape. Impedance: Total resistance to fl ow of alternating current as a result of resistance and reactance. Impurities: Undesirable elements or compounds in a material. Inch switch: A switch used to feed wire to the gun at a rela- tively slow speed to prevent kinking the wire. Inclusion: Foreign matter introduced into and remaining in welds or castings. Incomplete fusion: Less-than-complete fusion of weld material with the base metal or with the preceding bead. Incomplete joint penetration: Lack of fusion between metals, appearing as elongated darkened lines. May occur in any part of a weld groove. Incomplete penetration: Incomplete root penetration or failure of two weld beads to fuse. Indentation: A depression left on the surface of the base metal after spot, seam, or projection welding. Indentation hardness: The degree of resistance of a mate- rial to indentation. This is the standard test used to measure a material’s hardness. Indication, magnetic: Magnetic particle pattern on the surface of a material being tested. Indication, penetrant: Visual evidence of a discontinuity (the penetrant can be seen in the crack). Indication, ultrasonic: Signal on ultrasonic equipment indicating a crack or discontinuity in a material being tested. Induced current: Secondary current that is set in motion when a second conductor in the shape of a closed loop is placed in the magnetic fi eld around another current- carrying conductor. Inductance: In the presence of a varied current in a circuit, the magnetic fi eld surrounding the conductor gener- ates an electromotive force in the circuit itself. If another circuit is next to the fi rst, the changing magnetic fi eld of the fi rst circuit will cause voltage in the second. Induction: The infl uence of an outside magnetic force that produces a corresponding current in a nearby ferromag- netic material. Induction hardening: Process of quench hardening using electrical induction to produce the heat. Induction heating: Using high-frequency alternating current to create eddy currents in the metal to heat it throughout its thickness. Induction soldering: Soldering method that uses induction heating of the base metal. Inductive reactance: Force that opposes fl ow of alternating current through a coil. This force is independent of the resis- tance of a conductor to a fl ow of current. Industrial robots: Devices that perform the same sequence of moves automatically and repeatedly with a high degree of accuracy and speed. Inert: Stable and unreactive. Inert gas: A gas that does not normally combine chemically with the base metal or fi ller metal. Infrared rays: Heat rays coming from either an arc or a welding fl ame. Infrared soldering: Similar to oven soldering, except that the parts are heated by infrared lamps. Ingot: Large mass of metal shaped in a mold. Injector-type torch: A type of oxyfuel gas welding torch that is usually used with an acetylene generator. Inorganic fl uxes: Fluxes that do not contain carbon compounds. In-phase: All the particles or waves of a laser light beam move together and are concentrated to have a higher energy level. Inside corner joint: Two metal pieces placed at an angle to each other (usually 90°), and fused along the inside vertex of the angle. Inside diameter (ID): The distance between (diameter of) the inside walls of a tube, pipe, hose, or other hollow cylindrical object. Interface: Surface that forms a common boundary between two bodies. Intergranular corrosion: Corrosion occurring, for the most part, between grains or on the edges of the grain in a ferrous material. Intermittent current: Current that is interrupted at regular intervals. Intermittent weld: Method of joining two pieces, with sections of the weld joint left unwelded. Intermittent welding: The spacing of short sections of weld across the joint. Interpass heating: Heating the weldment during welding.