vol03 pt16 issue 01

UNCLASSIFIED

AUSTRALIAN DEFENCE FORCE MARITIME MATERIEL REQUIREMENTS SET

DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Dated: 2 Oct 2008

Replacing/Superseding

NIL

Volume 03 Hull System Requirements

Part 16 Cathodic Protection of Naval Vessels

Usage: Maritime

© Commonwealth of Australia 2008

This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, non-commercial use within your organisation. All rights are reserved. Requests and enquiries concerning reproduction and rights should be addressed to the Manager, Legislative Service, AusInfo: GPO Box 1020, CANBERRA ACT 2601 or by e-mail to: [email protected]

UNCLASSIFIED Uncontrolled when printed or downloaded. Refer to web-site:

http://defweb.cbr.defence.gov.au/home/documents/navycoll.htm

mailto:[email protected]


UNCLASSIFIED

DEF(AUST)5000-VOI 03 Pt 16-ISS 01 Promulgation Page

PROMULGATION

ii

UNCLASSIFIED

SPONSOR

Author

Li+:/ Signed: .................................................... Name: M. Grimm

Appointment:

Acting Assistant Director

Material and Environmental Assurance

Date: ....................................... 271 s 12-73

Uncontrolled when printed or downloaded. Refer to web-site: http:lldefweb.cbr.defence.qov.aulhomeldocuments/navycoll.htm

1 >

(2

MRS-CMA

Audit Document Format Requirements

Signed: ..................................................... /??y Name: P.F. King

Appointment:

MRS - Configuration Management Authority

Date: .................................... 2 ~ / f ' ( a 8

I3 MRS PEER REVIEW GROUP

AssignAocument Maturity Level

ASSISTANT DIRECTOR

Pass Technical Content

J?&aQ_"- Signed: ........................................................

Name: M. Grimm

Appointment:

Acting Assistant Director

Material and Environmental Assurance

Date: ....................................... 271 g/ 2008

4 > Appointment:

Chairperson Platform MRS-PRG

Date: ..................................... / / ( 0 / & k 9 ~ DML 0

5

DIRECTOR

Approy4fchnical Content

Appointment:

Director Navy Platform Systems

Date:

.......................... 6

UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Change Proposal Page

iii



DEF(AUST)5000 CHANGE PROPOSAL INSTRUCTIONS

1. This page is to be used to report specific errors, omissions or to suggest improvements to this publication. 2. Please attach additional comments/drawings/sketches as necessary. 3. Copies are to be forwarded for follow-up action to:

a. Assistant Director, Material and Environmental Assurance

Directorate of Navy Platform Systems, CP4-5-031, Department of Defence, CANBERRA ACT 2600 and

b. Navy Specification and Technical Documents Centre (NSTDC), Campbell Park Offices, CP4-SP-WS013, MDP9401, Department of Defence, CANBERRA ACT 2600, or alternatively

c. Change proposals can be submitted electronically using the User Feedback form located on the DEF(AUST)5000 DEFWEB site: HTUhttp://defweb.cbr.defence.gov.au/home/documents/navycoll.htmUTH

PROPOSED CHANGE TProposal: T

TThe Above Discrepancy Materiel Safety Materiel Capability Other

TORIGINATING SOURCE’S CONTACT DETAILSTTT

TOrganisation/Ship/Establishment:T

TSubmitted by: T

Signature Printed Name Rank/Designation E-mail Address Date

TRecommended by Yes No


SPONSOR’S ACTION

TDocument Sponsor: T

TChange Proposal is Approved:T

Yes No

TComments: T


TAuthorised by MRS-PRG:T


UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Issue History Page

iv



ISSUE HISTORY

Issue No. Issue Date Description of Changes Affected Pages Sponsor’s Name

01 2 October 2008 Original Martin Grimm

02

03

04

05

06

07

08

09

10

UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Preface Page

v



PREFACE

1. This document was originally drafted by BMT Defence Services (Australia) and QinetiQ Ltd under contract to the Director Navy Platform Systems and is an element of the DEF(AUST)5000—ADF Maritime Materiel Requirements Set.

2. The general requirements specified herein are to be used in the generation of capability-specific function and performance specifications associated with procurement, modification, maintenance, and repair of maritime materiel.

3. This document will be updated at regular intervals to reflect lessons learned and changes in national standards, or to incorporate other nations’ standards required for collaborative activities.

4. Queries and comments regarding the use and/or interpretation of this document are to be directed to the sponsor.

UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Table of Contents

vi



TABLE OF CONTENTS Preliminary Pages Page No.

Title Page

Promulgation Page ii

Change Proposal Page iii

Issue History Page iv

Preface v

Table of Contents vi

Page No. Para No.

SECTION 1 SCOPE

Life Cycle 1 1.1

What is Covered 1 1.2

What is Not Covered 1 1.3

SECTION 2 DOCUMENTS

Applicable Documents 2 2.1

Referenced Documents 5 2.2

SECTION 3 DEFINITIONS AND ABBREVIATIONS

Definitions 7 3.1

Abbreviations 10 3.2

SECTION 4 BACKGROUND

TSignificance to RANT 11 4.1

SECTION 5 FUNCTIONAL AND PERFORMANCE REQUIREMENTS

TGeneral RequirementsT 12 5.1

TCathodic protection potential criterionT 14 5.2

Requirements specific to ICCP 17 5.3

TRequirements specific to sacrificial anode systems T 21 5.4

TRequirements for performance managementT 25 5.5

TShip fitting out and docking 27 5.6

TCorrosion and CP generated signaturesT 28 5.7

TRequirements T for design verification 29 5.8

SECTION 6 DESIGN AND PRODUCT CONSTRAINTS

TSpecific Design/Engineering Constraints T33 6.1 T

Navy Practice/Personnel Constraints 33 6.2

Interoperability Constraints 33 6.3

Commonality Constraints 34 6.4

UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Table of Contents

vii



Regulatory/Legislative Constraints 34 6.5

SECTION 7 DELIVERABLES (DIDs)

Test Regime 35 7.1

Safety Paper 35 7.2

System Engineering Management Plan (SEMP) 35 7.3

Function/System Specification 35 7.4

Means of Verification of Function and Performance 35 7.5

Through Life Support Documentation 35 7.6

ANNEX A - Outline of Cathodic Protection Systems A–1

UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01

1



1 SCOPE

1.1 Life Cycle 1.1.1 This specification has been produced to define the requirements for Cathodic Protection (CP)

systems designed and operated to protect Royal Australian Navy (RAN) or other ADF surface vessels and submarines. This document shall apply for all steel, aluminium and composite hulled vessels.

1.1.2 The CP system of the vessel shall operate for the whole lifecycle unless specific maintenance requirements on either the CP system or vessel dictate that parts of, or the whole system, needs to be isolated or switched off for a period of time.

1.1.3 This document shall apply for ADF vessels under all operating conditions. There is no intention to apply these requirements retrospectively to CP systems working successfully in current vessels except as discussed at section 1.2 below.

1.2 What is Covered 1.2.1 This document covers the requirements for both active (impressed current) and passive (sacrificial

anode) systems or a combination of both.

1.2.2 New vessel designs or significant modifications to existing vessels that impact on CP performance shall require a CP system design that complies with the requirements of this document. The CP system design verification and performance data shall be supplied as part of the procurement contract and must be shown to conform to the requirements of this document.

1.2.3 The requirements in this document shall be used as a basis for assessing compliance of existing CP systems installed in RAN or other ADF vessels when substantial renewal or upgrade of parts of the existing system is planned to be undertaken.

1.2.4 The requirements in this document shall be applied to any extension of existing hull geometry or retrofitting of a new CP system layout or design to any vessel. A verification process shall be completed to ensure that the required protection criteria are achieved for the whole vessel.

1.2.5 This document covers seawater-flooded internal spaces that require CP, such as sea chests, bilges and ballast tanks that are wetted with seawater under normal operational conditions.

1.2.6 When CP systems are proposed to be retrofitted to tank spaces or other internal spaces of existing vessels not previously covered by such CP systems, the requirements in this document shall also apply. A verification process shall be undertaken to ensure that the required protection criteria are achieved in the zone protected by the new installation.

1.3 What is Not Covered 1.3.1 This document does not cover the specific requirements of coating schemes used in combination

with CP and does not specifically cover galvanic corrosion issues.

1.3.2 While this document defines a limited number of requirements related to CP systems for seawater piping, corrosion prevention for seawater piping systems is not specifically covered in this document. Reference should instead be made to DEF(AUST)5000 Vol 04 Part 05.


2



2 DOCUMENTS

DISCLAIMER NOTICE

If any information in this publication is attributed to another work the reader should consult that work to ensure the accuracy of the information contained in this publication. Should there be any discrepancy between this publication and the other work no person should rely on the contents of this publication without first obtaining advice from the Office of the Chief Naval Engineer. The Commonwealth, the authors, consultants and editors are not responsible for the results of any actions taken on the basis of information in this publication which is attributed to another work if:

(a) the reader has failed to consult that other work to ensure the accuracy of the information contained in this publication which is attributed to that other work; or

(b) there is a discrepancy between the information contained in this publication which is attributed to another work and that other work and the person has failed to first obtain advice from the Office of the Chief Naval Engineer.

The Commonwealth, and the authors, consultants and editors, expressly disclaim all and any liability and responsibility to any person, whether a reader of this publication or not, in respect of anything, and of the consequences of anything, done or omitted to be done by any such person in reliance, whether wholly or partially, upon the whole or any part of the contents of this publication which is attributed to another work if:

(a) the reader has failed to consult that other work to ensure the accuracy of the information contained in this publication which is attributed to that other work; or

(b) there is a discrepancy between the information contained in this publication which is attributed to another work and that other work and the person has failed to first obtain advice from the Office of the Chief Naval Engineer.

If the reader of this publication discovers any item of information in this publication which appears to be incorrect, then the onus is on the reader to verify whether this information is correct with the Office of the Chief Naval Engineer.

2.1 Applicable Documents 2.1.1 The following documents are called up in this document. When applying this DEF(AUST)5000

document, the user is required to use the dated version if specified, or otherwise negotiate with the sponsor a suitably dated version for each applicable document.

2.1.2 In accordance with DI(G) LOG 4–5–11 Defence Policy on Materiel Standardisation document selection shall be based on the following order of precedence. Government, operational and/or technical imperatives can override preference to other standards:

Documents Mandated by Federal and/or State Legislation List of Applicable Documents Applicability and Availability

OH&S (Commonwealth Employment) Act 1991 and amendments

Australian health and safety legislation

http://HTwww.comlaw.gov.auTH


3



Australian Defence Documents

List of Applicable Documents Applicability and Availability

ABR 5225 Vol 2 RAN Marine Engineering Manual Ch. 46 Degaussing and Cathodic Protection

CP system reporting requirements,

Available through NSTDC (or on-line via DEFWEB for Defence employees)

ABR6303 NAVSAFE Manual - RAN Safety Management Safety Management and Risk Assessment,


DEF(AUST)5000 – Vol 02 Pt 010 Selection of Materials according to their Fire Safety Properties

Fire, smoke and toxicity requirements for shipboard materals,


CDEF(AUST)5000 – Vol 03 Pt 04 Painting C

Requirements for painting of ADF ships and boats


DEF(AUST)5000 – Vol 04 Pt 05 Pumps and Piping Systems C C

Requirements for piping systems,


CDEF(AUST)5000 – Vol 05 Pt 03 – General Requirements for Electrical installation in RAN Ships and Submarines C

Requirements for electrical installation in Navy ships,


CDEF(AUST)5000 – Vol 05 Pt 10 – Electrical Cables for RAN Ships and Submarines C

Requirements for electrical cables of Navy ships,


DEF(AUST)5000 – Vol 05 Pt 11 – Shore Electrical Power Supply for RAN Ships and Submarines

Requirements for shore power supply systems,


DEF(AUST)5000–Vol 07 Pt 21 – Standardised Methods of Verifying Ship Signature Requirements. Requirements for signatures of Navy ships,


International Documents List of Applicable Documents Applicability and Availability

ASTM STP 1370 Designing Cathodic Protection Systems for Marine Structures and Vehicles, H.P. Hack (Editor), American Society for Testing and Materials, West Conshohocken, PA 1999.

Modelling protocol, available through ASTM

ISO 12473:2006 General principles of cathodic protection in sea water.

HThttp://www.iso.orgTH

ABS – Naval Vessel Rules Part 8, Chapter 4 (Coatings and Corrosion Control) Section 4.3.1 Corrosion Monitoring

American Bureau of Shipping Naval Vessel Rules

Applicable to installation in new construction surface ships


4



Systems.

National Documents Implementing International Standards List of Applicable Documents Applicability and Availability

Nil

National Documents List of Applicable Documents Applicability and Availability

CAS 2239-2003 - Galvanic (sacrificial) anodes for cathodic protectionC

Properties of anodes

Available through www.saiglobal.com

AS/NZS 60479:2002 (Parts 1-3) Effects of current on human beings and livestock.

