rules and regulations for the classification of mobile offshore...

Part 8Corrosion Control

June 2013

Rules andRegulationsfor theClassification ofMobile Offshore Units

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PART 1 REGULATIONS

PART 2 RULES FOR THE MANUFACTURE, TESTING AND CERTIFICATION OF MATERIALS

PART 3 FUNCTIONAL UNIT TYPES AND SPECIAL FEATURES

PART 4 STEEL UNIT STRUCTURES

PART 5 MAIN AND AUXILIARY MACHINERY

PART 6 CONTROL AND ELECTRICAL ENGINEERING

PART 7 SAFETY SYSTEMS, HAZARDOUS AREAS AND FIRE

PART 8 CORROSION CONTROL

Chapter 1 General Requirements for Corrosion Control

2 Cathodic Protection Systems

3 Coating and Paint Systems

4 Guidance Notes on Design of Cathodic Protection Systems and Coatings

1LLOYD’S REGISTER

Part 8RULES AND REGULATIONS FOR THE CLASSIFICATION OF MOBILE OFFSHORE UNITS, June 2013

Chapter Contents

Part 8

CHAPTER 1 GENERAL REQUIREMENTS FOR CORROSION CONTROL

Section 1 Corrosion protection1.1 Application1.2 Zone definitions1.3 External zone protection1.4 Internal zones1.5 Bimetallic connections1.6 Chain cables and wire ropes

Section 2 Riser systems2.1 General2.2 External coatings2.3 Internal protection2.4 Cathodic protection systems

Section 3 Plans and information3.1 Scope3.2 Cathodic protection systems3.3 Sacrificial anode systems3.4 Impressed current systems3.5 Coating systems3.6 Inhibitors and biocides

CHAPTER 2 CATHODIC PROTECTION SYSTEMS

Section 1 General requirements1.1 Objective1.2 Electrical continuity1.3 Criteria for cathodic protection

Section 2 Sacrificial anodes2.1 General2.2 Anode materials2.3 Steel insert preparation2.4 Chemical composition2.5 Conditions of supply2.6 Anode identification2.7 Anode inspection2.8 Dimensions2.9 Anode weight

2.10 Bonding and internal defects2.11 Electrochemical testing2.12 Certification2.13 Anode installation

Section 3 Impressed current anode systems3.1 General3.2 Protection after launching and during outfitting

Section 4 Fixed potential monitoring systems4.1 General

Section 5 Cathodic protection in tanks5.1 General5.2 Sacrificial anodes

Section 6 Potential surveys6.1 General

Section 7 Retrofits7.1 General

3LLOYD’S REGISTER

RULES AND REGULATIONS FOR THE CLASSIFICATION OF MOBILE OFFSHORE UNITS, June 2013

Contents

ContentsRULES AND REGULATIONS FOR THE CLASSIFICATION OF MOBILE OFFSHORE UNITS, June 2013

Part 8

LLOYD’S REGISTER4

CHAPTER 3 COATING AND PAINT SYSTEMS

Section 1 General requirements1.1 General

Section 2 Prefabrication primers2.1 General

CHAPTER 4 GUIDANCE NOTES ON DESIGN OF CATHODIC PROTECTION SYSTEMS AND COATINGS

Section 1 External steel protection1.1 Current density1.2 Sacrificial anode systems1.3 Location of anodes

Section 2 Protection of tanks2.1 Anode resistance2.2 Current density2.3 Anode distribution2.4 Reference electrodes

Section 3 Surface preparation, application and maintenance of coatings3.1 Application3.2 General requirements3.3 Coating selection3.4 Initial preparation3.5 Surface preparation3.6 Coating requirements3.7 Coating application3.8 Coating thickness3.9 Inspection and repair

3.10 Safety aspects3.11 Maintenance

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Part 8, Chapter 1Section 1

Section

1 Corrosion protection

2 Riser systems

3 Plans and information

■ Section 1Corrosion protection

1.1 Application

1.1.1 The requirements cover the corrosion protection ofmobile offshore units of the general types defined in Pt 1,Ch 2,2, see also Pt 3, Ch 1. Requirements are also given forriser systems, see Section 2.

1.1.2 All structural steel work is to be suitably protectedagainst loss of integrity due to the effects of corrosion. Ingeneral, suitable protective systems may include coatings,metallic claddings, cathodic protection, corrosion allowancesor other approved methods. Combinations of methods maybe used when agreed by LR. Consideration should be paidto the design life and the maintainability of the surfaces in thedesign of the protected systems.

General Requirements for Corrosion Control

1.1.3 The basic Rule scantl ings of the externalsubmerged steel structure of units which are derived fromPart 4 assume that a cathodic protection system will beeffective and in use continually. Unless agreed otherwise withLR no corrosion allowance will be included in the approvedscantlings, see Pt 3, Ch 1,5.

1.2 Zone definitions

1.2.1 The type of protection of the steelwork is to besuitable for the structural location of the unit and for thispurpose the steel structure is to be considered in terms ofzones.

1.2.2 Submerged zone. That part of the externalstructure below the maximum design operating draught.

1.2.3 Boot topping zone. That part of the externalstructure between the maximum design operating draughtand the light design operating draught. For column-stabilisedunits, see Table 1.1.1.

1.2.4 Splash zone. That part of the external structureabove the boot topping zone subject to wet and dryconditions.

1.2.5 Atmospheric zone. That part of the externalstructure above the splash zone.

Table 1.1.1 Minimum corrosion protection requirements for external structural steelwork

Unit typeCorrosion protection required and area

Method of protection requiredStructural steelworkZone

Column-stabilised units

Self-elevating units

Surface type units

Submerged zone

Boot topping and splash zonesSee Note 2

Atmospheric zone

Transit condition:Submerged, boot topping andsplash zones

Elevated condition:Submerged zone

Boot topping and splash zonesSee Note 3

Atmospheric zone

Submerged zone

Boot topping and splash zones

Atmospheric zone

Columns, lower hulls and bracings

Columns, lower hulls and bracings

All structure above the splash zone

Main hull

Legs, footings and mats

Legs


Main hull

Main hull


Cathodic protection and coatingsSee Notes 1 and 4

Coatings

Coatings only

Coatings only

Cathodic protection and coatingsSee Note 4

Coatings

Coatings only

Cathodic protection or coatingsSee Note 1

Coatings

Coatings only

NOTES1. For the assignment of the In-water Survey notation OIWS, corrosion protection by both cathodic protection and high resistance paint

coatings is required.3. For column-stabilised units, the boot topping zone is to be taken as that part of the external structure between the maximum design

operating draught and the transit draught.3. For self-elevating units, in the elevated position, the boot topping zone is to extend between the lowest and highest atmospheric tides at

the operating location.4. If In-water Survey notation, OIWS is not assigned, then coatings may be omitted except in the boot topping zone, see Note 2.

1.5 Bimetallic connections

1.5.1 Where bimetallic connections are made in thestructure, suitable measures are to be incorporated topreclude galvanic corrosion. Details are to be submitted forapproval on the structural plans required in Pt 4, Ch 1,4. Thecombination of painting the less noble material and leavingthe more noble material uncoated for an immersed bimetalliccouple is not permitted.

1.6 Chain cables and wire ropes

1.6.1 Chain cables and wire ropes for positional mooringsystems are to be protected from corrosion and therequirements of Pt 3, Ch 10 are to be complied with.

■ Section 2Riser systems

2.1 General

2.1.1 When riser systems are fitted in accordance withPt 3, Ch 12 the risers are to be suitably protected againstcorrosion. It is recommended that this be achieved using acoating combined with a cathodic protection system.Account should be taken of possible temperature effects.Other equivalent methods of protection will be considered.

2.1.2 The splash and boot topping zones of risers are tobe specially considered. A corrosion allowance will berequired in addition to any coatings. Risers in J-tubes, etc.,will require separate assessment of protection.

2.1.3 Where the cathodic protection system is designedto compensate for loss of protective coating, the systemshould be based on an initial loss of coating of between 5 and 10 per cent. Due allowance should be made for furtherbreakdown during the service life.

2.2 External coatings

2.2.1 Paint or protective coatings are generally to bechosen in conjunction with the system of cathodic protection.

2.2.2 The performance of the coating materials usedshould be proven by previous service or by extensive anddocumented laboratory testing.

2.2.3 Preparation of the riser surface before coating is tocomply with the approved specification relating to thatmaterial, see Ch 4,3.5.

