WO2004009436A1 - Impressed current cathodic protection system for marine structure without reference cell - Google Patents

Impressed current cathodic protection system for marine structure without reference cell Download PDF

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Publication number
WO2004009436A1
WO2004009436A1 PCT/KR2003/001417 KR0301417W WO2004009436A1 WO 2004009436 A1 WO2004009436 A1 WO 2004009436A1 KR 0301417 W KR0301417 W KR 0301417W WO 2004009436 A1 WO2004009436 A1 WO 2004009436A1
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WO
WIPO (PCT)
Prior art keywords
marine structure
reference cell
impressed current
power supply
protection system
Prior art date
Application number
PCT/KR2003/001417
Other languages
French (fr)
Inventor
Myung Kuk Jung
Original Assignee
Myung Kuk Jung
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Myung Kuk Jung filed Critical Myung Kuk Jung
Publication of WO2004009436A1 publication Critical patent/WO2004009436A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B59/00—Hull protection specially adapted for vessels; Cleaning devices specially adapted for vessels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B43/00—Improving safety of vessels, e.g. damage control, not otherwise provided for

Definitions

  • the present invention relates to an impressed current cathodic protection system for control of corrosion in a marine structure without a reference cell, and more particularly, to the control system for impressing the most suitable current in a condition of removing a reference cell conventionally and inevitably used in order to determine impressed current and voltage.
  • metallic surfaces on the marine structure make themselves electrodes.
  • the oxidation reaction occurs at anodic areas on metallic surfaces, and then metals loose their electrons and ionized metals
  • the sacrificial anode method two different metals are contacted with each other in electrolyte, and these two metals form a galvanic couple.
  • one metal having relatively higher corrosion potential is polarized as an anode
  • other metal having relatively lower corrosion potential is polarized as a cathode
  • the active former provides a flux of electrons to the latter, thereby being solved into anodic polarity; this phenomenon is corrosion.
  • a certain metal has more corrosion potential in active direction, thereby forming a couple together with the other metal for serving as a sacrificial anode. Then, the metal working as a cathode is electro-chemically protected from the corrosion.
  • magnesium, zinc, and aluminium are used as sacrificial anodes for steel materials in seawater.
  • the sacrificial anode method has problems that its control of the magnitude and density of current is not possible, it is not suitable for a big structure, and a system using this method has a certain life.
  • the impressed current method is accomplished by polarizing the surfaces on corroded metals as a cathode so that it may reduce corrosion speed.
  • Anodic reaction and cathodic reaction of iron corroded in neutral electrolyte solution are similar to above-described reaction formulas. If metallic surfaces are polarized as a cathode, a flux of excess electrons reverses equilibrium, thereby reducing corrosion speed.
  • the impressed current method is applicable to any metal or alloy.
  • FIG. 3 is a schematic sectional side view of the marine structure having an impressed current cathodic protection system for a marine structure with a reference cell according to the conventional system.
  • FIG. 4a and FIG. 4b are schematic views for showing the layout of electrodes in FIG. 3. While FIG. 4a and FIG. 4b show the distribution of electrodes at rear and front of hull 112, respectively, FIG. 4a and FIG. 4b are plan views of FIG. 3.
  • the marine structure 110 using the conventional impressed current cathodic protection system includes respective power supply units 120 at front and rear of hull 112. Furthermore, the marine structure 110 includes anodes 122 and reference cells 124 that are disposed at both sides of hull 112 and connected to the respective power supply units 120. The anodes 122 and the reference cells 124 installed by means of a structure such as a watertight cofferdam are disposed apart a predetermined distance. In the conventional system, potential difference between cathode (not shown) connected to the power supply unit 120 and the reference cell 124 are measured continuously. Also, the power supply unit 120 increases current progressively until potential impressed to the anode 122 approaches a suitable protection potential.
  • Fe and the reference cell 124 For example, potential difference between metallic surfaces on the marine structure and the reference cell 124 in seawater having about 2% salinity is assumed as about 320mV. Then, the power supply unit 120 supplies a flux of excess electrons to the surface of the marine structure until the potential difference value is 220mV, which is considered as a fixed target.
  • the impressed current cathodic protection system for a marine structure having a reference cell requires particular watertight structures in order to install the reference cell.
