ICCP Approval

CATHELCO: C-SHIELD ICCPMARINE IMPRESSED CURRENT CATHODIC PROTECTIONAPPROVAL DRAWINGS & INSTRUCTION MANUALCLIENT: KAUON SHIPYARD 57000 DWT BC VESSEL: KA101/ KA 102/ KA 103/TK101/TK102/TK103/TK104TK108CATHELCO REFERENCE: CA 35287/A-KRev: 0Issued: AIRDate: 19/07/07 MARINE HOUSE, HIPPER STREET SOUTH, CHESTERFIELD, DERBYS. S40 1SS, UK TEL: +44 (0)1246 246700. FAX: +44 (0) 1246 246701. E-MAIL: technical@C-SHIELDMARINE IMPRESSED CURRENTCATHODIC PROTECTION SYSTEMNOTES:a)Do not attempt to service or readjust the system operating levels without first readingand understanding this manual.b)The system operates at low d.c. voltage levels and may be severely damaged by highvoltage test equipment such as 500V Megger. Read the relevant section in this manual beforecarrying out any tests.c)Should any information be required which is not covered by this manual, please contactCathelco immediately. (Address on cover)C-SHIELD MANUAL INDEX:0.0 Scope of Supply0.1 List of drawings.1.0 Introduction.2.0 General Descriptions.3.0 Installation of Equipment.7.0 C-Shield Commissioning Check List.Section 0.0Page 1 of 1 SCOPE OF SUPPLYELLIPTICAL ANODES (FWD) WI-016REFERENCE CELLS (FWD) WI-008ELLIPTICAL ANODES (AFT) WI-016REFERENCE CELLS (AFT) WI-008SHAFT EARTHING SYSTEMWI-011POWER SUPPLY UNIT – THYRISTOR (AFT) WI-036POWER SUPPLY UNIT – THYRISTOR (FWD) WI-0361.0INTRODUCTION:1.0.1 PRINCIPLES OF CORROSION AND CATHODIC PROTECTION:Metallic corrosion is an electro-chemical reaction in which the metal combineswith a non metal, such as oxygen, to form a metal oxide or other compound.This depends upon the nature of the environment.Different metals have different tendencies to corrode, termed activity orpotential. These potentials can be tabulated and form the electro-chemicalseries.A more practical approach is the determination of the tendency of certain metalsto corrode in a particular electrolyte, such as sea water. This is termed thegalvanic series of which the following table is an abridged form.Active or AnodicMagnesiumZincMild SteelWrought IronCast IronNi-Resist18.8.3 % Molybdenum SS, Type 316 (Active)LeadTinManganese BronzeNaval BrassAluminium BronzeCopper70 Copper 30 NickelNickel (Passive)Monel, 70% Nickel - 30 % Copper18.8.3 % Molybdenum SS, Type 316 (Passive)Noble or CathodicNote Some metals and alloys have two positions in the series, marked Activeand Passive; the active position is equivalent to the position if corrosion isoccurring and approaches the electro-chemical series position for the material.The passive position relates to a non-corroding situation where the material isprotected by a self forming surface film. For example, type 316 stainless steel insea water is more likely to be passive than type 304 and is therefore generallypreferred for immersed marine applications.If two metals are placed in an electrolyte (e.g. sea water or damp soil) and are in direct electrical contact, a current will pass through the electrolyte from the more active metal onto the least active metal. The least active metal does not corrode and is termed the cathode. The more active metal, the anode, passes into solution and the flow of electrical current increases. This is a metal ion and electron transfer process i.e., it corrodes.This simple cell may be represented as:Figure 1.1 - Simple Corrosion CellThe Anodic and cathodic areas in a corrosion cell may be due to the electrical contact of two dissimilar metals, termed galvanic corrosion. Anodic and cathodic areas may be formed on a single metal surface as micro-cells for instance by rain drops on uncoated steel. Alternatively, they may be close but discrete cells found when accelerated corrosion occurs at uncoated Anodic areas on a generally coated cathodic structure. In addition there are long line type cells that occur on pipelines that pass through aggressive low resistivity soils. These sections form Anodic areas and corrode in preference to cathodic areas in less aggressive higher resistivity soils.Large currents can occur at small Anodic areas and lead to rapid corrosion of marine structures such as ship's internal tanks, external hull plates, sheet steel piling in harbours and tubular structures common in jetties and petrochemical drilling and production platforms.Cathodic Protection is a system of preventing corrosion by forcing all surfaces of a structure to be cathodes by providing external anodes.As described above, a galvanic corrosion cell occurs when dissimilar metals are in contact with