Patent Grant
7081187
This invention relates to cathodic protection systems and, more particularly, to cathodic protection systems for the internal surfaces of pipes.
Protection against the corrosion of metals, for example, iron and steel, has been provided successfully and at relatively low cost by cathodic protection either by the use of sacrificial anodes or by using permanent anodes coupled to one or more potential sources. These systems overcome and reverse the natural potential difference which is set up whenever a metal is immersed in an electrolyte such as saltwater. Apparatus and systems have evolved which satisfactorily protect ships, liquid-containing tanks, bridges and other structures, and the internal and external surfaces of ducts and pipelines.
Wherever an electrolyte such as saltwater is passed through pipelines, the problem of internal protection is acute. To give reasonable installed life of the pipelines under these circumstances it has been necessary to make the pipes substantially thicker than strength considerations would otherwise call for in order to avoid frequent and costly replacement. Since the pipes and the labor costs of replacing the pipes are costly, the need for providing effective and inexpensive internal protection is fully apparent.
Cathodic protection is accomplished by causing a flow of direct current (DC) between an electrode (called the anode) and the structure (called the cathode), e.g., the pipe. The direct current causes the surface of the structure (pipe) to become polarized, thus stopping or reducing corrosion.
In an impressed current cathodic protection system, a rectifier normally converts AC to DC and supplies the current. Typically, the anode is a relatively inert material that can transfer the current to the liquid in the pipe, which is the electrolyte. In a galvanic system, the anode is an electrochemically active metal compared to the cathode, and the current is a natural occurrence of connecting the anode and cathode together.
The chemical reaction at the anode is metal oxidation, with oxygen, or chlorine evolution. Both ions and electrons are formed at the anode. Ions generated by the reaction flow to the cathode via the electrolyte. The electrons flow to the cathode via a connection. Reduction occurs at the cathode, which consumes the electrons. Three common cathodic reactions in cathodic protection are as follows:
O2+2H2O+4e→4OH−
O2+4H++4e→2H2O
2H++2e→H2
In all cases, both electron and ionic currents are involved in cathodic protection. That is, both a continuous common electrolyte and a metallic connection between the anode and cathode are required. The metallic connection is provided through the rectifier. The saltwater or other conductive liquid provides the common electrolyte.
Common anode materials include pure metals, alloyed metals, platinum coated valve metals, valve metals having electrochemically active coatings, and certain ceramic materials.
Generally, the internal surfaces of pipelines have been protected in the past by probe anodes or sacrificial linear anodes. Probe anodes are placed into the pipeline at intervals along the pipeline. The probe anode consists of a rigid anode mounted in a fitting that is inserted into the pipeline, generally through a pressure-tight fitting. The probe anode is generally placed perpendicular to the axis of the pipeline and is of no greater length than the diameter of the pipeline. Probe anodes have several disadvantages. First, each probe anode can provide protection for only about four to eight pipe diameters along the length of the pipeline. It would be beneficial to have a system that is continuous and provides uniform protection along the entire length of the pipeline. Second, the probe anode must be installed at regular intervals. This is relatively costly and may affect the integrity of the pipeline. Additionally, the use of a probe anode system may not be possible with underground pipelines. It would be beneficial to provide a system that can cover long distances, for example, distances of five hundred feet or more. Finally, probe anode systems do not provide uniform current distribution. It would be beneficial to provide more uniform current distribution. In the present invention, there is less risk of hydrogen embrittlement of the pipeline metal and less risk of damage to internal coatings.
Sacrificial anodes also have several disadvantages. A sacrificial anode system consists of sacrificial anodes placed inside of the pipeline. The anode material is generally magnesium, zinc, or aluminum alloy. The anode can be in ribbon form of approximately one inch diameter or in block form. The anodes typically contain a steel core and are bolted or welded to the metal pipeline.
The anodes operate via the difference in potential of the metals. For example, zinc has an open circuit potential to a copper—copper sulfate reference electrode of −1.10 VDC, whereas steel would have a potential of −0.55 VDC. The driving voltage would be slightly higher with magnesium and some aluminum alloys. The system is self regulating and, once the anode material is used, the entire system must be replaced.
