bki vol2_section38

8/14/2019 BKI Vol2_Section38

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Section 38 - Corrosion Protection D 38 - 1

Section 38

Corrosion Protection

A. General Instructions

1. Field of Application

1.1 This section deals with the corrosion protection

measures specified by BKI with respect to seagoing steel

ships. Details of the documentation necessary for setting

up the corrosion protection system are laid down herein

(planning, execution, supervision).

1.2 Corrosion protection for other types of ship as well

as other kinds of material, e.g. aluminium, is to be agreed

separately in consultation with BKI.

1.3 Requirements with respect to the contractors

executing the work and the quality control are subject to

the conditions laid down in Section 1, N.1.1 and 1.2.

1.4 Any restrictions which may be in force concerning

the applicability of certain corrosion protection systems

for special types of vessels (e.g. tankers and bulk carriers)

must be observed. BKI must be consulted when clarifying

such issues.

1.5 Supplementary to this section, Regulations forCorrosion Protection and Coating Systems contain further

comments and recommendations for the selection of suitable

corrosion protection systems, as well as their professional

planning and execution.

B. Shop Primers

1. General

1.1 As a rule, shop primers are used to provide protectionfor the steel parts during storage, transport and work

processes in the manufacturing company until such time

as further surface preparation is carried out and the

subsequent coatings for corrosion protection are applied.

1.2 Customarily, coatings with a thickness of 15 m

to 20 m are applied.

Under normal yard conditions, this should provide corrosion

protection for a period of approx. 6 months.

1.3 The coating must be of good resistance to withstand

the mechanical stresses incurred during the subsequentworking of the steel material in the shipbuilding process.

1.4 Flame-cutting and welding speed are not to be

unduly impaired. It must be ensured that welding with all

welding processes customary in the building of ships

can be conducted without impermissibly impairing the

quality of the weld seam, see the Rules for Welding,

Volume VI, Section 6.

1.5 Due to the possible strain to the system presented

by cathodic protection, seawater and chemicals, only shop

primers are to be used which are alkali fast and not

hydrolyzable.

1.6 The suitability and compatibility of shop primer

for use in the corrosion protection system is to be guaranteedby the manufacturer of the coating materials.

2. Approvals

2.1 Only those overweldable shop primers may be used

for which the Society has issued a confirmation of accept-

ability based on a porosity test in accordance with the Rules

for Welding, Volume VI, Section 6.

C. Hollow Spaces

1. General

1.1 Hollow spaces, such as those in closed box girders,

tube supports and the like, which can either be shown to

be air tight or are accepted as such from normal shipbuilding

experience, need not have their internal surfaces protected.

During assembling, however, such hollow spaces must be

kept clean and dry.

D. Combination of Materials

1. General

1.1 Preventive measures are to be taken to avoid contact

corrosion associated with the combination of dissimilar

metals with different potentials in an electrolyte solution,

such as seawater.

1.2 In addition to selecting appropriate materials, steps

such as suitable insulation, an effective coating and theapplication of cathodic protection can be taken in order

to prevent contact corrosion.


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Section 38 - Corrosion Protection F38 - 2

E. Fitting-Out and Berthing Periods

1. General

1.1 For protection against corrosion arising from stray

currents, such as those occurring due to inappropriate direct

current electrical supply to the ship for welding or mains

lighting, as well as those arising from direct-current supplies

to other facilities (e.g. shore cranes) and neighbouring ships,

the provision of (even additional) cathodic protection by

means of sacrificial anodes is not suitable.

1.2 Steps are to be taken to prevent the formation of

stray currents, and suitable electric drainage is to be

provided.

1.3 Particularly in the event of lengthy fitting-out periods,

welding rectifiers are to be so arranged that stray currents

can be eliminated.

F. Corrosion Protection of Ballast Water Tanks

1. General

1.1 All seawater ballast tanks having boundaries formed

by the vessels shell (bottom, outside plating, deck) must

be provided with a corrosion protection system.

