System and method for reducing corrosion in a compressor   

Abstract: A system for reducing corrosion in a compressor includes a compressor blade having a corrosion potential. A sensor connected to the compressor blade generates a signal reflective of the corrosion potential. A power supply connected to the compressor blade at an electrical connection produces an electrical potential at the electrical connection. An electrolyte coats at least a portion of the sensor and the electrical connection. A method for reducing corrosion in a compressor includes sensing a corrosion potential of a compressor blade and generating a signal reflective of the corrosion potential. The method further includes generating an electrical potential at an electrical connection on the compressor blade and flowing an electrolyte over at least a portion of the compressor blade and the electrical connection.

FIELD OF THE INVENTION

The present invention generally involves a system and method for reducing and/or preventing corrosion in a compressor. Particular embodiments of the present invention may employ anodic protection, cathodic protection, and/or impressed current techniques to reduce and/or prevent general corrosion of compressor blades.

BACKGROUND OF THE INVENTION

A typical compressor includes multiple stages of rotating and fixed blades made from various steel alloys. Ambient air flows into the compressor, and the rotating blades progressively impart kinetic energy to the ambient air to produce a compressed working fluid at a highly energized state. The ambient air often includes various amounts of moisture, salts, acids, and other pollution and contaminants that may deposit or precipitate onto the rotating and fixed blades. The build up of pollution and contaminants on the blade surfaces results in an environment conducive to increased levels of general, crevice, and/or pitting corrosion on the compressor blades.

Various methods are known in the art for reducing and/or preventing corrosion of steel alloys. For example, a passive oxide film or layer may be formed on the surface of the steel alloy to inhibit general corrosion and the onset of crevice and/or pitting corrosion. A polarization plot or curve may be created to correlate the corrosion potential (Ecorr) and current density (I) across the surface of the passivated steel alloy to the onset of particular forms of corrosion. For example, as shown in FIG. 1, the passive oxide film may protect the surface of the steel alloy by reducing the increase in the current density (I), and thus the general corrosion rate, as the corrosion potential (Ecorr) increases across the surface of the steel alloy. Eventually, the corrosion potential (Ecorr) reaches the pitting breakdown potential (Eb), at which point the current density (I) increases dramatically, resulting in pitting corrosion, crevice corrosion, and/or other forms of localized corrosion on the surface of the steel alloy. The localized corrosion may continue to occur until the corrosion potential (Ecorr) decreases below the repassivation potential (Erp).

Anodic and cathodic protection systems have been successfully used to control or adjust the corrosion potential (Ecorr), and thus the amount and type of corrosion, in many industrial applications. However, anodic and cathodic protection systems generally require an electrically conductive path surrounding or connected to the component being protected. For example, soil around a pipeline, liquid in a tank, and seawater around marine structures and ships provide the electrically conductive path that enables anodic and cathodic protection systems to work in those environments. However, the structure and environment of a compressor generally lacks a similar conductive path suitable for anodic and cathodic protection systems. Specifically, the ambient air flowing across the rotating and fixed blades does not produce sufficient electrical conductivity to support an anodic or cathodic protection system. Therefore, an improved system and method that provides anodic and/or cathodic protection to compressors would be useful.

Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.

One embodiment of the present invention is a system for reducing corrosion in a compressor. The system includes a compressor blade having a corrosion potential. A sensor is connected to the compressor blade, and the sensor generates a signal reflective of the corrosion potential of the compressor blade. A power supply is connected to the compressor blade at an electrical connection, and the power supply produces an electrical potential at the electrical connection. An electrolyte coats at least a portion of the sensor and the electrical connection.

Another embodiment of the present invention is a system for reducing corrosion in a compressor that includes a compressor blade having a corrosion potential and a sacrificial anode connected to at least a portion of the compressor blade. An electrolyte coats at least a portion of the compressor blade and the sacrificial anode.

The present invention may also include a method for reducing corrosion in a compressor. The method includes sensing a corrosion potential of a compressor blade and generating a signal reflective of the corrosion potential of the compressor blade. The method further includes generating an electrical potential at an electrical connection on the compressor blade and flowing an electrolyte over at least a portion of the compressor blade and the electrical connection.

Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

FIG. 1 is an exemplary polarization graph;

FIG. 2 is a simplified diagram of a system according to one embodiment of the present invention;

FIG. 3 is a simplified diagram of a system according to a second embodiment of the present invention;

FIG. 4 is a simplified diagram of a system according to a third embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.

Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

Embodiments within the scope of the present invention provide a system and method for reducing and/or preventing corrosion in a compressor using anodic, cathodic, and/or impressed current techniques. In specific embodiments, an electrolyte may be supplied, flowed, or sprayed into the compressor to provide an electrically conductive medium that enables anodic and/or cathodic protection techniques to reduce or prevent corrosion on the compressor blades. In other specific embodiments, the corrosion potential (Ecorr) of the compressor blades may be sampled, and an electrical potential may be provided to specific areas or regions of the compressor blades to increase or decrease the local corrosion potential (Ecorr) at that area or region, as desired.