  • the conventional system has some problems that an initial cost is expensive, it is difficult to maintain the system, and the system cannot reflect all of the variable environments in seawater.
  • an object of the present invention to provide an impressed current cathodic protection system for reducing the installation cost by removing the reference cell in the marine structure such as a ship, performing installing operation and maintenance easily, and corrosion protecting the marine structure in optimum condition.
  • an impressed current cathodic protection system for a marine structure without a reference cell, the system comprising power supply units disposed at the certain positions of hull, and anodes connected to the power supply units and disposed at both sides of hull.
  • the most suitable protection potential impressed to the anodes from the power supply units is within the range of 1500 to 2500mV in seawater and 4000 to ⁇ OOOmV in freshwater in case of a marine structure made of steel material, while 2500 to 3500mV in seawater and 5000 to 7000mV in freshwater in case of a marine structure made of aluminium material.
  • FIG. 1 is a schematic side view of the marine structure having an impressed current cathodic protection system for a marine structure without a reference cell according to the present invention
  • FIG. 2a and FIG. 2b are schematic views for showing the layout of electrodes in FIG. 1 ;
  • FIG. 3 is a schematic side view of the marine structure having an impressed current cathodic protection system for a marine structure with a reference cell according to the conventional system; and, FIG. 4a and FIG. 4b are schematic views for showing the layout of electrodes in FIG. 3.
  • FIG. 1 is a schematic side view of the marine structure having an impressed current cathodic protection system without a reference cell according to the present invention
  • FIG. 2a and FIG. 2b are schematic views for showing the layout of electrodes in FIG. 1.
  • FIG. 2a and FIG. 2b show the layout of electrodes at rear and front of hull 12, respectively.
  • the marine structure 10 is represented in the form of a ship.
  • an impressed current cathodic protection system for a marine structure according to the present invention comprise power supply units 20 disposed at a certain positions of hull 12, and anodes 22 connected to the power supply units 20 and disposed at both sides of hull 12.
  • Reference cells in the conventional system are omitted in the present invention.
  • potential differences between the marine structure 10 to be protected and electrolyte, for example sea water are measured only by means of anodes 22.
  • Protection potential to be impressed actually is set to be lower than corrosion potential, which can be obtained from potential difference between any surface of hull 12 and an anode 22, preferably 100 ⁇ 200mV lower than the obtained potential difference. Accordingly, by adding 100 ⁇ 200mV to corrosion potential in order to supply a flux of excess electrons to the surface of hull 12, protection potential can be obtained. In the course of obtaining the protection potential, current impressed from the power supply unit 20 is increased progressively until protection potential approaches the most suitable value.
  • the most suitable protection potential impressed to the anodes from the power supply units could be obtained by using the trial and error method.
  • the value is within the range of 1500 to 2500mV in seawater and 4000 to ⁇ OOOmV in freshwater.
  • the value is within the range of 2500 to 3500mV in seawater and 5000 to 7000mV in freshwater.
  • An additional value 100 ⁇ 200mV, which is added for the purpose of supplying a flux of excess electrons to the surface of the marine structure is a reference value recommended by NACE (National Association of Corrosion Engineering) in U.S.A., which is adopted in marine associations of many other nations.
  • potential between surfaces of various marine structures including marine transportation or underwater structure and anodes is measured continuously in order for the marine structure to be in optimum corrosion protection, and enabling the system to automatic control by means of the computer.
  • reference cell disposed by means of a structure such as a watertight cofferdam which has been installed for four per the marine structure such as a ship, can be removed, thereby reducing the installation cost. Furthermore, installing operation and maintenance of the protection system can be performed easily, and the breakage of the marine structure can be minimized.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • Ocean & Marine Engineering (AREA)
  • Prevention Of Electric Corrosion (AREA)

Abstract

The present invention relates to an impressed current cathodic protection system for a marine structure without a reference cell, including power supply units (20) disposed at certain positions of hull (12), and anodes (22) connected to the power supply units (20) and disposed at both sides of hull (12). Therefore, the marine structure such as a ship does not need a reference cell installed by means of a watertight structure, thereby reducing the installation cost and minimizing the breakage of the marine structure.