1.2 The following corrosion protection systems are to

be used:

S coating,

S coating and cathodic protection,

2. Coatings

2.1 General

2.1.1 The coatings must be, in accordance with the

manufacturers specifications, resistant against sea-water,

coastal water, harbour water and the substances they may

contain.

2.1.2 The characteristics, composition and field of

application of a coating system must be documented, i.e.

prescribed by the manufacturer of the coating material.

Details of the coating material, how it is to be processed

and its suitability for the coating system must be contained

in the product data sheet.

2.2 Approvals

2.2.1 For new buildings, the applied coatings and coating

systems must be approved by BKI. The approvals must

be obtained by the manufacturers of the coating materialsfrom BKI Head Office.

2.2.2 Approved coatings and coating systems are compiled

in a list (Approved Coatings for Newbuildings). The current

list is obtainable from Head Office.

2.2.3 Approval does not constitute confirmation of the

suitability and compatibility of the coatings in the corrosion

protection system. These points are to be ensured by either

the yard or the manufacturer of the coating materials.

2.3 Surface Preparation

2.3.1 The surface must be prepared according to the

instructions of the manufacturer of the coating material.

2.3.2 Surface preparation is subject to specifications in

the product data sheet and must correspond to a valid surface

quality grade, e.g. SIS 055900, DIN 55928, Part 4, or ISO

8501 1-4.

2.3.3 Slag and loose weld spatters must be removed beforethe coating is applied.

2.3.4 Welded or otherwise attached accessory material

(tack plates, lugs etc.) must be completely integrated into

the corrosion protection, or otherwise removed.

2.4 Application

2.4.1 The process of application is to be carried out

according to the coating manufacturers instructions.

2.4.2 During application the ambient conditions and

procedural instructions are to be complied with, inaccordance with the details specified in the manufacturers

instructions and in the approvals.

2.4.3 Surface areas which are obstructed and are thus

inadequately exposed to the spraying, exposed edges and

corners, as well as weld seams, must be stripe coated in

advance to achieve a sufficient coating thickness.

2.5 Dry Film Thickness

2.5.1 The dry film thickness of the coating systems must

be in accordance with approvals and correspond to aminimum of 250 m.

2.5.2 The prescribed coating thicknesses represent the

minimum coating thickness which must be maintained in

all cases.

2.6 Documentation

2.6.1 The work processes involved in setting up a coating

system as well as the coating materials to be used must be

laid down in a coating plan.

2.6.2 The coating plan for ballast water tanks must be

submitted to BKI for approval.

2.6.3 The coating protocol is to be compiled in such a


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Section 38 - Corrosion Protection F 38 - 3

way that all work steps executed, including surface

preparation and coating materials used, are documented.

2.6.4 This documentation is to be compiled by the coating

manufacturer and/or the contractor executing the work

and/or the yard. An inspection plan must be agreed to

between the parties involved. The papers pertaining to the

documentation must be signed by these parties. On

completion of the coating system, the signed papers

constituting the documentation are to be handed to the

surveyor for acceptance. The documentation is to contain

the following data:

S location and date,

S ship and the tanks treated,

S manufacturers specifications for the coating system

(number of coatings, total coating thickness,

processing conditions),

S product data sheet for the coating and BKI approval

number,

S contractors and persons carrying out the work,

S surface preparation (procedure, working materials,

ambient conditions),

S condition of surface prior to coating (cleanness,

roughness, existing primer, surface quality grade

achieved),

S application (procedure, number of coatings),

S

application conditions (time, surface/ambienttemperature, humidity, dew point, ventilation),

S the date the tanks were first ballasted is to be

recorded,

S report of coating thickness measurement and visual

inspections,

S signatures of involved parties (yard, coating manu-

facturer, work contractor).

2.6.5 Coating protocols already in existence and used by

coating manufacturers, work contractors, yards and ship

owners will be accepted by BKI, provided they contain

the above data and are signed by all parties involved. Any

missing data is to be furnished.

3. Coatings combined with Cathodic Protection

3.1 Coating

3.1.1 In the case of coatings used in combination with

cathodic protection, the provisions under 2 shall apply.