Electrocution risk of ICCP systems

Available through HTwww.saiglobal.com TH

Commercial Documents List of Applicable Documents Applicability and Availability

Nil

International Military Agreements and Defence Documents Implementing International Military Agreements

List of Applicable Documents Applicability and Availability

Nil

Other Nation’s Military Documents List of Applicable Documents Applicability and Availability

Environmental Protection Agency, C40 CFR Part 9 and Chapter VII (Department Of Defense 40 CFR Chapter VII [FRL–6335–5]) C, CRIN 2040–AC96C, CUniform National Discharge Standards for Vessels of the Armed ForcesC.

Background document.

Available through HThttp://unds.bah.com/ TH

CEnvironmental Protection AgencyC C40 CFR Part 9 and Chapter VII (Department of Defense 40 CFR Chapter VII [FRL–6335–5]), C CRIN 2040–AC96C, CUniform National Discharge Standards for Vessels of the Armed ForcesC. CPhase 1 Uniform National Discharge Standards for vessels of the armed forces, Technical development document, EPA 821-R-99-001, April C1999CC

Background document,

available through: http://www.epa.gov/OST/guide

NAVSEA T-9633-AT-DSP-010/ALL USN, Ship’s Cathodic Protection, Design Calculations, Design Requirements Manual, Apr 2007

Background and Physical Scale Modelling of CP systems.

US Naval Sea Systems Command


5



2.2 CReferenced Documents C 2.2.1 The following documents were used in the development of this document. The appropriate

information from these documents has been included and the authors are hereby acknowledged.

Australian Defence Documents List of Applicable Documents Applicability and Availability

Nil

International Documents List of Applicable Documents Applicability and Availability

CBS EN 12473 – General Principles of Cathodic Protection in Seawater, European Standard, British Standards Institution (BSI), LondonC

HTwww.bsOnline TH

CBS EN 12596 – Galvanic (sacrificial) Anodes for Cathodic Protection in Seawater, European Standard, British Standards Institution (BSI), LondonC

HTwww.bsOnline TH

CBS EN 13509:2003 – Cathodic Protection Measurement Techniques, European Standard, British Standards Institution (BSI), LondonC

HTwww.bsOnline TH

National Documents List of Applicable Documents Applicability and Availability

AS 2832.4-2006 - Cathodic protection of metals - Internal surfaces

HTwww.saiglobal.com TH

CAS 2832.3-2005 - Cathodic protection of metals - Fixed immersed structures C

HTwww.saiglobal.com TH

Commercial Documents List of Applicable Documents Applicability and Availability

Lucas, K.E.C; Thomas, E.D.; Kaznoff, A.I.; and Hogan, E.A., Design of Impressed Current Cathodic Protection (ICCP) Systems for US Navy Hulls, in Designing Cathodic Protection Systems for Marine Structures and Vehicles, STP 1370, H.P. Hack (Editor)., American Society for Testing and Materials, West Conshohocken, PA 1999.C

Modelling protocol, available through ASTM

CDET NORSKE VERITAS (Industri Norge), Recommended Practice, DNV-RP-B401 - Cathodic Protection Design, January 2005 C

HThttp://exchange.dnv.com/OGPI/OffshorePubs/ViewArea/RP-B401.pdf TH

NORSOK StandardC M-CR-503, Common Requirements - Cathodic Protection, Ed. 3 May 2007 C

HThttp://www.standard.noTH

CGermanischer Lloyds: Rules and guidelines 2006; III Naval Ship Technology, Part 1, Chapter 1, Section 3, Materials and Corrosion Protection; VI Additional rules and guidelines, Part 9, Chapter 6, Section 7, Cathodic Corrosion Protection.C

HThttp://www.gl-group.com/infoServices/rules/pdfs/english/glrp-e.pdf TH


6



Meillier A., A review of galvanic anode cathodic protection design procedure, Corrosion Control Services Limited, Telford UK, 1998.

Other Nation’s Military Documents List of Applicable Documents Applicability and Availability

Defence Standard 02-704 (Issue 1), Requirements for Cathodic Protection, Parts 1-5, UK Ministry of Defence, April 2000

Available from http://www.dstan.mod.uk/

CNAVSEA S9086-VF-STM-010 - NSTM Chapter 633 (Cathodic Protection), Naval Sea Systems Command, 1994C

Available through DNPS

DeGiorgi, V.G. & Hogan, E.A. & Wimmer, S.A, US Naval Research Laboratory, New Horizons in Cathodic Protection Design, 2004

Available from NRL website: HThttp://www.nrl.navy.mil/content.php?P=04REVIEW51 TH


7



3 DEFINITIONS AND ABBREVIATIONS

3.1 TDefinitions 3.1.1 Definitions used throughout DEF(AUST)5000 documents are contained in the DEF(AUST)5000–Vol

01 Pt 03—MRS Definitions and Abbreviations. Additional definitions not currently provided in the fore mentioned reference are listed as follows: T

Acidity presence of excess of hydrogen ions over hydroxyl ions (pH <7). Aerobic conditions presence of oxygen dissolved in the electrolyte. Alkalinity presence of excess hydroxyl ions over hydrogen ions (pH >7). Anaerobic conditions absence of oxygen dissolved in the electrolyte. Anion negatively charged ion in solution. Anode positively charged surface that acts as a source of current to the

electrolyte, and on the surface of which electrons are released during oxidation reactions. The anode in a CP system provides cathodic protection to the structure.

Calcareous deposit minerals precipitated on the cathode as a result of increased

alkalinity caused by cathodic protection. Calomel reference electrode reference half-cell of mercury (Hg) and mercurous chloride

(HgB2BClB2B) in saturated potassium chloride (common abbreviation SCE).

Cathode negatively charged surface that acts as sink of current from the

electrolyte, and on the surface of which electrons are consumed during reduction reactions. The cathode in a CP system is the structure being cathodically protected.

Cathodic disbonding failure of adhesion between a coating and a metallic surface as a

direct result of application of cathodic protection. Cathodic Protection system complete installation including active and passive elements that

provides cathodic protection. CP system life is the period for which the CP system is designed to function. For

sacrificial anode CP systems this should also be the replacement life of the anodes. The CP system life is strongly influenced by the rate of coating degradation and determined by the vessel drydock maintenance / repainting cycle.

Cation positively charged ion in solution. Coating breakdown factor predicted increase in cathodic current density due to breakdown of

an electrically insulating coating on the cathode. Coating resistance electrical resistance between a coated metal and the electrolyte

dependent largely upon number and size of coating defects (discontinuities) indicating the condition of the coating.


8



Continuity bond bond designed and installed to ensure electrical continuity of a whole structure with the intention of distributing potential evenly across the protected surface by current flow through electrical conductors.

Dielectric shield alkaline-resistant, electrically insulating plastic material or organic

coating applied to the structure in the vicinity of an impressed current anode to minimise the risk of hydrogen damage to the protected surface due to over protection.

Driving potential difference between the structure/electrolyte potential and the

anode/electrolyte potential. Electrochemical cell complete electrolytic system comprising an anode and cathode in

electrical contact immersed in an electrolyte. Electrolyte a liquid such as seawater in which electric current may flow by

charge transfer between ions. Electronegative describes a metallic electrode that has a more negative potential in

an electrolyte in comparison to another metallic electrode in the system.

Environmentally assisted corrosive action of the environment contributing to brittle fracture cracking of a ductile material. Free corrosion potential potential of a freely corroding metal in the absence of any external

applied potential or electrical load. Galvanic action spontaneous electrochemical reaction between anode and cathode

in electrical contact when immersed in an electrolyte resulting in corrosion of the anode.

Impressed current anode the electrode connected to the positive terminal of an impressed

current power supply. Impressed Current A method to cathodically protect a structure with a direct current Cathodic Protection (ICCP) supplied by an external power source. Microbiologically Influenced Corrosion influenced by the presence of naturally occurring Corrosion (MIC) bacteria in seawater or fresh water. Such bacteria are responsible

for accelerated corrosion in tanks, bilges and piping systems. Open circuit potential see Free corrosion potential. Over protection describes the condition when the structure is over polarised such

that the structure/electrolyte potential is more negative than recommended for cathodic protection.

Polarisation change in potential of a surface as the result of current flow to or

from the surface. Potential voltage difference between surface and known voltage source;

potentials in this document are measured relative to the Silver/Silver Chloride in seawater cell (Ag/AgCI in seawater).


9



Protection current current supplied to a metal surface by electrolytic action in the environment to protect the surface cathodically.

Reference electrode stable, non-polarisable half cell with a reproducible potential value

used to measure the surface to electrolyte potential. Resistivity resistivity of the electrolyte is defined by resistance of an

electrolyte of unit cross section and unit length (expressed in ohm metres: Ωm). The resistivity depends upon amount of dissolved salts in the electrolyte (salinity).

Sacrificial Anode The electrode of a passive CP system where corrosion occurs and

metal ions enter the seawater thereby protecting the surrounding metal structure and equipment. Sacrificial anodes for ships are typically manufactured from zinc, aluminium or magnesium alloys.

Silver/silver chloride silver (Ag) and silver chloride (AgCl) half-cell in electrolyte reference electrode containing chloride ions. CSulphateC Reducing Bacteria A species of bacteria found in most natural waters but active only (SRB) in conditions of near neutrality and freedom from oxygen. Main

reaction is to reduce sulphates in their environment to sulphides that accelerate the corrosion of structural metals. See MIC.

Surface potential difference in potential between a metal surface and a specified

reference electrode, both immersed in an electrolyte and in close proximity to avoid potential drop (referred to as IR drop) associated with current flowing in the electrolyte.

Transformer rectifier device that transforms the alternating voltage to a suitable value

and then rectifies it to direct current; the output is used as a power source for ICCP systems.


10



3.2 TAbbreviations 3.2.1 The majority of acronyms used in this document are contained in the ADFP 103—Abbreviations and

Military Symbols or the Macquarie Dictionary. Additional acronyms not currently provided in the fore mentioned reference are provided as follows:

Ag Silver

Ag/AgCl Silver / Silver Chloride

BE Boundary element (modelling)

CD Coating Damage (percentage)

EBCORRB Free corrosion (open circuit) potential of a metal

HTS High Tensile Steel

ICCP Impressed Current Cathodic Protection

MIC Microbiologically Influenced Corrosion

MMO Mixed Metal Oxide

mV Millivolts (1 x 10P

-3 PV)

NAB Nickel Aluminium Bronze

PSG Passive Shaft Grounding

PSM Physical Scale Modelling

PSU Power Supply Unit

SE Static Electric (signature) (see UEP)

SRB Sulphate Reducing Bacteria

UEP Underwater Electric Potential (signature) (also SE)


11



4 BACKGROUND

4.1 Significance to RAN 4.1.1 Corrosion protection policy

4.1.1.1 CP is intended to be used to protect the hull and internal spaces wetted by seawater, including pipe work, of all vessels operated by the ADF. CP shall form a major part of the corrosion protection measures for the operating life of all vessels. It should be noted that CP systems will not make the vessel immune to corrosion, however should reduce corrosion to an acceptable rate, even in the event of coating breakdown.

4.1.1.2 The reference documents listed in Section 2 should be consulted for detailed descriptions of the corrosion processes involved and their mitigation.

4.1.1.3 For the purposes of this document, CP shall define the concept of polarising a metal surface to a potential more negative than the free corrosion potential (E BCORR B) in seawater, at which point all significant metal corrosion processes have ceased.

4.1.1.4 This document adopts commonly accepted EBCORR B values for steel or aluminium alloys corroding in seawater to set the CP potential criterion for the whole system.

4.1.1.5 The functional components of CP systems referred to in the requirements of this document are briefly outlined in A.2.2 for ICCP and A.2.3 for sacrificial CP systems.


12



5 FUNCTIONAL AND PERFORMANCE REQUIREMENTS

5.1 TGeneral requirements 5.1.1 TDesign parameters

5.1.1.1 The main objective of a CP system for any vessel shall be to provide protection to the hull against corrosion for the life of the vessel.

5.1.1.2 ICCP systems are considered to be the best protection for steel-hulled vessels and should be specified for new vessels. In planning of any major refit or upgrade of existing ADF steel hull vessels fitted with only sacrificial anode CP systems, the cost benefit of retrofitting an ICCP system for the remaining operational life of the vessel should be assessed.

5.1.1.3 CP of aluminium-hulled vessels shall be performed with sacrificial anode CP systems.

5.1.1.4 The CP of all other vessel areas such as bilges, ballast tanks, sea chests and internal spaces and equipment shall be performed with sacrificial anode CP systems.

