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
  • B63B59/04—Preventing hull fouling

Definitions

• the invention relates to a method for protecting surfaces against biological macro-fouling by applying a potential that fluctuates over time.
• cathodic protection to protect metal-containing surfaces which come into contact with water against oxidative corrosion. This method is based on the application of a constant negative potential.
• a description of the effect of cathodic protection can be found in “Cathodic and Anodic Protection”, Chapter 10 in “Corrosion”, Volume 2, edited by L. L. Shreir, R. A. Jarman, G. T. Burstein, 3 rd edition (1994), published by Butterworth-Heien Ltd, Oxford, UK.
• cathodic protection is usually employed on conducting surfaces which are provided with a non-conducting coating, so that the underlying conducting surface is effectively safeguarded against macro-fouling, by cathodic protection, only after the coating has been damaged.
• the electrically conducting surface to be protected is either in direct contact with the water-containing medium or is provided with a conducting coating.
• Organisms will settle on virtually all materials that are placed in water. This starts with the formation of a very thin biofilm by microorganisms. At a later stage larger organisms will nestle on the material, as a result of which macro-fouling is produced.
• Macro-fouling on ships, constructions and in installations that are in contact with (sea)water constitutes a significant problem.
• macro-fouling by, for example, barnacles or mussels can lead to a substantial increase in the resistance of ships in water, to blockages in pipeline systems, to microbiological corrosion, to deposit attack, to erosion/corrosion or to a reduction in heat transfer.
• a coating must be applied with a view to anti-fouling, even if this is not necessary or even undesirable from the corrosion standpoint, with a view to heat transfer or from the structural engineering standpoint.
• the invention is aimed at overcoming the above disadvantages and relates to a method for protecting surfaces (S) which are in contact or come into contact with a water-containing medium (M) against biological macro-fouling, wherein
• Such a potential (P) fluctuating over time is applied to S that it inhibits the growth of organisms that live in M and/or propagate therein and which have the tendency to form deposits on S, characterised in that P does not assume values that are higher than the corrosion potential of S in M and the average value of P is lower than the said corrosion potential.
• the corrosion potential is defined as the potential of a corroding surface in an electrolyte with respect to a reference electrode, as defined in “Principles and Prevention of Corrosion” by D. A. Jones, 2 nd edition, Prentice-Hall, Upper Saddle River, N.J. 07458. In this description the values cited for the potential (P) are always with respect to a saturated calomel electrode (SCE).
• biological macro-fouling is also used to refer to deposits as a consequence of the presence of (micro)organisms which are (can be) present in seawater, brackish water and freshwater or water-containing media or systems.
• the method according to the invention has the significant advantage that no use is made of potentials that are higher than the corrosion potential. Therefore no precautionary measures have to be taken to prevent accelerated corrosion occurring on parts susceptible to corrosion, such as a ship's hull.
• the method according to the invention thus offers the significant advantage that it can be employed for simultaneous protection of surfaces in an aqueous environment against macro-fouling by organisms and against corrosion. This is effectively achieved by the use of an adequate negative base potential so as to obtain cathodic protection in combination with fluctuating negative potential pulses which prevent or impede the growth of organisms.
• macro-fouling As far as macro-fouling is concerned, it is mainly the following organisms that are of importance: algae, diatoms, ascidians, hydroids, anthozoans, bryozoans, tube worms, bivalve molluscs and crustaceans, especially barnacles, mussels, algae and tubercles.
• the settling of microorganisms such as bacteria and the formation of their biofilm are prevented or controlled. This has the following beneficial effects:
• microbiological corrosion is prevented or the risk of MIC occurring is reduced;
• the surfaces (S) that can be protected according to the invention are, for example:
• the method according to the invention is particularly suitable for protecting vessels against macro-fouling and corrosion.
• the surface (S) to be protected preferably consists of or contains:
• electrically conducting or semiconducting coating or top layer such as a metallic coating, ceramic coating, intrinsically conducting polymer or paint system to which electrically conducting components have been added,
• the surface (S) to be protected consists of the materials mentioned under a) or b).
• S contains steel
• S contains stainless steel.
• S consists predominantly of steel or stainless steel, it optionally being possible for an electrically conducting coating (for example a coat of paint) also to have been applied to the steel.
• the method according to the invention not only protects against biological macro-fouling but also counteracts corrosion of metals present in S that do not belong to the group of noble metals. This effect is even detected under conditions where a potential pulse that is well below the potential that would normally be used in order to achieve cathodic protection is employed for a prolonged period.
