CA2141127C - Corrosion protection system - Google Patents
Corrosion protection system Download PDFInfo
- Publication number
- CA2141127C CA2141127C CA 2141127 CA2141127A CA2141127C CA 2141127 C CA2141127 C CA 2141127C CA 2141127 CA2141127 CA 2141127 CA 2141127 A CA2141127 A CA 2141127A CA 2141127 C CA2141127 C CA 2141127C
- Authority
- CA
- Canada
- Prior art keywords
- vessel
- strap
- electrode
- corrosion protection
- electrolyte
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
- C23F13/005—Anodic protection
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
- C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
- C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
- C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
- C23F13/20—Conducting electric current to electrodes
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F2213/00—Aspects of inhibiting corrosion of metals by anodic or cathodic protection
- C23F2213/20—Constructional parts or assemblies of the anodic or cathodic protection apparatus
- C23F2213/22—Constructional parts or assemblies of the anodic or cathodic protection apparatus characterized by the ionic conductor, e.g. humectant, hydratant or backfill
Abstract
An electrolyte protection system has a strap extending from an electrode to the base of the vessel. The strap is non-conductive and porous to carry electrolyte into contact with the electrode. A secondary current path is thus established to inhibit electrical discharge from the electrode.
Description
~14~1~'~
CORROSION PROTECTION SYSTEM
The present invention relates to a corrosion protection system.
It is well known that the storage of certain liquids in vessels may lead to corrosion of the vessel and subsequent weakening of the structure. Although materials are available that are impervious to corrosion, it may be necessary for reasons of economy or structural strength to utilize materials, particularly metals, that are subject to corrosion. To inhibit the effect of corrosion, various techniques have been developed that utilize the electrolytic action of the liquid and the material of the vessel.
One such technique is cathodic protection which utilizes a sacrificial anode in electrical contact with the metal of the vessel. Alternatively, an impressed EMF
method may be utilized, in which a direct current is provided by an external source and is passed through the system by the use of essentially non-sacrificial anodes that may be buried in the ground or suspended in the electrolyte in the case of an aqueous system.
A relatively new form of corrosion control involves pacifating a metal used in the vessel by applying an external current that makes it more anodic. Such a technique is known as "anodic protection".
With anodic protection, the current is applied from an external source between an anode formed as the walls of the vessel and a cathode located within the vessel. The cathode is normally immersed in the liquid to be stored which acts as an electrolyte and establishes a current path between anode and cathode. The current is maintained within predetermined limits by a control system utilizing reference electrodes and an adjustable potentiometer.
The current will be maintained at a level determined by the material of the vessel and the liquid to be stored. It has been found that by maintaining the current within predefined limits, a potential is maintained that generates a film at the surface of the vessel to inhibit corrosion. This technique has been found particularly beneficial with vessels of steel or stainless steels and liquids with extreme Ph valves, i.e. strongly acid or strongly alkali.
The control system associated with such anodic systems is sensitive to the level of liquid within the vessel and operates to cut off the current flow if the liquid level drops below the cathode. However, situations may arise where the cathode is intermittently covered and uncovered by liquid in the tank. In these circumstances, the inductance of the electrical circuit established between the current source and the cathode may permit a relatively large potential to be induced on the cathode as it is uncovered, which then may result in a spark or discharge as the liquid again approaches the cathode. As explosive gases may be present within the vessel, it is clearly undesirable to permit an electrical discharge ~1412~~
CORROSION PROTECTION SYSTEM
The present invention relates to a corrosion protection system.
It is well known that the storage of certain liquids in vessels may lead to corrosion of the vessel and subsequent weakening of the structure. Although materials are available that are impervious to corrosion, it may be necessary for reasons of economy or structural strength to utilize materials, particularly metals, that are subject to corrosion. To inhibit the effect of corrosion, various techniques have been developed that utilize the electrolytic action of the liquid and the material of the vessel.
One such technique is cathodic protection which utilizes a sacrificial anode in electrical contact with the metal of the vessel. Alternatively, an impressed EMF
method may be utilized, in which a direct current is provided by an external source and is passed through the system by the use of essentially non-sacrificial anodes that may be buried in the ground or suspended in the electrolyte in the case of an aqueous system.