3.1.2 In addition, the coatings must be resistant against

the cathodic protection, i.e. the coatings must not exhibit

any impairment of their purpose up to a potential of 1200mV against the copper/copper-sulphate electrode. Proof

of resistance against cathodic corrosion protection can be

provided in accordance with recognized standards, e.g.

DIN 50928, or equivalent.

3.2 Cathodic Protection

3.2.1 General

For the cathodic protection of ballast water tanks in

combination with coatings, sacrificial anodes made of zinc

or aluminium are used. Tables 38.1 and 38.2 contain

recommended alloy compositions for conventional

aluminium and zinc anodes.

Zinc and aluminium anodes of differing chemical

composition may also be used, provided proof of the

cathodic protection ability is provided.

Zinc anodes may not be used in the event that operating

temperatures in excess of 60 C can be expected.

Impressed current systems are not permitted in ballast water

tanks.

Connections between the anodes and the surface to be

protected must provide good conducting properties.

The anodes are therefore to be welded on, wherever

possible. In exceptional circumstances, where bolting on

the anodes offers the only practicable alternative, an

adequate and durable metallic conducting connection must

be provided, e.g. cable connection.

Sacrificial anodes are not to be coated over and must be

free from dirt and other impurities.

3.2.2 Protection Current Requirement

For coated surfaces a protection current density of

0,02 A/m2

shall be applied.

In the event that ballast water tanks may be subjected to

higher temperatures, for instance due to adjacent heating-oil

tanks, the protection current density is to be increased as

follows:

For each C over 25 C by 1 mA/m2

The protection period must be designed to last for a

minimum of 5 years.

Deviations from the values stated for protection currentdensity and protection period could be accepted if a written

confirmation of the owner exists.

3.2.3 Anode Weight

The required total anode weight is calculated according

to:

mG = [kg]AG JS tS

Qg

where:

AG = the total area to be protected in [m2

]

JS = protection current requirement in [A/m2]

according to 3.2.2.


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Section 38 - Corrosion Protection G38 - 4

tS = protection period in [h]

Qg = electrochemical efficiency of the anode material

in [Ah/kg]

The electrochemical efficiency of the anode material is to

be taken out of the manufacturers specification.

Table 38.1 Sacrificial anodes of zinc alloys for

applications in seawater

Element KI-Zn1 KI-Zn2

Al 0,10 - 0,50 0,10

Cd 0,025 - 0,07 0,004

Cu 0,005 0,005

Fe 0,005 0,0014

Pb 0,006 0,006

Zn 99,22 99,88

Potential

(T = 20oC)

1,03 V

Ag/AgCl/Seawater

1,03 V

Ag/AgCl/Seawater

Qg(T = 20

oC)

780 Ah/kg 780 Ah/kg

Efficiency

(T = 20oC)

95%

Table 38.2 Sacrificial anodes of aluminium alloys for

applications in seawater

Element KI-Al1 KI-Al2 KI-Al3

Si 0,10 0,10 Si + Fe

0,10Fe 0,10 0,13

Cu 0,005 0,005 0,02

Mn N/A N/A 0,15 - 0,50

Zn 2,0 - 6,0 4,0 - 6,0 2,0 - 5,0

Ti 0,01 - 0,05

In 0,01 - 0,03 0,01 - 0,05

Sn 0,05 - 0,15

Other El. 0,10 0,10 0,15

Al Residue Residue Residue

Potential

(T = 20oC)

1,05 V

Ag/AgCl/Sea-

water

1,05 V

Ag/AgCl/Sea-

water

1,05 V

Ag/AgCl/Sea-

water

Qg

(T = 20

o

C)

2000 Ah/kg 2000 Ah/kg 2700 Ah/kg

Efficiency

(T = 20oC)

95%

3.2.4 Arrangement of Anodes

The arrangement of the anodes in the tank is to be such

that the required protection current density can be achieved

in all areas.

The number and size of the anodes depends on the structuraldesign and the calculated current output of the anodes. When

compiling the anode plan, the current output is to be taken

into account for the calculation.