each other within an electrolyte. Care should be taken in theconstruction of structures that will be buried or immersed in an electrolyte to ensure a galvanic cell is not created.Typical examples of galvanic cells are:a ) Steel or cast iron water boxes in contact with non ferrous (often copperbased) tube plates in condenser water boxes in ships or generatingplant. Rapid corrosion of the ferrous water box occurs close to the tubeplate.b) Brass or bronze valves fitted to immersed steel buoyancy tanks orflooding chambers on marine petrochemical structures. Acceleratedcorrosion of the steel occurs near the valve.c) The connection of steel pipes into an otherwise cast iron system.Accelerated corrosion of the steel occurs near the cast iron sections. Sacrificial anode cathodic protection achieves corrosion prevention on a particular structure or component by forming a galvanic cell where an additional anode of zinc, magnesium or aluminium corrodes in preference to the structure. The galvanic corrosion current (see simple cell before) available from this anode / electrolyte / structure combination should be sufficient to overcome the local surface corrosion currents on the structure until no current flows from Anodic areas of the structure i.e the structure is entirely cathodic or under complete cathodic protection.The potential, or measure of activity, between the structure and the electrolyte is a relatively easily measured indication of whether the structure is Anodic or cathodic. For steel under normal non anaerobic conditions it can be shown theoretically, and is accepted practically, that a steel/electrolyte potential more negative than -0.85 volts measured against a standard copper/copper sulphate electrode indicates that cathodic protection is achieved. This is equivalent to -0.80 volts measured against silver / silver chloride electrode and + 0.24 volts against a zinc electrode as indicated in figure 1.3.SACRIFICIAL ANODE CATHODIC PROTECTION:As indicated previously, a metal can be made cathodic by electrically connecting it to a more Anodic metal within the electrolyte. The most commonly used Anodic metals are alloys of aluminium, zinc and magnesium. Anodes of these metals corrode preferentially; the corrosion current of the anode achieving cathodic protection of the structure to which they are connected. The anodes deteriorate as an essential part of their function and they are therefore termed sacrificial.2.0DESCRIPTIONS:GENERAL2.1.1 IMPRESSED CURRENT CATHODIC PROTECTION:A metal also can be made cathodic by electrically connecting it to anothermetallic component in the same electrolyte through a source of direct electriccurrent and directing the current flow to occur off the surface of added metalliccomponent (anode), into the electrolyte and onto the metal (cathode). This caneasily be visualised by reference to the simple cell and assuming yet anotherelectrode with a power source is introduced and that the current flow from thiselectrode is sufficient to overcome the natural corrosion current.Because an external current source is employed, this type of protection istermed 'IMPRESSED CURRENT CATHODIC PROTECTION'.Figure 1.2 - Cathodic Protection Applied to a Simple Corrosion CellA source of direct current is required, this is generally obtained from mainspower units that contain a transformer and rectifier. The magnitude of thiscurrent may be automatically controlled in response to a continuous monitor ofthe cathode / electrolyte potential or may be manually controlled afterintermittent measurement.The impressed current anode material is ideally non-consumed by the passageof current from it into the electrolyte, in practice the materials used are acompromise between this ideal and the cost and physical properties of availablematerials. Impressed current anodes are made from graphite, silicon iron, leadalloys some with platinum bi-electrodes, platinised titanium or more exoticcombinations such as platinum clad niobium. The selection of the correct anodematerial is critical in the formulation of an effective and economic cathodicprotection scheme.Generally, for a given current demand, less impressed current anodes thansacrificial anodes are required for protection, as high anode currents arefeasible. Impressed current systems of cathodic protection are more sophisticated in design than sacrificial systems.Figure 1.3 - Comparison of Reference Electrodes & Interpretation2.2.0 MARINE IMPRESSED CURRENT SYSTEM:The C-Shield