A relatively new form of corrosion control involves pacifating a metal used in the vessel by applying an external current that makes it more anodic. Such a technique is known as "anodic protection".
With anodic protection, the current is applied from an external source between an anode formed as the walls of the vessel and a cathode located within the vessel. The cathode is normally immersed in the liquid to be stored which acts as an electrolyte and establishes a current path between anode and cathode. The current is maintained within predetermined limits by a control system utilizing reference electrodes and an adjustable potentiometer.
The current will be maintained at a level determined by the material of the vessel and the liquid to be stored. It has been found that by maintaining the current within predefined limits, a potential is maintained that generates a film at the surface of the vessel to inhibit corrosion. This technique has been found particularly beneficial with vessels of steel or stainless steels and liquids with extreme Ph valves, i.e. strongly acid or strongly alkali.
The control system associated with such anodic systems is sensitive to the level of liquid within the vessel and operates to cut off the current flow if the liquid level drops below the cathode. However, situations may arise where the cathode is intermittently covered and uncovered by liquid in the tank. In these circumstances, the inductance of the electrical circuit established between the current source and the cathode may permit a relatively large potential to be induced on the cathode as it is uncovered, which then may result in a spark or discharge as the liquid again approaches the cathode. As explosive gases may be present within the vessel, it is clearly undesirable to permit an electrical discharge ~1412~~
within the vessel.
It is therefore an object of the present invention to provide a corrosion protection system in which the above disadvantages are obviated or mitigated.
In general terms, the present invention provides a non-conductive strap extending from an electrode to the vessel. The strap is porous and absorbs electrolyte and, through wicking action, carries the electrolyte into contact with the electrode. A current path is therefore provided through the electrolyte carried by the strap to inhibit the generation of potential at the cathode.
More particularly, the present invention provides a corrosion protection system for a vessel containing an electrolytic fluid comprising a first electrode electrically connected to said vessel, a second electrode disposed within said vessel and electrically isolated therefrom, a current source connected between said electrodes and a non-conductive strap extending between said second electrode and the vessel. The strap is porous to absorb electrolyte and thereby through a capillary action, establishes an electrolytic path between said vessel and the second electrode whereby a current path is provided through said strap.
Preferably, the strap is a braided rope and a mass is secured to the distal end of the strap to bias the strap towards the base of the vessel.
In a further aspect, the present invention provides a corrosion protection device for use with a vessel having a base and upstanding side walls to contain a fluid electrolyte. The device comprises an electrical source connected to the vessel to provide an anode and connected to an electrode disposed within the vessel. A
non-conductive strap is connected to the electrode and extends to the vessel. The strap is porous to absorb electrolyte within the vessel and maintain an electrolytic current path between the vessel and electrode with electrolyte in the vessel. Voltages induced on the electrode by said electrical source are therefore mitigated.
In a further aspect, the present invention provides a fluid storage system having a vessel to store an electrolytic fluid and having a corrosion protection system associated therewith to inhibit corrosion of the vessel.
The improvement comprises a strap extending from an electrode of the protection system to the vessel. The strap is non-conductive and porous to absorb electrolyte within the vessel and thereby establish a current path between the vessel and the electrode upon application of a potential difference therebetween.
An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which Figure 1 is a side elevation of a storage vessel;
and Figure 2 is a view on an enlarged scale of a portion of the storage vessel shown in Figure 1 within the i circle II.
Referring therefore to the drawings, a storage vessel indicated at 10 has a base 12, a cylindrical side wall 14, and a domed roof 16. The vessel 10 is formed from 5 a material subject to corrosion by the liquid to be stored in the vessel and is typically carbon steel or stainless steel.
Liquid indicated at 18 is introduced into the vessel 10 through an inlet 20 and is extracted from the vessel through an outlet 22.
An anodic protection system generally indicated at 24 includes an external current source 26 electrically connected through cable 28 to the wall 14. The wall 14 defines the anode of the protection system. It will be understood that cathodic protection systems could also be implemented if appropriate.
