Electricity: measuring and testing – Magnetic
Reexamination Certificate
2001-10-30
2003-09-16
Patidar, Jay (Department: 2858)
Electricity: measuring and testing
Magnetic
C324S076490, C324S444000, C324S694000
Reexamination Certificate
active
06621263
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the testing of corrosion of metals in corrosive environments, and in particular to test devices for simulating the conditions encountered in the oil field industry to determine the corrosion rates of metals subjected to such environments.
BACKGROUND OF THE INVENTION
In the oil field industry, drill bits, pipelines and their support structures often face highly corrosive environments including but not limited to hydrogen sulfide environments. Moreover, the drill bit in operation will encounter these corrosive fluids at high rotation speeds. In order to maintain the drilling structures, ex situ tests measuring the corrosive effects of these fluids are performed, advantageously under conditions simulating the aggressive flow regimes usually encountered in the field.
However, conventional lab-based test devices for ex situ monitoring of the corrosive rates of various metals in response to these highly corrosive flowing fluids suffer from several drawbacks. First, conventional lab-based test devices are unable to simulate the aggressive flow regimes sufficiently over the relatively long periods of time necessary for useful test devices, e.g. over a week or more. In particular, the creation of vortex phenomena in the vicinity of the test electrodes disturbs the flow regimes and renders the results inaccurate, since the flow of corrosive fluid past the test electrodes will be unstable. Such vortex phenomena are created, for example, by an asymmetrical shape of the test electrodes, in particular the working electrode of a conventional three electrode structure. However, even in the case of a cylindrical working electrode, such as disclosed in U.S. Pat. No. 5,006,786, insufficient attention has been given to preventing the creation of vortices.
A further limitation of conventional test devices is their inability to handle very corrosive test environments, for example, wet hydrogen sulfide, carbon dioxide, high temperature and test solutions with high salt content. This inability arises from the insufficient corrosion resistance of the materials of the test devices themselves. The result is a significant reduction in the useful lifetime of the test device. A significant limitation of conventional rotating cylinder devices of the prior art is their inability to safely contain hazardous gases such as hydrogen sulfide gas.
Accordingly, it is an object of the present invention to provide a test device for simulating the highly corrosive environments encountered in the oil field industry that overcomes the above-noted limitations of the prior art.
It is a further object of the present invention to provide a test device for simulating the highly corrosive environments encountered in the oil field industry that eliminates or substantially reduces vortex phenomena at the electrode structure, thereby providing a more accurate simulation.
It is a still further object of the present invention to provide a test device for simulating the highly corrosive environments encountered in the oil field industry that has an increased useful lifetime by the use of highly corrosive-resistant materials.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a high-speed corrosion-resistant rotating cylinder electrode system for ex situ testing and monitoring of corrosion rates of metals comprises an electrochemical/permeation cell body adapted to contain a fluid whose corrosive effect is to be monitored, the cell body having a base at a lower surface thereof and the base having an aperture therethrough. A counter electrode/reference electrode complex is mounted within the cell. The system further comprises a cylindrical working electrode and a rotatable system shaft having a lower portion below the base and extending therefrom through the aperture into the cell body, the working electrode being mounted on an upper portion of the system shaft to be positioned within the cell body for rotation.
In accordance with further especially preferred aspects of the present invention, the system shaft above the cylindrical working electrode has a top in the shape of a cone, and the combination system shaft/working electrode and cone-shaped top projects a relatively short distance up into the cell body. In a further preferred embodiment, the base of the cell body can be depressed below the working electrode. Each of these features of the cylindrical working electrode, the cone-shaped top, the relatively short projection of the system shaft/working electrode and the base depression, serves to completely or substantially eliminate vortex phenomena in the fluid as the system shaft rotates. Any combination these features provides such a significant reduction as to effectively eliminate such phenomena. With the reduction in vortices, the system shaft can be rotated at selected speeds, for example 5,000 rpm, to more effectively simulate the severe flow regimes encountered in the field than was possible with the methods and apparatus known to the prior art.
It is yet a further particularly advantageous aspect of the present invention that the components of the test device are made of corrosion-resistant materials. Specific examples of the advantageous materials for the components of the apparatus are identified below.
Still another aspect of the invention resides in a high-speed corrosion-resistant rotating cylinder electrode combination system for use in monitoring of corrosion rates of metals, said system comprising a plurality of test cells, each test cell including an electrochemical/permeation cell body adapted to contain a fluid whose corrosive effect is to be monitored, the cell body having a base at a lower portion thereof, the base having an aperture therethrough, a counter electrode/reference electrode complex mounted within the cell, a cylindrical working electrode, a rotatable system shaft having a lower portion below the base and extending therefrom through the aperture into the cell body, the working electrode being mounted on an upper portion of the system shaft to thereby be positioned within the cell body for rotation, and a motor connected to the system shaft to cause its rotation; and a base means for mounting the plurality of test cells.
Yet another aspect of the invention resides in a method of operating a high-speed corrosion-resistant rotating cylinder electrode system for the ex situ monitoring of corrosion rates of metals, wherein the system comprises a plurality of test cells, where each test cell comprises an electrochemical/permeation cell body adapted to contain a fluid whose corrosive effect is to be monitored, the cell body having a base at a lower portion thereof and the base having an aperture therethrough, a counter electrode/reference electrode complex mounted within the cell, a cylindrical working electrode, and a rotatable system shaft having a lower portion below the base and extending therefrom through the aperture into the cell body, the working electrode being mounted on an upper portion of the system shaft to be positioned within the cell body for rotation, and a motor connected to the system shaft for rotating the shaft, the system further comprising an overall base for mounting the plurality of test cells, the method comprising the steps of, independently for each test cell, preparing a working electrode formed of a material whose resistivity to a selected corrosive fluid is to be measured, preparing the test cell with the prepared working electrode and the selected fluid, measuring a current flowing between the counter electrode and the working electrode, and calculating a corrosion rate of the sample based upon the measured current.
These and other advantages, aspects and features of the present invention will become apparent upon review of the following detailed description of the preferred embodiments, taken in conjunction with the following drawings.
REFERENCES:
patent: 3694338 (1972-09-01), Weingarten
patent: 3882011 (1975-05-01), Hines et al.
patent: 4605626 (1986-08-01), Beck
patent: RE32920 (1989-05-0
Al-Janabi Yahya T.
Lewis, II Arnold L.
Abelman ,Frayne & Schwab
Nguyen Vincent Q.
Patidar Jay
Saudi Arabian Oil Company
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