Marine Impressed Current System comprises the followingcomponents, as illustrated in figure 1.4.2.2.1 Impressed Current AnodesThe function of the anode is to conduct the d.c. protective current into the seawater. C-Shield anodes have been designed to perform this function whilstmaintaining a low electrical resistance contact with the sea water. Standardsurface mounted anodes are available with from 50 to 300 Ampere ratings. Forforward mounted systems and for special applications 50 and 75 Ampererecessed anodes are available.Materials now used by C-Shield for Anodes have now gone beyond lead alloywith specialist coated titanium based Anodes now available. All C-Shield anodedesigns utilise a tough, chlorine resistant, but slightly flexible plastic carrier.The use of a 24 volt system reduces the number and length of the anodes fromthat required with a 12 volt system. The increased anode/sea water resistanceresulting from this decrease in anode size is overcome by the additional voltage.Recommended cable sizes for various run lengths are tabulated in section 3.4.The potential of the hull steel to the sea water is unaffected by this increase indriving voltage, as the resistive effects are local to the anode and the hull/seapotential is a function of the current flow, the sea water and the coatingcondition, not the driving voltage.The electrical connections to the active surface are made at the back of theanode and are fully encapsulated and protected by the hull penetration.Recessed anodes of essentially similar construction are provided for bowsection applications.All hull penetrations are provided with substantial doubler plates and cofferdams. The penetrations themselves are made watertight with heavy dutypacking glands, the cofferdams are fully sealed and provided with watertightcable glands, all conforming to the requirements of Classification Societies.2.2.2 Impressed Current Reference Electrodes.The high purity, high stability, zinc reference electrodes are designed to give astable reference against which the hull/sea potentials can be measured and asmall current flow that is used in the closed loop circuit to maintain the pre-setlevels of protection.The construction and the quantity of zinc employed within the electrodes aresuch that a minimum life of fifteen years is available without maintenance orreplacement.The minimum number of reference electrodes per power supply is one althoughnormally two will be fitted. Ideally, these should be located a minimum of 7.5metres distant from the anodes. In the case of a stern only installation with theanodes more than 150 metres from the bows, one reference electrode may belocated in the bows.A novel feature of the C-Shield closed circuit is that additional reference cellsmay be placed at areas that may be susceptible to over-protection such asadjacent to the anode dielectric shields. These additional reference cells providea permanent check, thus preventing any coating damage due to over-protectionif conditions of operation change from those anticipated. This feature is offeredas an optional extra to the standard schemes.All hull penetrations are provided with substantial cofferdams. The penetrationsthemselves are made watertight with heavy duty packing glands. The cofferdams are fully sealed and provided with watertight cable glands allconforming to the requirements of the Classification Societies.2.2.3 Power Supply Unit:The C - Shield impressed current Cathodic protection power supply unit is athyristor system housed in a range of different sized cabinets. The specificpower supply unit supplied is illustrated on the drawing included with thismanual. The system comprises of a control PCB, a Thyristor PCB and aThyristor unit (consisting of a transformer, a choke and a thyristor bridge)ranging in size from 100 Amperes upto 800 Amperes. The supplyrequirements are 415 Vac +/-10%, three phase, 50/60 Hz.The control PCB is a micro-processor based system having a 2 line 16character backlit LCD display which is located in the top centre of thecabinet door. The display is used to monitor and allow control of thesystem. Below the LCD are four push buttons, which are the controls forchanging the system parameters. To the right of the LCD is a power onindicator, which also acts as an alarm indicator. On the reverse side are arotary switch and a potentiometer. The switch toggles between manualoverride and normal operation. This allows the operator, in the event of afault, to disable the