The current source 26 is also connected through a cable 30 to a cathode assembly 32 mounted on the roof 16.
Cathode assembly 32 includes a cathode 34 that extends vertically from the roof 16 into the interior of the vessel 1o and terminates prior to the base 12. Typically it is spaced in the order of 12"-18" from the base. Cathode 34 is electrically isolated from the vessel 10 and is located on the longitudinal axis of the tank. The cathode 34 is formed from a rigid rod of a suitable cathode material such TM
as hastalloy, as is well known in the art.
Reference electrodes 36,38 are also located within the vessel 10 and provide control signals to the current source 26 to maintain the applied current within predetermined parameters. Such control systems are again well known in the art and will not be described in further detail.
As can be seen in Figure 2, a strap 40 is secured to the lower end of the cathode 34 by means of clamps 42.
The strap 40 is formed from a braided or woven fibreglass rope which is therefore electrically non-conductive but which is porous to the liquid 18. As such, it will absorb the liquid 18 and carry it by capillary action into contact with the cathode 34. The strap 40 is flaccid and has a weight 44 secured at the opposite end to the cathode to bias the strap 40 into contact with the base 12.
In operation, the liquid 18 is normally above the lower limit of the cathode 34 and acts as an electrolyte.
An electrical current path is established between the walls 14 through the liquid 18 to the cathode 34. With the current controlled within the appropriate range of parameters, a passive film is generated at the inner surface of vessel 10 that inhibits corrosive action on the base 12 and walls 14. The current will depend upon the material of the tank and the liquid. As noted above, the parameters controlling the current are well known in the art.
In the event that the level of liquid drops below the end of the cathode 34, the reference electrodes will switch off the current source 26. However, in certain circumstances, the liquid level 18 may be adjacent to the 2~~? ~~~
lower end of the electrode 34 so that contact is intermittently made and lost between the liquid 18 and the cathode due to bodily movement within the liquid 18. In this condition, the strap 40 acts as a wick to bring the liquid 18 into contact with the cathode 34. A secondary current path is established through the liquid within the strap 40 to the cathode and so inhibits the accumulation of electrical charge on the cathode 34 due to the inductance of the electrical circuit. The strap 40 is maintained within the liquid 18 by virtue of the mass 44 which holds the strap 40 against the base 12.
In a practical embodiment, the strap 40 has been formed from a ~Ys inch fibreglass braided rope such as that available from A.R. Thompson Limited under Part No. G-38.
With a spacing between the cathode 34 and tank 12 of 18 inches, it was found that a 36-inch length of such rope was effective to maintain contact with the base of the tank and provide the secondary leakage. The strap 40 was effective to inhibit the formation of sparks such as might occur with intermittent contact between the cathode 34 and liquid 18.
It will be seen, therefore, that a very simple but effective device is provided to inhibit the formation of sparks and to provide a secondary current path through the liquid between the anode and cathode.
It is therefore an object of the present invention to provide a corrosion protection system in which the above disadvantages are obviated or mitigated.
In general terms, the present invention provides a non-conductive strap extending from an electrode to the vessel. The strap is porous and absorbs electrolyte and, through wicking action, carries the electrolyte into contact with the electrode. A current path is therefore provided through the electrolyte carried by the strap to inhibit the generation of potential at the cathode.
More particularly, the present invention provides a corrosion protection system for a vessel containing an electrolytic fluid comprising a first electrode electrically connected to said vessel, a second electrode disposed within said vessel and electrically isolated therefrom, a current source connected between said electrodes and a non-conductive strap extending between said second electrode and the vessel. The strap is porous to absorb electrolyte and thereby through a capillary action, establishes an electrolytic path between said vessel and the second electrode whereby a current path is provided through said strap.
Preferably, the strap is a braided rope and a mass is secured to the distal end of the strap to bias the strap towards the base of the vessel.
In a further aspect, the present invention provides a corrosion protection device for use with a vessel having a base and upstanding side walls to contain a fluid electrolyte. The device comprises an electrical source connected to the vessel to provide an anode and connected to an electrode disposed within the vessel. A
non-conductive strap is connected to the electrode and extends to the vessel. The strap is porous to absorb electrolyte within the vessel and maintain an electrolytic current path between the vessel and electrode with electrolyte in the vessel. Voltages induced on the electrode by said electrical source are therefore mitigated.