2.3 Internal protection

2.3.1 The method of internal protection is to take intoaccount the corrosivity, bacterial content, solids/abrasivecontent, flow characteristics and temperature and pressure.


General Requirements for Corrosion Control Part 8, Chapter 1Sections 1 & 2

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1.2.6 Internal zones. Ballast tanks, liquid storage tanks,and other compartments.

1.3 External zone protection

1.3.1 The minimum requirements for corrosionprotection of the external steelwork of offshore units is givenin Table 1.1.1.

1.3.2 The structural steelwork in the boot topping andsplash zones is normally to be protected by suitable coatingsbut consideration may be given to the following:(a) Extra steel in excess of the Rule requirements.(b) Metallic cladding where appropriate.

1.3.3 The structural steelwork in the atmospheric zone isto be protected by suitable coatings.

1.3.4 The structural steelwork in the submerged zone isto be protected by an approved means of cathodicprotection using sacrificial anodes or an impressed currentsystem, except where noted otherwise in Table 1.1.1. Highresistance coatings may be required or used in conjunctionwith a cathodic protection system but they will not beaccepted in lieu of cathodic protection except where noted inTable 1.1.1. An alternative means of protection such asincreased scantlings may be considered in special areas.

1.4 Internal zones

1.4.1 Ballast tanks shall be protected from corrosion bya combination of anti-corrosion coatings and cathodicprotection.

1.4.2 At the time of new construction, all salt-waterballast tanks shall have an efficient protective coating, epoxyor equivalent, applied in accordance with the manufacturer’srecommendations. The durability of the coatings could affectthe frequency of survey of the tanks and light colouredcoatings would assist in improving the effectiveness ofsubsequent surveys. It is therefore recommended that this betaken into account by those agreeing the specification for thecoatings and their application.

1.4.3 Storage tanks and other compartments requirecorrosion protection where the storage product may becorrosive. Particular attention should be paid to the likelihoodof water in the bottom of hydrocarbon storage tanks and theeffects of bacterially induced corrosion. Suitable protectivemeasures may include coatings, corrosion inhibitors, togetherwith biocides.

1.4.4. In deep draught caisson units and other units withcombined oil storage and ballast tanks which remain fullduring the service life of the unit, special consideration will begiven to the requirement for internal corrosion protection ofthe tanks. In general, the minimum Rule scantlings of tanksas required by Pt 4, Ch 6,7 are to be suitably increased.

2.3.2 Materials or systems (e.g., l iners) are to beevaluated against the service nature of the product to beconveyed. Proprietary specifications and in-service historyare to be submitted as required by LR.

2.3.3 Where internal protection is proposed by use ofcorrosion inhibitors, the properties, compatibility and effecton product conveyed are al l to be documented andsubmitted.

2.4 Cathodic protection systems

2.4.1 Cathodic protection systems are to comply withthe requirements of Chapter 2.

2.4.2 Measurements of potential are to be taken and anydeficiencies corrected by the addition of extra sacrificialanodes.

2.4.3 Measurements are to be taken to confirm thatthere is no over-protection.

2.4.4 Stray currents from ships, other vessels orinstallations in the vicinity are to be evaluated and appropriatemeasures taken.

■ Section 3Plans and information

3.1 Scope

3.1.1 In order that an assessment may be made ofprotection systems full details as outlined in this Section areto be submitted.

3.2 Cathodic protection systems

3.2.1 The following plans and information are to besubmitted:(a) A surface area breakdown for all areas to be protected

including secondary steelwork and detai ls ofappurtenances.

(b) The resistivity of the sea-water.(c) All current densities used for design purposes.(d) The type and location of any reference electrodes and

their methods of attachment.(e) Full details of any coatings used and the areas to which

they are to be applied.(f) Details of any electrical bonding.

3.3 Sacrificial anode systems

3.3.1 In addition to the information required by 3.2 thefollowing plans and information are to be submitted:(a) The design life of the system in years.(b) Anode material and minimum design capacity of anode

material, in Ah/kg.

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General Requirements for Corrosion Control Part 8, Chapter 1Sections 2 & 3

(c) The dimensions of anodes including details of the insertand its location.

(d) The net and gross weight of the anodes, in kg.(e) The means of attachment.(f) Plans showing the location of the anodes.(g) Calculation of anodic resistance, as installed and when

consumed to their design and utilisation factor, in ohms.(h) Closed circuit potential of the anode material, in volts.(j) Details of any computer modelling.(k) The anode design utilisation factor.

3.4 Impressed current systems

3.4.1 In addition to the information required by 3.2, thefollowing plans and information are to be submitted:(a) The anode composition and where applicable the

thickness of the plated surface, consumption and lifedata.

(b) Anode resistance, limiting potential and current output.(c) Details of construction and attachment of anodes and

reference electrodes.(d) Size, shape and composition of any dielectric shields.(e) Diagram of the wiring system used for the impressed

current and monitoring systems including details ofcable sizes, underwater joints, type of insulation andnormal working current in circuits, and the capacity, typeand make of the protected devices.

(f) Details of glands and size of steel conduits.(g) Plans showing the locations of the anodes and

reference electrodes.(h) If the system is to be used in association with a coating

system then a statement is to be supplied by the coating manufacturer that the coating is compatible withthe impressed current cathodic protection system.

3.5 Coating systems

3.5.1 The following plans and information are to besubmitted:(a) Evidence that any primers used will have no deleterious

effect on subsequent welding or on subsequent coatings.(b) Details of the painting specification with regard to:

(i) the generic type of the coating and confirmationof its suitability for the intended environment;

(ii) the methods to be used to prepare the surfacebefore the coating is applied and the standard tobe achieved. Reference should be made toestablished International or National Standards;

(iii) the method of application of the coating; and(iv) the number of coats to be applied and the total

dry film thickness.(c) Details of the areas to be coated.



General Requirements for Corrosion Control Part 8, Chapter 1Section 3

3.5.2 In addition to the information required by 3.5.1 thefollowing may also be required:(a) When a coating contains aluminium and is intended to

be used on decks or in areas where flammable gasesmay accumulate, a statement from an independentlaboratory confirming that appropriate tests have shownthat the coating does not increase the incendivesparking hazard in the area to which it is to be applied.

(b) Where a coating is to be applied in accommodationspaces, machinery spaces and areas of similar fire risk,a statement that the coating is not formulated on anitrocellulose or other highly flammable base and haslow flame spread characteristics (complying to at leastBS476: Part 7: Classification 2 or any other equivalentNational Specification).

3.6 Inhibitors and biocides

3.6.1 Where it is proposed to use inhibitors, biocides, orother chemicals for the protection of storage tanks, fulldetails, including compatibility with each other and evidenceof satisfactory service experience or suitable laboratory testresults or any other data to substantiate the suitability for theintended purpose, are to be submitted for consideration.

1LLOYD’S REGISTER


Part 8, Chapter 2Sections 1 & 2

Section

1 General requirements

2 Sacrificial anodes

3 Impressed current anode systems

4 Fixed potential monitoring systems

5 Cathodic protection in tanks

6 Potential surveys

7 Retrofits

■ Section 1General requirements

1.1 Objective

1.1.1 The cathodic protection system for the externalsubmerged zone is to be designed for a periodcommensurate with the design life of the structure or the dry-docking interval and it should be capable of polarising thesteelwork to a sufficient level in order to minimise corrosion.

1.1.2 This may be achieved using either sacrificialanodes or an impressed current system or a combination ofboth, see 3.2.1.

1.2 Electrical continuity

1.2.1 All parts of the structure should be electricallycontinuous and where considered necessary, appropriatebonding straps should be fitted across such items aspropellers, thrusters, rudders and legs, etc., and the joints ofarticulated structures are to be efficiently completed to theSurveyor’s satisfaction.

1.2.2 Where bonding straps are not fitted, a supplementarycathodic protection system should be considered.

1.2.3 Particular attention to earthing and bonding isrequired in hazardous areas where flammable gases orvapours may be present, see Part 7.To avoid dangerous sparking between metallic parts of struc-tures, potential equalisation is always required for installationsin Zone 1 and may be necessary for installations in Zone 2Areas; this is achieved by connecting all exposed and extra-neous conductive parts to the equipotential bonding system.Notwithstanding this, cathodic protection installations shallnot be connected to the equipotential bonding system unlessthe cathodic protection system is specifically designed for thispurpose. See IEC 61892-7 Section 5.6.3.Cathodically protected metallic parts are live extraneousconductive parts. If located in hazardous areas, they shall beconsidered potentially dangerous (especially if equipped withthe impressed current method) despite their low negativepotential.

