Ministry of Defence Defence Standard 02-704 (NES 704)

Issue 1 Publication Date 01 April 2000

Incorporating NES 704 Category 2

Issue 3 Publication Date August 1990

Requirements For Cathodic Protection

Part 5General Information On

Bi-Metallic Couples

DStanDStan is now the publishing authority for all Maritime Standards (formerly NESs). Any reference to any other publishing authority throughout this standard should be ignored.Any queries regarding this or any other Defence Standard should be referred to the DStan Helpdesk as detailed at the back of this document.

AMENDMENT RECORD

Amd No Date Text Affected Signature and Date

REVISION NOTE

This standard is raised to Issue 1 to update its content.

HISTORICAL RECORD

This standard supersedes the following:

Naval Engineering Standard (NES) 704 Part 5 Issue 3 dated August 1990.

Ministry of Defence

Naval Engineering Standard

NES 704 Part 5 Issue 3 (Reformatted) August 1990

REQUIREMENTS FOR CATHODIC PROTECTION

PART 5

GENERAL INFORMATION ONBI-METALLIC COUPLES

This NES Supersedes

NES 704 PART 5 ISSUE 2

Record of Amendments

AMDT INSERTED BY DATE

1 INCORPORATED

2

3

4

5

6

7

8

9

10

i

NAVAL ENGINEERING STANDARD 704

REQUIREMENTS FOR CATHODIC PROTECTION

PART 5

ISSUE 3 (REFORMATTED)

GENERAL INFORMATION ON BI-METALLIC COUPLES

The issue and use of this Standard

is authorized for use in MOD contracts

by MOD(PE) Sea Systems and

the Naval Support Command

ECROWN COPYRIGHT

Published by:

Director of Naval ArchitectureProcurement Executive, Ministry of DefenceSea Systems, Foxhill, Bath BA1 5AB

ii

NES 704Part 5

Issue 3 (Reformatted)

iii

SCOPE

1. Part 5 of this NES covers general information on Bi-metallic couples, those to be used ascathodic protection and those to be avoided.

NES 704Part 5Issue 3 (Reformatted)

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NES 704Part 5

Issue 3 (Reformatted)

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FOREWORD

Sponsorship

1. ThisNaval Engineering Standard (NES) is sponsored by theProcurement Executive, Ministryof Defence, Chief Naval Architect (CNA), Section NA 132.

2. It is to be applied as required by any Ministry of Defence contract for cathodic protection ofHM Surface Ships and Submarines. The various systems and methods used in a design of acathodic protection system for fitting in HM Ships and Submarines are described; systemsinclude Sacrificial Anode (or Self-energized) and Impressed Current. For more detailedinformation on the theory of cathodic protection, reference should be made to BS CP1021.

3. NES 704 comprises:

Requirement for Cathodic Protection

Part 1 Systems General.

Part 2 Impressed Current Cathodic Protection System.

Part 3 Sacrificial Anode Self-energized System.

Part 4 Ships Fitting-out; Ships in Refit or Laid-up.

Part 5 General Information on Bi-metallic Couples.

4. If it is found to be technically unsuitable for any particular requirement the Sponsor is to beinformed in writing of the circumstances with a copy to CNA, Section NA 145.

5. Any user of this NES either within MOD or in industry may propose an amendment to it.Proposals for amendments which are:

a. not directly applicable to a particular contract are to be made to the Sponsor of theNES;

b. directly applicable to a particular contract are to be dealt with using existing proceduresor as specified in the contract.

6. No alteration is to be made to this NES except by the issue of a formal amendment.

7. Unless otherwise stated, reference in this NES to approval, approved, authorized or similarterms, means by the Ministry of Defence.

Conditions of Release

General

8. This Naval Engineering Standard (NES) has been prepared for the use of the Crown and ofits contractors in the execution of contracts for the Crown. The Crown hereby excludes allliability (other than liability for death or personal injury) whatsoever and howsoever arising(including but without limitation, negligence on the part of the Crown, its servants or agents)for any loss or damage however caused where the NES is used for any other purpose.

9. This document is Crown Copyright and the information herein may be subject to Crown orthird party rights. It is not to be released, reproduced or published without written permissionof the MOD.

NES 704Part 5Issue 3 (Reformatted)

vi

10. The Crown reserves the right to amend or modify the contents of this NES without consultingor informing any holder.

MOD Tender or Contract Process

11. ThisNES is the property of the Crown and unless otherwise authorized in writing by theMODmust be returned on completion of the contract, or submission of the tender, in connectionwith which it is issued.

