Electricity: measuring and testing – For insulation fault of noncircuit elements
Reexamination Certificate
1999-05-27
2001-05-08
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
For insulation fault of noncircuit elements
C324S330000, C324S345000
Reexamination Certificate
active
06229313
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to pipeline monitoring systems, and more particularly to a method and apparatus for monitoring pipelines and the like for current loss locations.
BACKGROUND OF THE INVENTION
Major pipelines, for transport of gases, liquids and slurries over long distances, are commonly made of steel which provides both strength and economy. Customarily, the pipelines are buried beneath the surface of the ground for protection, or pass under rivers or lakes in their paths. Under these conditions, such pipelines are subject to corrosion, due to electrochemical action, as a result of portions of the metal surface of the pipe coming into contact with electrolytes in the ground. To reduce the probability of corrosion occurring, these pipelines are commonly coated with an impermeable (electrically resistive) material, such as bitumens and mylar, etc.
Nevertheless, no coating is perfect, and all coatings deteriorate with time, aided by ground movement or as a result of attack by water, chemical or biological agents, resulting in ground contact points being developed. Such contact points are generally known as “holidays” in the pipeline industry. It is at such holidays that corrosion may occur.
Metal ions escape from the pipe at the ground contact point when the metal of the pipe is electropositive in potential relative to the electrolyte with which it is in contact in the ground. This causes corrosion. In the extreme, the pipe is so weakened by the loss of metal that a leak is formed, and the contents being transported start to escape. To reduce the possibility of such a condition occurring along the pipeline, corrosion engineers take steps to lower the potential of the pipe relative to the ground, by applying a negative DC voltage, using a DC generator. This is the practice of “cathodic protection” or “CP”.
Further details of cathodic protection practices may be found in such sources as:
1) Parker, Marshal, E.; Pipeline Corrosion and Cathodic Protection: a Practical Manual for Corrosion Engineers. 3
rd
Edition. Gulf Publishing Co., Houston, Tex. 1984, or
2) Morgan, John, H. Cathodic Protection (Second Edition), National Association of Corrosion Engineers. Houston, Tex., 1987.
SUMMARY OF THE INVENTION
As discussed in greater detail below, according to the present invention, a method and apparatus is provided for monitoring pipelines and the like for locations where current losses through leakage will indicate where the metal of the pipe comes into direct contact with ground water and may be the sites for pipeline corrosion.
It is an object of one aspect of the invention to provide a method and apparatus for the rapid and economical determination of the presence and location of any large holidays along major pipelines. It is a further aim to allow the measurements necessary to achieve these objectives to be made without the necessity to contact the pipeline, and, in fact, that they can be made from an aircraft or helicopter. It is a further object of an aspect of the invention to map the CP voltage-to-ground along the pipeline. It is still a further object of an aspect of the invention to provide a system which does not require modification of the existing CP system on the pipeline in order for the invention to be applied.
A second embodiment of this invention is disclosed, which may be applied when there is no active CP system in place on the pipeline, or when the pipeline traverses a region of high magnetic noise, due to natural or man-made sources, which may act to introduce errors into the measurements made with the first embodiment.
REFERENCES:
patent: 4628266 (1986-12-01), Dzwinel
patent: 5119028 (1992-06-01), Mooney
patent: 5610523 (1997-03-01), Elliot
patent: 5923170 (1999-07-01), Kuckes
patent: 1184974 (1985-04-01), None
Kerveros James C.
Metjahic Safet
Scintrex Limited
Sim & McBurney
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