Cathodic Protection Systems

No cathodic protection shall be provided for metallic parts inZone 0 unless it is specially designed for this application.See IEC 61892-7 Section 5.6.6.

1.2.4 Consideration should be given to the influence ofany connecting structures, such as risers and pipelines, onthe efficiency of the cathodic protection system. A floatingstructure may be permanently or temporarily connected toanother neighbouring structure. In this situation, therequirements of BS EN 13173 shall be met, including thetaking of measurements to ensure that there are nodeleterious effects of electrical stray current on the protectedstructure.

1.3 Criteria for cathodic protection

1.3.1 Cathodic protection systems shall comply with BSEN 13173 - Cathodic protection for steel offshore floatingstructures or BS EN 12495 - Cathodic protection for fixedsteel offshore structures.

1.3.2 The cathodic protection system is to be capable ofpolarising the steelwork to potentials measured with respectto a silver/silver chloride/sea-water (Ag/AgCl) referenceelectrode to within the following ranges:(a) –0,80 to –1,10 volts for aerobic conditions.(b) –0,9 to –1,10 volts for anaerobic conditions.

1.3.3 Potentials more negative than –1,10 volts Ag/AgClmust be avoided in order to minimise any damage due tohydrogen absorption and reduction in the fatigue life. Forsteel with a tensile strength in excess of 700 N/mm2 themaximum negative potential should be limited to –0,95 volt.But where the steel is prone to hydrogen-assisted crackingthe potential should not be more negative than –0,83 volt(Ag/AgCl reference cell).

1.3.4 High strength fastening materials should beavoided because of the possible effects of hydrogen, and thehardness of such bolting materials should be limited to amaximum of 300 Vickers Diamond Pyramid Number.

1.3.5 The potential for steels with surfaces operatingabove 25°C should be 1 mV more negative for each degreeabove 25°C.

1.3.6 For guidance on the design of sacrificial anodesystems, see Ch 4,2.

■ Section 2Sacrificial anodes

2.1 General

2.1.1 Sacrificial anodes intended for installation onoffshore units are to be manufactured in accordance with therequirements of this Section.


2.1.2 Plans showing anode nominal dimensions,tolerances and fabrication details are to be submitted forapproval prior to manufacture.

2.1.3 Approval for the manufacture of anodes is notrequired although the anodes should preferably be typeapproved in accordance with LR’s List of Type ApprovalEquipment.

2.1.4 The works should have a quality managementsystem certified by a recognised third party certification body.However, alternative arrangements may be acceptedprovided they ensure a consistent quality for the anodes.

2.2 Anode materials

2.2.1 The anode materials are to be approved alloys ofzinc or aluminium with a closed circuit potential of at least–1,00 volt (Ag/AgCl reference electrode). Magnesium-basedanodes may be used for short-term temporary protection ofmaterials not susceptible to hydrogen embrittlement, see also2.13.12. Anode materials and anode designs specified in BSEN 13173 or BS EN 12495 are also permitted.

2.3 Steel insert preparation

2.3.1 The anode material is to be cast around a steelinsert so designed as to retain the anode material even whenit is consumed to its design utilisation factor.

2.3.2 The steel inserts are to have sufficient strength towithstand al l external forces that they may normallyencounter such as wave, wind, ice loading and operatingconditions.

2.3.3 The anodes are to be sufficiently rigid to avoidvibration in the anode support.

2.3.4 The steel inserts are to be of weldable structuralsteel bar, section or pipe with a carbon equivalent not greaterthan 0,45 per cent determined using the following formula.

Carbon equivalent, Ceq = C + + +

Rimming steel is not permitted.

2.3.5 Requirements for welded fabrication and non-destructive testing are to be in accordance with Chapter 13of the Rules for Materials.

2.3.6 The steel insert is to be degreased if necessaryand blast cleaned to a standard equivalent to ISO 8501-1 Sa21/2 with a minimum surface profile of 50 μm. This standardof cleanliness is to be maintained up until the time ofcastings. For zinc anodes, blast cleaning may be followed bygalvanising or by an approved zinc plating process.

Mn6

Cr + Mo + V5

Ni + Cu15


Cathodic Protection SystemsRULES AND REGULATIONS FOR THE CLASSIFICATION OF MOBILE OFFSHORE UNITS, June 2013

2.4 Chemical composition

2.4.1 The chemical composition of the heat is to bedetermined prior to casting. No alloying additions are to bemade following chemical analysis without further analysis. Forheats greater than 1 tonne, a further sample is to be analysedat the end of the cast. All anodes cast are to comply with theapproved specification.

2.5 Conditions of supply

2.5.1 Generally anodes are to be supplied in the as-castcondition although certain aluminium anodes may be heattreated in accordance with the approved specification.

2.5.2 Where heat treatment is carried out, it is to be inproperly constructed furnaces which are eff icientlymaintained and have adequate means for the control andrecording of temperature. The furnace dimensions are to besuch as to allow the whole item to be uniformly heated to thenecessary temperature.

2.6 Anode identification

2.6.1 The manufacturer is to adopt a system ofidentification of the anodes to enable the material to betraced back to its original cast.

2.6.2 The anodes are to be clearly marked with thefollowing:(a) Name or initials of the anode manufacturer.(b) Number and/or initials to identify the batch.(c) Agreed identification mark for the anode material.

2.6.3 Where the anodes are heat treated they are also tobe marked with the appropriate heat treatment batchnumber.

2.7 Anode inspection

2.7.1 All anodes are to be cleaned and adequatelyprepared for inspection. The surfaces are not to behammered, peened or treated in any way which may obscuredefects. However, any flash or other protrusions should beremoved prior to inspection.

2.7.2 Anodes are to be inspected prior to the applicationof any coating which may be applied to the underside of theanode or to the exposed steelwork.

2.7.3 The surface should be free of any significant slagor dross or anything that may be considered detrimental tothe satisfactory performance of the anodes.

2.7.4 Shrinkage depressions should not exceed thesmaller of 10 per cent of the nominal depth of the anode or50 per cent of the depth to the anode insert.

2.10 Bonding and internal defects

2.10.1 I t wil l be necessary for the manufacturer todemonstrate that there is a satisfactory bond between anodematerial and the steel insert and that there are no significantinternal defects. This may be carried out by sectioning of ananode selected at random from the batch or by otherapproved means.

2.10.2 Where sectioning is carried out, at least one anodeor at least 0,5 per cent of each production run is to besectioned transversely at 25 per cent, 33 per cent and 50 percent of the nominal length of the anode or at other agreedlocations for a particular anode design.

2.10.3 The cut surfaces are to be essentially free fromslag or dross.

2.10.4 Small isolated gas holes and porosity may beaccepted, provided their surface area is not greater than two per cent of the section.

2.10.5 No section is to show more than 10 per cent lackof bond between the insert and the anode material.

2.11 Electrochemical testing

2.11.1 Electrochemical performance testing is to becarr ied out by the manufacturer in accordance withpreviously approved procedures designed to demonstratebatch consistency of the as-cast electrochemical properties.

2.12 Certification

2.12.1 The manufacturer is to provide copies of theMaterial Certificate or shipping statement for all acceptableanodes.

2.12.2 The certificate is to include at least the followinginformation:(a) Name of manufacturer.(b) Description of anode, alloy designation or trade name.(c) Cast identification number.(d) Chemical composition.(e) Details of heat treatment where applicable.(f) Results of electrochemical test.(g) Weight data.(h) Purchaser’s name and order number, and the name of

the structure for which the material is intended.

2.12.3 The manufacturer is to confirm that the tests havebeen carried out with satisfactory results in accordance withthe approved specification and the Rules.

2.13 Anode installation

2.13.1 The location and means of attachment of anodesis to be submitted for approval.


Cathodic Protection SystemsRULES AND REGULATIONS FOR THE CLASSIFICATION OF MOBILE OFFSHORE UNITS, June 2013

3LLOYD’S REGISTER

2.7.5 Cracks in the longitudinal direction are notacceptable. Small transverse cracks may be permittedprovided:(a) they are not more than 5 mm in width,(b) they are within the section wholly supported by the steel

insert,(c) they do not extend around more than two faces or 180°

of the anode circumference, and(d) the Surveyor is satisfied that there has been no break-

down in Quality Control procedures.