12. When this NES is used in connection with aMOD tender or contract, the user is to ensure thathe is in possession of the appropriate version of each document, including related documents,relevant to each particular tender or contract. Enquiries in this connection may be made ofthe local MOD(PE) Quality Assurance Representative or the Authority named in the tenderor contract.

13. When NES are incorporated into MOD contracts, users are responsible for their correctapplication and for complying with contracts and any other statutory requirements.Compliance with an NES does not of itself confer immunity from legal obligations.

Related Documents

14. In the tender and procurement processes the related documents listed in each section andAnnex A can be obtained as follows:

a. British Standards British Standards Institution,389 Chiswick High Road,London W4 4AL

b. Defence Standards Directorate of Standardization and Safety Policy,Stan 1, Kentigern House, 65 Brown Street,Glasgow G2 8EX

c. Naval Engineering Standards CSE3a, CSE Llangennech, Llanelli,Dyfed SA14 8YP

d. Other documents Tender or Contract Sponsor to advise.

Note: Tender or Contract Sponsor can advise in cases of difficulty.

15. All applications to Ministry Establishments for related documents are to quote the relevantMOD Invitation to Tender or Contract Number and date, together with the sponsoringDirectorate and the Tender or Contract Sponsor.

16. Prime Contractors are responsible for supplying their subcontractors with relevantdocumentation, including specifications, standards and drawings.

Health and Safety

Warning

17. ThisNESmay call for the use of processes, substances and/or procedures thatmay be injuriousto health if adequate precautions are not taken. It refers only to technical suitability and inno way absolves either the supplier or the user from statutory obligations relating to healthand safety at any stage of manufacture or use. Where attention is drawn to hazards, thosequoted may not necessarily be exhaustive.

NES 704Part 5

Issue 3 (Reformatted)

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CONTENTSPage No

TITLE PAGE i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCOPE iii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOREWORD v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Sponsorship v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Conditions of Release v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .MOD Tender or Contract Process vi. . . . . . . . . . . . . . . . . . . . . . . . . .

Related Documents vi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Health and Safety vi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Warning vi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONTENTS vii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 1. GENERAL INFORMATION AND TABLES 1.1. . . . .TABLE 1.1 POTENTIALS IN SEA WATER(AGAINST ICE) 1.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . .TABLE 1.2 GALVANIC SERIES IN SEA WATER 1.3TABLE 1.3 ACCELERATION FACTORS FORCORROSION DUE TO DISSIMILAR METALCOUPLING IN FLOWING SEAWATER(ACCELERATION FACTOR FOR COUPLEDMATERIAL UNLESS INDICATED BY SUFFIXESOF THE APPROPRIATE SYMBOL FOR THEOTHER MATERIAL) 1.4. . . . . . . . . . . . . . . . . . . . . . . .TABLE 1.4 COMPARISON OF POTENTIALSUSING ZINC, COPPER/COPPER SULPHATEAND SILVER/SILVER CHLORIDE, REFERENCEELECTRODE 1.5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX A. RELATED DOCUMENTS A.1. . . . . . . . . . . . . . . . . . . .

ANNEX B. DEFINITIONS AND ABBREVIATIONS B.1. . . . . . . .

ALPHABETICAL INDEX

NES 704Part 5Issue 3 (Reformatted)

viii

NES 704Part 5

Issue 3 (Reformatted)

1.1

1. GENERAL INFORMATION AND TABLES

a. Defence Standard 012 and BR 3008 give data sheets for various materials inuse in HM Ships.

b. TABLE 1.1 shows the open circuit potentials of various metals in flowing seawater at a temperature of 25 C. In order to minimize the bi-metallic corrosionthat may take place, very careful consideration must be given to the selectionofmaterials used. Great care must be taken to avoid a pair ofmaterials (coupled)having a potential difference of more than 0.25 volts.

c. The open circuit potentials given in TABLE 1.1 will vary in sea water due to anyof the following factors and hence considerable variations in measuredpotentials of materials is possible and the Table should only be used as a guideto selection:

(1) Temperature of sea water.

(2) Flow rate of sea water.

(3) Composition of sea waterespecially oxygen content and pollutants suchas sulphides.

(4) Corrosion product filmsthickness and composition.

(5) Metallurgical structure of alloys and inclusions.

(6) Surface condition of material (eg heat treatment, welds, roughness).