Description

IMPRESSED CURRENT CATHODIC PROTECTION SYSTEM FOR MARINE STRUCTURE WITHOUT REFERENCE CELL
BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an impressed current cathodic protection system for control of corrosion in a marine structure without a reference cell, and more particularly, to the control system for impressing the most suitable current in a condition of removing a reference cell conventionally and inevitably used in order to determine impressed current and voltage.
2. Description of the Related Art
In general, metallic surfaces on the marine structure such as a ship make themselves electrodes. The oxidation reaction occurs at anodic areas on metallic surfaces, and then metals loose their electrons and ionized metals
(M) are discomposed, thereby going into water or solution. Formula (1-1) shows this oxidation reaction.
M→ M + e- (1-1)
The reduction reaction occurs at cathodic areas on metallic surfaces, thereby cathode attracts electrons that are generated in the process of oxidation of metals and electrons combine with the ionized hydrogen, thereby hydrogen gas is generated. Formula (1-2) and (1-3) show the generation of molecules of water and hydrogen gas, respectively. Also, formula (1-4) and (1-5) show the generation of hydroxyl.
09 + 4H+ + 4e-→2H20 (1 -2)
2H1" + 2e → H (1-3) 02 + 2H20 + 4e-→ 4(OH)- (1-4)
2H20 + 2e'→H2 f + 2(OH)" (1-5)
It can be thought of surfaces on the marine structure in seawater as an electrolytic model. The reason that surfaces on the marine structure are corroded is mostly because of the oxidation reaction at their anodic areas and the reduction reaction at their cathodic areas. Also, although the marine structures are made of the same metal, they could be corroded because the metal is separated into two electrodes, which are anode and cathode, according to the degree of electrolysis with respect to seawater or the electrolytic concentration in seawater.
Since surfaces on the marine structure are corroded easily by direct exposure to seawater, painting operation is performed so that it could prevent their corrosion. At this time, metals contacted with electrolyte react electrically and then the marine structure is corroded at the spots of defects in painting operation or local harm on painted surfaces. Finally, the corrosion damages the marine structure rapidly. Accordingly, electron-chemical protection methods such as the sacrificial anode method and the impressed current method are performed in order to protect metallic surfaces.
In the sacrificial anode method, two different metals are contacted with each other in electrolyte, and these two metals form a galvanic couple. In this method, one metal having relatively higher corrosion potential is polarized as an anode, whereas other metal having relatively lower corrosion potential is polarized as a cathode, then the active former provides a flux of electrons to the latter, thereby being solved into anodic polarity; this phenomenon is corrosion. A certain metal has more corrosion potential in active direction, thereby forming a couple together with the other metal for serving as a sacrificial anode. Then, the metal working as a cathode is electro-chemically protected from the corrosion. Generally speaking, magnesium, zinc, and aluminium are used as sacrificial anodes for steel materials in seawater. However, the sacrificial anode method has problems that its control of the magnitude and density of current is not possible, it is not suitable for a big structure, and a system using this method has a certain life.
The impressed current method is accomplished by polarizing the surfaces on corroded metals as a cathode so that it may reduce corrosion speed. Anodic reaction and cathodic reaction of iron corroded in neutral electrolyte solution are similar to above-described reaction formulas. If metallic surfaces are polarized as a cathode, a flux of excess electrons reverses equilibrium, thereby reducing corrosion speed. The impressed current method is applicable to any metal or alloy.
In a conventional technology using the impressed current method, a reference cell has been used in order to determine a quantity of protection current while the metal serves as a cathode, and it will be described with reference to FIG. 3, FIG. 4a, and FIG. 4b. FIG. 3 is a schematic sectional side view of the marine structure having an impressed current cathodic protection system for a marine structure with a reference cell according to the conventional system. FIG. 4a and FIG. 4b are schematic views for showing the layout of electrodes in FIG. 3. While FIG. 4a and FIG. 4b show the distribution of electrodes at rear and front of hull 112, respectively, FIG. 4a and FIG. 4b are plan views of FIG. 3.
In general, the marine structure 110 using the conventional impressed current cathodic protection system includes respective power supply units 120 at front and rear of hull 112. Furthermore, the marine structure 110 includes anodes 122 and reference cells 124 that are disposed at both sides of hull 112 and connected to the respective power supply units 120. The anodes 122 and the reference cells 124 installed by means of a structure such as a watertight cofferdam are disposed apart a predetermined distance. In the conventional system, potential difference between cathode (not shown) connected to the power supply unit 120 and the reference cell 124 are measured continuously. Also, the power supply unit 120 increases current progressively until potential impressed to the anode 122 approaches a suitable protection potential.
In the conventional system, platinum (Pt) works as the anode 122, whereas zinc (Zn) works as the reference cell 124. Furthermore, impressed current in the conventional system is higher than current obtained from potential difference between metallic surfaces on the marine structure having
