Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Reexamination Certificate
1999-05-08
2001-04-17
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
C324S067000, C174S037000, C405S157000
Reexamination Certificate
active
06218840
ABSTRACT:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to isolating cathodic protection of underground utilities while permitting signals, such as underground locating signals, to be transmitted along the underground utilities. Such signals include, but are not restricted to, radio signals.
2. Background Information
Cathodic protection of underground pipe including steel gas mains is a common practise to prevent corrosion in the utilities industries. This can be a galvanic protection system or an impressed current protection system.
In a galvanic protection system, it is a common practise to have a corrosion protection anode electrically connected to a metal gas main so as to provide galvanic protection to the metal gas main. In galvanic protection, a metal substance that is strongly anodic to steel, usually magnesium or zinc, is buried in the ground adjacent to the steel gas main and connected to it with copper wire. This establishes an electrochemical cell or battery in which the buried metal is the anode, the steel gas main is the cathode, and the soil is the electrolyte.
In an impressed-current protection system, a large mass of expendable metal or graphite, called a ground bed, is buried in the ground some distance from the pipe. This ground bed is connected to the positive side of a source of direct current and the pipe is connected to the negative side. The current source can be viewed as a pump for electrons with its suction side connected to the ground bed and its discharge connected to the pipe. As electrons are removed from the material in the ground bed, an electron-generating or anodic reaction occurs at its surface. The exact nature of the reaction depends primarily on the material of the ground bed.
In both types of cathodic protection, flow of current occurs through the soil, from the buried material to the pipe.
The anode deteriorates, but the metal gas main is protected from corrosion.
In original installations there are metal service lines from the metal gas main to customers' gas meters. As these deteriorate, it is a common practise to insert plastic gas service tubing through the deteriorated metal gas service lines. In the United States, it is a Dept. of Transportation requirement, (RE 49 CFR Ch.1 Part 192.321 e) to have a method of locating the plastic gas service tubing. A common way to do this is to have a tracer wire installed with the plastic tubing so signals such as radio signals can be transmitted through the tracer wire. When one is searching for the location of the plastic gas service tubing, one can send a signal, such as a radio signal, through the tracer wire while a person with a detector can detect the location of the plastic tubing.
A problem with using a tracer wire with the plastic tubing within a metal pipe is that if a short occurs between the tracer wire and the metal pipe, there is a direct electrical connection between that metal pipe and the gas main to which the tracer wire was connected. This causes the corrosion protection anode to deteriorate much faster, as it is now trying to protect not only the gas main, but also the metal pipe through which the plastic tubing was inserted. This is not desirable.
FIG. 3
illustrates a prior art solution to the problem of how to attach a tracer wire
2
to a metal gas mains
3
while keeping the gas main
3
isolated so shorts in the tracer wire
2
do not compromise the cathodic protection of the gas mains. Valve boxes
24
with covers
25
are used as check points, where sections of tracer wire
2
are isolated from other sections of tracer wire
2
. A problem with this is that if one of the valve boxes
24
with a cover
25
is removed, plowed under, paved over, or otherwise lost, tracing the elements of a utility distribution system becomes more difficult. Also shown in
FIG. 3
are the prior art steel to plastic transition mains
21
which are connected to the gas mains
3
by means of the welds
22
. The steel to plastic transition mains
21
are then coupled to the plastic main
23
, typically by a plastic weldment
26
. The steel to plastic transition mains
21
are typically a steel pipe coupled to a plastic pipe and serve as a bridge between the metal gas mains
3
and the plastic main
23
. Tackwelds
9
connect sections of tracer wire
2
to the steel side of the steel to plastic transition mains
21
.
As will be shown in the subsequent description of the preferred embodiments of the present invention, these and other shortcomings of the prior art are overcome.
SUMMARY
The present invention is a means of allowing continuous radio detection of underground utilities while maintaining cathodic insulation of metal utility conduits such as gas mains and pipes. By using a capacitor between a metal gas main and an old metal gas service line, the gas main is isolated from the service line. A short in the tracer line against the old metal gas service line will not result in an electrical connection with the metal gas line that increases the rate of deterioration of the cathodic protection anode. Using the capacitor in the tracer wire system eliminates check points isolating tracer wire sections. In the preferred embodiment of the present invention, the capacitor assembly comprises a ceramic nonpolar capacitor ranging from 0.01 microfarad to 1.0 microfarad encased in an epoxy plastic, contained in a case which is a schedule 40 PVC, i.e. polyvinylchloride, cap such as is common in the plumbing industry, with insulated tracer wire leads of 14 gauge oxygen free copper.
REFERENCES:
patent: 4143251 (1979-03-01), Clark
patent: 4767237 (1988-08-01), Cosman et al.
patent: 4866388 (1989-09-01), Cosman et al.
patent: 5116654 (1992-05-01), Cosman et al.
Morgan George H.
Strecker Gerard R.
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