• the maximum value of P that is applied by polarisation is lower than the corrosion potential of S in M, since conditions which could lead to corrosion of S, especially in those cases where S contains one or more metals which do not belong to the group of noble metals, are thus prevented.
• the maximum value of P is at least 50 mV lower than, more particularly at least 100 mV lower than, the corrosion potential.
• the fluctuations of P with respect to SCE are within the range of ⁇ 300 to ⁇ 3000 mV, and preferably ⁇ 400 to ⁇ 2000 mV. Particularly good results are obtained with stainless steel if the said fluctuations are within the range from ⁇ 800 to ⁇ 1800 mV.
• the amplitude of the potential fluctuations is preferably at least 50 mV and more particularly at least 100 mV.
• the frequency of the fluctuations is preferably at least once per 24 hours. A method in which the amplitude is at least 200 mV and the frequency at least once per 6 hours is to be particularly preferred.
• the desired biological inhibition can he achieved by applying (P) to (S) at intervals (T), or by varying (P) in some way or other over time. All conceivable variations of (P) over time are possible in this context, but in general the method according to the invention will make use of pulse patterns (use of so-called spikes) where the periods in which (P) is applied to (S) have a duration of 0.01-600 seconds, preferably 5-120 seconds, and (T) is 0.1second-48 hours, preferably 10 seconds-4 hours.
• the invention relates to the use of a negative potential (P) that fluctuates over time for the protection of electrically conducting surfaces (S) which are in contact or come into contact with a water-containing medium (M), characterised in that P both
• the present invention also relates to a device for the protection of external walls of vessels and/or other constructions that usually come into long-term contact with water, as well as of internal walls of systems through which water is fed, against biological macro-fouling, which device comprises:
• a voltage source that is connected to the internal or external wall and that preferably is able to achieve a reduction in potential of at least 300 mV on the wall within one minute, characterised in that the voltage source is capable of producing a negative polarisation that varies over time on the surface to be protected. against macro-fouling.
• a counter-electrode which is positively polarised by the voltage source, is used in this polarisation.
• This counter-electrode is electrically insulated from (S) and preferably (but not necessarily) is made of a material that is inert in the medium (M).
• the voltage source is preferably controlled with the aid of a reference electrode to be positioned close to (S).
• test cell in which the settlement behaviour of barnacle larvae can be investigated on a substrate having a potential that can be controlled electrochemically.
• This test cell consisted of a plexiglas tube that was glued to a test plate.
• barnacle larvae were introduced into the plexiglas “inner cell” thus produced and fresh seawater was supplied continuously. Discharge of the seawater was via a very fine filter gauze, so that the barnacle larvae were not able to leave the inner cell.
• test plate was connected via a time switch to a potentiostat, whilst a reference electrode was fitted in the inner cell.
• a platinum counter-electrode was fitted on the external wall of the plexiglas cell, in the so-called ‘outer cell’. This means it was possible to polarise the test plate without the reaction products of the counter-electrode being able to influence the barnacle larvae.
• test conditions were as follows:
• Reference cell 1 was used to ensure that the reaction products which are produced on the platinum auxiliary electrode in the outer cell (such as chlorine gas) do not have any influence on the barnacles in the inner cell.
• auxiliary electrode such as chlorine gas
• a strip of stainless steel which was fitted around the plexiglas (in the outer cell) was polarised.
• the reaction products on the auxiliary electrode are consequently the same as in the case of test cells 1, 2, 3, 4 and 5, but there is no polarisation of the test piece whatsoever.
• a working electrode (W) made of stainless steel (316 L) was placed, together with a counter-electrode and a reference electrode, in a large glass beaker containing natural seawater. All electrodes were connected to a potentiostat by means of which increasingly more negative potentials were successively applied to the working electrode. The working electrode was partially protected by placing this separately in a smaller glass beaker inside the large glass beaker.
• a piece of universal pH indicator paper (Riedel-de-Ha ⁇ n (RdH Laborchemikalien GmbH & Co.): PANPEHA (Multi-colour special and universal indicator paper pH 0-14) was placed both on the base of the large glass beaker and on the working electrode itself. The color change of two areas of the indicator paper (3 rd and 4 th areas from the top) was observed.

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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)
• Water Treatment By Electricity Or Magnetism (AREA)
• Paints Or Removers (AREA)

Applications Claiming Priority (3)

Publications (1)

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ID=19772938

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Cited By (3)

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Citations (15)

Family Cites Families (2)

• 2001
  • 2001-02-21 NL NL1017412A patent/NL1017412C2/nl not_active IP Right Cessation
• 2002
  • 2002-02-20 WO PCT/NL2002/000111 patent/WO2002066318A1/en not_active Application Discontinuation
  • 2002-02-20 EP EP02700894A patent/EP1361977A1/en not_active Withdrawn
  • 2002-02-20 US US10/468,667 patent/US20040112762A1/en not_active Abandoned

Patent Citations (16)

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