Electricity: measuring and testing – Testing potential in specific environment
Reexamination Certificate
2002-03-12
2004-11-23
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Testing potential in specific environment
C324S072500, C324S071200, C340S505000, C340S645000, C205S775500, C455S067110
Reexamination Certificate
active
06822432
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to underground pipelines, and more specifically to maintenance and testing of underground pipelines.
Pipelines and other metallic structures are inherently inclined to corrode. The corrosion process involves the removal of electrons or oxidation of the metal, and consumption of those electrons by some other reduction reaction, such as oxygen or water reduction. Corrosion is encouraged by the presence of moist soil in contact with a metal pipeline.
The electrochemical nature of the corrosion process provides opportunities to detect and mitigate corrosion of underground structures. Typical mitigation methods include applications of coatings to the structures and neutralizing the voltages and currents associated with the corrosion process through application of external voltages and currents.
Corrosion mitigation processes can be monitored to determine the extent of corrosion activity and to verify the effectiveness of electrical corrosion prevention systems. One known electrical corrosion prevention system for application of external voltages and currents to an underground structure, such as a pipeline, is referred to as a cathodic protection system. As part of the maintenance process, corrosion mitigation processes are monitored to determine the extent of corrosion activity. As a result, effectiveness of the cathodic protection system is also monitored.
The U.S. pipeline industry has standardized methods for assessing the performance of a cathodic protection rectifier system. One method used to detect corrosion activity and to assure the proper performance of the cathodic protection systems includes reading and verifying the output voltage of cathodic protection rectifiers, and reading and verifying the impressed current on the pipeline by measuring the voltage drop across a shunt resistor connected in series with the output of a cathodic protection rectifier. U.S. governmental regulations currently in place require measurement of rectifier voltage outputs at least once every two months.
Another conventional pipeline test, sometimes called an “on” potential measurement, includes reading the pipe-to-soil voltage at test points along the pipeline with cathodic protection rectifiers turned on, and verifying a potential between the structure and a reference electrode in the ground adjacent to the test point. One known U.S. testing standard requires verification of at least 850 mV between the structure and the reference electrode.
One proposed testing methodology includes reading a polarized voltage of the pipeline by reading the pipe-to-soil voltage at test points along the pipeline (typically located 100 yards to 1 mile apart) 100 msec to 1000 msec after all cathodic protection rectifiers affecting the test point have been simultaneously turned off. Such a test is sometimes referred to herein as an “instant off” potential measurement. The polarized voltage is a measurable potential between the structure and a reference electrode in the ground adjacent to the test point. Such a test would attempt to verify at least
100
mV between the pipeline structure and a reference point.
Another test, sometimes referred to as a close interval survey, involves measuring potential differences at very close intervals (around 3 feet) between the pipeline structure and adjacent soil both with cathodic protection rectifiers turned on as well as an instant after the rectifiers have been simultaneously turned off. Current close interval survey testing seeks to verify at least 100 mVolts of potential between the soil and the pipeline structure. However, conducting close interval surveys is a highly manual process, with a potential for errors, as described below. Therefore it is typical to only accomplish a close interval survey of about 20% of a pipeline in any given year.
When conducting close interval surveys, the current applied by all rectifiers affecting a particular segment of pipe are synchronously turned off and on (cycled) so that an applied voltage and a polarized voltage are recorded. Usually, survey crews are used to set up synchronized interruption equipment at each rectifier. The equipment initiates synchronized cycling and then the pipe to soil potentials are measured. Following the survey, the team returns to each rectifier location where synchronizing equipment has been temporarily installed to verify that the cycling activity occurred as expected and to remove the equipment for installation at a different pipeline segment. If the team cannot verify that the cycling activity was properly conducted at each rectifier location, the resulting collected data is rendered questionable and the survey may have to be repeated.
Underground pipelines may be adjacent to or near other structures which have ground contact and are therefore subject to corrosion. Cathodic protection systems sometimes are provided fir such structures. The structure, as well as its protection system, may interfere electrically with the cathodic protection systems for the pipeline. The interference is typically manifested as undesired currents flowing between the pipeline and the structure. To control such currents, a shunt resistance may be placed between the structure and the pipeline. Such an installation is sometimes referred to as a critical bond. Testing of critical bonds is performed to ensure that the corrosion mitigation processes in place continue to be effective, and simply to verify that the current path between the structure and the pipeline has not been opened.
There is an increasing interest in checking the polarized voltage (or instant off potential) at pipe-to-soil test points as well as the constant potential at these sites. The polarized voltage tests supply pertinent pipeline corrosion data. Further, close interval surveys are becoming more common. However, the above described testing, as currently performed, is largely manual, and difficult to synchronize, utilizing known testing equipment.
BRIEF DESCRIPTION OF THE INVENTION
In one aspect, a method for testing a cathodic protection system is provided. The system includes a cathodic protection rectifier configured to apply a voltage between a pipeline and a reference point. The method comprises measuring a magnitude of an output voltage of the cathodic protection rectifier and transmitting the measured output voltage magnitude to a site remote from the rectifier using a cellular control channel. The transmitted measurements are received at the remote site and using the transmitted measurements, it is determined whether the cathodic protection system is operational.
In another aspect, a cathodic protection rectifier system for an underground pipeline is provided. The pipeline is configured with a plurality of testing points. Each test point is an access point for making measurements and is electrically coupled to the pipeline. The system comprises at least one cathodic rectifier coupled to a power source and configured to apply a voltage across the pipeline and a ground reference point in the soil. A cathodic system monitor is coupled to the rectifier and configured to act as a switch between the rectifier and the pipeline. The cathodic system monitor is further configured to receive primary power from the power source, and to measure voltages applied to the pipeline. The cathodic system monitor also communicates the voltage measurements as pipeline test data. The system also includes a computer system configured to receive the pipeline test data from the cathodic system monitor.
In another aspect, a method for testing effectiveness of galvanic corrosion mitigation equipment along a length of an underground pipeline is provided. The equipment includes at least one cathodic protection rectifier (CPR) electrically coupled across the pipeline and a reference point through a switching device. The CPR is configured to apply a voltage to the pipeline. A plurality of test points are electrically coupled to the pipeline and dispersed at intervals along the pipeline, providing an access point for meas
Armstrong Teasdale LLP
Deb Anjan K.
Network Technologies Group, LLC
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