5.1.1.5 ICCP systems are not recommended for use in enclosed spaces such as ballast tanks or semi-enclosed free-flood spaces because of the risk of the evolution of dangerous gases. In addition, the use of ICCP is generally not beneficial to tank spaces due to the complexity of the tank’s surface geometry.

5.1.2 TProtection potential criteria

5.1.2.1 The CP system shall supply sufficient current to each part of the protected hull to maintain the surface potential within the limits given by the protection criteria in Section 5.2.

5.1.2.2 The protection criteria are based upon the measured potential of the hull, and individual metallic parts that are bonded electrically to the hull, when the system is energised. These protection criteria are recognised and accepted globally for maritime vessels and structures.

5.1.2.3 Experience has shown that a negative potential change of 200mV from the free corrosion potential is a good measure of adequate protection for steel structures under all operating conditions. It is accepted that other metals may not require such a large potential swing to be protected adequately by the CP system. This is addressed in this document by the accepted regime of a minimum potential for adequate protection and maximum potential to prevent damage to coatings caused by CP.

5.1.2.4 The protection potential criteria shall apply to the hull under all seawater conditions throughout the life of the vessel. Environmental conditions will vary both locally and globally but the key parameters affecting CP system performance are salinity, dissolved oxygen content, flow rate, temperature and marine growth. These variables need to be taken into consideration in the design of any CP systems.

5.1.3 TCoating scheme

5.1.3.1 A coating scheme will significantly reduce the magnitude of the current required for protection and increase the uniformity of current distribution, which means that the life expectancy of sacrificial anode systems in particular can be extended. As such, all steel or aluminium-hulled naval vessels shall be painted externally with an anti-corrosion paint as primary corrosion protection and antifouling paint in accordance with DEF(AUST)5000 Vol 03 Pt 04. CP shall be supplementary to this corrosion protection.

5.1.3.2 DEF(AUST)5000 Vol 03 Pt 04 gives the requirements for painting internal spaces, bilges and tanks where CP systems may be considered for additional protection. For maximum protection these internal areas shall be painted and CP system designs applied to offset coating damage in service. The CP system will only provide effective corrosion protection when immersed in seawater or similarly conductive solutions. CP is not appropriate to potable fresh water tanks due to the low conductivity, and the OH&S requirements for potable water preventing the use of sacrificial anodes which would contaminate the water on dissolution.


13



5.1.3.3 The CP system design shall not damage the coating or interfere with the function of the coating at any location on the vessel. The coating shall be compatible with the chemical reactions generated by CP and shall have passed a recognised cathodic disbonding test.

5.1.3.4 Coatings applied to external hull surfaces will invariably deteriorate gradually in service and the CP system designer must factor in this coating breakdown when calculation the CP system design life. The predicted level of coating damage for each metal, or individual coated areas, covered by the CP system shall be defined. The rate of coating damage shall be based upon existing experience where applicable.

5.1.3.5 The Commonwealth will define the required CP system life in consultation with the CP system designer. For sacrificial anode systems, the system life shall be the replacement life of the anodes. For ICCP systems, the system life will match the intended service life of the vessel with allowances made for primary coating degradation and the requirement to renew or replace the primary paint scheme several times during the life of the vessel.

5.1.4 TAppendages

5.1.4.1 The current demand for all CP system designs is highest in the area of exposed propellers and shafts and CP system designs will need to ensure adequate protection of adjacent hull structure in this area. Adequate means adjacent hull is protected to potentials given in Table 5.1.

5.1.4.2 For CP system design and evaluation, the propellers and shafts shall normally be considered as unpainted unless the Commonwealth specifies coatings for the propellers and/or sheathing of shafts. The CP system design shall however include provision for the propellers and shafting to be painted during the life of the vessel.

5.1.4.3 The CP system designer shall ensure that there is electrical continuity between the hull and appendages such as propellers and shafts unless the ship design specifically requires that these items are isolated. In the majority of vessels, a shaft grounding system shall be used to ensure electrical continuity for shaft lines.

5.1.4.4 Appendages such as rudders, trim tabs and stabilisers shall also be electrically bonded to the hull to ensure that they receive protection from the CP system unless the ship design specifically requires that these items are isolated. Such continuity can be achieved through the use of bonding straps.

5.1.4.5 In GRP or other non-conductive hulled vessels there is no natural conductive path through the hull material to hull penetrations and fittings, such as hull valves and seawater system pipe work penetrations. If metallic hull penetrations and attachments are not electrically connected inside the vessel to the CP system installed to protect these attachments, serious corrosion can occur, especially in non-ferrous materials that might normally be protected by being coupled to a ferrous or aluminium hull. As such, for these vessels, all appendages and hull penetrations such as seawater system inlets/outlets require low resistance internal electrical connections to ensure continuity with the installed CP system. The continuity of such internal attachments must be monitored in service to prevent inadvertent isolation of hull penetrations from the CP system.

5.1.4.6 Alternatively, individual metallic hull fittings can be cathodically protected with their own externally mounted sacrificial anodes. In all cases, anodes should be fitted as close to the protected attachment as possible, and electrically bonded to it. All metallic hull appendages that are individually cathodically protected shall be electrically isolated from one another and the vessel’s earthing system and grounding plates (usually copper). Failure to isolate systems will lead to galvanic corrosion and can cause rapid wastage of sacrificial anodes and possible stray current corrosion in seawater piping systems.

5.1.4.7 Underwater electromagnetic signature implications associated with CP systems shall also be taken into consideration, particularly for vessels such as minehunters.

5.1.4.8 The CP system designer shall provide numerical data for assessment of CP system design against the protection criteria set by the Commonwealth in accordance with Section 5.2 for all operational and environmental conditions.


14



5.1.5 TSeawater pipe work systems

5.1.5.1 TThe internal surfaces of seawater pipe work systems, heat exchangers and other equipment may benefit from the application of CP, often using sacrificial anodes.

5.1.5.2 TAny CP installations must not interfere with the required flow of water through the pipe work/equipment.

5.1.5.3 TDetachment of sacrificial anodes from their mountings or the release of fragments from anodes shall not cause subsequent obstruction/damage of the pipe work system and associated equipment.

5.1.5.4 TNote: TThe typically uncoated surfaces of seawater pipe work and the continuous seawater flow velocities through them will generally demand increased protection current from CP systems. However, the CP potential required for non-ferrous seawater system materials may not be as electronegative as that required by ferrous hulls (see Section 5.2). The distance away from an anode at which CP is effective may be limited in pipe work compared to wetted hull applications. This is due to the reduction in the seawater volume connecting the anode to the cathodically protected surface.

5.1.6 TEnvironmental parameters

5.1.6.1 The Commonwealth will provide guidance on the geographical areas where the vessel will operate on request from the CP system designer through the prime contractor. The CP system shall be designed to maintain protection of the hull under the harshest conditions likely to be encountered in the operational life of the vessel. The system design shall account for static and dynamic performance in that environment. This includes operation underway in cold water.

5.1.6.2 The CP system for internal spaces and tanks shall be designed to operate under the worst case condition for coating damage or loss. For the purpose of this document this shall be taken as 15% unless other figures are provided by the Commonwealth. This figure is significantly higher than the Commonwealth expectation for coating performance degradation as specified in DEF(AUST)5000 Vol 03 Pt 04 Painting and is intended to provide a safeguard in the event of unexpected paint system failure or higher than normal mechanical damage to a coating. The design life of internal CP systems shall be determined by consideration of the inspection and maintenance policies applied to the vessel.

5.2 Cathodic protection potential criterion 5.2.1 TProtection potential

5.2.1.1 The CP criterion for a metal in seawater shall be that the surface potential is maintained at or below 200mV (0.2V) more negative than the free corrosion (open circuit) potential (E BCORR B) in seawater. This approach is accepted globally by many navies and maritime organisations concerned with the protection of metallic structures in seawater. An exception to this is that aluminium alloys intended for marine service need only be maintained at or below 100mV (0.1V) more negative than the free corrosion potential. All potentials are measured relative to a silver/silver chloride (Ag/AgCl) electrode in seawater.

5.2.1.2 This protection potential criterion shall be applied for all metals used in constructing the hull or underwater metal parts electrically bonded to the hull.

5.2.1.3 The CP system design must account for all metals that require CP. The accepted practice is to protect the most active metal at the required protection potential such that a negative potential is maintained on all other metallic parts of the structure

5.2.1.4 The same protection potential criterion shall apply to internal space, bilges and tanks needing CP.

5.2.2 TMinimum protection potentials

5.2.2.1 The free corrosion potential (EBCORR B) of a metal in seawater will change in relation to seawater properties such as composition, temperature, oxygen content, flow rate, etc. The requirement for the protection potential in 5.2.1 will ensure the hull and attachments are protected at or below the minimum potential required by the vessel under all seawater conditions.


15



5.2.2.2 Experience and best practice with acceptable CP system designs has shown that an upper and lower potential limit may be quoted for common construction materials used for vessels and fixed or floating structures in seawater. The CP system design shall maintain the potential within these limits to avoid under protection or over protection of parts of the structure.

5.2.2.3 Acceptable CP system designs must achieve potentials more negative than the minimum potential provided in table 5.1 for the expected life of the structure. Table 5.1 provides typical values of minimum potential values for only common metals used in maritime construction. Where metals other than those identified in table 5-1 are used, engineering justification shall be provided to demonstrate that all metals are provided with adequate through life CP.

5.2.3 TMaximum protection potentials

5.2.3.1 CP causes hydroxyl ion (OH P

−P) and hydrogen formation on the protected surface under most

seawater conditions. These chemical reactions are detrimental to surface layers or applied coatings and can result in cathodic disbonding of the protective coating.

5.2.3.2 Avoidance of cathodic disbonding is achieved by setting a maximum limit to the negative potential applied by the CP system as indicated in Table 5.1.

5.2.3.3 High strength low alloy steels (>700MPa proof stress) and certain grades of stainless steel are prone to hydrogen embrittlement and hydrogen-induced cracking under excessive CP. To mitigate the risk of over protection of these materials by the CP system, the accepted requirement is for a maximum potential that is lower (less negative) than that for mild CsteelC or aluminium as indicated in Table 5.1.

5.2.3.4 Marine grade aluminium alloys are prone to accelerated corrosion in highly alkaline conditions. The CP system design must not allow the potential to exceed the maximum indicated in Table 5.1 for aluminium hulls.

TABLE 5.1 TYPICAL VALUES OF MINIMUM AND MAXIMUM NEGATIVE PROTECTION POTENTIALS

Limits of the protection potential

(vs Ag/AgCl/seawater)

Material protected

Minimum potential Maximum potential

Mild Steel

- aerobic environment

- anaerobic environment*

-0.80V

-0.90V*

-1.15V

-1.15V

High strength steel

(>700MPa)

-0.80

-0.95V**

Aluminium alloys

(Al-Mg and Al-Mg-Si)

-0.85V

-1.00V P

†P

Stainless steels -0.60V -0.95V**

Nickel aluminium bronze -0.45V -1.10V

* Presence of active anaerobic bacteria e.g. sulphate-reducing bacteria (SRB) lowers the EBCORRB of steel; a lower minimum protection potential is required for adequate CprotectionC.

** High strength steels and certain grades of stainless steel suffer from hydrogen embrittlement and cracking as a consequence of CP; over protection should be avoided.

P

† PAluminium alloys suffer increased corrosive damage in highly alkaline conditions.


16



5.2.4 TCurrent densities required for protection

5.2.4.1 The protection potential criterion for CP system designs dictates that the surface shall be polarised to the required potential in the environment. To rationalise CP system designs, the current demand to maintain the structure at the protection potential shall be calculated based on the total wetted surface area of the hull and other immersed surfaces and estimated values of current density.

5.2.4.2 The CP system shall provide sufficient current to achieve and maintain the protection potential between the limits specified. The current requirements for CP may be determined by experience from similar structures, trials, testing or calculated data. The CP system designer shall document all assumptions, trial and calculated data used in derivation of the total current required. Testing to verify the system can maintain required protection potentials are detailed in subsequent sections.

5.2.4.3 When current densities are used to evaluate total system performance, the CP system designer shall provide supporting values for the following:

− initialisation current density required to achieve initial polarisation to the protection potential; − maintenance current density required to maintain polarisation; − final current density required for repolarisation after damage to coatings, removal of calcareous

deposits or hull cleaning.

5.2.4.4 The CP system design shall be divided into zones to facilitate calculation of, and adjustments in, the current demand from different metals or special areas of the structure. The designer shall provide data to support current densities for all wetted zones describing the dimensions of each zone and shall show that the protection potential criterion is achieved in each individual zone.

5.2.4.5 It is accepted that a single CP system design may not adequately protect a given area of a vessel under all operational conditions. For vessels restricted to specific geographical locations, the protection currents required are predictable for the majority of their operational life. For vessels with world-wide operation, estimates shall be made based upon the time the vessel will be located in the worst operating environment such as Arctic or Antarctic waters. Polar waters place the largest requirement on CP systems of ships which do not operate in fresh water.