2.7.6 Cold shuts or surface laps should not exceed adepth of 10 mm or extend over a total length equivalent tomore than three times the width of the anode. All material isto be completely bonded to the bulk material.

2.8 Dimensions

2.8.1 The accuracy and verification of dimensions is theresponsibility of the manufacturer unless otherwise agreed.

2.8.2 The diameter of cylindrical anodes should be within±5 per cent of the nominal diameter.

2.8.3 For long slender anodes the following dimensionsshould apply:(a) Mean length ±3 per cent of nominal length or ±25 mm

whichever is smaller.(b) Mean width ±5 per cent of nominal width.(c) Mean depth ±10 per cent of nominal depth.

2.8.4 The maximum deviation from straightness shouldnot exceed two per cent of the length.

2.8.5 The steel insert should be within ±5 per cent of thenominal position in anode width and length and within 10 percent of the nominal position in depth. Some anodes mayhave the insert close to one surface, in which case a closertolerance may be more appropriate.

2.8.6 Except where previously agreed, the anode insertfixing dimensions are to be within ±1 per cent of the nominaldimensions or 15 mm, whichever is the smaller.

2.8.7 Anode nominal dimensions, tolerances andfabrication details are to be shown on manufacturing plansprepared by the manufacturer and submitted for approval,see Ch 1,3.3.

2.9 Anode weight

2.9.1 Anodes are to be weighed and individual anodesshould be within ±5 per cent of the nominal weight foranodes less than 50 kg or ±3 per cent of the nominal weightfor anodes 50 kg and over.

2.9.2 No negative tolerance is permitted on the totalcontract weight and the positive tolerance should be limitedto two per cent of the nominal contract weight.



Cathodic Protection Systems Part 8, Chapter 2Sections 2 & 3

2.13.2 The anodes are to be attached to the structure insuch a manner that they remain secure throughout theservice life.

2.13.3 Where bracelet anodes are proposed, thetightness of the anodes are not to rely on the anode materialbeing in direct contact with the structure.

2.13.4 The location and attachment of anodes is to takeaccount of the stresses in the members concerned. Anodesare not to be directly attached to the shell plating of main hullcolumns or primary bracings.

2.13.5 The anode supports may be welded directly to thestructure in low stress regions provided they are not attachedin way of butts, seams, nodes or any stress raisers. They arenot to be attached to separate members which are capableof relative movement.

2.13.6 The attachment of all anodes to primary bracingmembers and nodes is to be submitted for approval. Anodesare not to be welded directly to the structure and thesupports are to be welded to small doubler plates which areattached by continuous welds to the structure.

2.13.7 All welding is to be carried out by qualified weldersusing a qualified welding procedure in accordance withChapters 12 and 13 of the Rules for Materials.

2.13.8 The welds are to be examined using magneticparticle inspection or other acceptable means of non-destructive testing in accordance with Chapter 13 of theRules for Materials.

2.13.9 Anodes attached to studs ‘fired’ into the structureare not permitted.

2.13.10 The anodes are to be located on the structure toensure rapid polarisation of highly stressed areas such asnode welds and with due regard to a possible reduction inthrowing power in re-entrant angles.

2.13.11 Anodes should not be located in positions wherethey may be damaged by craft coming alongside.

2.13.12 Magnesium anodes are not to be used in way ofhigher tensile steel or coatings which may be damaged bythe high negative potentials unless suitable dielectric shieldsare fitted, see 2.2.1.

■ Section 3Impressed current anode systems

3.1 General

3.1.1 Impressed current anode materials may be of lead-silver alloy or platinum over such substrates as titanium,niobium, tantalum, or of mixed oxides-activated titanium.Anode materials and anode designs specified in BS EN13173 or BS EN 12495 are also permitted.

3.1.2 The design and installation of electrical equipmentand cables is to be in accordance with the requirements of Pt 6, Ch 2.If hazardous areas are present on the facility, the impressedcurrent cathodic protection system and equipment shallcomply with the requirements of: Pt 6, Ch 2 (in particularSection 5.1.3), Pt 7, Ch 2,8, 9, 10 and 11, IEC 60079 seriesand IEC 60092-502. IEC 60092-502 Clause 5.7 ‘Cathodically protected metallicparts’ states ‘No impressed current cathodic protection shallbe provided for metallic parts in hazardous areas, unless it isspecially designed for this application and acceptable to theappropriate authority’.The insulating elements required for the cathodic protection,for example, insulating elements in pipes and tracks, should ifpossible be located outside the hazardous area. SeeIEC 61892-7 Section 5.6.6.

3.1.3 All equipment is to be suitable for its intendedlocation. Cables to anodes are not to be led through tanksintended for the storage of low flash point oils. Where cablesare led through cofferdams of oil storage units they are to beenclosed in a substantial steel tube of about 10 mmthickness.

3.1.4 The arrangement for glands, where cables passthrough shell boundaries, are to include a small cofferdam.

3.1.5 Cable and insulating material should be resistant tochloride, hydrocarbons and any other chemicals with whichthey may come into contact.

3.1.6 The electrical connection between the anode cableand the anode body is to be watertight and mechanically andelectrically sound.

3.1.7 Where the power is derived from a rectified a.c.source, adequate protection is to be provided to trip thesupply in the event of:(a) a fault between the input or high voltage windings of the

transformer (i.e., main voltage) and the d.c. output of theassociated rectifier; or

(b) the ripple on the rectified d.c. exceeding five per cent.The requirements for transformers and semi-conductor equip-ment are given in Pt 6, Ch 2,9.

3.1.8 Anodes may be installed by mounting in insulatingholders attached directly to the submerged structuralmember, provided the general requirements given in 2.13regarding attachments to the structure are complied with.

3.1.9 Suitable dielectric shields are to be fitted in order toavoid high negative potentials.

3.1.10 A warning light or other warning indicator is to bearranged at the control position from which divers arecontrolled to indicate that the impressed current cathodicprotection system has been switched off when divers are inthe water.

3.2 Protection after launching and during outfitting

3.2.1 Where protection is primarily by an impressedcurrent cathodic protection system, sufficient sacrificialanodes are to be fitted, capable of polarising the criticalregions of the structure from the time of initial immersion untilfull commissioning of the impressed current system.

■ Section 4Fixed potential monitoringsystems

4.1 General

4.1.1 A permanent monitoring system is to be installedon structures protected by an impressed current cathodicprotection system, and, although not essential, such amonitoring system is recommended for use in conjunctionwith sacrificial anodes. Monitoring schemes shall comply withBS EN 13509 – Cathodic protection measurementtechniques.

4.1.2 Zinc or Ag/AgCl reference electrodes should beused. Reference electrode materials and design specified inthe above standard are also permitted.

4.1.3 The location and attachment of the referenceelectrodes is to take account of the stresses in the membersconcerned and they should not be attached in highly stressedareas or in way of butts, seams, nodes or any stress raisers.

4.1.4 The location of the reference electrodes should besuch as to enable the performance of the cathodic protectionsystem to be adequately monitored.

4.1.5 The reference electrodes may be connected to thetopside display and control equipment by suitable cabling orby any other agreed means.

4.1.6 Provision is to be made for the regular recording atan agreed interval of the potential of the steelwork and logsheets are to be made available for inspection when requiredby LR Surveyors.



Cathodic Protection Systems Part 8, Chapter 2Sections 3, 4 & 5

■ Section 5Cathodic protection in tanks

5.1 General

5.1.1 Impressed current cathodic protection systems arenot to be fitted in any tank.

5.2 Sacrificial anodes

5.2.1 Particular attention is to be given to the locations ofanodes in tanks that can contain explosive or otherinflammable vapour, both in relation to the structuralarrangements and openings of the tanks.

5.2.2 Aluminium and aluminium al loy anodes arepermitted in tanks that may contain explosive or flammablevapour, or in ballast tanks adjacent to tanks that may containexplosive or flammable vapour, but only at locations wherethe potential energy of the anode does not exceed 275 J (28kgfm). The weight of the anode is to be taken as the weightat the time of installation, including any inserts and fittingdevices. The height is to be taken as the distance from thebottom of the tank to the centre of the anode, but exceptionto this may be given where the anodes are located on widehorizontal surfaces from which they cannot fall.

