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Corrosion Monitoring & Inspection Glossary - P

  • Passivity: The loss of chemical reactivity of certain materials under specific environmental conditions, i.e. the corrosion rate drops to negligible levels.

  • pH: The measure of acidity of a solution, where a pH of 7 at 25 C indicates neutrality, <7 increasing acidity, >7 increasing alkalinity.

  • Pig: A generic term signifying any independent, self-contained device, tool or vehicle that moves through the interior of the pipeline for purposes of inspecting, dimensioning, or cleaning. All pigs in this report are either utility pigs or instrumented tools.

  • Pig Signal: Usually a mechanical sensor on the pipe activated by the passage of a pig.

  • Pigging: See In-Line Inspection.

  • Pipeline: That portion of the pipeline system between compressor or pump stations including the pipe, protective coatings, cathodic protection system, field connections, valves, and other appurtenances attached or connected to the pipe.

  • Pipeline Component: A feature, such as a valve, cathodic protection connection, or tee that is a normal part of the pipeline. The component may produce an indication that is recorded as part of an inspection by an in-line inspection tool or configuration pig.

  • Pipeline System: All portions of the physical facilities through which gas, oil, or product moves during transportation, including pipe, valves, and other appurtenances attached to the pipe, compressor units, pumping units, metering stations, regulator stations, delivery stations, breakout tanks, holders, and other fabricated assemblies.

  • Pit Gauge or US Pit Gage:  a device to measure the depth of corrosion.  A pit gauge can take various forms, in the most basic as a simple lever and pointer or more accurate units using a dial or digital indicator to provide the measurement displacement.   Pit depth gauge, depth gauge, bridging bar.

  • Pitting: Local corrosion with the majority of the surface remaining intact. Usually occurs where the surface passivity has broken down.

  • Planktonic: Bacterial corrosion from bacteria suspended in the medium. (See also Sessile.)

  • Plastic Strains: Strains beyond the elastic limit of a material due to mechanical damage. Plastic strains and cold working are related, but not the same.

  • Pole Piece: A magnetic material that channels a magnetic field from a magnet into a pipe material.

  • Pole Spacing: The distance between pole pieces of a magnetizing assembly.

  • Porosity: Small voids or pores, usually gas filled, in the weld metal.

  • Prandtl number: Used in heat exchange calculations, where (Specific heat capacity at constant pressure x dynamic viscosity) is divided by (Thermal conductivity).

  • Preferential weld corrosion: A galvanic corrosion which occurs due to the weld metal and parent plate representing different metallurgical zones with different microstructures and compositional differences. (See also Heat affected zone.)

  • Pressure: Level of force per unit area exerted on the inside of a pipe or vessel.

  • Pressure Reversal: Failure of a defect (e.g., crack) at a pressure level below the maximum level reached on a prior loading (e.g., hydrostatic retest).

  • Process measurement: Corrosion monitoring technique which provides a measure of the corrosion from an analysis of the process conditions present. Involves the use ofDeWaard-Milliams and Oldfield & Todd equations.

  • Proportional limit: See Elastic Limit.


Corrosion Inspection and Monitoring