5.2.4.6 In many standards and recommended codes of practice, current densities required for protection at or below -0.80V (vs Ag/AgCl/seawater) are quoted as advisory values for designers based upon assumptions at various points in the life-cycle of the structure.

5.2.4.7 Note: The current required to protect a surface throughout the life of the structure will depend upon several environmental factors, such as seawater temperature, dissolved oxygen concentration and salinity that will vary with geography and operational conditions. Operation in cold Arctic or Antarctic waters with high dissolved oxygen concentration increases the CP current requirement. Operation in brackish waters with decreased salinity and conductivity also increases the CP current requirement. The oxygen concentration available at the cathode (hull) surface varies with flow rate CsuchC that the current required for protection will increase with vessel speed up to a limiting level.

5.2.4.8 Note: A surface under stable CP system control will have precipitates of calcareous deposits (insoluble carbonates and hydroxides) that reduce the oxygen available for corrosion processes and therefore decrease the current demand.

5.2.4.9 A balance between the factors that influence the available oxygen has to be accounted for when predicting current demand from a CP system.

5.2.5 TCoating damage (coating breakdown factors)

5.2.5.1 Experience has shown that all coatings have an initial level of damage, defects or porosity. For the initial current calculations, the designer shall assume 1% damage (i.e. where bare metal is exposed) of the total surface area as a minimum value.


17



5.2.5.2 Coatings shall be applied in accordance with the requirements of the appropriate naval standards for painting and to the paint supplier specification. Unless indicated otherwise in a contract, reference shall be made to DEF(AUST)5000 Vol 03 Pt 04.

5.2.5.3 In service, the coating will suffer increasing amounts of damage or loss and as a consequence the current required for maintaining the protection potential will increase. Coating loss up to 15% must be expected. Where operational experience with a particular class of vessel is available, it shall be used to apply realistic coating damage levels for CP requirement calculations.

5.2.5.4 Each separate material (steel, aluminium, nickel aluminium bronze, etc) or separate coated area shall be considered to have its own initial level of coating damage. The rate of increase in coating damage shall be considered separately for each area. The CP system designer shall assign an average coating damage value (for each area of the surface) over the life of the system up to a predicted percentage of final coating damage.

5.2.5.5 The Commonwealth and paint coating supplier should be consulted by the CP system designer to provide appropriate advice on the final percentage damage for the scheme used on the vessel. The paint supplier will recommend replacement interval for anti-corrosion paint coatings. The time between dry-docking and hull coating replacement shall be the agreed ‘minimum’ system life for a sacrificial anode CP system. ICCP systems are to be designed to remain operational for the life of the vessel.

5.2.5.6 Where existing data for coating loss is not available, recognised standards given in the reference list in Section 2 should be consulted. Typical coating breakdown factors in seawater conditions are given as examples.

5.3 Requirements specific to ICCP 5.3.1 TIntroduction

5.3.1.1 This section describes the design requirements for ICCP systems for both surface ships and submarines. Key elements of ICCP systems are listed in A.2.2.

5.3.1.2 As noted in 5.1.1.5, ICCP systems are not recommended for use in enclosed spaces.

5.3.1.3 The development of ICCP systems for application to aluminium alloy vessels remains immature and special demands on the system are required to avoid damage to the ship structure. An ICCP system shall be considered for aluminium alloy vessels only with appropriate verification data and justification given for the chosen design.

5.3.1.4 ICCP is an active method of cathodic protection, in which the current is supplied to the protected surface using power supplies internal to the vessel. The current requirements for CP shall be determined by testing or by calculation. The CP system designer shall document all values and assumptions made to derive the total current requirement.

5.3.1.5 The CP system designer shall ensure that sufficient current is supplied by the system to maintain the structure at the protection potential within the limits given in Section 5.2 for the life of the structure. The CP system shall have sufficient capacity to allow for hull coating deterioration over the life of the vessel.

5.3.2 TICCP system design parameters

5.3.2.1 The ICCP system shall be tailored for the specified hull geometry or class of vessel. The designer shall be responsible for determining the layout and positioning of reference electrodes and anodes around the vessel hull. The CP system shall be designed and performance characteristics derived from calculations supported by computational or physical scale models.

5.3.2.2 For Major Fleet Units (MFU), taken to be over 1000 tonnes full load displacement for the purposes of this document, Cthe C ICCP system installation shall be divided into CP zones. Each CP zone shall be protected by a dedicated system of power supply, anodes and reference electrode as specified by the designer. Multi-zone CP systems shall be designed to interact so that the control system can adapt and optimise the current distribution.


18



5.3.2.3 The current density requirement for individual CP zones will be different and different types of CP system may be employed for such zones. The division of vessels into CP zones allows the appendages such as propellers and shafts to be accounted for separately to meet their required protection criteria. Localised CP zones such as free-flooding sea chests or bilge compartments need to be considered independently, with different protection demands during the life of the vessel.

5.3.2.4 In situations where the hull is protected by ICCP, the designer shall describe separately the CP system for bilges, internal spaces (e.g. sea chests) or tanks. The preferred choice of CP system for these areas shall be sacrificial (galvanic) anodes for the reason stated in 5.1.1.5.

5.3.2.5 For the purposes of this document it is assumed that the individual equipment or components of the ICCP system will be commercial off-the-shelf (COTS) items where applicable. The supplier of the equipment or component will be responsible for their own design. The CP system designer will ensure the equipment or component, including their integration, are fit for service as part of the design verification process. The ICCP system components shall meet the operating environment requirements of the vessel (i.e. electromagnetic compatibility, vibration, temperature, humidity, etc).

5.3.3 TAnodes

5.3.3.1 For the purposes of this document, except as noted below, the specification for the ICCP anode type is the responsibility of the supplier with specific knowledge of their own standard hardware.

5.3.3.2 The anodes used for impressed current systems shall be inert, such as titanium or niobium with a thin layer of platinum (platinised). Alternative acceptable commercially available anodes are titanium-coated with mixed metal oxides (iridium/tantalum oxides).

5.3.3.3 Anodes should be suitable for the life of the vessel. Rugged designs must be chosen for anode assemblies and attachments and the anodes must be positioned to avoid mechanical damage in service. The loss of an anode can significantly reduce the performance of the system.

5.3.3.4 The CP system designer shall determine the number, size and location of anodes in order to distribute current from the power supplies evenly across the hull. There is a high current output from impressed current anodes and a small number of anodes are used compared to sacrificial anode systems. The anodes shall be capable of working at the required voltages with sustained current output for extended operating periods.

5.3.4 TAnode dielectric shields

5.3.4.1 It is accepted that the operation of all CP systems generate hydroxyl ions (alkalinity) and hydrogen gas that can cause cathodic dis-bonding damage to hull coatings. The high current densities on ICCP anodes produce the additional problem of chlorine gas evolved from anodes by electrolysis of seawater.

5.3.4.2 In proximity of an anode, the hull and hull coating shall be protected by additional shielding to avoid large CP current entering the hull immediately adjacent to the anode. The shielding will improve current distribution to areas remote from anodes and increase the efficiency of the CP system.

5.3.4.3 The ICCP system design shall include anode (dielectric) shields to isolate anodes from hull coatings. The operating potential of the anode is more negative than the safe level for paint dis-bonding (e.g. -1.2V). The shield must be designed to the geometry of the anode to ensure the potential at the edge of the shield is less than the maximum allowable potential for the hull. It is recommended that the hull should be protected within 0.8m of any anode by a suitable dielectric shield material or coating.

5.3.4.4 The material chosen shall be electrically insulating, resistant to cathodic disbonding and to corrosive chemicals such as chlorine and hypochlorous (HOCl) acid produced on the anode. The design life of the system and deterioration of shielding with age may need to be considered for long term installations. The designer shall specify the shielding requirement to be applied to the hull in the proximity of each anode.


19



5.3.5 TReference electrodes

5.3.5.1 It is the responsibility of the CP system designer to ensure that there are sufficient reference cells to characterise adequately the state of the hull. Reference electrodes must be provided to measure the hull potential so that corrosion protection can be maintained throughout the life of the vessel. The reference electrode must have a stable operating potential throughout its life and be resistant to chemical degradation or environmental contamination, including growth of marine fouling.

5.3.5.2 It is generally accepted that silver/silver chloride (Ag/AgCl) reference electrodes are the preferred choice for naval vessels. The CP system designer will stipulate the type of silver/silver chloride reference cell to be used.

5.3.5.3 A shielded Ag/AgCl electrode in saturated potassium chloride (KCl) will be used for control systems and calibration of all reference electrodes used. Unshielded Ag/AgCl in seawater may be used to monitor the hull potential although the reference cell may be prone to a small voltage drift (<5mV) relative to the concentration of chloride ions in seawater.

5.3.6 TPower supply unit and controller

5.3.6.1 The CP system designer shall be responsible for specifying the type and number of power supply unit(s) required for the CP system design. It is expected that standard commercial power supply units (PSU) will be procured for ICCP systems. The design and specification for commercial units will be the responsibility of the supplier.

5.3.6.2 The amount of current output from the power supplies is calculated by a controller which may be a simple analogue feedback circuit or a more complex computer-controlled digital feedback system. The controller establishes the required current to be supplied to anode(s) by the PSU by measuring the variation in potential measured at hull mounted reference electrodes relative to the preset protection potential at the controller.

5.3.6.3 The CP system designer should ensure that the controller and PSU is capable of measuring and responding, over a short response time, to variations between the preset potential and the hull potential being tracked by the reference electrodes. The ICCP system shall be tested to ensure adequate response time to potential variation and the anode current output measured to avoid over protection of areas of the hull close to anodes.

5.3.6.4 It is the responsibility of the CP system designer to ensure that the PSU and control system are stable allowing for possible alterations to the system current demand caused by hull coating damage and changes to the external environment.

5.3.7 TElectrical connections

5.3.7.1 Electrical cabling is required to connect anodes and primary structure (cathode) to power supplies and reference electrodes to the controller. All electrical cables and wires used in the CP system shall be rated as suitable for intended service. All cables shall comply with the requirements of DEF(AUST) 5000 Vol 05 Pt 10. Anode, cathode and reference electrode cabling shall be clearly identified by individual colours.

5.3.7.2 Cable insulation and sheathing shall be resistant to degradation in seawater and to chlorine and hypochlorous acid produced at the anode. Insulation and sheathing shall also be fire retardant and have very low risk of toxic fumes produced during melting or burning. Reference shall be made to DEF(AUST)5000 Vol 05 Pt 10 and Vol 02 Part 10 for specific requirements.

5.3.7.3 The cabling required for connecting the reference electrodes to the controller shall comply with the requirements of DEF(AUST) 5000 Vol 05 Pt 10 for shielded multi-strand cables.

5.3.7.4 The CP system designer shall be responsible for cable runs and layout. Cables must be suitably protected against mechanical damage in service or electromagnetic interference. Cable installation shall be in accordance with DEF(AUST)5000 Vol 05 Pt 03. Cabling must be routed to avoid fuel tanks, magazines and compartments where explosive atmospheres may form. Where this is unavoidable, cabling and cable ducting must meet the Intrinsically Safe requirements applicable to any such compartments.


20



5.3.7.5 Hull penetrators shall be included to carry the current for anodes or voltage signal from reference cells from the wetted hull surface to the PSU and controller inboard. For surface vessels, the ICCP system will require hull penetrators (cofferdams) to guarantee waterproof connection for each anode and reference cell. For submarines, the ICCP system will require a pressure hull penetrator and an external hull penetrator to accommodate multiple leads from anodes or reference cells.

5.3.8 TTesting & installation

5.3.8.1 The CP system designer shall be responsible for testing the installed system against the design parameters determined by calculation or modelling data. The CP system designer shall be required to carry out all pre-energisation checks on the system. The start-up procedure shall be provided to the Commonwealth as part of an Operations and Maintenance Manual covering the CP system.

5.3.8.2 The CP system designer must verify that all anodes are working and there is a good response time for the anodes when the system is energised. The initial polarisation of the hull shall be monitored to verify that the CP system can achieve the protection potential criteria.

5.3.8.3 The designer shall ensure that all reference electrodes are calibrated against a standard reference cell to within 2mV or better. The designer shall determine that all reference electrodes are measuring correctly and that the reference electrode readings ensure sufficient current is supplied to protect the whole hull. The CP controller system set points must be adjusted, if necessary, to comply with the protection potential criterion.

5.3.8.4 The correct operation of the ICCP system shall be confirmed through trials undertaken by the designer and validated by the Commonwealth. Trials are to include automatic logging of anode current and reference electrode values when the vessel is both static and underway at different speeds. The system should both correctly sense and respond to the changed conditions, by changing the anode currents to maintain the hull potential at the set point (preset potential). The designer is responsible for taking any corrective action necessary to achieve the performance requirements stated in this document.