5.2.3 Aluminium anodes are not to be located undertank hatches or other openings unless protected by adjacentstructure.

5.2.4 Magnesium or magnesium al loy anodes arepermitted only in tanks intended solely for water ballast, inwhich case adequate venting must be provided.

5.2.5 Anodes fitted internally should preferably beattached to stiffeners, or aligned in way of stiffeners on planebulkhead plating. Where they are welded to assymetricalstiffeners, they are to be connected to the web with thewelding at least 25 mm away from the edge of the web.

5.2.6 In the case of stiffeners or girders with symmetricalface plates, the connection may be made to the web or tothe centreline of the mild steel face plate but well clear of thefree edges. Where higher tensile steel face plates are fittedthe anodes are to be attached to the webs.

5.2.7 Anodes are not to be attached directly to the shellplating of main hulls, columns or primary bracings.

5.2.8 For guidance on the design of sacrificial anodesystems in tanks, see Ch 4,2.

■ Section 6Potential surveys

6.1 General

6.1.1 Potential surveys of the external submerged zonesare to be carried out at agreed intervals, see also Pt 1, Ch 3.

6.1.2 Should the results of any potential surveymeasured with respect to a Ag/AgCl reference cell indicatevalues more positive than –0,8 volt for aerobic conditions or–0,9 volt for anaerobic conditions then remedial action is tobe carried out at the earliest opportunity.

■ Section 7Retrofits

7.1 General

7.1.1 Where it is proposed to fit additional anodes orreplace existing ones then full details are to be submitted forconsideration.

7.1.2 Where it is necessary to weld anodes to thestructure then only approved welding procedures andconsumables are to be used in accordance with Chapters 12and 13 of the Rules for Materials.



Cathodic Protection Systems Part 8, Chapter 2Sections 6 & 7

Section

1 General requirements

2 Prefabrication primers

■ Section 1General requirements

1.1 General

1.1.1 The painting specification is to be submitted forapproval, see Ch 1,3.5.1.

1.1.2 Paints, varnishes and similar preparations havingnitrocellulose or other highly flammable base are not to beused in accommodation or machinery spaces or in otherareas with an equal or higher fire-risk.

1.1.3 Where a coating is to be applied in accommodationspaces and areas of similar fire-risk, the coating is to have lowflame spread characteristics, see Ch 1,3.5.2(b).

1.1.4 Paints or other similar coatings containingaluminium should not be used in positions where flammablevapours may accumulate, unless it has been shown byappropriate tests that the paint to be used does not increasethe incendive sparking hazard.

1.1.5 Any sheathing or composition to protect decks isto be applied in such a manner that corrosion will not occurunseen beneath the covering.

1.1.6 Deck coatings or coverings used on decks formingthe crown of spaces with a high fire-risk (such as helidecks,machinery and accommodation spaces) or which are withinaccommodation spaces, control rooms, emergency escaperoutes, etc., are to be of a type which will not readily ignite,see Ch 1,3.5.2(b).

1.1.7 Paints or other coatings are to be suitable for theintended purpose in the locations where they are to be used.

1.1.8 Coatings are to be applied to blast cleanedsurfaces prepared to at least an equivalent of ISO 8501-1 Sa 21/2. All resulting dust is to be removed from the surfaceprior to the application of any paint.

1.1.9 The selection, application and maintenance ofcoatings for dedicated sea-water ballast tanks (including pre-load tanks on self-elevating units), double-side skin spaces,etc., shall also comply with IMO Resolution MSC.215(82),Performance Standards for Protective Coatings. Al ldedicated sea-water ballast tanks and double-side skinspaces are to comply with all of the requirements of theResolution.

1.1.10 Maintenance of the protective coating systemsshall be included in the unit's overall maintenance scheme.

1LLOYD’S REGISTER



Coating and Paint Systems

1.1.11 The paint (and/or primer) used on the inner hull ofsome LNG containment systems (particularly membrane type)requires the use of a suitable paint system to provide adhesion of the containment system (via a curing mastic) tothe inner hull, in accordance with the designer's specification,as approved by LR.

■ Section 2Prefabrication primers

2.1 General

2.1.1 Where a primer is used to coat steel after surfacepreparation and prior to fabrication, the composition of thecoating is to be such that it will have no significant deleteriouseffect on subsequent welding work and that it is compatiblewith the paints or other coatings subsequently applied.

2.1.2 To determine the influence of the primer coating onthe characteristics of welds, tests are to be made as detailedin 2.1.3 to 2.1.5. See LR’s List of Paint Resins, Reinforcementsand Associated Materials.

2.1.3 Three butt weld assemblies are to be tested usingplate material 20 to 25 mm thick. A vee preparation is to beused and prior to welding, the surfaces and edges are to betreated as follows:(a) Assembly 1 – Coated in accordance with the manufac-

turer’s instructions.(b) Assembly 2 – Coated to a thickness approximately twice

the manufacturer’s instructions.(c) Assembly 3 – Uncoated.

2.1.4 Tests as follows are to be taken from each testassembly:(a) Radiographs. These are to have a sensitivity of better

than two per cent of the plate thickness under examina-tion, as shown by an image quality indicator.

(b) Photo-macrographs. These may be of actual size andare to be taken from near each end and from the centreof the weld.

(c) Face and reverse bend test. The test specimens areto be bent by pressure or hammer blows round a formerof diameter equal to three times the plate thickness.

(d) Impact tests. Tests are to be carried out, at ambienttemperature, on three Charpy V-notch test specimensprepared in accordance with the requirements of the Rules for Materials. The specimens are to benotched at the centreline of the weld, perpendicular tothe plate surface.

2.1.5 The tests are to be carried out in the presence ofan LR Surveyor or by an independent laboratory specialisingin such work. A copy of the test report is to be submitted,together with radiographs and macrographs.

1.2.2 The type of anode selected must be of sufficientmass with appropriate dimensions to ensure an adequatecurrent output throughout its design life.

1.2.3 The current output of the anode should becalculated using the following formula:

Ia =

whereIa = current output of anode, in amps

ΔV = driving potential, i.e., the difference between thepotential of the anode and the protected steelpotential, in volts

Ra = anodic resistance, in ohms.

1.2.4 The potential of the polarised steel should be takenas –0,8 volt (Ag/AgCl/sea-water reference electrode),although a more negative value may be used for thoselocations where sulphate reducing bacteria may be active,see Ch 2,1.3.

ΔVRa

Section

1 External steel protection

2 Protection of tanks

3 Surface preparation, application andmaintenance of coatings

■ Section 1External steel protection

1.1 Current density

1.1.1 The current density required for the externalprotection of the submerged zone of mobile offshore units willdepend on many factors such as water temperature, oxygencontent, resistivity of the water, suspended solids, watercurrents and biological activity.

1.1.2 Design current density values are given in Table 4.1.1 for guidance purposes, but the values to be usedshould be based on the environmental conditions prevailingat the site. It should be noted that these values may beappreciably different from values actually measured onsteelwork in the vicinity of the site.

1.1.3 In order to minimise pitting, the cathodic protectionsystem must be capable of rapidly polarising the steelworkand it is recommended that the initial current density shouldbe appreciably higher than the values given in Table 4.1.1.

1.1.4 Although a lower current density may be capableof maintaining polarisation, the cathodic protection systemmust be capable of re-polarising the steelwork rapidly afterstorms even when the anodes are well wasted.

1.1.5 Where suitable high resistance coatings are usedconsideration will be given to use of current densities lowerthan those given in Table 4.1.1.

1.1.6 Coatings will deteriorate with time and there islikely to be mechanical damage. In order to take this intoaccount at the design stage, appropriate coating breakdownfactors should be applied and these are to be based on thepercentages given in 1.1.7.

1.1.7 For an epoxy or coal tar epoxy coating applied togive a dry film thickness of 250 to 500 microns, an initialcoating breakdown of one to two per cent for the submergedzone and an annual degradation rate of one to three per centper year should be used.

1.2 Sacrificial anode systems

1.2.1 The following indicates an acceptable method fordetermining the number and weight of anodes to achieve therequired level of polarisation on most structures. Othermethods may be accepted provided they give reasonableequivalence.

Location Current density mA/m2

Cook inlet 400

North Sea (Northern) Above 62°N 13055°N to 62°N 120

US (West Coast) 100

North Sea (Southern) Below 55°N 90Africa 90Brazil 90China 90India 90Mediterranean 90

Australia (Western) 80Gulf 80Gulf of Mexico 80

Mud – Most locations 20

Drainage per well 5A

NOTES1. The current density values are intended for guidance

purposes in the design of sacrificial anode systems using themethods as outlined in this Chapter. However, other valuesmay be accepted provided that there is adequate justification.