In a further aspect, the present invention provides a fluid storage system having a vessel to store an electrolytic fluid and having a corrosion protection system associated therewith to inhibit corrosion of the vessel.
The improvement comprises a strap extending from an electrode of the protection system to the vessel. The strap is non-conductive and porous to absorb electrolyte within the vessel and thereby establish a current path between the vessel and the electrode upon application of a potential difference therebetween.
An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which Figure 1 is a side elevation of a storage vessel;
and Figure 2 is a view on an enlarged scale of a portion of the storage vessel shown in Figure 1 within the i circle II.
Referring therefore to the drawings, a storage vessel indicated at 10 has a base 12, a cylindrical side wall 14, and a domed roof 16. The vessel 10 is formed from 5 a material subject to corrosion by the liquid to be stored in the vessel and is typically carbon steel or stainless steel.
Liquid indicated at 18 is introduced into the vessel 10 through an inlet 20 and is extracted from the vessel through an outlet 22.
An anodic protection system generally indicated at 24 includes an external current source 26 electrically connected through cable 28 to the wall 14. The wall 14 defines the anode of the protection system. It will be understood that cathodic protection systems could also be implemented if appropriate.
The current source 26 is also connected through a cable 30 to a cathode assembly 32 mounted on the roof 16.
Cathode assembly 32 includes a cathode 34 that extends vertically from the roof 16 into the interior of the vessel 1o and terminates prior to the base 12. Typically it is spaced in the order of 12"-18" from the base. Cathode 34 is electrically isolated from the vessel 10 and is located on the longitudinal axis of the tank. The cathode 34 is formed from a rigid rod of a suitable cathode material such TM
as hastalloy, as is well known in the art.
Reference electrodes 36,38 are also located within the vessel 10 and provide control signals to the current source 26 to maintain the applied current within predetermined parameters. Such control systems are again well known in the art and will not be described in further detail.
As can be seen in Figure 2, a strap 40 is secured to the lower end of the cathode 34 by means of clamps 42.
The strap 40 is formed from a braided or woven fibreglass rope which is therefore electrically non-conductive but which is porous to the liquid 18. As such, it will absorb the liquid 18 and carry it by capillary action into contact with the cathode 34. The strap 40 is flaccid and has a weight 44 secured at the opposite end to the cathode to bias the strap 40 into contact with the base 12.
In operation, the liquid 18 is normally above the lower limit of the cathode 34 and acts as an electrolyte.
An electrical current path is established between the walls 14 through the liquid 18 to the cathode 34. With the current controlled within the appropriate range of parameters, a passive film is generated at the inner surface of vessel 10 that inhibits corrosive action on the base 12 and walls 14. The current will depend upon the material of the tank and the liquid. As noted above, the parameters controlling the current are well known in the art.
In the event that the level of liquid drops below the end of the cathode 34, the reference electrodes will switch off the current source 26. However, in certain circumstances, the liquid level 18 may be adjacent to the 2~~? ~~~
lower end of the electrode 34 so that contact is intermittently made and lost between the liquid 18 and the cathode due to bodily movement within the liquid 18. In this condition, the strap 40 acts as a wick to bring the liquid 18 into contact with the cathode 34. A secondary current path is established through the liquid within the strap 40 to the cathode and so inhibits the accumulation of electrical charge on the cathode 34 due to the inductance of the electrical circuit. The strap 40 is maintained within the liquid 18 by virtue of the mass 44 which holds the strap 40 against the base 12.
In a practical embodiment, the strap 40 has been formed from a ~Ys inch fibreglass braided rope such as that available from A.R. Thompson Limited under Part No. G-38.
With a spacing between the cathode 34 and tank 12 of 18 inches, it was found that a 36-inch length of such rope was effective to maintain contact with the base of the tank and provide the secondary leakage. The strap 40 was effective to inhibit the formation of sparks such as might occur with intermittent contact between the cathode 34 and liquid 18.