micro-processor control system, and to control theoutput current with the potentiometer.DISPLAY:This allows the operator to control and monitor the running and setparameters of the system. It comprises of a 2 line 16 character backlit LCDdisplay, 4 push button switches and an Alarm LED. This is mounted on thedoor of the cabinet.MAIN CONTROL PCBThis board controls the operation of the system. It provides control signalsto the thyristor driver PCB, which allow control over the output current andvoltage of the system. This is mounted on the back of the cabinet door.PCBTHYRISTORThis board monitors and conditions the signals supplied to the thyristorunit.2.2.4 BondingTo enable the rudder to receive protection it is provided with a dedicatedelectrical bond in the form of a flexible cable from the top of the rudderstock to the main ship structure. In the same way any stabilisers are bondedto allow protective current to these surfaces.To allow protection of the bare propeller and any exposed shafting and toprevent electrical arcing between shaft and bearings the propeller shaft isfitted with a slipring assembly. A set of brushes provide the completion of alow resistance path to allow current to flow to the propeller blades alongthe shaft and back to the hull. The slipring is formed from a copper stripclamped around the shaft with high copper content heavy current capacitybrushes held in geared brush holders. The C-Shield slipring track is silverplated as standard and in addition silver graphite brushes are used tominimise contact resistance.3.0 INSTALLATION OF EQUIPMENT:3.0.01 Description:The C-Shield Impressed Current System consists of anodes and electrodesfor installation through the hull using penetration and cofferdamarrangements, a power supply unit for location internally and bondingarrangements for appendages such as propeller and rudder. The system usesidentical cofferdams for both surface mount linear and recessed anodes. Thecofferdams for the reference electrodes are longer than those for the anodesso that there is a necessity to differentiate between cofferdams beforestarting assembly.3.0.02 Locations for components are shown on the C-Shield drawings supplied forthe particular vessel, but are normally subject to final confirmation betweenthe C-Shield engineer on site and the yard/owner.3.0.03 It is very important that the installation instructions given are followed. Thebiggest cause of future problems found with the running of impressedcurrent systems is incorrect installation. Should any problems occur duringinstallation of this system or should any instruction appear unclear pleasecontact Cathelco for advice.3.3ELLIPTICAL RECESSED ANODE:3.3.01 Select the required area and mark out using a template the steelworklocation. Make sure that the internal stiffening will not be touched.Ensure the ellipse will be located within a steel plate and notinterfere with existing weld seams.3.3.02 Cut an elliptical hole. The ellipse may be easily marked out bypositioning the anode on the hull and scribing around it and allowinga margin of 6mm around the anode periphery. Alternatively, atemplate may be made using the doubler plate. Refer to drg. C1186.3.3.03 Clean the profile of the elliptical hole and grind a nominal 3mmradius on the outer edge and a weld preparation on the inner edge tomatch the one provided on the doubler plate3.3.04 Position the doubler plate internally and line it up with the ellipse.Tack weld the doubler plate in position. When you are sure that thedoubler plate is correctly located and that the anode will fit cleanlyinto the recess continuously weld the doubler plate to the inboard andoutboard surface of the hull plating. Grind the recess weld flush asshown.3.3.05 Place the cofferdam concentrically over the cable gland hole in therear of the doubler plate. Position the cable exit tube from thecofferdam to suit site conditions and weld internally and externally inposition with penetration welds with single bevel full penetrationweld complete with a backing run.3.3.06 Cover the anode holding studs with plastic tubing to prevent damagefrom shot blasting.3.3.07 Shot blast the doubler plate and recess to SA 2 1/2 minimum3.3.08 Fit a suitable cable gland into the doubler plate from the inboard sideinside the cofferdam recess.3.3.09 Mix equal quantities of the 2 part epoxy filler material supplied.Apply epoxy to back of anode and spread evenly.3.3.10 Prepare an Anode for installation. The dimensions of the Anode areshown by