2. For impressed current cathodic protection systems, currentdensities higher than the values given in the Table may benecessary but this will depend on the type and location of theanodes.

1LLOYD’S REGISTER



Guidance Notes on Design of Cathodic ProtectionSystems and Coatings

Table 4.1.1 Current density values for designpurposes

In order to optimise the performance and efficiency of theanodes, the values for both equations should be similar.

1.2.9 It is to be shown by appropriate calculations thatthe system is capable of polarising the structure initially andalso when the anodes are consumed to their designutilisation factor.

1.2.10 It should be assumed that, at the end of its life, theanode length has been reduced by 10 per cent and that theremaining material is evenly distributed over the steel insert.

1.3 Location of anodes

1.3.1 Having determined the number and size of theanodes to comply with the recommended nominal currentdensity and the required l i fe, the anodes should bedistributed over the steel surfaces according to the requiredlevel of protection on the steelwork but with some emphasison the area adjacent to joints, etc. The anodes associatedwith the structure likely to become buried, such as footings,etc., should be positioned on the steelwork immediatelyabove the mudline.

■ Section 2Protection of tanks

2.1 Anode resistance

2.1.1 Where large stand-off anodes are used for theprotection of tanks, the resistance should be determinedusing the formula as given in 1.2.5(a).

2.1.2 Where flat plate anodes are used, their resistanceis to be determined from the following formula:

R =

however, if the flat plate anodes are close to the structure orpainted on the lower face then the resistance is to bedetermined using:

R =

where ρ is as defined in 1.2.5lm = mean length of anode sides, in cm.

2.2 Current density

2.2.1 The design current density to be used forpermanent water ballast tanks should be based on a minimumvalue of 110 mA/m2 but this may have to be increased to atleast 130 mA/m2 if hot oil is stored on the opposite side of thebulkhead. For a coating allowance, see 1.1.6.

2.2.2 Uncoated tanks used for the storage of crude oil atambient temperature alternating with water ballast are tohave a minimum current density of 90 mA/m2; however, thisshould be increased for higher temperatures.

ρ2lm

ρ4lm





1.2.5 The resistance of an anode, R, with small cross-section in relation to its length and with a stand-off distancefrom the bottom of the anode surface to the structure of notless than 300 mm, is given by:

(a) R = ln – 1( )where

ρ = resistivity of sea-water, in ohm.cmla = length of anode, in cmr = equivalent radius of anode, in cm

ln = loge

r =

a = cross-sectional area of the anode, in cm2

(b) When bracelet anodes are used, the resistance may bedetermined using:

R =

whereAe = the exposed surface area of the anode, in cm2.

1.2.6 In order to achieve a suitable anode distribution ontubular structures, each appropriate section of steelworkshould be considered separately.

1.2.7 The current required for each section may bedetermined from the following:

Ir =

whereIr = current, in ampsA = area of steelwork, in m2

I = current density, in mA/m2.

1.2.8 The number of anodes, N, required should satisfyboth of the following:

(a) N =

(b) N =

whereIr = current, in ampsIa = current output of anode, in amps

Wr = net weight of anode material, in kgWa = net weight of individual anode, in kg

Wr =

Y = life of structure or appropriate dry-docking intervalin years, see Ch 2,1.1.1

C = practical electrochemical capacity of the alloy, inAh/kg

U = utilisation factor, i.e., proportion of net weightconsumed at end of anode life. For fully supportedtubular insertsU = 0,9U = 0,8 for bracelet (half shell)U = 0,75 for bracelet (segmental type).

Ir Y 8760CU

Wr

Wa

Ir

Ia

A I1000

0,315ρ

Ae

aπ

4lar

ρ2π la

2.2.3 Unless otherwise agreed the resistivity of the waterin ballast tanks should be assumed to be 25 ohm.cm.

2.3 Anode distribution

2.3.1 Once the number and size of anodes have beendetermined, they are to be distributed as follows:(a) Ballast only tanks: evenly over all the steelwork.(b) Crude oil/ballast tanks: evenly but with some emphasis

on horizontal surfaces in proportion to the area of thesesurfaces.

2.4 Reference electrodes

2.4.1 Variations between electrodes of ±30 mV havebeen reported for zinc/sea-water reference electrodes and ±5 mV for silver/silver chloride/sea-water electrodes butunless a high degree of stability is required either electrodemay be used for comparison purposes. The zinc/sea-waterelectrode may be taken as approximately 1,03 V morepositive than the silver/silver chloride/sea-water electrode.

■ Section 3Surface preparation, applicationand maintenance of coatings

3.1 Application

3.1.1 These notes have been prepared to give generalguidance on those aspects of surface preparation andapplication and the subsequent maintenance of coatings thatshould be taken into account by those agreeing the coatingspecification.

3.1.2 These notes are not intended to be used forcontractual purposes or as representing the minimumrequirements as these are a matter for the interested partiesto agree.

3.1.3 The guidelines do not intend to replace thetechnical aspects of any specific coating system, to becovered by the product and job specifications, which are atthe discretion and under the responsibility of Owners,manufacturers and construction yards.

3.1.4 Owners should select and maintain a corrosionprotection system to ensure an adequate level of protection.

3.1.5 Coating manufacturers should give evidence of thequality of the product and its ability to satisfy the Owner’srequirements.





3.1.6 Coating manufacturers should have products withdocumented service performance records. Coatingsrecognised by Lloyd’s Register (hereinafter referred to as LR)are considered as satisfying this requirement, see list of LRapproved PSPC compliant coatings on CDLive. Where it isproposed to use coatings without satisfactory performancerecords, coating selection should be supported byappropriate laboratory test data carried out in accordancewith recognised Standards (e.g., ISO 20340) in order toverify their suitability for the intended service condition.

3.1.7 The construction yard and/or its subcontractorsshould provide clear evidence of their experience in coatingapplication. The coating Standard, job specif ication,inspection, maintenance and repair criteria should be agreedby the construction yard and/or its subcontractors, Ownerand manufacturer.

3.2 General requirements

3.2.1 At present, hard coatings are the most commonlyused for new construction.

3.2.2 As their effectiveness and life are influenced byseveral factors it is essential that the manufacturer’s technicalproduct data sheet and job specifications are followed.

3.2.3 Multi-coat applications with coating layers ofcontrasting colours are recommended. The last coating layerin ballast tanks should be of a light colour in order to facilitatein-service inspections.

3.2.4 Measures should be adopted at the design stageto reduce scallops, using rolled profiles (provided this doesnot adversely affect fatigue performance) or three-passgrinding where possible, and ensuring that the structuralconfiguration permits easy access for personnel andequipment and facilitates cleaning, draining and drying oftanks.

3.2.5 Where a coating is supplemented by cathodicprotection, the coating must be compatible with the cathodicprotection system.

3.3 Coating selection

3.3.1 In the selection of a coating for use in ballast tanksthe following should be taken into account:• Service conditions and planned maintenance.• Frequency of ballasting/deballasting operations.• Location of tank relative to heated surfaces.• Required surface condition.• Required surface cleanliness and dryness.• Whether cathodic protection is to be fitted.• Requirements of IMO Resolution MSC.215(82),

Performance Standards for Protective Coatings.





3.3.2 Coatings intended for use underneath solar heateddecks or on bulkheads forming boundaries of heated cargoor fuel oil spaces should be able to withstand constant orrepeated heating without becoming brittle or subject to a lossof adhesion. Due regard should be given to the possible pooredge covering properties of hard coatings with a high solidcontent.

3.4 Initial preparation

3.4.1 Tubular scaffolding should not mask surfaces to becoated. Where contact is necessary, spade ends should beused.

3.4.2 Staging should afford easy and safe access to allsurfaces to be coated.

3.4.3 Tubular scaffolding should be plugged or cappedprior to blast cleaning to prevent the ingress of grit and dirt.

3.4.4 Staging should be designed to allow thoroughcleaning.

3.4.5 Staging layout should be such that ventilation isnot rendered ineffective.

3.4.6 Care should be taken when removing scaffolding inorder to keep damages to a minimum. Any damages shouldbe repaired in accordance with the paint manufacturer’srecommendations.