FIG. 2 provides a simplified diagram of a system 10 according to one embodiment of the present invention. In this particular embodiment, the system 10 provides anodic protection against corrosion and generally includes a sensor 12 and a power supply 14 connected to one or more compressor blades 16. The system 10 further includes an electrolyte 18 that coats or covers at least a portion of the compressor blades 16. The compressor blades 16 may be fixed or rotating blades. If the compressor blades 16 are fixed, the wiring for the sensor 12 and the power supply 14 may pass through the inside of the compressor blades 16 and out of the stationary portion of the compressor. Alternately, if the compressor blades 16 are rotating blades, brushes and slip rings (not shown) may be used to provide electrical connectivity between the rotating blades and the stationary sensor 12 and power supply 14, as is known in the art. In either event, the compressor blades 16 may include a nonconductive liner 20 to electrically insulate the compressor blades 16 from any stray currents that may affect the accuracy or sensitivity of the sensor 12.

The sensor 12 may comprise any instrument capable of detecting and/or measuring a voltage or current flow across at least a portion of the compressor blade 16. For example, the sensor 12 may comprise a voltmeter 22, an ammeter, and/or a conventional corrosion sensor 24 installed on a surface of the compressor blade 16. The corrosion sensor 24 may connect to the component surface 16 at a sensor connection 26 and also to a reference electrode 28 in the electrolyte 18 to complete the electrical circuit.

The corrosion sensor 24 and/or the voltmeter 22 may produce a signal 30 reflective of a corrosion potential of the compressor blade 16. The signal 30 may comprise, for example, a current or voltage magnitude which may be proportional to the amount and/or rate of general corrosion occurring on the compressor blade 16. The signal 30 may be manually interpreted and acted on by an operator to adjust the power supply 14 as desired. Alternately, or in addition, as shown in FIG. 2, the system 10 may include a controller 32 configured or programmed to receive the signal 30 and adjust the power supply 14. As described herein, the technical effect of the controller 32 is to adjust the power supply 14 to achieve a desired voltage and/or current out of the power supply 14. The controller 32 may be a stand alone component, such as a potentiometer, or a sub-component included in any computer system known in the art, such as a laptop, a personal computer, a mini computer, or a mainframe computer. The various controller and computer systems discussed herein are not limited to any particular hardware architecture or configuration. Embodiments of the systems and methods set forth herein may be implemented by one or more general-purpose or customized controllers adapted in any suitable manner to provide the desired functionality. For example, the controller 32 may be adapted to provide additional functionality, either complementary or unrelated to the present subject matter. When software is used, any suitable programming, scripting, or other type of language or combinations of languages may be used to implement the teachings contained herein. However, some systems and methods set forth and disclosed herein may also be implemented by hard-wired logic or other circuitry, including, but not limited to, application-specific circuits. Of course, various combinations of computer-executed software and hard-wired logic or other circuitry may be suitable as well.

The power supply 14 may comprise any variable source of direct current and may connect to each compressor blade 16 at an electrical connection 34 and also to a counter electrode 36 in the electrolyte 20 to complete the electrical circuit. For example, the power supply 14 may comprise a battery capable of providing 5 to 500 milliamps of current at voltages less than 15 V DC. However, the size and capacity of the power supply 14 will depend on the particular use, and the present invention is not limited to any particular size or capacity of the power supply 14 unless specifically recited in the claims. As shown in FIG. 2, an ammeter 38 may be used with the power supply 14 to measure and/or supply the desired current and voltage to the component surface 16.

As shown in FIG. 2, the electrolyte 18 coats or covers at least a portion of the compressor blade 16, the sensor connection 26, and/or the electrical connection 34. The electrolyte 18 may comprise any fluid capable of conducting electron flow. For example, the electrolyte 18 may comprise a solution of bicarbonate of soda, salt water, or other ionized solutions known to one of ordinary skill in the art. The electrolyte 18 may be supplied, flowed, or sprayed into the compressor as the compressor operates so that the electrolyte 18 flows over the compressor blades 16 and coats or covers at least a portion of the compressor blades 16, the sensor connection 26, and/or the electrical connection 34. In this manner, the electrolyte 18 provides the conductive medium that enables electron flow between the power supply 14 and the compressor blades 16.

During operation of the system 10, the sensor 12 detects and/or measures the corrosion potential across at least a portion of the compressor blades 16 and generates the signal 30 reflective of the corrosion potential of the compressor blade 16. The controller 32, if present, or an operator may receive the signal 30 and adjust the power supply 14 to produce a desired electrical potential at the electrical connection 34. The electrical potential produced at the electrical connection 34 combines with the existing corrosion potential to result in a desired corrosion potential across the compressor blades 16. For example, referring to the exemplary polarization graph previously described with respect to FIG. 1, the electrical potential produced across the electrical connection 34 would ordinarily dampen or reduce the current density (I) across the compressor blade 16, shifting the polarization curve to the left. The resulting lower current density (I) for a given corrosion potential thus results in reduced general corrosion across the surface of the compressor blade 16.