5.3.9 TIn-service Performance Monitoring

5.3.9.1 It is accepted that all ICCP systems will be designed to operate in association with a suitable hull coating. The CP system designer and Commonwealth shall have identified a level of coating damage and predicted rate of loss during design verification. It is the responsibility of the Commonwealth to schedule regular docking intervals to ensure that the coatings are maintained within the specified design margins.

5.3.9.2 It is recommended that hull inspections for coating damage are carried out at regular intervals so that a data base of coating loss for a particular class of vessel can be established. A system performance test in the form of a hull potential survey shall be undertaken before coating inspection. Further details of conduct of hull potential surveys are provided in paragraph 5.5.1.3. The frequency of hull potential surveys will be determined by the Commonwealth.

5.3.9.3 It is recommended that the performance of ICCP systems in service are monitored by collection of anode currents and reference electrode potentials under operational conditions. The ICCP settings and environmental conditions shall, as far as practical, be achieved via automated logging systems that can be downloaded periodically for processing or review.

5.3.10 TShaft grounding system

5.3.10.1 ICCP systems shall have a shaft grounding assembly connecting propeller shafts to the hull. This assembly is designed to conduct current entering a bare, non-ferrous metal propeller from the seawater back to the hull. For most vessels a significant proportion of the ICCP current flows directly into the propeller and along the shaft, over 90% when the hull coating is new. A shaft grounding assembly shall be fitted to prevent accelerated corrosion of seals, propeller shaft, gearbox and bearing components.

5.3.10.2 The CP system designer shall calculate the total current expected to return to each shaft from data used to verify the design. The shaft grounding system shall be designed to be capable of


21



grounding all current that is expected to flow in the shaft. The grounding capacity of the system shall be no less than 150% of the total current flow expected in each shaft. Each shaft shall be fitted with a separate grounding assembly.

5.3.10.3 The shaft grounding supplier shall provide the grounding capacity for their system. The designer will ensure that sufficient grounding devices are installed on each shaft to handle the expected current. Any new ICCP system installed on a vessel shall incorporate a shaft grounding device.

5.3.10.4 Shaft grounding assemblies are supplied for installation in two types: (1) passive and (2) active. Passive shaft grounding systems (PSG) shall be fitted as an upgrade to existing ICCP systems or retrospectively to existing vessels with partial ICCP installations.

5.3.10.5 Where active shaft grounding (ASG) is fitted, there shall be specific instruction (and preferably an interlock) to switch off ASG if the ICCP system is shut down to avoid the power supply polarising the hull positively causing accelerated corrosion damage to the hull.

5.3.10.6 The fitting of ASG shall be specified for vessels where a low Extra Low Frequency Electromagnetic (ELFE) signature is a major requirement. See DEF(AUST)5000 Vol 07 Pt 21.

5.3.10.7 Commercially available passive shaft grounding (PSG) devices consist of silver rings electrically bonded to the shaft with a brush assembly conducting current directly away to the hull. The PSG device shall be designed such that the shaft-to-hull voltage can be maintained at less than 50mV at maximum ICCP current output.

5.3.10.8 Where the shaft grounding system supplied is equipped with a meter that shows the shaft-to-hull voltage, it is recommended that meter readings are routinely recorded manually onto log sheets by trained personnel or by automated logging systems that can be downloaded periodically in an electronic file format. This will enable detection of deterioration of the PSG slip rings and brushes apparent as a high resistance. The detection of a high resistance in the shaft grounding system will trigger maintenance of the brush and slip ring.

5.3.10.9 New class ships or the complete refit of ICCP systems on existing ships shall include Active Shaft Grounding (ASG). ASG devices are designed with three sets of slip ring assemblies on the shaft. The active shaft grounding system consists of a potential monitor connected to the first slip ring and a power supply connected to a second set of slip rings. The ASG power supply effectively places a very low resistance between the shaft and the hull, better than that obtainable from a new PSG system, and not subject to the gradual deterioration of a PSG system. The final slip ring assembly shall have a standard PSG device in place in case the active components of the system fail.

5.3.10.10 The ASG power supply is required to supply sufficient current to the hull from ring 2 to control the shaft-to-hull voltage at ring 1 such that it remains less than 2 mV. This requirement of the ASG system indicates that the shaft had been grounded fully (all current has left the shaft at ring 2) and the shaft-to-hull voltage approaches 0mV measured at ring 1. Any voltage at or above 2mV at ring 1 should induce more current supply from the ASG unit to the hull at ring 2.

5.4 Requirements specific to sacrificial anode systems 5.4.1 THull sacrificial anode CP systems

5.4.1.1 This section gives the requirements for CP systems designed using sacrificial (galvanic) anode layouts for hull protection. The requirements for sacrificial anode CP systems for bilges, ballast tanks and sea-chests are given in Sections 5.4.7 to 5.4.11.

5.4.1.2 It is expected that future CP system designs for all ADF vessels shall concentrate on ICCP systems for hulls and sacrificial CP systems will be used for localised CP or internal applications. As such, the requirements of this section are mainly intended to apply to refurbishment of existing vessels that already have sacrificial anode systems installed, in particular aluminium-hulled vessels and small vessels with limited service life.

5.4.1.3 The requirements do not cover detailed anode designs or configurations necessary to protect specific structures or hull types. The CP system designer shall be responsible for verifying detailed designs by empirical data or modelling.


22



5.4.1.4 For the purposes of this document, it is assumed that most areas covered by a sacrificial anode CP system design will be protected initially by a suitable coating scheme. Large areas of uncoated steel or aluminium on the hull will require excessive anode mass to achieve protection and should be discouraged at the design stage.

5.4.1.5 Where ever possible, anode layout on the external hull should be such that it minimises additional hydrodynamic resistance. This is particularly the case for smaller vessels. Where necessary, multiple anodes in a particular location should be aligned end to end and approximately aligned with expected streamlines around the hull. Anodes should be placed such that they create minimal disruption to the flow into propellers or around rudders to minimise risks of causing cavitation, erosion, increased vibration and reduced performance.

5.4.2 TAnode materials - external

5.4.2.1 The primary components of sacrificial (galvanic) CP systems are anodes. The anodes applied to ship hulls or within internal spaces (see Section 5.4.7) are primarily alloys of aluminium or zinc. The chemical composition of zinc and aluminium alloy anodes shall comply with AS 2239-2003, Tables 2.2 and 2.3 respectively.

5.4.2.2 The anodes for current RAN vessels shall be the metric versions of Navy Type 1, Type 2, Type 3 zinc anodes, and butted Type 4A, Type 4B, Type 4C, and Type 5 aluminium anodes.

5.4.2.3 Note: Navy Type 1, 2 and 3 zinc anodes have a cast-in galvanized steel strap with protruding ends and pre-drilled holes for bolt/stud attachment.

5.4.2.4 Note: Type 4A, 4B and 4C aluminium anodes have a cast-in internal steel strap with access holes in the casting and pre-drilled holes in the strap to allow mounting on studs. Long continuous butted arrays of anodes can be formed by combining the different types, as Type 4A has one rounded end, whereas Type 4B and Type 4C have square ends, but different lengths.

5.4.2.5 Note: Type 5 aluminium anodes are identical in dimensions to Type 1 zinc anodes.

5.4.2.6 Where COTS anodes are used these shall be cast or extruded forms for flush mounting, stand-off, direct (bolt) mounting or bracelet types to the weight and dimensions given in AS 2239-2003, Appendix B. Flush mounted anodes are preferred for external hulls to reduce flow rate and drag on the anodes and improve fuel consumption for the vessel.

5.4.2.7 Typical physical and electrochemical properties of sacrificial (galvanic) anodes are given in Table 5.2.

5.4.2.8 Magnesium alloy anodes are not considered suitable for long-term protection of ships hulls or within closed tank spaces where hydrogen gas may accumulate unless adequate venting is available. The use of magnesium alloys is recommended for protection in high resistivity environments such as rivers and inland waterways; this application is considered to be outside the scope of this document.

TABLE 5.2. TYPICAL SACRIFICIAL ANODE ELECTRICAL PROPERTIES

Anode Material

Open circuit

potential vs Ag/AgCl

Closed circuit

potential vs Ag/AgCl

Current capacity (Ah/kg)

Anode

consumption (in seawater)

(kg/A.y)

Density (kg/m P

3P)

Zinc -1.05V -1.00V

740-780 10-12 7130

Aluminium -1.10V -1.05V 2000-2300 3-3.5 2700


23



5.4.3 THull protection current requirements

5.4.3.1 The sacrificial CP system shall be designed to provide sufficient current to polarise the entire hull and external attachments to a potential within the protection potential limits specified in Section 5.2. The exact location and distribution of different types of anode shall be part of the detailed corrosion protection design.

5.4.3.2 The CP system designer shall be responsible for calculating the current necessary for protection. The current capacity for the anode material chosen shall determine the number of anodes required for the hull. The designer shall provide data with any assumptions made to verify that the design complies with the current demand.

5.4.3.3 The CP system designer shall be responsible for the exact anode configuration around the hull to ensure that the necessary current is distributed to all external underwater areas. The designer shall provide surface area calculations based upon detailed drawings of the hull and all separate attachments with the current requirements to protect each area of the external surface. The design configuration shall be verified by modelling before acceptance.

5.4.3.4 The CP system designer will be responsible for listing all areas and items protected by the design with a description of the surface treatment (i.e. bare, painted or coated) in each area.

5.4.3.5 The CP system designer shall specify the intended anode life for the system based upon the current output per anode under normal operations. The designer should detail any assumptions made for calculation of anode consumption, such as mean current demand, or assumed rate of paint coating damage, such as 1% per year, or maximum expected percentage damage to coatings.

5.4.4 TOperational requirements – hull protection

5.4.4.1 The sacrificial CP system designer shall specify the choice of anode type, including the number of different types to be used, exact layout of the types of anodes over the protected surface and the total mass (kilograms) of each anode type.

5.4.4.2 The CP system designer and the Commonwealth shall agree the operating parameters for all parts of the protected surface based upon the anode consumption rate and anode design life. The design life of the system should normally be based on a minimum 5-year period between refit or hull survey for the vessel. CThis C will determine dry-docking periods when the sacrificial anodes must be inspected for excessive metal loss, uniformity of metal loss, mechanical damage and evidence of passivation (non-activation).

5.4.5 TSacrificial anode bonding

5.4.5.1 The performance of sacrificial CP systems requires a low resistance connection between the anode and the protected surface. The CP system designer shall specify the bonding onto the protected surface that each anode type will require.

5.4.5.2 The CP system designer shall state the total resistance requirement for all anodes used in the system to ensure electrical continuity. The core to anode resistance shall be specified by the anode supplier; the anode to hull resistance will be determined by the method of attachment such as welding, bolting or stud mounting.

5.4.5.3 The anode supplier shall specify the predicted anode utilisation factor. This value is a measure of the percentage of an anode which can be consumed before it ceases to function as an anode. Sacrificial anodes are consumed during operation such that their surface area decreases, the anode to seawater resistance increases and as a consequence the ability of the anode to supply current is reduced.

5.4.5.4 The sacrificial CP system shall be designed to compensate for the reduction in current as a result of anode utilisation under normal conditions. The CP system designer shall use the anode utilisation factor as part of empirical data supplied for the design life.


24



5.4.6 TTesting and through-life maintenance

5.4.6.1 The composition of sacrificial anode materials supplied shall comply with the requirements of AS 2239-2003. The supplier shall supply electrochemical test data to prove that anode material of the specified composition will have the correct open circuit potential (and in the case of aluminium anodes, closed circuit potential) and current capacity.

5.4.6.2 Any anode supplied for fitting shall be inspected for visible cracks and surface defects; no visible cracks should be allowed other than in the immediate region of the core insert.

5.4.6.3 Fitted anodes shall be tested for anode to surface resistance to ensure a connection resistance of less than 0.1Ω. Testing should be made with a device suitable for low impedance measurement.

5.4.6.4 During refit periods anodes shall be removed, or all anode and contact surfaces shall be masked off if re-coating of the hull surface is to take place. Any temporary covering applied to the anode to prevent over-coating shall be removed once refit is CcompleteC, and any removed anodes shall be replaced.

5.4.6.5 Through-life maintenance of sacrificial anode systems shall be limited to periodic replacement.

5.4.7 TSacrificial CP systems for internal spaces

5.4.7.1 This section covers the requirements for sacrificial anode protection of sea-chests, ballast tanks, bilges and other tanks where the use of ICCP systems is not CrecommendedC.

5.4.7.2 Currently many seawater-flooded internal spaces and tanks in RAN surface vessels are not protected by sacrificial anode systems and the protection of these areas is achieved by frequent monitoring of protective paint and renewal where necessary. Installation of sacrificial anodes to increase protection of the structure and to minimise the inspection and re-painting CcostsC is mandatory for all new-build ADF vessels, and highly recommended for retrofit of existing vessels..

