Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2001-07-20
2004-02-03
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C405S154100
Reexamination Certificate
active
06686745
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrical testing of electrically heated subsea pipelines. More particularly the invention relates to electrical testing pipelines with a pipe-inside-pipe configuration.
2. Description of Related Art
Offshore hydrocarbon recovery operations are increasingly moving into deeper water and more remote locations. Often satellite wells are completed at the sea floor and are tied to remote platforms or other facilities through extended subsea pipelines. Some of these pipelines extend through water that is thousands of feet deep and where temperatures of the water near the sea floor are in the range of 40° F. The hydrocarbon fluids, usually produced along with some water, reach the sea floor at much higher temperatures, characteristic of depths thousands of feet below the sea floor. When the hydrocarbon fluids and any water present begin to cool, phenomena occur that may significantly affect flow of the fluids through the pipelines. Some crude oils become very viscous or deposit paraffin when the temperature of the oil drops, making the oil practically not flowable. Hydrocarbon gas under pressure combines with water at reduced temperatures to form a solid material, called a “hydrate.” Hydrates can plug pipelines and the plugs are very difficult to remove. In deep water, conventional methods of depressuring the flow line to remove a hydrate plug may not be effective. Higher pressures in the line and uneven sea floor topography require excessive time and may create operational problems and be costly in terms of lost production.
The problem of lower temperatures in subsea pipelines has been addressed by a variety of heating methods, including electrical heating. Heating by a variety of electrical methods is well known in the industry. Most of the proposals for electrical heating of pipelines have related to pipelines on land, but in recent years industry has investigated a variety of methods for electrical heating of subsea pipelines. (“Direct Impedance Heating of Deepwater Flowlines,” OTC 11037, May, 1999). One electrical heating method is the pipe-in-pipe method. In one configuration of this method, a pipe-in-pipe subsea pipeline is provided by which a flow line for transporting well fluids is the inner pipe and it is surrounded concentrically by and electrically insulated from an electrically conductive outer pipe until the two pipes are electrically connected at the distal end of a heated segment. Voltage is applied between the inner and outer pipes at the opposite end and electrical current flows along the exterior surface of the inner pipe and along the interior surface of the outer pipe. This pipe-in-pipe method of heating is disclosed, for example, in U.S. Pat. No. 6,142,707, which is commonly assigned and incorporated by reference herein. Apparatus that can be used in the annulus is disclosed, for example, in a U.S. patent application entitled “Annulus for Electrically Heated Pipe-in-Pipe Subsea Pipeline,” filed concurrently herewith and incorporated by reference herein. Various embodiments of pipe-in-pipe subsea pipelines having an electrically insulating coating over the inner pipe in first selected segments of the annulus, an electrically insulating layer ring surrounding the inner pipe in second selected segments of the annulus, and a thermally insulating layer ring surrounding the inner pipe in third selected segments of the annulus are disclosed. The inner and outer pipes are shorted together at a distal end by a welded bulkhead. The electrical power is supplied through an electrical isolating joint at the power input end of a segment of line to be heated. Alternating current, normally at about 60 Hz, is used. The voltage across the annulus is highest at the isolating joint and falls linearly to zero at the bulkhead. The current is essentially constant along the entire length of the pipe segment that is heated. Two key electrical effects, the skin effect and the proximity effect, confine the current flow largely to the annulus surfaces. Consequently, most of the current is effectively isolated from the produced fluidsand the seawater around the pipeline.
As post-installation repair of the pipe-in-pipe subsea pipeline may be difficult or impractical due to the general inaccessibility of the system's location on the seabed, it is desirable to determine the electrical integrity and/or operability of the pipe-in-pipe subsea pipeline during the construction or installation phases of the pipe-in-pipe subsea pipeline. Faults or weak spots may indicate low breakdown voltage. Thus, it is further desirable to detect the electrical integrity of the pipe-in-pipe subsea pipeline before operation to determine any faults or weak spots that have occurred during construction, installation, or commissioning phases or may occur during operation phases of the pipe-in-pipe subsea pipeline. It would also be advantageous to perform quality assurance tests to detect any variations in the electrical integrity of the pipe-in-pipe subsea pipeline during construction, installation, commissioning, or operation phases. Moreover, it would be advantageous to determine the approximate location of an electrical defect or fault along the length of a pipe-in-pipe pipeline segment or along the length a pipe-in-pipe subsea pipeline.
SUMMARY OF THE INVENTION
Towards providing these and other goals, the present invention is directed to a method and apparatus for testing a pipe-in-pipe pipeline before, during, and after subsea electrical heating operation. The present invention is generally directed to a method and an apparatus for electrically testing a pipe-in-pipe pipeline during the construction, installation, commissioning, operation, or dismantling phases of an electrically heated pipe-in-pipe subsea pipeline.
One embodiment of the present invention is directed to a high voltage qualification test of the electrical integrity of a pipe-in-pipe pipeline. The method and apparatus disclosed herein for high voltage qualification testing of the electrical integrity of a pipe-in-pipe pipeline involve a power supply electrically connected to the inner pipe of a pipe-in-pipe pipeline, a return lead electrically connecting the outer pipe to the power supply, applying a voltage from the power supply to the pipe-in-pipe pipeline and measuring the resulting current across the pipe-in-pipe pipeline.
Another embodiment of the present invention is directed to a method and an apparatus for performing a voltage pulse test of the electrical integrity of a pipe-in-pipe pipeline. The method and apparatus disclosed herein for voltage pulse testing of the electrical integrity of a pipe-in-pipe pipeline involve a power supply electrically connected to a voltage pulse generator, the voltage pulse generator electrically connected to the inner pipe of a pipe-in-pipe pipeline, and an output device electrically connected to the voltage pulse generator, wherein the output device indicates the voltage pulse. For a low voltage pulse test, the voltage pulse generator provides a voltage pulse output of less than about 400 volts. For a high voltage pulse test, the voltage pulse generator provides a voltage pulse output of greater than about 400 volts.
Yet another embodiment of the present invention is directed to a method and an apparatus for performing a low voltage pulse test of the electrical integrity of a pipe-in-pipe pipeline, comprising a time domain reflectometer electrically connected to the inner pipe of a pipe-in-pipe pipeline and a voltage pulse of less than about 100 volts applied to the pipe-in-pipe pipeline.
REFERENCES:
patent: 972308 (1910-10-01), Williamson
patent: 1231202 (1917-06-01), Saylor
patent: 2096279 (1937-10-01), Karcher
patent: 2178720 (1939-02-01), Daniels
patent: 2206831 (1940-03-01), Berthelsen
patent: 2217857 (1940-04-01), Byck
patent: 2224403 (1940-12-01), Lines
patent: 2306831 (1942-12-01), Proctor
patent: 2660249 (1953-11-01), Jakosky
patent: 2678377 (1954-05-01), Justiz
patent: 2714930 (1955-08-01), Carpenter
pa
Lair Donald M
Le N.
Shell Oil Company
LandOfFree
Apparatus and method for electrical testing of electrically... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for electrical testing of electrically..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for electrical testing of electrically... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3339355