Fe and the reference cell 124. For example, potential difference between metallic surfaces on the marine structure and the reference cell 124 in seawater having about 2% salinity is assumed as about 320mV. Then, the power supply unit 120 supplies a flux of excess electrons to the surface of the marine structure until the potential difference value is 220mV, which is considered as a fixed target.
However, the impressed current cathodic protection system for a marine structure having a reference cell according to the conventional system requires particular watertight structures in order to install the reference cell.
Furthermore, the conventional system has some problems that an initial cost is expensive, it is difficult to maintain the system, and the system cannot reflect all of the variable environments in seawater.
SUMMARY OF THE INVENTION
To solve the above-described problems, it is an object of the present invention to provide an impressed current cathodic protection system for reducing the installation cost by removing the reference cell in the marine structure such as a ship, performing installing operation and maintenance easily, and corrosion protecting the marine structure in optimum condition.
In accordance with an aspect of the present invention, there is provided an impressed current cathodic protection system for a marine structure without a reference cell, the system comprising power supply units disposed at the certain positions of hull, and anodes connected to the power supply units and disposed at both sides of hull. In accordance with another aspect of the present invention, the most suitable protection potential impressed to the anodes from the power supply units is within the range of 1500 to 2500mV in seawater and 4000 to ΘOOOmV in freshwater in case of a marine structure made of steel material, while 2500 to 3500mV in seawater and 5000 to 7000mV in freshwater in case of a marine structure made of aluminium material.
BRIEF DESCRIPTION OF THE DRAWINGS The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:
FIG. 1 is a schematic side view of the marine structure having an impressed current cathodic protection system for a marine structure without a reference cell according to the present invention; FIG. 2a and FIG. 2b are schematic views for showing the layout of electrodes in FIG. 1 ;
FIG. 3 is a schematic side view of the marine structure having an impressed current cathodic protection system for a marine structure with a reference cell according to the conventional system; and, FIG. 4a and FIG. 4b are schematic views for showing the layout of electrodes in FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic side view of the marine structure having an impressed current cathodic protection system without a reference cell according to the present invention, FIG. 2a and FIG. 2b are schematic views for showing the layout of electrodes in FIG. 1. FIG. 2a and FIG. 2b show the layout of electrodes at rear and front of hull 12, respectively. In the drawing, the marine structure 10 is represented in the form of a ship. Referring to the drawing, an impressed current cathodic protection system for a marine structure according to the present invention comprise power supply units 20 disposed at a certain positions of hull 12, and anodes 22 connected to the power supply units 20 and disposed at both sides of hull 12. Reference cells in the conventional system are omitted in the present invention. Thus, potential differences between the marine structure 10 to be protected and electrolyte, for example sea water, are measured only by means of anodes 22.
Protection potential to be impressed actually is set to be lower than corrosion potential, which can be obtained from potential difference between any surface of hull 12 and an anode 22, preferably 100 ~ 200mV lower than the obtained potential difference. Accordingly, by adding 100 ~ 200mV to corrosion potential in order to supply a flux of excess electrons to the surface of hull 12, protection potential can be obtained. In the course of obtaining the protection potential, current impressed from the power supply unit 20 is increased progressively until protection potential approaches the most suitable value.
In the present invention, the most suitable protection potential impressed to the anodes from the power supply units could be obtained by using the trial and error method. In case of a marine structure made of steel material, the value is within the range of 1500 to 2500mV in seawater and 4000 to ΘOOOmV in freshwater. Also, in case of a marine structure made of aluminium material, the value is within the range of 2500 to 3500mV in seawater and 5000 to 7000mV in freshwater. An additional value 100 ~ 200mV, which is added for the purpose of supplying a flux of excess electrons to the surface of the marine structure, is a reference value recommended by NACE (National Association of Corrosion Engineering) in U.S.A., which is adopted in marine associations of many other nations. Also, potential between surfaces of various marine structures including marine transportation or underwater structure and anodes is measured continuously in order for the marine structure to be in optimum corrosion protection, and enabling the system to automatic control by means of the computer.
According to the impressed current cathodic protection system for a marine structure without a reference cell, reference cell disposed by means of a structure such as a watertight cofferdam, which has been installed for four per the marine structure such as a ship, can be removed, thereby reducing the installation cost. Furthermore, installing operation and maintenance of the protection system can be performed easily, and the breakage of the marine structure can be minimized. Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

