half-cell—(1) the single oxidation or reduction half reactions in the complete electro-chemical cell. (The potential of a half-cell can only be calculated from the thermodynamic properties of its components.) [thermodynamic use] (2)commonly used in the field to refer to a reference electrode, but this is not a preferred use.
half-cell potential—the potential in a given electrolyte of one electrode of a pair relative to a standard state or a reference state. (Potentials can only be measured and expressed as the difference between the half-cell potentials of a pair of electrodes.)
hand tool cleaning—removal of loose rust, loose mill scale, and loose coating by hand chipping, scraping, sanding, and wire brushing. [See SSPC-SP 2.]
hardener—see curing agent.
hardness—(1) resistance of a material to plastic deformation, usually by indentation. (2)the concentration of inorganic polyvalent cations (generally calcium and magnesium) in water.
heat-affected zone—that portion of the base metal that is not melted during brazing, cutting, or welding, but whose micro structure and properties are altered by the heat of these processes.
heat treatment—heating and cooling a solid metal or alloy in such a way as to obtain desired properties. Heating for the sole purpose of hot working is not considered heat treatment.
high-pressure water cleaning—water cleaning performed at pressures from 34 to 70 MPa (5,000 to 10,000 psig).
high-pressure water jetting—water jetting performed at pressures from 70 to 210 MPa (10,000 to 30,000 psig).
high-temperature hydrogen attack—a loss of strength and ductility of steel by high-temperature reaction of absorbed hydrogen with carbides in the steel,resulting in decarburization and internal fissuring.
holiday—a discontinuity in a protective coating that exposes unprotected surface to the environment.
holiday detection—testing of a coating system for holidays using an instrument that applies a voltage between the external surface of the coating and a conductive substrate.
hot corrosion—an accelerated corrosion of metal surfaces that results from the combined effect of oxidation and reactions with sulfur compounds and other contaminants, such as chlorides, to form a molten salt on a metal surface that fluxes, destroys,or disrupts the normal protective oxide.
hot-dip galvanizing—applying a coating of zinc by immersion in a bath of molten zinc.
hot working—deforming metal plastically under conditions of temperature and strain rate that recrystallization takes place simultaneously with the deformation, thus avoiding any strain hardening. [contrast with cold working]
hydrogen blistering—the formation of subsurface planar cavities, called hydrogen blisters, in a metal resulting from excessive internal hydrogen pressure. Growth of near-surface blisters in low-strength metals usually results in surface bulges.
hydrogen embrittlement—embrittlement caused by the presence of hydrogen within a metal or alloy.
hydrogen-induced cracking—stepwise internal cracks that connect adjacent hydrogen blisters on different planes in the metal, or to the metal surface. [also known as stepwise cracking]
hydrogen over voltage—over voltage associated with the liberation of hydrogen gas.
hydrogen stress cracking—cracking of a metal or alloy under the combined action of tensile stress and the presence of hydrogen in the metal or alloy.