GB2025667A - Cathodic protection - Google Patents

Cathodic protection Download PDF

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Publication number
GB2025667A
GB2025667A GB7830178A GB7830178A GB2025667A GB 2025667 A GB2025667 A GB 2025667A GB 7830178 A GB7830178 A GB 7830178A GB 7830178 A GB7830178 A GB 7830178A GB 2025667 A GB2025667 A GB 2025667A
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United Kingdom
Prior art keywords
current
ship
hull
anodes
source
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.)
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Application number
GB7830178A
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Morgan Berkeley and Co Ltd
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Morgan Berkeley and Co Ltd
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Filing date
Publication date
Application filed by Morgan Berkeley and Co Ltd filed Critical Morgan Berkeley and Co Ltd
Priority to GB7830178A priority Critical patent/GB2025667A/en
Publication of GB2025667A publication Critical patent/GB2025667A/en
Withdrawn legal-status Critical Current

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Classifications

    • CCHEMISTRY; METALLURGY
    • C23COATING 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
    • C23FNON-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
    • C23F13/00Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Prevention Of Electric Corrosion (AREA)

Abstract

A cathodic protection system, for use on the hull 4 of a ship, is capable of providing a variable distribution of current to protection anodes 5, 6, 7, 8, 9, 10, 13, 14 on the hull 4. Sensing electrodes 11, 12 supply a signal indicative of the potential of the hull 4 to a controller 3 which controls the different currents supplied to various anodes or groups of anodes. The anodes are so placed on the hull that, when each is passing a given maximum current, the distribution of current flowing to the anodes is suitable for protection of the hull 4 when the ship is moving at relatively high speeds. The system is also such that at low speeds, when the total current required for protection is less than at high speeds, the controller adjusts the distribution of currents so that it is suitable for protection at low speeds. <IMAGE>