It will be seen, therefore, that a very simple but effective device is provided to inhibit the formation of sparks and to provide a secondary current path through the liquid between the anode and cathode.
Claims (19)
1. A corrosion protection system for a vessel containing an electrolytic liquid comprising a first electrode electrically connected to said vessel, a second electrode disposed within said vessel and electrically isolated therefrom, a current source connected between said first electrode and said second electrode and a non-conductive strap extending between said second electrode and said vessel, said strap being porous to absorb said electrolytic liquid and thereby establish an electrolytic path between said vessel and said second electrode whereby a current path is provided through said strap.
2. A corrosion protection device according to claim 1 wherein said strap extends between said second electrode and a base of said vessel.
3. A corrosion protection device according to claim 2 wherein said strap is flaccid.
4. A corrosion protection device according to claim 2 wherein said strap is a braided rope.
5. A corrosion protection device according to claim 4 wherein said rope is braided from glass fibres.
6. A corrosion protection device according to claim 4 wherein a mass is secured to a distal end of said strap to bias said strap toward said base.
7. For use with a vessel having a base and upstanding side walls to contain a liquid electrolyte, a corrosion protection device comprising an electrical source connected to said vessel to provide a first electrode and connected to a second electrode disposed within and electrically isolated from said vessel and a non-conductive strap connected to said second electrode and extending to said vessel, said strap being porous to absorb electrolyte within said vessel and carry it into contact with said second electrode to maintain an electrolytic current path between said vessel and said second electrode whereby voltages induced on the second electrode by said electrical source are mitigated.
8. A device according to claim 7 wherein said second electrode is disposed vertically within said vessel and said strap extends from said second electrode to said base of said vessel.
9. A device according to claim 8 wherein said strap is flaccid.
10. A device according to claim 9 wherein a mass is attached to said strap at the distal end thereof to bias said strap toward said base.
11. A device according to claim 9 wherein said strap is a rope.
12. A device according to claim 11 wherein said rope is formed of glass fibres.
13. A device according to claim 12 wherein said rope is braided.
14. In a fluid storage system having a vessel to store an electrolytic fluid and having a corrosion protection system associated therewith to inhibit corrosion of said vessel, the improvement comprising a strap extending from an electrode of said protection system to said vessel, said strap being non-conductive and porous to absorb electrolyte within said vessel and thereby establish a current path between said vessel and said electrode upon application of a potential difference therebetween.
15. The improvement of claim 14 wherein said strap is flaccid.
16. The improvement of claim 15 wherein said strap is woven from glass fibres.
17. The improvement of claim 15 wherein a mass is attached to said strap adjacent one end thereof.
18. A method of inhibiting an electrical discharge in a vessel having a corrosion protection system incorporated therein to inhibit corrosion of said vessel, said system including a current source connected between said vessel and an electrode located in said vessel to establish an electrical current through electrolyte stored in said vessel, said method comprising the steps of extending a non-conductive porous strap from said electrode to said vessel, immersing at least a portion thereof in said electrolyte and allowing said strap to absorb said electrolyte to establish a current path between said electrode and said vessel and thereby inhibit accumulation of electrical potential at said electrode in the absence of electrolyte around said electrode.
19. A method according to claim 18 including the step of biasing said strap into engagement with said vessel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2141127 CA2141127C (en) | 1995-01-26 | 1995-01-26 | Corrosion protection system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2141127 CA2141127C (en) | 1995-01-26 | 1995-01-26 | Corrosion protection system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2141127A1 CA2141127A1 (en) | 1996-07-27 |
| CA2141127C true CA2141127C (en) | 2004-08-17 |
Family
ID=4155121
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2141127 Expired - Lifetime CA2141127C (en) | 1995-01-26 | 1995-01-26 | Corrosion protection system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2141127C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2706215C (en) | 2010-05-31 | 2017-07-04 | Corrosion Service Company Limited | Method and apparatus for providing electrochemical corrosion protection |
-
1995
- 1995-01-26 CA CA 2141127 patent/CA2141127C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2141127A1 (en) | 1996-07-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20150126 |