Again, a sacrificial anode system has several disadvantages. First, it is of relatively high cost. Second, the life of the anodes is limited. Third, the sacrificial anode system is relatively heavy. For example, a sacrificial anode may be about one pound per linear foot or more. Fourth, a sacrificial anode may not have sufficient driving voltage to produce a required DC voltage. With an impressed current system, a transformer rectifier can be provided that will produce much higher driving voltages. Fifth, a sacrificial anode may put metals such as zinc into the liquid stream. Finally, replacement of anodes is difficult.
The present invention improves or corrects these deficiencies.
Several patents are now discussed as general background information. U.S. Pat. No. 6,238,545 (Allebach et al.) discloses an anode embedded in an electrolyte layer applied to the surface of a pipe section to provide an ionic conductive path between the anode and the structure to supply cathodic protection to the structure where the natural environment may not provide a continuous electrolyte. This design protects the exterior of pipes.
U.S. Pat. No. 4,140,614 (McKie) teaches an anode arrangement for use for the internal cathodic protection of a pipe. Here, a hollow anode carrier is connected along the length of the pipe. The anode is offset, but communicates with the channel defined by the pipe so that the anode lies within the recess, but does not obstruct flow in the pipe.
The references cited herein are incorporated herein by reference in their entireties.
A cathodic protection system is provided for internal surfaces of a pipeline. The pipeline has an internal volume. The cathodic protection system includes a flexible anode assembly having a first end and a second end and having at least one flexible anode wire having a first end and a second end. A first removable pressure seal fitting is provided for the first end of the anode assembly. The first pressure seal fitting provides for electrical contact between the first end of the anode assembly and a first contact outside of the internal volume of the pipeline. A second removable pressure seal fitting is provided for the second end of the anode assembly. The second pressure seal fitting provides for electrical contact between the second end of the anode assembly and a second contact outside of the internal volume of the pipeline. The cathodic protection system further includes a DC power source, a first anode conductor attached between the first contact and the DC power source, and a second anode conductor attached between the second contact and the DC power source.
The cathodic protection system may optionally include a flexible, non-electrically conductive anode housing where the housing substantially surrounds the anode wire and preferably extends generally from the first pressure seal fitting to the second pressure seal fitting. The anode housing may be fabricated from, for example, a perforated, semi-rigid plastic material, or, for example, from plastic mesh tubing.
The anode wire may be, for example, mixed metal oxide with or without a copper core, or may be platinum coated titanium with or without a copper core, or may be platinum coated niobium with or without a copper core.
The first and the second pressure seal fittings preferably permit installation, removal, and repair of the anode assembly. The DC power source preferably is a rectifier. A waterproof coating over at least one the pressure seal fittings may be provided such that the anode assembly is adapted for underground use. One or more reference electrodes may be provided to measure cathodic protection levels and to monitor the anode assembly. Finally, a separate anode cable may be provided to provide supplemental tensile strength to the anode wire.
In an alternate embodiment of the present invention, a cathodic protection system is provided for internal surfaces of a pipeline. The pipeline has an internal volume. The cathodic protection system includes a flexible anode assembly having a first and a second end and having at least one flexible anode wire having a first end and a second end. A first removable pressure seal fitting is provided for the first end of the anode assembly. The first pressure seal fitting provides for electrical contact between the first end of the anode assembly and a first contact outside of the internal volume of the pipeline. The cathodic protection system further includes a DC power source and a first anode conductor attached between the first contact and the DC power source. The length of the anode assembly has a greater dimension than that of a diameter of the pipeline and is free to move within the pipeline due to the flexibility of the anode assembly.
A flexible, non-electrically conductive anode housing may be provided where the housing substantially surrounds the anode wire and extends generally from the first pressure seal fitting to the second end of the anode assembly. The anode housing may be fabricated from, for example, a perforated, semi-rigid plastic material or from plastic mesh tubing.
The anode wire may be, for example, mixed metal oxide with or without a copper core, platinum coated titanium with or without a copper core, or platinum coated niobium with or without a copper core.
Preferably, the first pressure seal fitting permits installation, removal, and repair of the anode assembly. Preferably, the DC power source includes a rectifier. A waterproof coating may be provided over the first pressure seal fitting such that the anode assembly is adapted for underground use. At least one reference electrode may be provided to measure cathodic protection levels and to monitor the anode assembly. Finally, a separate anode cable may be used to provide supplemental tensile strength to the anode wire.