3.4.7 External surfaces of pipelines which will be coveredby pipe clips should be blasted and coated prior to fitting.

3.4.8 Pipeline exteriors should be blasted and coated atthe same time as the lowermost parts of the tank. Any over-blast or over-spray affecting surrounding areas should berepaired.

3.4.9 Lighting during blasting and painting must beelectrically safe and provide suitable illumination for all work.

3.4.10 Powerful spotl ighting must be provided forinspection work.

3.4.11 Adequate ventilation during application and dryingof all paints is essential.

3.4.12 Flexible ventilation trunking should be used to allowthe point of extraction to be reasonably close to theapplicator.

3.4.13 The ventilation system and trunking should be soarranged that ‘dead spaces’ do not exist. Ventilation must bemaintained during application and continued whilst solvent isreleased from the paint film during drying.

3.4.14 The ventilation system must prevent the vapourconcentration exceeding 10 per cent of the lower explosivelimit (or less than this if required by Regulations).

3.4.15 For coatings containing organic solvents, duringthe drying period an adequate number of air changes mustbe effected, depending on the type of coating being used.This ventilation should be maintained for at least 48 hoursafter the application of the system.

3.5 Surface preparation

3.5.1 Good surface preparation is one of the mostimportant factors governing the performance of a coating. Ifcontaminants such as oil, grease, dirt and chemicals are notremoved from the surface they will prevent the adhesion ofthe coatings. Soluble salts on the surface may lead toosmotic blistering in the coating. Rust left on the surface willloosen, resulting in a loss of adhesion and if mill scale is notcompletely removed it will cause accelerated corrosion.

3.5.2 Good surface preparation roughens the surfaceand enables a good mechanical bond to be achieved.

3.5.3 The surface preparation for coatings should be inaccordance with the coating manufacturer’s specification. Alloil and grease is to be removed from the surface with suitablesolvents prior to blast cleaning.

3.5.4 All welded areas and attachments are to be givenspecial attention for the removal of welding flux and weldspatter. Sharp edges should be smoothed and any surfaceirregularities, including rough weld caps and slag, togetherwith rough edges, fins and burrs, should be mechanicallytreated using power wire brushing, grinding or chipping, asappropriate.

3.5.5 Only dry abrasive blast cleaning techniques are tobe employed and the conditions under which blast cleaningis carried out should preclude condensation. In this respectblasting should not normally be carried out under any of thefollowing conditions:(a) The surface temperature of the steel is less than 3°C

above the dew point.(b) The relative humidity is above 85 per cent.(c) When there is any possibility that the surface of the steel

is wetted before the first coat is applied.

3.5.6 The compressed air supply used for blasting is tobe free of water and oil and adequate separators and trapsare to be provided. Prior to using compressed air, the qualityof the air downstream of the separator should be tested byblowing the air on to a clean white blotter or cloth for twominutes to check for any contamination, oil or moisture. Thistest should be performed at the beginning and end of eachshift and at not less than four-hour intervals. The test alsoshould be made after any interruption of the air compressoroperation. The air should be used only if the test indicates novisible contamination, oil or moisture. If contaminants areevident, the equipment deficiencies should be corrected andthe air stream should be retested.

3.5.7 Accumulations of oil and moisture are to be removedby regular purging of the system. Air compressors should notbe allowed to work at temperatures in excess of 115°C.

3.5.8 The abrasive used for blasting should be dry andfree from dirt, oil or grease and suitable for producing thestandard of cleanliness and profile specified. Additionally anyorganic or water soluble matter should be a maximum of0,05 per cent by weight.

3.5.9 I ron or steel abrasives are not normallyrecommended for in-situ open blasting. If used, careful andthorough cleaning must be carried out to remove all traces ofabrasive from the surface.

3.5.10 Although not recommended, recycled grit may beused providing it is correctly graded, dry and free from dirt,oil, grease, organic or water soluble matter. Recirculated gritshould be checked for the presence of oil by immersing asample in water and examining for oil flotation. Tests shouldbe made at the start of blasting, and every four hours untilthe end of blasting. If compressor operations are interruptedfor longer than five minutes, the air supply should be retestedprior to use. If oil is evident, the contaminated abrasiveshould be cleaned or replaced. All surfaces blasted since thelast successful test should be completely reblasted.

3.5.11 The amplitude of blast profile from trough toadjacent peak depends upon the type of coating to beapplied. The amplitude should be not more than 50 μm forcoatings of the zinc silicate type and not more than 75 μm ofthe high build coatings. A procedure to measure the surfaceprofile of abrasive blast cleaned steel on site is given in NACERP 0287.87. The technique utilises a tape that replicates thesurface profile and the thickness of the tape is then measuredusing a micrometer.

3.5.12 Generally, where the final dry fi lm coating is 125 μm or less, i t should be in accordance with ISO 8501-1Sa3 or an equivalent standard, i.e., the surface isto be cleaned to white metal such that a uniformly metallic,slightly roughened surface is produced, completely free fromforeign matter. Shadowed areas may only be accepted if theyare due to differences in the structure of the steel or to a blastcleaning pattern. It should be noted that the possibility ofachieving a uniform standard of Sa3 throughout the tanks isremote and a more real ist ic achievement would besomewhere between Sa21/2 and Sa3.

3.5.13 The standard of surface preparation for themajority of the coatings is to be at least in accordance withISO 8501-1 Sa21/2 or an equivalent standard, i.e., the blastcleaned surface is to consist of at least 95 per cent cleanedbare steel and not more than 10 per cent of any single 25 mm square of the surface area is to be discoloured byareas of rust stain or mill scale residues.

3.5.14 In cases where the substrate is corroded or pittedit may be necessary to fresh water-wash the areas afterabrasive blasting, then reblast, in order to ensure completeremoval of soluble corrosion products.

3.5.15 No acid washes or cleaning solutions are to beused on metal surfaces after they have been blasted. Thisincludes inhibitive washes intended to prevent rusting.





3.5.16 Any sub-standard areas should be identified andmust be brought up to the specified standard. Grease freechalk should be used to identify sub-standard areas and itshould be removed after the sub-standard areas have beenrectified.

3.5.17 After blast cleaning, all surfaces are to be freed ofabrasive and dust by:(a) blowing with dry compressed air; or(b) vacuum cleaning.To confirm that the blasted surfaces are sufficiently dust-freeto al low successful coating, they shal l be tested inaccordance with ISO 8502-3 or an equivalent standard, to anextent and with acceptance criteria defined by the coatingmanufacturer.

3.5.18 Where surfaces have been coated with aprefabrication primer, they are to be similarly cleaned beforeapplication of the coatings. If there is extensive breakdown ofthe primer, the surface affected is to be reblasted.

3.5.19 Since fresh blast cleaned surfaces are subject toimmediate corrosion, particularly in areas of high humidity orin a marine atmosphere, it is essential that all cleanedsurfaces are coated within four hours of cleaning. In any casethe surfaces are to be coated prior to the end of the workingday and before any visible rusting occurs, unless humiditycan be maintained overnight at a low level.

3.5.20 Checks on the steel surface cleanliness androughness profile should be carried out at the end of thesurface preparation and before the application of the primerand in accordance with the manufacturer’s specifications.

3.5.21 Where abrasive blast cleaning is demonstrated tobe impracticable at specific locations, alternative mechanicalsurface cleaning techniques may be applied. In suchcircumstances, the surface cleanl iness should be inaccordance with ISO 8501-1 St3 or an equivalent standardand particular attention must be given to ensuring that thesurface profi le and soluble salt concentrations are inaccordance with the coating manufacturer’s specification.

3.6 Coating requirements

3.6.1 The composition of any primer used to coat steelafter surface preparation and prior to fabrication must besuch that it will have no significant deleterious effect onsubsequent welding work.

3.6.2 The coatings are to be compatible with anyprefabrication primer used and suitable for the intendedapplication.

3.6.3 Materials are to be delivered in original containerswith labels intact and the seals unbroken. Containers are tobe kept in a safe, clean, well ventilated storage space.

3.6.4 Before use, coatings are to remain unopened inthe original containers. Covers are to be kept on openedcoating containers when not in use. Coatings are to be usedin strict date order and not stored longer than six monthsunless permitted by the paint manufacturer.





3.6.5 The coating manufacturer’s instructions are to befollowed for storage, mixing, thinning and application ofcoatings along with the recommended time limit betweencoats and health and safety precautions. Only the thinnersrecommended by the manufacturer are to be used to thincoatings.

