Corrosion Protection

Section 35

Corrosion Protection

A. General Instructions

1. Field of application

1.1 This section deals with the corrosion protec-tion measures specified by GL with respect to seago-ing 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 GL.

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 con-cerning the applicability of certain corrosion protec-tion systems for special types of vessels (e.g. tankers and bulk carriers) have to be observed. GL is to be consulted when clarifying such issues.

1.5 Supplementary to this Section, VI Addi-tional Rules and Guidelines, Part 10 Corrosion Pro-tection, Chapter 2 Guidelines for Corrosion Protec-tion and Coating Systems contain further comments and recommendations for the selection of suitable corrosion protection systems, as well as their profes-sional planning and execution1.

B. Shop Primers

1. General

1.1 Shop primers are used to provide protection for 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 In addition, GL also offers advisory services for general ques-

tions concerning corrosion and corrosion protection.

1.3 The coating shall be of good resistance to withstand the mechanical stresses incurred during the subsequent working of the steel material in the ship-building process.

1.4 Flame-cutting and welding speed are not to be unduly impaired. It shall be ensured that welding with all welding processes customary in the building of ships can be conducted without impermissibly im-pairing the quality of the weld seam, see the Construc-tion Rules II Materials and Welding, Part 3 Weld-ing, Chapter 1 General Requirements, Proof of Qua-lifications, Approvals, Section 6.

1.5 Due to the possible strain to the system pre-sented 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 prim-er for use in the corrosion protection system is to be guaranteed by the manufacturer of the coating materials.

2. Approvals Only those overweldable shop primers may be used for which the Society has issued a confirmation of acceptability based on a porosity test in accordance with the Rules II Materials and Welding, Part 3 Welding, Chapter 1 General Requirements, Proof of Qualifications, Approvals , Section 6.

C. Hollow Spaces

1. General

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 have to 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 elec-trolyte solution, such as seawater.

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1.2 In addition to selecting appropriate materials, steps such as suitable insulation, an effective coating and the application of cathodic protection can be taken in order to prevent contact corrosion.

E. Fitting-Out and Berthing Periods

1. General

1.1 For protection against corrosion arising from stray currents, such as those occurring due to inappro-priate 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

Note

On 8. December 2006 the International Maritime Or-ganization (IMO) has adopted a Performance Stand-ard for Protective Coatings (PSPC). This new coating standard applies to ballast water tanks on newbuild-ings in all types of ships and is settled in the Resolu-tion MSC.215(82). With the new standard technical regulations for the coating of ballast water tanks come into force as well as inspection and verification items. These are statutory requirements for ship newbuild-ings which have to be observed and fulfilled. Further information under www.gl-group.com > Mari-time Services > Ship Newbuilding > Ship Safety & Environment > Protective Coatings (IMO PSPC).

1. General

1.1 All seawater ballast tanks shall be provided with a corrosion protection system.

1.2 The following corrosion protection systems are to be used:

coating

coating and cathodic protection

2. Coatings

2.1 General

2.1.1 The coatings shall be, in accordance with the manufacturer's 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 shall 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 shall be contained in the product data sheet.

2.2 Approvals

2.2.1 For new buildings, the applied coatings and coating systems shall be approved by Germanischer Lloyd. The approvals shall be obtained by the manu-facturers of the coating materials from GL Head Of-fice.

2.2.2 A list with approved coatings and coating systems is obtainable on the GL-Homepage or from GL 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 shall be prepared according to the instructions of the manufacturer of the coating material.

2.3.2 Surface preparation is subject to specifica-tions in the product data sheet and shall correspond to a valid surface quality grade, e.g. SIS 055900, ISO 12944-4 or ISO 8501.

2.3.3 Slag and loose weld spatters have to be re-moved before the coating is applied.

2.3.4 Welded or otherwise attached accessory ma-terial (tack plates, lugs etc.) shall be completely inte-grated into the corrosion protection, or otherwise re-moved.

2.4 Application

2.4.1 The process of application is to be carried out according to the coating manufacturer's instructions.

2.4.2 During application the ambient conditions and procedural instructions are to be complied with, in accordance with the details specified in the manufac-turer's instructions and in the approvals.

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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, shall be sripe 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 shall be in accordance with approvals and correspond to a minimum of 250 m.

2.5.2 The prescribed coating thickness is the mini-mum coating thickness which shall not be undercut at any spot of the coated surface.

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 shall be laid down in a coating plan.