5.4.8 TAnode materials - internal

5.4.8.1 Zinc anodes are chosen for bilges or flooded internal spaces such as sea-chests or ballast tanks. Typical physical and electrochemical properties of zinc sacrificial anodes are given in Table 5.2.

5.4.8.2 Magnesium anodes shall not be used in closed tanks or internal spaces where hydrogen gas may accumulate creating an explosion risk.

5.4.8.3 Low voltage aluminium alloy anodes (potential -0.85V vs Ag/AgCl) are available but at high cost compared to other aluminium or zinc anodes, for protection of high strength steel surfaces. Where these anodes are specified for CP system designs mainly in tanks or confined internal spaces, the design shall be verified using modelling before acceptance.

5.4.8.4 Sacrificial anodes fitted in internal spaces shall have the same bonding requirements as external anodes (see Section 5.4.5).

5.4.9 T Protection current requirements - internal

5.4.9.1 The sacrificial CP requirement for sea-chests, bilges and tanks shall be determined from the internal surface area, condition of coatings (assumed damage), types of metal, dissimilar metal joints or welds as well as access opportunities for inspection. The CP system designer shall specify the number and exact location of anodes to supply the protection current requirement.

5.4.9.2 The designer shall supply empirical data and all necessary calculations, stating any assumptions made, to demonstrate that the protection potential criteria can be achieved. The performance of the CP system will subsequently be verified as required in Section 5.8.6.

5.4.9.3 As ballast tanks always contain a residual level of seawater below the suction point, it is a requirement that pit-guard anodes are located in each immersed section of the tank, such that they are always immersed and provide protection to these areas of the tank even when nominally empty. The remainder of the anodes required for protection of the tank when it is partly or completely filled should be distributed to provide the best overall protection.


25



5.4.10 Operational requirements - internal

5.4.10.1 Individual areas of bilge compartments or tanks may require longer CP system design lives based upon the periods when these areas are wet. The actual period determined by the Commonwealth may be different from the stated design life. The system designer will make allowance for periods when tanks are not wet or areas are not flooded with seawater. Sacrificial CP system design life shall be at least 5 years for internal spaces and bilges based upon anode consumption and the expected degree of damage to the coatings in these areas. A design life of 15 years is desirable for ballast tanks and other tanks which are infrequently accessed.

5.4.10.2 Note: For anodes fitted into seawater tanks or bilges, inspection in-situ can be expected to be limited mainly to visual observation for excessive wastage but, where possible, corrosion products would be removed from anodes and the surfaces checked for excessive pitting or metal wastage.

5.4.10.3 Noting that some internal compartments may be relatively inaccessible , consideration should be given to installation of remote monitoring systems to assess coating and CP system performance and remaining life.

5.4.11 Testing and through-life maintenance - internal

5.4.11.1 The composition of sacrificial anode materials supplied for sea-chests, bilges and tanks shall comply with the requirements of AS 2239-2003. The supplier shall provide electrochemical test data to prove that anode material of the specified composition will have the correct open circuit potential and current capacity.

5.4.11.2 Ballast tanks sacrificial anode installations have been developed that incorporate anode current measurement and tank potential measurement features, coupled to in-tank data collection hardware. These can be used to continuously monitor the condition of tank protective coatings and when periodically interrogated, provide warning of coating deterioration and incipient coating failure. It is desirable for such anode installations to be used in seawater ballast tanks for in-service performance monitoring.

5.5 Requirements for performance management 5.5.1 TPotential measurement system

5.5.1.1 CP systems shall be monitored by measurement of the potential between the protected surface and the electrolyte.

5.5.1.2 For ICCP systems, the hull potential will be monitored automatically by reference electrodes integral to the system. The CP system designer shall incorporate sufficient reference electrodes to measure all protected parts of the underwater hull and appendages bonded electrically to the hull. The Commonwealth, through trained personnel, shall be responsible for setting the ICCP controller set point potential and adjusting settings when required. The reference electrodes shall be calibrated against a standard reference cell periodically during the life of the vessel. The CP system designer shall determine the frequency at which such calibration is required based on component manufacturer recommendations.

5.5.1.3 Potential surveys of the hull or internal spaces protected by sacrificial anodes shall be conducted with a high impedance voltmeter and a suitable reference electrode cell (Section 5.5.2). Direct potential measurements shall be taken from either a fixed point on the structure or multiple underwater points (away from anodes) with the measuring electrode immersed close to the surface of the structure. As a minimum, a dipping reference electrode hull potential survey would involve measurements around the perimeter of the main deck, at port and starboard bow, midships and stern, and at a constant immersion depth of 2 m. Alternatively a diver or ROV can obtain more localised potential measurements of the underwater hull or attachments. Anomalously high or low potential readings require investigation as to their cause.

5.5.1.4 The Commonwealth shall determine the frequency of hull potential surveys required for each class of vessel.

5.5.1.5 Vessels fitted only with sacrificial anodes shall be fitted with a CP monitoring and alarm system that comprises a hull-mounted reference electrode and a display/monitor system with high and


26



low set points. The monitor system must trip an alarm when the hull potential falls outside the allowable range which has the potential consequence of rapid galvanic corrosion of the vessel. The monitoring and alarm system is required to ensure rapid awareness of deleterious hull potential changes when the vessel is berthed alongside wharves, piers or other vessels, bonded to shore ICCP systems, on shore power, or when welding activity is undertaken. Such alarms allow appropriate corrective action to be taken by the crew.

5.5.1.6 ICCP systems shall be provided with continuous data logging of potential settings and current output by each anode and relevant seawater parameters such as conductivity, temperature, etc. Electronic logging systems will enable systems information to be downloaded periodically for off-vessel analysis.

5.5.1.7 The control and monitoring / logging elements of the CP system should be easy to read and understandable by appropriately trained personnel who may need to adjust settings during a voyage.

5.5.2 TReference cell system

5.5.2.1 The corrosion potential (EBCORR B) is measured as a relative potential for the metal against an arbitrary half-cell (reference electrode) in a specific electrolyte. For this document the electrolyte is always seawater.

5.5.2.2 There are several reference electrode systems employed for potential measurement, e.g. calomel/mercury/saturated potassium chloride, silver/silver chloride/saturated potassium chloride, silver/silver chloride/seawater, or high purity zinc/seawater.

5.5.2.3 The preferred reference electrode for the purposes of this document shall be silver/silver chloride in seawater (Section 5.3.5) . The use of different reference electrodes is not excluded but the measured potentials will be different. The reference electrode system shall be recorded for all potentials quoted in data sets for design purposes and must be given in the recording log for whole ship potential hull surveys.

5.5.3 TOperations and maintenance issues

5.5.3.1 An Operation and Maintenance Manual shall be provided by the CP system designer. The manual should be clearly written with instruction and guidance including:

5.5.3.1.1 details of the CP system installed

5.5.3.1.2 requirements for commissioning system,

5.5.3.1.3 operating instructions,

5.5.3.1.4 The requirement for grounding of onboard electrical equipment such as welding equipment onto the CP protected hull,

5.5.3.1.5 requirements and instructions for monitoring and maintain the system, including:

5.5.3.1.5.1 Tonboard system test and maintenance requirements and Tpreventative maintenance that can be carried out with the CP system operating,

5.5.3.1.5.2 detailed maintenance requirements for components in the system,

5.5.3.1.5.3 the frequency of scheduled refit, docking or maintenance requirements for the system, for the life of the vessel,

5.5.3.1.5.4 required frequency of visual inspection of sacrificial anode CP systems installed in internal space, where accessible,

5.5.3.1.5.5 guidance on assessing the condition of anodes and determining the need for replacement,

5.5.3.2 The Commonwealth may require additional detailed instructions on CP system operation for complex systems.

5.5.3.3 The Operation and Maintenance Manual is required to be updated to reflect any changes in CP system configuration through life.


27



5.5.4 TSafety issues

5.5.4.1 The Operation and Maintenance Manual shall detail the requirements for safe operation of the CP system.

5.5.4.2 The manual shall detail any potential risk to personnel operating the CP system, the risk to the structure of the vessel, particularly internal spaces, of CP system operation and the risk to onboard electrical systems while the CP system is operating. The manual shall identify risk mitigation measures for the identified risks.

5.5.4.3 Divers or swimmers in the vicinity of ICCP anodes risk death by electrocution at electric field strengths greater than 3 V/m (see AS/NZS 60479.1 and AS/NZS 60479.2). The ICCP Operation and Maintenance Manual shall highlight the need for the ICCP system to be shutdown and the power supply isolated (“tagged out”) when divers or swimmers are in the water close to ICCP anodes.

5.5.4.4 The Operation and Maintenance Manual shall highlight the requirement that closed tanks or confined spaces protected by CP systems shall be vented to avoid hydrogen gas accumulation from CP CanodesC. An explosive hazard may endanger personnel or cause critical damage to the vessel.

5.6 TShip fitting out and docking 5.6.1 In association with the ship designer, the Commonwealth shall specify the maintenance periods

required by each class of vessel. During refit and normal docking, the Commonwealth shall specify the requirements for maintaining CP and the contractor shall propose means of satisfying such requirements. The Commonwealth shall agree the frequency of hull potential surveying with the contractor during the course of the refit period.

5.6.2 The majority of shipyards and naval base jetties will have CP systems installed to protect this infrastructure. The operation and maintenance of these systems is not covered by this document and local advice and guidance may need to be requested if ADF ships are moored alongside such facilities.

5.6.3 Protection of vessels alongside shall normally be provided by means external to the vessel. The contractors shall be responsible for provision of either suitable suspended anode (sacrificial or ICCP) system, ground bed CP system or jetty CP system.

5.6.4 Temporary or permanent docking of CP protected vessels to harbour structures with CP systems requires electrical bonding checks of both CP systems before connecting. The potential of the vessel shall be measured after connecting to ensure there are no deleterious stray currents to or from the vessel that may cause either hull corrosion or cathodic disbonding of underwater coatings.

5.6.5 A vessel with ICCP shall have the onboard system shut down, particularly during maintenance on the onboard CP system or diver activity around the hull, when adequate CP systems and power supplies are in operation on the wharf or dock. In this case, the wharf or dock CP system should be sufficient to protect both the shore infrastructure and vessel. The potential on the seaboard side of the vessel shall be monitored to ensure the protection potential criteria are maintained.

5.6.6 Vessels protected externally by sacrificial anodes shall require physical monitoring while alongside. Temporary docking to jetties without CP systems shall require measurement of the vessel protection to ensure that the protection potential criteria are maintained. Ships that are regularly required to dock to jetties where no CP is in operation shall have provision to electrically isolated the CP system from mains earth to avoid current drain from the ship’s sacrificial anodes to the jetty, which would result in excessive anode wastage. This can be achieved through either installation of an isolation transformer in the shore power, and therefore no mains earth cable, or installation of a suitably rated polarisation cell or cathodic isolator in the connection to mains earth. This separates the ship’s DC CP system from the AC shore earth.

5.6.7 Polarisation cells and cathodic isolators allow fault current AC to flow safely from the ship to mains earth via the shore power earth cable. Whether such an isolation device is installed shipboard or as part of shore power facilities is dependent on Commonwealth advice as to the extent to which the vessel’s operations will necessitate such docking.


28



5.6.8 Note: Where electrical safety and shore power delivery requires that the vessel be bonded to a wharf bonding point this shall take priority. Refer to DEF(AUST)5000 Vol 05 Pt 11.

5.6.9 Vessels protected externally by sacrificial anodes may need isolation from ICCP protected jetties to avoid over protection (cathodic disbonding) damage to the vessel. The ship crew shall be responsible for checking compatibility of the CP systems before connecting to shore-based structures.

5.6.10 Where several vessels are tied in tandem onto a single berth, it is possible for the outermost vessel to use onboard ICCP protection. In this special case, the seaboard reference electrodes only shall be used for control input and the interactions with any jetty ICCP system monitored.

5.6.11 Due to the extended periods that ADF vessels spend berthed alongside wharves and jetties, and the potential for deleterious interactions with wharf ICCP systems, shore power, adjacent vessels and welding activities, there is a need for all vessels to be able to continuously monitor hull potential so that remedial action can be taken quickly before damage occurs. All vessels fitted only with a sacrificial anode hull CP system shall have a CP monitoring system installed, and if a vessel equipped with an ICCP system has the system PSU turned off while berthed, the controller must be capable of remaining activated in a mode that will enable monitoring of hull potential and signalling an alarm if hull potential deviates from the allowable range. Otherwise, a separate CP monitoring system shall be installed.

5.7 Corrosion and CP generated signatures 5.7.1 This section covers requirements for vessels that have a specific naval role that require the control or

elimination of electromagnetic signatures. For signature requirements, reference should primarily be made to DEF(AUST)5000 Vol 07 Pt 21. The requirements in this section are relevant only to the ship and CP system designers who need to consider the impact of electromagnetic signatures and may be required to minimise the corrosion related signatures of the vessel.