Description

SPECIFICATION Cathodic protection system for ships This invention relates to cathodic protection systems. A commonly used system for the protection of the hulls of ships consists of one or more sensing electrodes which measure the potential of the ship's hull and in response to a signal from these elec tor'odes a particular cathodic protection current is supplied to anodes spaced on the hull of the ship. As the speed of the ship increases the protection current supplied is increased by a control system in accordance with the signal from the sensing electrodes. Two separate systems as described above may be provided on larger vessels, alternatively separate fore and aft anode arrangements with separate current sources may be controlled by a master signal from a single controller.
Not only may the total cathodic protection current need to be increased with increasing speed of a vessel in order to give adequate protection, but it may also be desirable to vary the distribution of the current over the hull according to the speed of the ship. For example, at high speeds the stern areas of a ship may require a relatively higher protection current compared to the bow.
According to the present invention there is provided a cathodic protection system for the hull of a ship comprising: a controller responsive to a signal supplied by sensing means and indicative of the potential of the hull of the ship; and a plurality of anodes spaced on the hull of the ship which are supplied with current, the currents to various anodes being varied by the controller so that the distribution of current supplied to anodes on different regions of the hull is different at different levels of the signal provided by said sensing means.
In a preferred embodiment of the invention there may be two separate sources of current, the output of each varied in response to a controller with a single input signal. Further the controller may cause only one source to operate at relatively low values of total protection current, this first source supplying anodes spaced to give protection to the whole of the hull of the ship; when the ship is stationary; the second source only becoming active in response to the controller when relatively high values of total protection current are required, as when the ship is moving at relatively high speeds. The second source r,5ay be connected to anodes spaced generally towards that area which requires, when the ship is moving, a higher proportion of protection current than when it is stationary.
An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows, schematically an embodiment of the invention, and Figure 2 shows the characteristic curves of two amplifiers suitable for use in the embodiment shown in Figure 1.
In figure 1 protection anodes 5, 6, 7, 8, 9, 10 13 and 14 are placed on the hull of the ship 4 in pairs, one member of each pair on opposite sides of the centreline of the hull. The arrangement of the anodes is chosen so that, when they are passing their maximum current, the distribution of current is that which will give the desired protection when the ship is moving at relatively high speeds.
Two controllable D.C. sources which may be transformer rectifiers 1 and 2 are connected to the anodes 5, 6, 7, 8, 9 ,10,13 and 14. Source 1 is connected to the anodes 5,6,9 and 10 which are spaced so that they provide a substantially uniform current distribution over the hull and its appendages, suitable to protect the hull when the ship is stationary. Source 2 is connected to the anodes 7, 8, 13 and 14 which are situated in the stern of the hull which requires an additional current when the ship is moving to give adequate protection.
A controller 3 regulates the currents supplied by sources 1 and 2 in response to an input signal, representing the potential of the hull, supplied by two electrodes 11 and 12 attached to the hull. The response of the controller 3 is such that for low values of the input signal only the source 1 supplies current, but as the input signal increases, the source 2 begins to supply current, the supply of current from each source increasing as the input signal increases. Thus as the total protection current supplied by sources 1 and 2 increases an increasing proportion of the total protective current is supplied to anodes located in the stern to the hull.
A suitable control system may consist of two amplifiers (not shown) of which the inputs are connected to receive the signal provided by the electrodes 11 and 12, the output of one amplifier being arranged to control the current source 1 and the output of the other amplifier being arranged to control the current source 2. Suitable response curves for the amplifiers are shown in Figure 2 in which the abscissa represents the input signal (corresponding to the potential of the hull) and the ordinate represents the output signal from each amplifier which, in turn, controls the current provided by the two current sources 1 and 2. The curve PU1 shows the response of the amplifier controlling the source 1 and curve PU2 shows the response of the amplifier controlling the second current source 2.
The output from each amplifier reaches a limit. At this limit, the amplifiers are operating at maximum output and the distribution of current supplied to the anodes 5, 6, 7, 8, 9,10,13 13 and 14 is that which is required when the ship is moving at relatively high speeds. Because the amplifier with curve PU2 has a higher gain than the amplifier controlling the output of current source 1, but does not provide an output at relatively low levels of input (when the ship is stationary or moving relatively slowly), only current source 1 will be providing current to the protection anodes 5,6,9, 10 and these anodes are arranged to provide a suitable current distribution when the ship is stationary or moving relatively slowly.
1. A cathodic protection system for the hull of a ship comprising: a controller responsive to a signal supplied by said sensingtneans and indicative of the
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cathodic protection system for ships This invention relates to cathodic protection systems. A commonly used system for the protection of the hulls of ships consists of one or more sensing electrodes which measure the potential of the ship's hull and in response to a signal from these elec tor'odes a particular cathodic protection current is supplied to anodes spaced on the hull of the ship. As the speed of the ship increases the protection current supplied is increased by a control system in accordance with the signal from the sensing electrodes. Two separate systems as described above may be provided on larger vessels, alternatively separate fore and aft anode arrangements with separate current sources may be controlled by a master signal from a single controller. Not only may the total cathodic protection current need to be increased with increasing speed of a vessel in order to give adequate protection, but it may also be desirable to vary the distribution of the current over the hull according to the speed of the ship. For example, at high speeds the stern areas of a ship may require a relatively higher protection current compared to the bow. According to the present invention there is provided a cathodic protection system for the hull of a ship comprising: a controller responsive to a signal supplied by sensing means and indicative of the potential of the hull of the ship; and a plurality of anodes spaced on the hull of the ship which are supplied with current, the currents to various anodes being varied by the controller so that the distribution of current supplied to anodes on different regions of the hull is different at different levels