What is claimed is:
1. An impressed current cathodic protection system for a marine structure without a reference cell comprising; power supply units disposed at certain positions of hull; and anodes connected to the power supply units and disposed at both sides of hull.
2. The system according to claim 1 , the most suitable protection potential impressed to the anodes from the power supply units is within the range of 1500 to 2500mV in seawater and 4000 to ΘOOOmV in freshwater in case of a marine structure made of steel material, while 2500 to 3500mV in seawater and 5000 to 7000mV in freshwater in case of a marine structure made of aluminium material.
PCT/KR2003/001417 2002-07-19 2003-07-18 Impressed current cathodic protection system for marine structure without reference cell WO2004009436A1 (en)

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KR10-2002-0042467A KR100523331B1 (en) 2002-07-19 2002-07-19 Impressed current cathodic protection system for marine structure without reference cell
KR10-2002-0042467 2002-07-19

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9353446B2 (en) 2013-04-29 2016-05-31 Transistor Devices, Inc. Systems and methods for impressed current cathodic protection

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DE3822168A1 (en) * 1986-12-30 1990-02-15 Waertsilae Meriteollisuus Cathodic corrosion protection
DE4110504A1 (en) * 1991-03-30 1992-10-01 Ingenieurzentrum Schiffbau Gmb Cathodic protection of ship propellers - using an automatically adjustable resistor between the propeller shaft and the ship hull
JPH10147894A (en) * 1996-09-17 1998-06-02 Mitsubishi Materials Corp Method for mounting sacrificial anode and cap used for the same
US6209472B1 (en) * 1998-11-09 2001-04-03 Brunswick Corporation Apparatus and method for inhibiting fouling of an underwater surface

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JPS59102686A (en) * 1982-12-06 1984-06-13 Mitsui Eng & Shipbuild Co Ltd Preventive method against attachment of living things
JPS60169577A (en) * 1984-02-10 1985-09-03 Mitsubishi Heavy Ind Ltd Method for preventing corrosion and contamination of shell plate
JPS61136689A (en) * 1984-12-07 1986-06-24 Mitsubishi Heavy Ind Ltd Device for preventing sticking of marine life
US5055165A (en) * 1988-01-19 1991-10-08 Marine Environmental Research, Inc. Method and apparatus for the prevention of fouling and/or corrosion of structures in seawater, brackish water and fresh water
JPH02296592A (en) * 1989-05-12 1990-12-07 Nkk Corp Ship's bottom fouling prevention method
JPH06344978A (en) * 1993-06-02 1994-12-20 Hitachi Zosen Corp Electric anti-corrosion method in ship

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Publication number Priority date Publication date Assignee Title
DE3822168A1 (en) * 1986-12-30 1990-02-15 Waertsilae Meriteollisuus Cathodic corrosion protection
DE4110504A1 (en) * 1991-03-30 1992-10-01 Ingenieurzentrum Schiffbau Gmb Cathodic protection of ship propellers - using an automatically adjustable resistor between the propeller shaft and the ship hull
JPH10147894A (en) * 1996-09-17 1998-06-02 Mitsubishi Materials Corp Method for mounting sacrificial anode and cap used for the same
US6209472B1 (en) * 1998-11-09 2001-04-03 Brunswick Corporation Apparatus and method for inhibiting fouling of an underwater surface

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9353446B2 (en) 2013-04-29 2016-05-31 Transistor Devices, Inc. Systems and methods for impressed current cathodic protection

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KR20040008778A (en) 2004-01-31
KR100523331B1 (en) 2005-10-24

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