2.6.2 The coating plan for ballast water tanks is to be submitted to GL for approval.

2.6.3 The coating protocol is to be compiled in such a 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 shall be agreed to between the parties involved. The papers pertaining to the documentation shall 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 documen-tation is to contain the following data:

location and date

ship and the tanks treated

manufacturer's specifications for the coating system (number of coatings, total coating thick-ness, processing conditions)

product data sheet for the coating and GL ap-proval number

contractors and persons carrying out the work

surface preparation (procedure, working materi-als, ambient conditions)

condition of surface prior to coating (cleanness, roughness, existing primer, surface quality grade achieved)

application (procedure, number of coatings) application conditions (time, surface/ambient

temperature, humidity, dew point, ventilation)

the date the tanks were first ballasted is to be recorded

report of coating thickness measurement and visual inspections

signatures of involved parties (yard, coating manufacturer, 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 GL, pro-vided they contain the above data and are signed by all parties involved. Any missing data is to be furnished.

3. Coatings combined with cathodic protec-tion

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 have to be resistant against the cathodic protection, i.e. the coatings shall not exhibit any impairment of their purpose up to a potential of 1200 mV 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 similar.

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 35.1 and 35.2 contain recommended alloy compositions for conven-tional aluminium and zinc anodes.

Table 35.1 Sacrificial anodes of zinc alloys for applications in seawater

Element GL-Zn1 GL-Zn2

Al 0,10 0,50 0,10

Cd 0,0250,07 0,004

Cu 0,005 0,005

Fe 0,005 0,0014

Pb 0,006 0,006

Zn 99,22 99,88 Potential

(T = 20 C) 1,03 V

Ag/AgCl/Sea 1,03 V

Ag/AgCl/Sea Qg

(T = 20 C) 780 Ah/kg 780 Ah/kg Efficieny

(T = 20 C) 95 %

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Table 35.2 Sacrificial anodes of aluminium alloys for applications in seawater

Element GL-Al1 GL-Al2 GL-Al3

Si 0,10 0,10 Si + Fe

Fe 0,10 0,13 0,10

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 Remainder Remainder Remainder

Potential (T = 20 C)

1,05 V Ag/AgCl/Sea

1,05 V Ag/AgCl/Sea

1,05 V Ag/AgCl/Sea

Qg (T = 20 C) 2000 Ah/kg 2000 Ah/kg 2700 Ah/kg

Efficieny (T = 20 C) 95 %

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 operat-ing temperatures in excess of 60 C can be expected.

Impressed current systems are not permitted in ballast water tanks.

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 recommendation. In the selec-tion 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 shall 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 shall be adhered to.

1.4 The minimum thickness of the coating shall be 250 m in the complete area defined under 1.1.

2. Documentation

2.1 The coating plan is to be submitted for ex-amination.

A description of the work necessary for setting up a coating system and the coating materials to be used shall 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 coat-ing materials used, are recorded.

2.3 This documentation is to be compiled by the coating manufacturer and/or the contractor executing the work and/or the yard. An inspection plan shall be agreed to between the parties involved. The papers pertaining to the documentation shall 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 approval (see also F.2.6.4).

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 suit-able 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 regard to surface preparation as well as application conditions and processing shall be observed.

1.4 The coating system, without antifouling, shall have a minimum dry film thickness of 250 m on the complete surface, 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 protec-tion current density of at least 10 mA/m2 is to be en-sured.

1.6 In the case of impressed current systems, overprotection due to inadequately low potential is to

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be avoided. A screen (dielectric shield) is to be pro-vided 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 alumin-ium for instance, special conditions are to be agreed with GL.

2. Documentation

2.1 The coating plan and the design data for the cathodic protection are to be submitted for examina-tion.

2.2 In the case of impressed current systems, the following details shall also be submitted:

arrangement of the ICCP system

location and constructional integration (e.g. by a cofferdam) of the anodes in the vessel's shell

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

electrical supply and electrical distribution sys-tem

design of the dielectric shield

2.3 The work processes involved in setting up the coating system as well as the coating materials to be used shall 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 coat-ing materials used, are recorded.

2.5 This documentation is to be compiled by the coating manufacturer and/or the contractor executing the work and/or the yard. An inspection plan shall be agreed to between the parties involved. The papers pertaining to the documentation have to 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 approval.

2.6 In the case of impressed current systems, the functionability of the cathodic corrosion protection is to be tested during sea trials. The values obtained for the protection current and voltage shall be recorded.

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GLRP - ContentChapter I-1-1 - ContentSection 35 Corrosion ProtectionA. General Instructions1. Field of application

B. Shop Primers1. General2. Approvals

C. Hollow Spaces1. General

D. Combination of Materials1. General

E. Fitting-Out and Berthing Periods1. General

F. Corrosion Protection of Ballast Water Tanks1. General2. Coatings3. Coatings combined with cathodic protection

G. Corrosion Protection of Cargo Holds1. General2. Documentation

H. Corrosion Protection of the Underwater Hull1. General2. Documentation

Documents

Corrosion Protection