of the signal provided by said sensing means. In a preferred embodiment of the invention there may be two separate sources of current, the output of each varied in response to a controller with a single input signal. Further the controller may cause only one source to operate at relatively low values of total protection current, this first source supplying anodes spaced to give protection to the whole of the hull of the ship; when the ship is stationary; the second source only becoming active in response to the controller when relatively high values of total protection current are required, as when the ship is moving at relatively high speeds. The second source r,5ay be connected to anodes spaced generally towards that area which requires, when the ship is moving, a higher proportion of protection current than when it is stationary. An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows, schematically an embodiment of the invention, and Figure 2 shows the characteristic curves of two amplifiers suitable for use in the embodiment shown in Figure 1. In figure 1 protection anodes 5, 6, 7, 8, 9, 10 13 and 14 are placed on the hull of the ship 4 in pairs, one member of each pair on opposite sides of the centreline of the hull. The arrangement of the anodes is chosen so that, when they are passing their maximum current, the distribution of current is that which will give the desired protection when the ship is moving at relatively high speeds. Two controllable D.C. sources which may be transformer rectifiers 1 and 2 are connected to the anodes 5, 6, 7, 8, 9 ,10,13 and 14. Source 1 is connected to the anodes 5,6,9 and 10 which are spaced so that they provide a substantially uniform current distribution over the hull and its appendages, suitable to protect the hull when the ship is stationary. Source 2 is connected to the anodes 7, 8, 13 and 14 which are situated in the stern of the hull which requires an additional current when the ship is moving to give adequate protection. A controller 3 regulates the currents supplied by sources 1 and 2 in response to an input signal, representing the potential of the hull, supplied by two electrodes 11 and 12 attached to the hull. The response of the controller 3 is such that for low values of the input signal only the source 1 supplies current, but as the input signal increases, the source 2 begins to supply current, the supply of current from each source increasing as the input signal increases. Thus as the total protection current supplied by sources 1 and 2 increases an increasing proportion of the total protective current is supplied to anodes located in the stern to the hull. A suitable control system may consist of two amplifiers (not shown) of which the inputs are connected to receive the signal provided by the electrodes 11 and 12, the output of one amplifier being arranged to control the current source 1 and the output of the other amplifier being arranged to control the current source 2. Suitable response curves for the amplifiers are shown in Figure 2 in which the abscissa represents the input signal (corresponding to the potential of the hull) and the ordinate represents the output signal from each amplifier which, in turn, controls the current provided by the two current sources 1 and 2. The curve PU1 shows the response of the amplifier controlling the source 1 and curve PU2 shows the response of the amplifier controlling the second current source 2. The output from each amplifier reaches a limit. At this limit, the amplifiers are operating at maximum output and the distribution of current supplied to the anodes 5, 6, 7, 8, 9,10,13 13 and 14 is that which is required when the ship is moving at relatively high speeds. Because the amplifier with curve PU2 has a higher gain than the amplifier controlling the output of current source 1, but does not provide an output at relatively low levels of input (when the ship is stationary or moving relatively slowly), only current source 1 will be providing current to the protection anodes 5,6,9, 10 and these anodes are arranged to provide a suitable current distribution when the ship is stationary or moving relatively slowly. CLAIMS
1. A cathodic protection system for the hull of a ship comprising: a controller responsive to a signal supplied by said sensingtneans and indicative of the potential of the hull oftheship; and a plurality of anodes spaced on the hull of the ship which are supplied with current, the currents to various anodes being varied by the controller so that the distribution of current supplied through anodes to different regions of the hull is different at different levels of the signal provided by said sensing means.
2. A cathodic protection system as claimed in claim 1 in which that proportion of total protective current that is supplied to anodes in the stern of the hull increases as the said potential increases.
3. A cathodic protection system as claimed in any previous claim in which said controller controls a first and a second current source, said first source supplying anodes which alone are suitable to give protection to a ship when the ship is stationary said second source connected to anodes such that when both sources are supplying a given maximum current the distribution of current to the anodes is suitable to provide protection when the ship is moving at maximum speed.
4. A cathodic protection system as claimed in claim 3 in which said controller includes a first and a second amplifier with outputs controlling respectively said first and second current sources, said first amplifier having a lower gain than said second amplifier, both said amplifiers having as a common input the signal provided by said sensing means and arranged to cause only said first source to provide a current for a range of signals from said sensing means corresponding to relatively low speeds of the ship, but outside that range to cause both said sources to supply current.
5. A cathodic protection system as claimed in claim 3 or claim 4 in which each current source is connected to four anodes arranged in pairs one member of each pair on each side of the centreline of the hull of the ship, the pairs of anodes connected so that the sternmost pair is connected to the second source and the next sternmost pair is connected to the first source and the foremost pair is connected to the first source and the next foremost pair is connected to the second source.
6. A cathodic protection system as claimed in any of the preceding claims in which said sensing means comprise a pair of electrodes, one on each side of the centreline of the ship.
7. A cathodic protection system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
GB7830178A 1978-07-18 1978-07-18 Cathodic protection Withdrawn GB2025667A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB7830178A GB2025667A (en) 1978-07-18 1978-07-18 Cathodic protection

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB7830178A GB2025667A (en) 1978-07-18 1978-07-18 Cathodic protection

Publications (1)

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GB2025667A true GB2025667A (en) 1980-01-23

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GB7830178A Withdrawn GB2025667A (en) 1978-07-18 1978-07-18 Cathodic protection

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GB (1) GB2025667A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114737191A (en) * 2022-03-23 2022-07-12 中国船舶重工集团公司第七二五研究所 Distributed impressed current cathodic protection system for ship

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114737191A (en) * 2022-03-23 2022-07-12 中国船舶重工集团公司第七二五研究所 Distributed impressed current cathodic protection system for ship

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