5.7.2 The CP system designer, on behalf of the ship designer, shall be responsible for determining the impact that the CP system design will have on underwater electric and corrosion related magnetic (CRM) signatures of the vessel.

5.7.3 Detailed signature design requirements are beyond the scope of this document; the requirement within this document is that all design variations shall be verified by computational or physical models.

5.7.4 The Commonwealth may agree with the ship and CP system designers that the ICCP system can be used for signature control. The UEP (or SE) and CRM signatures should be addressed by optimising anode and reference electrode configurations and ELFE signatures addressed by active shaft grounding (Section 5.3.10) and low ripple power sources.

5.7.5 DEF(AUST)5000 Vol 07 Pt 21 provides requirements for RAN ship signatures which are also relevant to submarines. The Commonwealth and CP system designer for submarines shall be aware of the sources of electromagnetic signature from corrosion currents around the vessel.

5.7.6 For the purposes of this document, the following brief signature descriptions should be sufficient:

− The static electric (SE) or underwater electric potential (UEP) signature of a vessel is the electric field generated spatially around the underwater areas of the hull by corrosion occurring on the surface. The CP system contributes to the electric signature through current flow into the electrolyte. The electric signature is dependent mainly upon the seawater conductivity and parameters affecting conductivity such as oxygen concentration, temperature and salinity, and by the proximity to the seabed and the conductivity of the seabed strata.

− The electric currents generated by corrosion and the CP system flowing in seawater and

through the hull have an associated magnetic field referred to as corrosion-related magnetic (CRM) signature. This magnetic field is dependent upon the conduction paths through the vessel as well as the ionic current flow through the seawater to metallic components, such as propellers, shafts, etc. The magnetic field arising from the seawater current paths cannot be effectively degaussed by the ship’s degaussing system.


29



− Electric or magnetic fields generated by any alternating frequency source on the vessel

contribute to the Extra Low Frequency Electromagnetic (ELFE) Signature. The alternating electric sources onboard the vessels generally have their origin in the CP system whilst the magnetic sources are typically from the on-board machinery (both mechanical and electrical). The three main CP ELFE sources are:

o the modulation of the CP current flowing through the shaft at the rotation frequency due to

variable resistance between the shaft and the hull (via passive shaft grounding slip rings); o the modulation of the CP current as it flows into the propeller blades generates ELFE at the

frequency of the blade rotation; and o direct modulation of the ICCP anode current by the power supply output ripple.

5.7.7 CP systems will contribute to UEP, CRM and ELFE signatures for a vessel. The overall ELFE signature is a summation of CP-derived ELFE and power frequency ELFE signatures arising from on-board electrical equipment such as transformers, switchboards, cables, generators and motors. Submarines fitted with ICCP systems will generate a CRM signature that unlike the electric signature resulting from corrosion, can be measured in the air region above the seawater such that a submerged vessel can be detected above water.

5.7.8 For submarines, it is advantageous for the CP anode currents to be set such that the signature is minimised, at the same time as the potential over the wetted surface is optimised for corrosion protection. It is the requirement of this document that CP systems provide adequate corrosion protection. It should be noted that an effective CP system design that is controlling corrosion may be detrimental to the achievement of low signatures. The electromagnetic signature will be a function of the hull state, coating integrity and the ICCP current settings as well as the environment. The ICCP signature shall be optimised by modelling potential profiles and current flow around hull for different anode and reference cell configurations and thereafter adopting the most suitable configuration to achieve both satisfactory CP and minimal signature.

5.7.9 For sacrificial anode CP equipped vessels, there is only scope to influence the electromagnetic signature during the design phase, as unlike ICCP systems there is no capability to adjust anode currents once the anode numbers and distribution over the hull have been decided and installed. There is also no ability to “turn off” a sacrificial anode CP system, or to deliberately adjust the anode outputs to produce a deceptive signature. Therefore, close consideration needs to be given by the Commonwealth to the signature requirements of the vessel, and establishment of signature Functional Performance Specifications which may dictate the selection and design of a multi-zone ICCP system to meet the signature requirements.

5.8 Requirements for design verification 5.8.1 TDesign verification

5.8.1.1 CP systems shall be designed to operate effectively for the life of the vessel. The CP system shall be integrated with an appropriate anti-corrosion coating to provide the overall corrosion protection system for any vessel.

5.8.1.2 For consumable items of CP systems such as sacrificial anodes, the design life shall be at least the time between refit/dry-docking when the coating and anodes may require replacement. The Commonwealth and CP system designer shall agree the lifetime criteria for any class of vessel.

5.8.1.3 The designs for new CP systems fitted to ADF vessels shall be verified by empirical calculation or modelling or both to ensure that the protection potential criteria can be achieved for the life of the vessel. Modelling is required for all new CP systems for vessels greater than 1000 tonnes full load displacement.

5.8.1.4 The CP system designer shall determine at what stage modelling should be used to verify the CP system performance. An ICCP system shall require performance verification through modelling as part of the iterative process of system design.


30



5.8.1.5 The CP system designer shall produce evidence to demonstrate performance under variable environmental conditions and with varying degrees of coating damage or loss predicted during the life of the vessel. The designer shall document the degree of coating damage used for calculation or modelling.

5.8.1.6 Note: Documents ASTM STP 1370 and NAVSEA T-9633-AT-DSP-010/ALL USN, should be consulted to estimate the rate of coating damage under particular environmental conditions.

5.8.1.7 It is accepted that the requirements for most sacrificial CP systems for vessels, internal space and tanks can be generated by empirical calculations but the design life, anode consumption and distribution are inter-related closely with environmental conditions and coating breakdown factors. Computational modelling is an accepted process for optimising the configuration of the sacrificial CP system in complex areas.

5.8.1.8 The CP systems fitted to existing vessels do not require design verification. Existing CP systems undergoing like-for-like component replacement during refit shall be reviewed against the protection potential criteria defined in this document.

5.8.1.9 The Commonwealth may review operating procedures and manuals for existing systems to ensure they comply with the requirements in this document.

5.8.1.10 The CP system designer shall provide empirical or modelling data to verify extensions to existing system designs or any upgraded system designs, particularly where such changes are implemented to resolve problems with the existing system.

5.8.2 TCalculation procedures

5.8.2.1 Sacrificial anode CP system designers shall provide empirical data to demonstrate compliance of the system with the protection criteria for the design life of the system. The designer shall ensure that the anode life is in excess of the design life of these consumables as defined in paragraph 5.8.1.2.

5.8.2.2 Sacrificial anode CP system designers shall provide all data and any assumptions made in calculations to verify the design life. The design life shall be calculated from the utilisation factor for anodes, the total surface area (including all separate CP zones); total current required; total mass of anode material required and total number of anodes required. The designer must arrange the anodes to achieve an even current distribution over the total surface to be protected.

5.8.2.3 The design life for anodes used in internal areas, bilges and tanks may differ from those set for the vessel refit or docking cycle. This is due to the possibility for either increased or reduced rate of coating CdamageC compared to the exterior hull as well as consideration of accessibility to such internal compartments. As far as possible, the shortest design life for internal CP systems shall be at least equal to the planned docking cycle period. The empirical data used for design life assessment shall be based on the worst case scenario of internal coating breakdown (typical values are 12 to 15% damage) and anode utilisation factors.

5.8.2.4 The required design life for CP of internal spaces, including tanks, shall be a minimum of 5 years. The design life may be qualified by time of wetness of the spaces, criticality of protection in that area and ease of anode replacement. The designer shall provide empirical data for internal surfaces, including experience with the lifetime of coating system used, to ensure the anode life is sufficient.

5.8.2.5 If the vessel is expected to occasionally operate under exceptional environmental conditions outside of the normal range specified in an OCD or FPS, then where the protection parameters for the CP system design have been verified by computational modelling, such modelling shall be extended to also assess the design life of the vessel when operate under such exceptional conditions.

5.8.3 TModelling Techniques

5.8.3.1 There are three modelling techniques applicable to CP system designs; computational techniques such as finite element (FE) or boundary element (BE) modelling, and physical scale modelling (PSM). The CP system designer shall identify the technique most applicable and cost-effective to


31



verify the design. The Commonwealth shall agree the verification method chosen by the CP system designer before acceptance of the system design.

5.8.3.2 There are several commercially available BE modelling suites that can be used to investigate the action of the ICCP system on the hull. PSM is available at specially equipped laboratories and concentrates on the engineering requirements of the design.

5.8.4 TPhysical Scale Modelling (PSM)

5.8.4.1 PSM is an experiment-based ICCP design technique, in comparison to computer simulation from BE or FE models, used to obtain a description of the potential distribution over a surface. PSM is worthwhile where optimising signatures is an important consideration. The Commonwealth and designer shall agree the requirement and benefits of applying PSM to ICCP designs. Use of PSM is also dependent upon CP system designer and Commonwealth agreeing upon the protocol and specification for building the model. Unless otherwise agreed, the protocol described in ASTM STP 1370 is to be used.

5.8.4.2 PSM shall not be required for sacrificial anode CP system designs, due to difficulty in modelling the polarisation characteristics of sacrificial anodes. However PSM may be used for sacrificial anode CP system design when modelling underwater static electric signatures, and for hull potential modelling. This is provided the sacrificial anodes are simulated by ICCP anodes with monitoring reference electrodes to maintain the ICCP anode at the simulated sacrificial anode output potential. This is -1.0V for simulated zinc anodes and -1.05V for simulated aluminium anodes.

5.8.4.3 Physical scale models shall be manufactured to the design methodology of the actual vessel with, as near as possible, an exact scaling of the actual vessel hull form and the same hull and appendage materials as used in the vessel. The environment should be scaled to create modelled ‘seawater’ with physical and electrochemical responses nearly identical to a full scale vessel in undiluted seawater.

5.8.4.4 Where the vessel is procured with an ICCP system installed that has been developed on the basis of PSM, the Commonwealth shall be provided with the PSM verification during development stages to identify areas of potential risk during the life of the vessel. The protection potential criteria shall be the overriding requirement.

5.8.4.5 Note: PSM is an older modelling method than BE analysis and has been the preferred method for complex ICCP design for the US Navy. The cost of model construction and special laboratory equipment need to be weighed against the evidence gained from the model. For the most part, the designer shall determine the type of verification model accessible for development of the CP system.

5.8.4.6 The value of PSM has been that, once constructed to a rigid engineering design, the physical model is best for determining ICCP component placement, life-cycle performance and various failure modes under static and dynamic operational conditions. PSM is likely to be the option for modelling complex geometries, restricted areas and coating degradation over the life-cycle.

5.8.4.7 A comprehensive understanding of PSM can be gained from reference sources particularly NAVSEA T-9633-AT-DSP-010/ALL USN, Ship’s cathodic protection, design calculations, design requirements manual.

5.8.5 TComputational Modelling

5.8.5.1 The CP system designer shall determine the type of computational corrosion model required as part of the design development for any new ICCP system application. Boundary element analysis of ICCP systems has been accepted as a standard method for new vessels.

5.8.5.2 A computational model, and any constraints applied to the model, should be constructed for ICCP systems during the design stage. This will allow several iterations and modifications to be made to the anode and reference cell configuration before the design is consolidated. The designer shall provide evidence that the ICCP system meets the design intent of the system. The Commonwealth may require evidence to be supplied at each stage of model iteration to ensure that the design requirement can be met.


32



5.8.5.3 The CP system designer and Commonwealth must recognise that coating loss or damage occurs randomly dependent upon the environmental conditions in service. This limits the computer model that can be constructed by BE and may not allow verification of common designs that may be close to the design margin in harsh environmental conditions. The Commonwealth shall provide to the CP system designer and modeller details on known coating performance relative to environmental conditions.

5.8.5.4 Coating loss or damage is considered an emergent issue that changes during the service life of the vessel and this issue should be accounted for within the model chosen for design verification (whether BE or PSM). In most cases, the ICCP system designer and Commonwealth shall agree on construction of models for resolution of complex configurations or unknown coating performance in harsh environments.

5.8.5.5 It is important that the data sets used to construct BE models shall be representative of cathodic polarisation behaviour of the hull material in the correct environment. Non-representative data may lead to inadequate protection applied to parts of the hull or over-estimate of the current demand.

5.8.5.6 The Commonwealth and system designer shall agree on the requirement for numerical modelling of sacrificial anode systems. Both parties should be aware that the application of numerical modelling to sacrificial CP systems may not contribute to an improved design, as experimental anodic polarisation behaviour is required for the lifetime of the anode, and at a range of hull speeds. The validity of the modelled design is highly dependent on the validity of the polarisation data used.