3.6.6 Coatings are to be mixed immediately prior toapplication. All coating materials are to be thoroughly mixedto give a homogeneous liquid without pigment settling outduring application. Mechanical mixers are to be used for allcoating mixing operations. The entire contents of the coatingcontainer are to be used in mixing to ensure the correctproportion of the base coat and pigment.

3.6.7 Coating material which has livered, discoloured,gelled, or otherwise deteriorated during storage is not to beused. Thixotropic materials which may be stirred to obtainnormal consistency may be acceptable.

3.6.8 For coating materials requiring the addition of acatalyst, the pot life under application conditions is to beclearly stated on the label, and this pot life is not to beexceeded. When the pot life limit is reached, the spray pot isto be emptied, material discarded, and new material mixed.

3.6.9 Specification and data sheets on the coatingmaterials are to be available at all times.

3.7 Coating application

3.7.1 The application of a coating should be a wellplanned activity, integrated in the yard’s construction plansand carried out under controlled conditions to avoid conflictswith other yard operations.

3.7.2 Coatings should be applied in controlled humidityand surface temperature conditions to surfaces which havebeen blast cleaned to the coating manufacturer’srecommended standard and immediately coated with acompatible prefabrication primer or applied after blastcleaning if this is permitted by the specification.

3.7.3 Areas where the prefabrication primer is damagedin any way may be touched up in accordance with themanufacturer’s specifications.

3.7.4 Each coating layer should have the maximum/minimum thicknesses in accordance with the coatingspecification. Generally, an 80/20 practice may be adoptedwhich means that 80 per cent of all thickness measurementsshould be greater than or equal to the nominal dry filmthickness (DFT), and none of the remaining 20 per cent isbelow 80 per cent of the DFT. In the case of tanks (andespecially ballast tanks), consideration should be given toadopting a 90/10 practice, which means that 90 per cent ofall thickness measurements should be greater than or equalto the nominal DFT, and none of the remaining 10 per cent isbelow 90 per cent of the DFT.

3.7.5 All paints should be applied by airless spray exceptfor stripe coats where brushes or, if recommended by thecoating manufacturer as a preferred option, rollers may beused.

3.7.6 Conventional spray may be used for the sprayingof zinc silicate tank coatings.

3.7.7 Efficient mechanical stirrers for the correct mixingof paint should be used.

3.7.8 The spray equipment should comply with the paintmanufacturer’s recommendations. Adequate moisture trapsshould be fitted where appropriate so that water or oil can becontinuously bled off from the air supply.

3.7.9 Lines and pots are to be thoroughly cleaned beforeusing different materials.

3.7.10 With the possible exception of wet blast primersand moisture cured products, coatings should not be appliedto damp surfaces and the specification should stipulate thatcoatings are not to be applied to surfaces where the relativehumidity of the atmosphere is such that:(a) condensation is present on the surface; or(b) it will affect the application or drying of the coating.

3.7.11 No coating is to be applied if the temperature isbelow that specified by the coating manufacturer and, ingeneral, the metal surface temperature should be at least 3°Cabove the dew point before painting is commenced. Thetemperature, dew point, and relative humidity should bedetermined with a sling psychrometer. Suitable proceduresare given in ASTM E337. Readings are required at the start ofwork and every four hours.

3.8 Coating thickness

3.8.1 Generally, high duty coatings should be applied inat least two coats, however, ‘wet-on-wet’ application may beconsidered as a two coat system provided:(a) there is a time interval between the coats; and(b) there is adequate attention to difficult areas such as

welds, edges and any other changes in section and thatthe recommended coating thickness is achieved over allthe structure.

3.8.2 Where coatings other than the zinc silicate typehave been accepted as a single coat application then allwelds, edges and any other changes in section may require astripe coat to be applied.

3.8.3 Successive coats should preferably be of differentcolours or with a significant shade variation to give contrastand ensure complete coverage of the surface, see also 3.2.3.

3.8.4 All surfaces are to receive the full thicknessspecified as a minimum. Areas with inadequate coatingthickness should receive additional compatible coats until thespecified coating thickness is attained. Coatings are to bebrushed on to all areas which cannot be properly coated byspray.

3.8.5 Care should be taken to avoid an excessivecoating thickness as this could lead to seriousconsequences, such as solvent and thinner retention, filmcracks, gas pockets, etc. Wet coating thickness should bechecked during application.

3.8.6 Each coating layer should be adequately curedbefore application of the next coat, in accordance withcoating manufacturer’s recommendations. Intermediate coatsmust not be contaminated with dirt, grease, dust, salt, overspray, etc. Job specifications should include the dry-to-re-coat times given by the manufacturer.

3.8.7 Thinners should be limited to those types andquantities recommended by the manufacturer.

3.9 Inspection and repair

3.9.1 Wet film thickness checks should be made as thework progresses, using appropriate thickness gauges.

3.9.2 Dry film thickness determinations should be carriedout on all significant areas using suitable gauges. (The simplepull-off type gauges are not considered sufficiently accuratefor this work).

3.9.3 The full number of coats specified should beapplied and the specified film thickness achieved.

3.9.4 All coatings should be free of pin holes, voids,bubbles and other ‘holidays’. Holiday testing should becarried out using a suitable ‘holiday detector’ set at anappropriate voltage for the coating system.

3.9.5 Any defective areas are to be marked up andappropriate repairs effected. All such repairs are to berechecked for any uncoated areas.

3.9.6 A daily log of the following is to be prepared:(a) Air and steel temperatures.(b) Relative humidity.(c) Paint thicknesses measured.(d) Extent of coating.(e) Any other relevant information.

3.9.7 Damage to coatings is to be repaired by cleaningback to a sound base, recoating the affected areas asrequired in the specification and feathering to tie withadjoining areas. Prior to the application of any coating, alldamage to previous coats is to have been repaired.

3.9.8 The area to be cleaned is to be carried over ontothe firm surrounding coating for not less than 25 mm allround the edges. These are to be feathered by a suitablemethod to ensure continuity of the subsequent repaircoating.

3.9.9 Areas with inadequate coating thickness are to bethoroughly cleaned and, if necessary, abraded and whereapplicable additional coats applied until the specification iscomplied with. These additional coats are to blend in with thefinal coating at adjoining areas.





3.9.10 Where welding has to take place on coated areas,unless they are approved prefabrication primers, the coatingsare to be removed locally and the surface after welding is tobe prepared and recoated in accordance with therecommended procedures.

3.9.11 When dry film thicknesses are less than thosespecified, additional coats are to be applied as necessary toachieve specified thickness. For inorganic zinc silicate, areasof low film thickness should not be repaired by additionalcoats. In this case the coating is to be removed and the areare-coated to the specified thickness.

3.10 Safety aspects

3.10.1 It should be noted that paints, coatings andthinners are potentially hazardous from health and safetypoints of view if not strictly controlled in accordance withgood practice. Detailed advice on the safe working practicesto be fol lowed should be obtained from the relevantgovernmental safety agencies.

3.11 Maintenance

3.11.1 Maintenance of the corrosion protection systemshould be included in the overall maintenance schemes.

3.11.2 The most efficient way to preserve the corrosionprotection system is to repair any defects found during the in-service inspections (e.g., spot rusting, local breakdown atedges of stiffeners, etc.).

3.11.3 During maintenance hard coatings should berestored using the type originally applied or by a compatiblehard coating recognised by LR. The compatibility of coatingsshould normally be agreed by the paint manufacturer, and thecoatings should be appl ied in accordance with themanufacturer’s requirements.

3.11.4 The restoration of the damaged hard coatings bycompatible coatings not recognised by LR will be accepted,provided such coatings are applied and maintained inaccordance with the manufacturer’s specification. Details ofsuch coatings are to be reported for information and recordpurposes.

3.11.5 If the required conditions for the application of theoriginal coating are not achievable, a coating more tolerant ofa lower qual ity of surface treatment, humidity andtemperature conditions may be considered, provided that it isappl ied and maintained in accordance with themanufacturer’s specifications.

3.11.6 Currently there are numerous non-oxidising softcoatings which are being marketed for the purpose ofrepairing hard coatings. Proposals to use this type of coating,including the manufacturer’s confirmation of theircompatibility with the existing coatings, are to be referred forconsideration.





3.11.7 It should be noted that soft coatings are, ingeneral, not suitable for use in association with cathodicprotection.

Document1 12/04/02 15:23 Page 1

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