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Corrosion Glossary - H
- Handhole: an access opening in a pressure
part usually not exceeding 17 cm in its longest dimension.
- Handhole cover: a handhole closure.
- Hardener: curing agent for
epoxies or fiberglass.
- Hard chromium plating: the electrolytic
deposition of chromium to form a very hard (1000 Hv), tough coating with good
wear resistance. The structure is micro-cracked.
- Hard water: water which contains calcium
or magnesium in an amount which require an excessive amount of soap to form
a measure of the amount of calcium and magnesium salts in
water. usually expressed
as grains per gallon or ppm as calcium carbonate (CaCO3).
- Hardness test: a test designed to assess
the resistance to penetration from a load. The surface is indented under a defined
load and the depth or area of penetration is measured.
- Hardfacing: the application of a
coating of material designed
to resist wear.
- Haze: a general term applied to virtually
any dulling of a paint surface. It is used to cover a wide variety of defects.
Haze may be due to material that has exuded to the surface, fine solvent popping,
roughening of the surface because of flocculation or poor coalescence, microvoids,
- Hazop: a structured process intended
to proactively identify equipment modifications and/or safety devices required
in order to avoid any significant safety or environmental incident as a result
of equipment failure.
- Head: a measure of the pressure at a
point in a water system.
- Head loss: the same as "pressure drop".
- Heat balance: an accounting of the distribution
of the heat input, output and losses.
- Heat exchanger: a vessel in which heat
is transferred from one medium to another.
- Heat release rate: rate that describes
the heat available per square foot of heat-absorbing surface in the furnace
or per cubic foot of volume.
- Heating surface: those surfaces which
are exposed to products of combustion on one side and water on the other. This
surface is measured on the side receiving the heat.
- Heating value: the quantity of heat
released by a fuel through complete combustion. it is commonly expressed in
btu per lb, per gallon, or cu-ft.
- Helium (He): monatomic noble gas, Most
inert element, atomic number 2. Used as a plasma gas in plasma spraying.
- Hexavalent chromium: or
- Hiding power: the ability of a
paint to mask the color or pattern
of a surface.
- High velocity oxy-fuel spraying (HVOF):
a Thermal spray process. The spray powder particles are injected into a high
velocity jet formed by the combustion of oxygen and fuel, heated and accelerated
to the workpiece.
- 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 which fluxes, destroys, or disrupts the normal protective
- Hot cracking: also called solidification
cracking. Hot cracking of weldments is caused by the segregation at grain boundaries
of low-melting constituents in the weld metal. Hot cracking can be minimized
by the use of low-impurity welding materials and proper joint design.
- Hot dip coating: a metallic coating
obtained by dipping the base metal or substrate into a molten metal.
- Hot isostatic processing (HIPping):
the high temperature/high pressure consolidation of a powder metallurgy component
or thermally sprayed coating. Density is greatly increased and metallurgical
changes provide enhanced corrosion and wear properties.
- Hot-rolling, hot-rolled steel (HR):
rolling steel slabs into flat-rolled
steel after it has been reheated.
- Hot shortness: a tendency for some alloys
to separate along grain boundaries when stressed or deformed at temperatures
near the melting point. Hot shortness is caused by a low-melting constituent,
often present only in minute amounts, that is segregated at grain boundaries.
- Hot working: deforming metal plastically
at such a temperature and strain rate that recrystallization takes place simultaneously
with the deformation, thus avoiding any strain hardening.
- Huey test: corrosion testing in a boiling
solution of nitric acid. This test is mainly used to detect the susceptibility
to intergranular corrosion
of stainless steel.
test: a corrosion test involving exposure of specimens at controlled
levels of humidity and temperature.
- HVOF: See high velocity oxygen fuel
- Hydration: the chemical combination
of water into a
- Hydrocarbon: a chemical compound of
hydrogen and carbon.
- Hydrogen: diatomic gas, atomic number
1, The lightest element, very reactive and powerful reducing agent. Used as
a secondary plasma gas in the plasma spraying process and as a fuel gas in combustion
thermal spray processes (CWS, CPS and HVOF).
- Hydrogen blistering: the formation of
blisters on or below a metal surface from excessive internal hydrogen pressure.
(Hydrogen may be formed during cleaning, plating, corrosion, etc.).
a general term for the
cracking, blistering, and hydride formation that can occur when hydrogen is
present in some metals.
hydrogen-induced cracking or severe loss of ductility caused by the presence
of hydrogen in the metal. Hydrogen absorption may occur during electroplating,
pickling, or other processes that favor the production of nascent or elemental
- Hydrogen overvoltage: overvoltage or
overpotenttial associated with the liberation of hydrogen gas.
- Hydrogen-induced cracking (HIC): same
as hydrogen embrittlement.
- Hydraulic cements:
hydraulic cements are waterproof and will even set underwater. Such materials
are identified by the presence of finely pulverized material added to the cement
binder which will cause discoloration from white to pale browns or pinks.
- Hydrolysis: a) decomposition or alteration
of a chemical substance by water. b) in aqueous solutions of electrolytes, the
reactions of cations with water to produce a weak base or of anions to produce
a weak acid.
- Hydrophilic: having an affinity for
- Hydrophobic: lacking an affinity for,
repelling, or failing to absorb or adsorb water.
- Hydrostatic test: a pressure test procedure
in which a vessel or system is filled with water, purged of air, sealed, subjected
to water pressure, and examined for leaks, distortion and/or mechanical failure.
- Hydroxide: a chemical compound containing
hydroxyl ion. (see pH)
- Hydroxyl: the OH- anion which
has a single negative charge, and provides the characteristics common to bases.
- Hygroscopic: possessing a marked ability
to accelerate the condensation of water vapor; applied to condensation nuclei
composed of salts that yield aqueous solutions of a very low equilibrium vapor
pressure compared with that of pure water at the same temperature.
- Hypochlorite: the OCl- anion;
calcium and sodium hypochlorite are commonly used as bleaches and disinfecting