drg.C1202. Carefully insert the Anode Cable through thecentre hole in the doubler plate and through the cable gland takingcare not to damage the insulation. Locate the anode over the sixfixing points in the backing plate.3.3.11 Slowly draw anode into recess by tightening the Anode fixing nuts.The epoxy filler will slowly ooze out of the sides as anode settlesinto position, ensure the Anode cable does not become trapped.When anode is flush with hull and the bolts are resting within anodefixing point recess ensure the head of the holding nut is below the toplevel of the anode. Fill stud holes with epoxy and smooth level.3.3.12 Smooth epoxy at edge of anode so that gap between anode andsteelwork is completely filled.3.3.13 Inside the Ship fully tighten the gland onto the cable.3.3.14 Before proceeding further, ensure that all other welding work, eitherinboard or outboard, has been completed for the entire area to becovered by the di-electric shield. Any welding carried out after theapplication of the di-electric shield will damage the shield materialeven if the welding is not associated with the cathodic protectionsystem.3.3.15 The dimensions of the di-electric shield are shown on drg. C1196.3.3.16 Inspect the area to be covered and grind off all weld splatter, andsurplus weld material to a smooth profile.3.3.17 Remove all oil and grease from the area using clean, dry, oil free ragssoaked in a hydrocarbon solvent such as Xyol, Yoluene or whitespirit, do not use petrol or paraffin. Change the rags frequently toavoid merely spreading contamination.3.3.18 Ensure that the anode face is protected with masking tape or similar.Abrasive blast clean the entire area to a white metal finish, SA 2 1/2Swedish standard using grit or sand. Check the surface profile heightusing test tape and that it is within the range 50 - 70 micron.3.3.19 Form the primary di-electric shield by applying the anode epoxymastic within four hours of blasting and before the formation of anyvisible rust bloom. Fill the four threaded temporary anode retainingmounting holes with mastic. Technical details and health precautionsfor the anode mastic are available on request from Cathelco.3.3.20 Thoroughly mix the contents of each can before mixing the two partstogether. Follow the mixing instructions on the epoxy masticmaterial packs, using a power driven mixer if possible.3.3.21 Apply by trowel to produce a film 4mm thick at the edge of theanode surface tapering to 1mm thick at the shield edge. Form acircular shield of mastic of 900mm radius. A one coat application isessential.3.3.22 Ensure that the di-electric shield mastic covers the resin of the anodebut do not allow mastic on the metal anode face. Allow the mastic toharden fully before painting over. Remember to remove theprotective tape from the surface of the anode.3.3.23 Inside the ship, remove the blank flange from the cofferdam andcheck the cable for damage.3.3.24 Apply thread tape to the second anode cable gland, make sure theneoprene 'O' ring is fitted and pass the gland over the anode cable tofit it into position as detailed below. Tighten the main body fully intoposition, then tighten on to the cable.3.3.25 Dry Compartment Installation. Pass the cable through the side entryhole in the cofferdam and fit the cable gland in the same way asbefore, to the outside of the cofferdam, leaving slack cable betweeninner and outer glands.3.3.26 Fit the junction box at some convenient point adjacent to thecofferdam and connect the anode cable to the transformer/rectifiervia shipyard supply cable, see power supply unit instructions.3.3.27 Wet Compartment Installation. Pass the shipyard cable through theside entry hole into the cofferdam. Note that any cables running intanks should be in heavy wall conduit pipe. Fit the cable gland in thesame way as before, to the inside of the cofferdam side entry, overthe shipyard cable.3.3.28 Connect the anode cable tail to the shipyard cable internally in thecofferdam. Use a recognised splice kit or a C-Shield splice kit can beprovided. Refer to drg. M1043 for full instructions. Where cablesare spliced in a cofferdam it is recommended that the cofferdam befilled with paraffin wax or similar. Connect the shipyard cable to thepower supply unit.3.3.29 Check the insulation of the anode connection circuit to the hull usinga 500V earth insulation test meter. Note, if the anode is submergedthen this test will show a short circuit. Disconnect from power supplyunit before this test or permanent