An increase in the number of anodes required may be

necessary in the following circumstances:

S when frequently low filling levels lead to a limitation

in the area effectively protected by the anodes,

S when internal structures attenuate the effective

current for certain areas of the tank,

S when increased current densities are necessary for

the protection of more noble materials, e.g. internalsmade of stainless steel.

3.2.5 Documentation

The documentation of the coating must be in accordance

with 2.6. In addition, the papers concerning the design and

computation of the cathodic protection must be submitted

for perusal. An anode plan need not be submitted.

G. Corrosion Protection of Cargo Holds

1. General

1.1 On bulk carriers, all internal and external surfaces

of hatch coamings and hatch covers, and all internal surfaces

of the cargo holds, excluding the flat tank top areas and

the hopper tanks sloping plating approximately 300 mm

below the side shell frame and brackets, are to have an

effective protective coating (epoxy coating, or equivalent),

applied in accordance with the manufacturers recommend-

ation. In the selection of coating due consideration shall

be given in consultation with the owner to the intended

cargo and conditions expected in service.

1.2 The coating used must be approved by the

manufacturer for application in cargo holds.

1.3 The coating manufacturers instructions with regard

to surface preparation as well as application conditions and

processing must be adhered to.

1.4 The minimum thickness of the coating without

antifouling shall be 250 m, resistant to cathodic protection

in accordance with recognized guidelines and suitable for

mechanical underwater cleaning.

2. Documentation

2.1 The coating plan is to be submitted for examination.

A description of the work necessary for setting up a coating


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Section 38 - Corrosion Protection H 38 - 5

system and the coating materials to be used must be

contained in the coating plan.

2.2 A coating report is to be compiled in such a way

that details of all the work processes executed, including

the surface preparation as well as the coating materials used,

are recorded.

2.3 This documentation is to be compiled by the coating







surveyor for approval.

H. Corrosion Protection of the Underwater Hull

1. General

1.1 Vessels intended to be assigned the class notation

IW (In-Water Survey) shall provide a suitable corrosion

protection system for the underwater hull, consisting of

coating and cathodic protection.

1.2 Coatings based on epoxy, polyurethane and polyvinyl

chloride are considered suitable.

1.3 The coating manufacturers instructions with regardto surface preparation as well as application conditions and

processing must be observed.

1.4 The coating, system without antifouling, shall have

a minimum film thickness of 250 m, shall be compatible

to cathodic protection in accordance with recognized

standards, and shall be suitable for being cleaned underwater

by mechanical means.

1.5 The cathodic protection can be provided by means

of sacrificial anodes, or by impressed current systems. Under

normal conditions for steel, a protection current density

of at least 10 mA/m2 must be ensured.

1.6 In the case of impressed current systems, over

protection due to inadequately low potential is to be avoided.

A screen (dielectric shield) is to be provided in the

immediate vicinity of the impressed-current anodes.

1.7 Cathodic protection by means of sacrificial anodes

is to be designed for one dry-docking period.

1.8 In the case of other materials, such as aluminium

for instance, special conditions must be agreed with BKI.

2. Documentation

2.1 The coating plan and the design data for the cathodic

protection are to be submitted for examination.

2.2 In the case of impressed current systems, the

following details must also be submitted:

S location and constructional integration (e.g. by a

cofferdam) of the anodes in the vessels skin,

Sdescriptions of how all appendages, e.g. rudder,propeller and shafts, are incorporated into the

cathodic protection,

S electrical supply and electrical distribution system.

2.3 The work processes involved in setting up the coating

system as well as the coating materials to be used must be

laid down in the coating plan.

2.4 A coating protocol is to be compiled in such a way

that details of all the work processes executed, including

the surface preparation as well as the coating materials used,

are recorded.

2.5 This documentation is to be compiled by the coating







surveyor for approval.

2.6 In the case of impressed current systems, the function

ability of the cathodic corrosion protection is to be tested

during sea trials. The values obtained for the protectioncurrent and voltage must be recorded.

bki vol2_section38

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