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Corrosion Monitoring & Inspection Glossary - H

  • Half-cell reactions: Reaction of an electrolytic cell and the electrolyte with which it is in contact.

  • 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.

  • Hall-Effect Sensor, Hall Element: A type of sensor that directly measures magnetic field.

  • 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.

  • 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.

  • Heat affected zone (HAZ): The region around a weld which has been metallurgically affected during the welding process. (See also Preferential weld corrosion.)

  • 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 38C.

  • 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.

  • Hoop Stress: Stress around the circumference of a pipe (i.e., perpendicular to the pipe length) caused by internal pressure.

  • Hydrogen Embrittlement: A loss of ductility of a metal resulting from absorption of atomic hydrogen.

  • Hydrogen permeation (HP): The generation of hydrogen in a corrosive system such that it diffuses into the steel surface and causes further deterioration.

  • Hydrolysis: The reaction of metallic ions with water to form a precipitate while lowering the environment pH.

  • 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.

  • Hydrotest: A pressure test of a pipeline to ensure it meets design conditions and is free of leaks.

Corrosion Inspection and Monitoring