FIG. 3 provides a simplified diagram of a system 40 according to a second embodiment of the present invention. In this particular embodiment, the system 40 provides cathodic protection against corrosion and generally includes the compressor blades 16 and electrolyte 18 as previously described with respect to the embodiment shown in FIG. 2. In addition, this embodiment includes a sacrificial anode 42 connected to the compressor blades 16, and the electrolyte 18 coats or covers at least a portion of the sacrificial anode 42 and compressor blades 16.

The sacrificial anode 42 may comprise any suitable material known in the art that has a higher oxidation potential or more negative electrochemical potential than the steel alloy used in the compressor blades 16. For example, the sacrificial anode 42 may comprise a plate, rod, or fin made from aluminum, zinc, or another element in the galvanic series above martensitic steel. As the electrolyte 18 coats at least a portion of the compressor blades 16 and the sacrificial anode 42, the sacrificial anode 42 protects the compressor blades 16 from general corrosion by preferentially corroding before the steel alloy in the compressor blades 16. Although the electrolyte 18 coating at least a portion of the sacrificial anode 42 and compressor blades 16 enables the system 40 shown in FIG. 3 to operate, the preferential corrosion of the sacrificial anode 42 may cause portions of the sacrificial anode 42 to break off during operation, resulting in undesirable debris flowing through the compressor. This obvious disadvantage may be monitored and minimized through regular inspection and maintenance intervals that check the condition and/or replace the sacrificial anode 42 as necessary.

FIG. 4 provides a simplified diagram of a system 50 according to a third embodiment of the present invention that incorporates or combines aspects of the previous embodiments shown and described with respect to FIGS. 2 and 3 to provide impressed current cathodic protection against corrosion. Specifically, the system 50 includes a sensor 12 and a power supply 14 connected to one or more compressor blades 16 as previously described with respect to the embodiment shown in FIG. 2. In addition, the system includes a sacrificial anode 42 as previously described with respect to the embodiment shown in FIG. 3. Notably, the power supply 14 may connect to the compressor blade 16 at an electrical connection 34 on the sacrificial anode 42 and also to a counter electrode 36 in the electrolyte 18 to complete the electrical circuit. As a result, the electrical potential or impressed current provided by the power supply 14 increases the difference in the electrochemical potential between the sacrificial anode 42 and the compressor blades 16.

During operation of the system 50, the sacrificial anode 42 protects the compressor blades 16 from general corrosion by preferentially corroding before the steel alloy in the compressor blades 16, as previously described with respect to the embodiment shown in FIG. 3. In addition, in the event that the sacrificial anode 42 is unable to provide complete protection to the compressor blade 16, the sensor 12 detects and/or measures the corrosion potential across at least a portion of the compressor blades 16 and generates the signal 30 reflective of the corrosion potential of the compressor blade 16. The controller 32, if present, or an operator may receive the signal 30 and adjust the power supply 14 to produce a desired electrical potential at the electrical connection 34. As a result, the electrical potential produced at the electrical connection 34 increases the difference in the electrochemical potential between the sacrificial anode and the compressor blades 16 to enhance the cathodic protection to the compressor blades 16.

The systems 10, 40, 50 described and illustrated in FIGS. 2-4 may also provide a method for reducing corrosion in the compressor. The method may generally include sensing the corrosion potential of the compressor blade 16 and generating the signal 30 reflective of the corrosion potential. The method may further include generating the electrical potential at the electrical connection 34 on the compressor blade 16 and flowing the electrolyte 18 over at least a portion of the compressor blade 16 and the electrical connection 34. Particular embodiments of the method may further include connecting the sacrificial anode 42 to at least a portion of the compressor blade 16 and/or connecting the electrical connection 34 to the sacrificial anode 42.

One of ordinary skill in the art will readily appreciate that the systems and methods previously described enhance the ability to monitor and/or control the corrosion potential in the compressor related 16 to reduce corrosion in the compressor. By reducing the corrosion in the compressor, the compressor may be operated for longer periods between inspections and maintenance, and unplanned outages to repair or replace corroded compressor blades may be reduced or eliminated altogether. Alternately, or in addition, the reduced corrosion in the compressor may allow for lower-cost steel alloys to be incorporated into the compressor blades to reduce the initial capital cost of the compressor. Finally, the addition of the electrolyte 18 into the compressor may enhance cleaning of corrosive contaminants from the compressor blades 16 and/or more frequent increased power augmentation provided by the injected electrolyte 18.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.