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Half-cell reactions: Reaction
of an electrolytic cell and the electrolyte with which it is in contact.
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Hall effect (HE) probe:
A semiconductor device which, when biased by an electrical current generates
a voltage proportional to the magnetic field flowing perpendicular to the surface
of the semiconductor. The voltage generated is proportional to the strength
of the magnetic field, which is proportional to the thickness of the element
of a component under test.
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Hall-Effect Sensor, Hall Element:
A type of sensor that directly measures magnetic field.
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Hard Spots: Local changes
in hardness of the steel in the pipe resulting from nonuniform quenching procedures
during the manufacture or changes in chemistry of the steel. Hard spots, when
stressed, are subject to failure from mechanisms, such as hydrogen-stress cracking.
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Harmonic analysis (HA):
Corrosion monitoring technique that is a variation of electrochemical impedance
spectroscopy that uses a single frequency sine wave applied signal followed
by an harmonic analysis of the response.
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Heat affected zone (HAZ):
The region around a weld which has been metallurgically affected during
the welding process. (See also Preferential weld corrosion.)
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High Vapor-Pressure (HVP) Liquid:
Hydrocarbons or hydrocarbon mixtures in the liquid or quasi-liquid
state with a vapor pressure in excess of 107 kPa absolute at 38°C.
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Holiday: Discontinuity
in a coating, such as pinholes, cracks, gaps, or other flaws, that allow areas
of the base metal to be exposed to any corrosive environment that contacts the
coating surface.
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Hoop Stress: Stress around
the circumference of a pipe (i.e., perpendicular to the pipe length) caused
by internal pressure.
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Hydrogen Embrittlement:
A loss of ductility of a metal resulting from absorption of atomic hydrogen.
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Hydrogen permeation (HP):
The generation of hydrogen in a corrosive system such that it diffuses into
the steel surface and causes further deterioration.
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Hydrolysis: The reaction
of metallic ions with water to form a precipitate while lowering the environment
pH.
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Hydrostatic Testing (Re-Testing):
Testing of sections of a pipeline by filling the line with water and pressurizing
it until the nominal hoop stresses in the pipe reach a specified value.
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Hydrotest: A pressure
test of a pipeline to ensure it meets design conditions and is free of leaks.