5.8.5.7 The application of numerical modelling for sacrificial CP systems shall be confined to verification of protection in any regions where anode distribution may be of concern. The model shall be constructed with sufficient detail included to verify flow of current and potential distribution. The numerical model shall be used to determine the design life of the CP system.

5.8.6 TWhole-ship CP acceptance test

5.8.6.1 The Commonwealth shall require the CP system designer and contractor to perform a whole-ship CP system test Tto verify the performance meets the protection potential criteria. The Commonwealth shall validate the acceptance test before final hand over of the vessel T.

5.8.6.2 Vessels that are procured with a pre-installed CP system shall be verified against the design criteria given in this document. The acceptance criteria shall be based upon operational performance of the CP system under static and dynamic conditions.

5.8.6.3 The specifications and operating data for all components used in the CP system shall be provided by their suppliers. The component data shall demonstrate compliance with the whole-ship operating environment. The performance of the system shall be determined by a hull potential survey (paragraph 5.5.1.3) using a reference electrode system independent of the CP system itself.

5.8.6.4 A new system installation shall be accepted against the design verification data and on completion of a satisfactory hull potential survey under static conditions, using portable dipping reference electrodes. For sacrificial CP systems, the whole-ship CP system test by the installation contractor shall include resistance checks between the hull and anodes and continuity bond checks for appendages protected by the system.

5.8.6.5 Given the typical absence of hull-mounted reference electrodes, and that dipping reference electrodes are only suitable for static and low speed measurements, it is not possible to conduct a hull potential survey while underway on a vessel equipped with sacrificial anodes. However, where the Commonwealth requires CP design validation underway, underwater data loggers may be fitted to selected hull areas, and hull potential monitored over a range of hull speeds and environmental conditions. Such data-loggers can also be used to supplement the information obtained from the distributed hull reference electrodes on an ICCP equipped vessel, for CP design validation underway.


33



5.8.6.6 The whole-ship ICCP acceptance test shall include an electrical continuity check on all conductors and cable runs from anodes, reference electrodes or hull to power supplies, including a continuity check on any shaft grounding assembly. The CP system designer and contractor shall be required to carry out all start-up checks on the full system or on individual parts of a zonal CP system to confirm anodes work and reference electrodes track hull potentials.

5.8.6.7 The operation of the ICCP system shall be shown to achieve the protection potential criteria given in Section 5.1 for the whole ship by independent hull potential surveys at multiple underway points. The whole ICCP system shall not be accepted until the Commonwealth has confirmation that the required protection potential can be achieved and the system is stable under both static and dynamic conditions.

6 DESIGN AND PRODUCT CONSTRAINTS

Common constraints relating to the design and operation of CP systems are addressed throughout this document. Further recognised constraints placed upon the utilisation of this document are considered in the following sub sections.

6.1 Specific Design/Engineering Constraints 6.1.1 The installation of the CP system to vessels shall have minimum adverse impact on the

hydrodynamics of the hull. Drag from anodes leads to higher fuel consumption so anodes should be of a streamlined design and aligned with the flow as far as possible. Consideration should be given to recessed sacrificial anodes, particularly for smaller high speed vessels.

6.1.2 The locations of sacrificial anodes are integrated into hull designs and appropriate fixtures should be in place for anode attachment. Upgrading vessels to ICCP systems will require a new hull architecture that will require engineering development to optimise the position of anodes and reference electrodes.

6.1.3 ICCP systems rely on anodes and reference electrodes that are relatively fragile and exposed on the hull. The anodes/electrodes should be designed and positioned to protect them from excessive flow or mechanical damage as the loss of an anode/electrode will have a critical impact upon system performance.

6.1.4 Sacrificial anodes and ICCP anode/electrodes shall be positioned to avoid accumulation of marine growth.

6.2 Navy Practice/Personnel Constraints 6.2.1 THull sacrificial anode CP systems are relatively inaccessible to ship personnel, and impose no

training or control constraints. Similarly, sacrificial anodes in tanks are inaccessible and normally require no intervention by ship personnel.

6.2.2 TICCP systems require personnel to be trained in the operation and control of the system. There will be a requirement for certification and training of personnel. Incorrect operation of the system may cause rapid and significant damage to either the underwater hull or coatings.

6.2.3 TICCP systems will require onboard automatic data recording of CP system settings and environmental factors. TData logging provides the Commonwealth with a reliable record of the performance of the ICCP system on board the ship and also facilitates analysis of CP system performance across the fleet and direct comparisons within a class of vessels. Automated collection also replaced the requirement for manual logging in accordance with ABR 5225. T

6.2.4 Reports are required to be provided in accordance with ABR 5225 Ch.46, adapted to take advantage of the automated data collection.

6.3 Interoperability Constraints T

6.3.1 The operation of the CP system or parts of the system shall not interfere with other shipboard systems such as critical communications, control or detection systems.


34



6.4 Commonality Constraints T

6.4.1 The installation and design shall be common for a class of vessel. Different vessel classes should have compatibility of CP systems that allow them to come alongside or carry out transfers at sea without compromising the CP system of either vessel.

6.5 Regulatory/Legislative Constraints T

6.5.1 There is no legislation restricting the use of this document. Relevant Commonwealth Occupational Health and Safety regulations on the use of electrical equipment and maintenance requirements shall apply.

6.5.2 Environmental protection policy

6.5.2.1 While there is currently no environmental legislation restricting the use of CP as described in this document, Cincreased concern by Environmental Protection Agencies C(Australian and overseas) at the effect of heavy metal discharges on aquatic organisms in ports and harbours signals possible future regulatory/legislative constraints on the use of zinc sacrificial anodes for corrosion protection of ship hulls and ballast tanks.

6.5.2.2 The Uniform National Discharge Standards (UNDS) jointly developed by the US Environmental Protection Agency and US Department of Defense have identified discharges incidental to the normal operation of Armed Forces vessels, and determined that it is not reasonable or practicable to require use of a Marine Pollution Control Device to mitigate adverse impacts on the marine environment. This includes the constituents released into surrounding water from sacrificial anode or ICCP systems. For hull CP systems, the technical study EPA 821-R-99-001 considered both zinc and aluminium sacrificial anodes, and ICCP systems. The models showed that the discharges from all had a low potential for causing adverse environmental effects, as the respective zinc, aluminium and chlorine-produced oxidants were below ambient water quality criteria in the harbours modelled. Further detail is contained in Environmental Protection Agency, 40 CFR Part 9 and Chapter VII (Department Of Defense 40 CFR Chapter VII [FRL–6335–5]), RIN 2040–AC96, Uniform National Discharge Standards for Vessels of the Armed Forces.


35



7 DELIVERABLES ( CDIDsC)

7.1 Test Regime 7.1.1 The ICCP system designer shall provide verification that the system will maintain the required

protection potential. The verification shall be via empirical data supported by modelling (computational or physical) as agreed with the Commonwealth.

7.1.2 Verification analysis shall be based on a configuration of the CP system that is consistent with that finally offered on the class.

7.1.3 The performance of the CP system shall be monitored throughout the life of the vessel and reported via hull potential surveys. The periodicity of hull surveys shall be decided by the Commonwealth

7.2 System Safety T

7.2.1 Systems and equipment provided to the ADF shall be designed to reduce any hazards to as low as reasonably practicable (ALARP):

7.2.1.1 A risk assessment of the system including hazard and risk analyses shall be carried out in accordance with ABR 6303.

7.2.1.2 The risk assessment report shall be provided at the design stage and updated as necessary to reflect the actual configuration of the class.

7.3 System Engineering Management Plan (SEMP)T

7.3.1 The CP system will require a maintenance plan for overhaul of serviceable equipment or replacement of consumable items. The management plan shall indicate the docking schedules agreed upon by the Commonwealth and contractors. The required primary inspections or replacement of components (such as sacrificial anodes) shall be listed with an agreed timescale allocated for each inspection.

7.4 Functional/System Specification T

7.4.1 The CP system designer will provide a detailed functional specification and breakdown of parts for the system. The documentation will be used by the installation contractor to verify the correct installation and operation of each part of the system prior to commissioning.

7.4.2 The system specification will subsequently form part of the Operation and Maintenance Manual delivered to the Commonwealth prior to hand over of the vessel.

7.5 Means of Verification of Function and PerformanceT

7.5.1 The ICCP system designer shall provide verification by empirical data and modelling during the design stage that the performance requirement in this document can be achieved.

7.5.2 A sacrificial anode system shall be verified by empirical data to show the performance requirements can be met.

7.5.3 The verification of performance for either ICCP or Sacrificial Anode systems will be documented for acceptance by the Commonwealth.

7.5.4 A whole ship acceptance test of the CP system shall be performed and the results reported to the Commonwealth.

7.6 Through Life Support DocumentationT

7.6.1 Requirements for inclusions in the Operation and Maintenance Manual for the CP system to be supplied by the system designer are provided in Section 5.5.3.

7.6.2 The through life support requirements for the CP system are defined in the System Engineering Management Plan for the vessel.


36



7.6.3 Visual inspection reports for coating damage and sacrificial anode condition are to be prepared and maintained throughout the life of the system. Theses complement hull potential surveys at a periodicity determined by the Commonwealth.

UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Annex A

A–1



ANNEX A – OUTLINE OF CATHODIC PROTECTION SYSTEMS

A.1 CTATHODIC PROTECTION – ELECTROCHEMICAL PROCESSEST A.1.1 Corrosion A.1.1.1 For the purposes of this document, the term ‘corrosion’ describes the active anode half-cell reactions

(dissolution or oxidation) of steel or aluminium that occurs in seawater. The anode reactions are linked electrochemically to oxygen reduction as the natural cathode half-cell reaction. The corrosion current is used to describe the electronic current from anode to cathode and the ionic flow in seawater (equal and opposite in charge) during active corrosion of a metal.

A.1.1.1.1 The potential adopted by a metal corroding freely in seawater (EBCORR B) can be measured relative to a stable reference electrode in seawater connected through a high impedance voltmeter.

A.1.1.1.2 The electrochemical potential for any given metal corroding in seawater is dependent upon the concentration of oxygen in seawater as well as other parameters such as temperature, pressure, and the flow rate of seawater.

A.1.2 Cathodic protection concepts A.1.2.1 Reactive metals such as iron and aluminium have a favourable energetic (positive) driving force to

corrosive dissolution in seawater. Electrical energy equivalent in size and opposing the driving force has to be supplied to these metals by an external source to stop corrosion reactions.

A.1.2.2 CP involves application of an electrical current directly either from an external power source (active) or supplied by corrosion of a sacrificial metal (passive) to suppress the natural corrosion reactions of steel or aluminium alloy.

A.1.2.3 The current (electrical energy) supplied by the CP system will cause the protected metal to be polarised negatively to an electrochemical potential value where metal corrosion is negligible. The steel or aluminium alloy surface is held at this cathodic potential, which is more electronegative than the free corrosion potential, to maintain cathodic protection.

A.1.2.4 Other metals such as copper alloys, stainless steel and nickel alloys have their own regions of protection from corrosion at higher electropositive potentials than steel or aluminium, such that polarising these metals to the protection potential of steel or aluminium induces large protection currents to flow to the metal surface.

A.2 CATHODIC PROTECTION SYSTEMS A.2.1 General A.2.1.1 There are two types of CP system used to prevent corrosion of steel or aluminium alloys in seawater:

A.2.1.1.1 The more complex system is based upon connecting the steel or aluminium as cathode to a power supply and polarising the metal surface cathodically, referred to as Impressed Current Cathodic Protection (ICCP).

A.2.1.1.2 The simplest system is based upon galvanic corrosion of a sacrificial metal when connected to steel or aluminium in seawater, referred to as sacrificial (galvanic) CP.

A.2.2 Impressed Current Cathodic Protection (ICCP) systems A.2.2.1 The essential components of an ICCP (active) system include (but are not limited to) the following:

− Power Supply Unit (PSU) supplying direct current. This may utilise a transformer and rectifier to generate the direct current;

− PSU controller adjusting voltage and current supply to the protected surface to maintain the required potential;

− Anodes conducting current to seawater on the return path to the PSU; − Calibrated reference electrode measuring potential of the protected surface; − Dielectric shield to prevent high current flow directly to hull adjacent to the anodes; − Shaft ground assembly protecting shaft, gearbox and bearing on current return path when

UNCLASSIFIED DEF(AUST)5000–Vol 03 Pt 16–Iss 01 Annex A

A–2



system is energised; − Hull penetrators to allow anode and reference electrode connection to the power unit and

controller; and − Insulated and sheathed high current capacity cables connected to both anodes and protected

structure.

A.2.3 Sacrificial Anode Systems A.2.3.1 The essential components of a sacrificial (galvanic) CP system include:

− Sacrificial anodes of zinc, aluminium or magnesium alloys that corrode in seawater; − Low resistance bonding to connect electrically the anodes directly to protected surfaces; and − Calibrated reference electrode system to measure surface potential which allows monitoring of

the operation of the system.