The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements throughout the several views and wherein:
The internal cathodic protection system for pipelines of the present invention is an impressed current cathodic protection system to protect the internal surfaces of pipes, in, for example, pipelines. Generally, the system's primary application is for water lines including potable, brackish, and saltwater pipelines. However, the system may be installed with for use with any appropriate corrosive liquid.
Generally, the system consists of one or more continuous, linear, flexible anodes that is installed in the pipe. Associated with each flexible anode is a pair of pressure seal fittings located at each end of the length of the anode such that an electrical connection provides for the anode to be connected to a DC power source. There is substantially no limit to the length of piping that can be protected by the system since numerous anodes and their corresponding pressure seal fittings may be used. Preferably, each anode should be no longer than a little more than five hundred feet.
Referring now to the drawings, wherein like part numbers refer to like elements throughout the several views, there is shown in
Each of these elements will now be described in greater detail. For purposes of the present invention, only one end of the system 10 will be described in detail. However, for this preferred embodiment of the present invention, both ends are substantially identical. For purposes of the present invention where the two ends of the system are identical, like part numbers are used with the first end having an “a” suffix and the second end having a “b” suffix. For example, threaded rod 28a on the first side is equivalent to threaded rod 28b on the second side.
The anode wire 22 of the anode assembly 20 may be fabricated from a variety of materials, as well known in the art. For example, the anode wire 22 may be fabricated from a mixed metal oxide coating or a platinum coating over titanium or niobium. The anode wire 22 may or may not have a core of, for example, copper. The anode wire 22 has a first end 22a and a second end 22b and is preferably about 0.031 to about 0.125 inches in diameter. Outputs available for the anode may be desirable, for example, at about 16 milliamperes per linear foot to about 250 milliamperes per linear foot.
As can best be seen in
As can be seen in
Electrical contact between the rectifier 30 and the anode assembly is made through the first and second pressure seal fittings 40a, 40b. As can best be seen in
As can best be seen in
Conductor wires 50a, 50b then attach to the connectors 74a, 74b and provide an electrical path to the rectifier 30. The rectifier may similar to that provided by, for example, Matcor, Inc. of Doylestown, Pa. Specifications would differ based on the physical requirements of the system.
Optionally, the entire outer surface of the nipple 54a, 54b, lower flange 60a, 60b, upper flange 62a, 62b and associated parts and hardware may be coated with a waterproof coating 78 as known in the art, for, for example, underground use.
One or more reference electrodes, as known in the art, for example, probe-type reference electrode 80 (see
By using the present system 10, pressure seal fittings 40a, 40b seal the internal volume 14 such that no liquid escapes from within the piping through the nipples 54a, 54b. However, electrical access to the anode 20 is provided. The embodiment herein includes one specific example, but, one skilled in the art will realize that there are numerous ways of achieving the same result. The system provides for easy installation, maintenance and removal of the anode assembly through one of the pressure seal fittings 40a, 40b by disassembling the flanges 60a, 60b, 62a, 62b as described above.
To assemble the system 10, the pipe nipples 54a, 54b are welded to the piping 12, the anode assembly 20 is threaded through one of the nipples 54a and extended through the piping 12 to the other of the nipples 54b. The anode assembly 20 is then secured and sealed in place using the parts as described above. Electrical connections are made and the system is operable.
A cathodic protection system 10′ in accordance a second preferred embodiment of the present invention is shown in
Although illustrated and described herein with reference to specific embodiments, the present invention nevertheless is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims without departing from the spirit of the invention.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/398,275, entitled Internal Cathodic Protection Systemt, filed Jul. 24, 2002.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4140614 | McKie | Feb 1979 | A |
| 4400259 | Schutt | Aug 1983 | A |
| 4442903 | Schutt et al. | Apr 1984 | A |
| 4871328 | Wright et al. | Oct 1989 | A |
| 5055166 | Schutt | Oct 1991 | A |
| 5176807 | Kumar | Jan 1993 | A |
| 6238545 | Allebach et al. | May 2001 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 60398275 | Jul 2002 | US |
