| Global Positioning System (GPS): The
Global Positioning System (GPS) is a navigational system that allows a user to compute
position and time anywhere on earth. It has been developed and is controlled by the U.S.
Department of Defense (DoD). GPS consists of three elements: the space segment
(orbiting satellites), the control segment (ground level monitoring and
satellite tracking stations) and the user segment.
The user segment is represented by GPS receivers at ground level. These
receivers convert the radio signals transmitted by the satellites into three dimensional
position coordinates (x,y,z) and time. Velocity and direction of travel can also be
derived from the position and time signals. In practice, signals from at least four
satellites are required to compute the three-parameter position fix and the fourth time
parameter.
Uses of GPS technology in pipeline corrosion monitoring
include:
- Locating corrosion control hardware and monitoring points in the field.
- Establishing positional coordinates and mapping of assets for use in geographical
information systems (GIS).
- Linking corrosion data and identified coating defects to position coordinates
(especially important over water and in the desert, where there are no or limited
permanent geographic features).
- Establishing position coordinates for pipeline features/hardware (test stations,
rectifiers, bonds, crossings, etc.).
- Using the GPS time signal for synchronous timing of devices. Synchronous interrupting of
multiple rectifiers in close interval potential surveys is an example.
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References/Literature:
A.R. Kowalski: "The Use of Differential GPS as an Inspection Tool in
the External Corrosion Control of Buried Pipelines", Paper #670, Corrosion 98, NACE
International, 1998.
J.M. Leeds and M. Waterton: "Correlating Coating and Metal-loss Data
can save O&M Money", Pipeline and Gas Industry, March 1999.
M. Tullmin and J.W. Fourie: "GPS Technology in Pipeline Corrosion
Control", Paper #8A.4, Northern Area Eastern Conference and Exhibition, NACE
International, Ottawa, 1999.
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