damage may occur.3.3.30 Make a final visual check of all connections and finally fit the blindflange and gasket to seal the cofferdam. Do not over paint the anodewhen painting over the dielectric shield area.3.3.31 Note all welds used during installation should meet the Yard orClassification Society rules.3.4 REFERENCE ELECTRODE CELLS3.4.01 Cut a 170mm diameter hole in the hull at each electrode location.This is to enable installation of the cell mounting cofferdam asshown by drawing C11903.4.02 Grind off any surplus metal to ensure that the cofferdam body willlocate flat to the internal shell plating at the inboard side of the hole.3.4.03 Locate the cofferdam centrally over the hole, inside the hull.3.4.04 Secure the cofferdam in the position by a continuous fillet weldinternally to give a weld section at least equal to the platingthickness. Drawing C1162 gives a rough guide for welding andelectrode cell installation.3.4.05 Clean off all weld splatter from the surfaces including the cofferdamrecess, and grind flat all welds in the area to be occupied by thereference electrode.3.4.06 Ensure that the neoprene sealing gasket is on the back of thereference electrode assembly and that the inside of the cofferdamrecess into which the electrode will fit is clean and dry.3.4.07 Apply thread tape or sealing compound to the M20 threadedmounting sleeve of the reference electrode. The reference electrodecell is shown by drawing C1102. Remove the nut, dished washer andneoprene washer from the M20 sleeve but leave the neoprene sealingring in place.3.4.08 From the outboard of the shell thread the cable through the glandplate at the back of the cofferdam recess.3.4.09 Apply sealing compound to the recess and screw the referenceelectrode firmly into place in the cofferdam using the spannerprovided to fit the recesses in the front face of reference electrodecarrier. Do not Over Tighten !!3.4.10 Inside the ship, remove the blank flange from the Cofferdam andcheck the cable insulation for any possible damage.3.4.11 On completion of the inspection caulk the gap between the referenceelectrode carrier and the outer shell with sealing compound, to leavea smooth uniform surface.3.4.12 From the inboard of the shell fit the neoprene washer within thedished steel washer and locate over the reference electrode mountingsleeve within the cofferdam. Ensure that the neoprene washer facesoutboard and is in contact with the gland plate in the cofferdam.3.4.13 Fit the M20 full locking nut on the reference electrode mountingsleeve and tighten until the neoprene washer is fully compressed andthe dished washer is in contact with the gland plate.3.4.14 Pass the cable through the side entry hole in the cofferdam.3.4.15 Dry Compartment Installation: Apply thread tape to the referenceelectrode cable gland, and pass the gland over the anode cable to fitit into position outside the cofferdam as shown in the drawing.Tighten the main body fully into position then tighten onto the cableleaving slack cable inside the cofferdam.3.4.16 Fit a junction box at some convenient point adjacent to thecofferdam and connect the reference electrode cable to the powersupply unit via shipyard supplied cable see the Power Supply Unitinstructions in section 3.53.4.17 Wet Compartment Installation: Pass the shipyard cable through theside entry hole into the cofferdam. Any cables, which run throughtanks, must be housed in heavy walled conduit pipe. Fit the cablegland in the same way as before but to the inside of the cofferdamover the shipyard cable.3.4.18 Connect the anode cable tail to the shipyard cable using a cablesplice kit. Use an industry recognised kit or a C-shield splice kit asshown by drawing M1043. After splicing in submerged cofferdams itis recommended that the cofferdam recess void be filled withparaffin wax or similar. Connect the shipyard cable to the PowerSupply Unit see section 3.53.4.19 Check installation of the reference connection circuit to the hullusing 500 Volt earth insulation meter. If the electrode is submergedthen this test will show a short circuit.Disconnect from the power supply unit before this test or permanentdamage may occur.3.4.20 Make a final visual check of all connections and finally fit the blindflange and gasket to seal the cofferdam.3.4.21 Please ensure that if the vessel is going to be stood in water for along period of time during the outfitting period, the reference cellsare NOT to be connected to panel until the ICCP system iscommissioned.。