(7) Mechanical history of material (eg type of workingdrawing, rolling,forging).

d. TABLE 1.2 gives the Galvanic Series in sea water. This shows the relativepositions of various metals and alloys. The materials at the upper end of theTable will sacrifice to protect those below them (eg Aluminium will sacrifice toprotect Gunmetal or Phosphor Bronze).

e. TABLE 1.3 is a summary of work carried out onBi-metallic corrosion and showsthe depth of corrosion which can be expected when coupling metals in seawater.

f. Some useful information on the corrosion of sea water cooling system is givenin BR 1254.

g. TABLE 1.4 shows the different potentials obtained when using zinc,copper/copper sulphate and silver/silver chloride reference electrodes.

NES 704Part 5Issue 3 (Reformatted)

1.2

TABLE 1.1 POTENTIALS IN SEA WATER (AGAINST ICE)

NES 704Part 5

Issue 3 (Reformatted)

1.3

LEAST NOBLE(ie ANODIC, SACRIFICIAL)

MagnesiumZincAluminium AlloyCadmium

Low Carbon Steel and Mild SteelAlloy SteelCast IronStainless Steel (Active)

7030 BrassAdmiralty BrassAluminium Brass8515 BrassCopper

Nickel Aluminium Bronze and Aluminium Silicon BronzeGunmetal and Phosphor Bronze9010 Copper Nickel Alloy7030 Copper Nickel Alloy (Low Iron)7030 Copper Nickel Alloy (High Iron)

NickelInconel*SilverStainless Steel (Passive)

Monel*Hastelloy*TitaniumPlatinumGraphite

* Trade Mark

MOST NOBLE(ie CATHODIC, PROTECTED)

TABLE 1.2 GALVANIC SERIES IN SEA WATER

NE

S704

Part5Issue

3(R

eformatted)

1.4

UncoupledAcceleration Factors

Coupled Material (M)Uncoupled

Corrosion Rate(mm/year)

Carbon (C) Titanium (Ti) Copper (Cu) Mild Steel (MS) Aluminium (Al)p ( )(mm/year)

10C:1M 1C:1M 1C:10M 10Ti:1M 1Ti:1M 1Ti:10M 10Cu:1M 1Cu:1M 1Cu:10M 10MS:1M 1MS:1M 1MS:10M 10Al:1M 1Al:1M 1Al:10M

Zinc 0.05 35 20 5 35 4 2 20 10 3 20 10 3 5 2 1

SIC Aluminium 0.008 200 85 10 30 30 2 100 20 2 80 20 2 1 1 1

NS4 aluminium 0.01 200 85 10 30 30 2 100 20 2 80 20 2 6 2 1

H30 Aluminium 0.008 200 85 10 30 30 2 100 20 2 80 20 2 1Al 2Al 10Al

Mild Steel 0.15 10 4 2 5 2 1 7 3 1 1 1 1 2Al 20Al 80Al

HY80 Steel 0.10 10 4 2 5 2 1 7 3 1 1MS 1MS 3MS 2Al 40Al 100Al

*Ni-Resist (Type Aus 202spheroidal) 0.05 10 4 2 3 2 1 7 3 1 1MS 1MS 3MS 2Al 40Al 100Al

Tin 0.01 75 3 1 3 1 1 20 4 1 1MS 2MS 5MS 2Al 20Al 60Al

Lead 0.01 8 2 1 3 1 1 20 4 1** 1MS 2MS 5MS 2Al 20Al 60Al

++Naval brass 0.04 50 8 1 8 4 1 2 2 1 1MS 3MS 7MS 2Al 20Al 100Al

Aluminium brass 0.01 50 8 1 8 4 1 2 2 1 1MS 3MS 7MS 2Al 20Al 100Al

++Aluminium bronze (10% Al) 0.02 25 5 1 4 2 1 2 2 1Cu 1MS 3MS 7MS 2Al 20Al 100Al

++Silicon aluminium bronze 0.015 50 8 1 8 4 1 1 1 1 1MS 3MS 7MS 2Al 20Al 100Al

++Nickel aluminium bronze 0.015 15 3 1 2 1 1 1Cu 2Cu 1Cu 1MS 3MS 7MS 2Al 20Al 100Al

Silicon bronze 0.035 40 8 1 10 5 1 1Cu 1Cu 1Cu 1MS 3MS 7MS 2Al 20Al 100Al

Copper 0.03 40 8 1 10 5 1 1 1 1 1MS 3MS 7MS 2Al 20Al 100Al

Phosphor bronze (5% Sn) 0.02 25 5 1 10 5 1 1Cu 2Cu 1Cu 1MS 3MS 7MS 2Al 20Al 100Al

*Phosphor bronze (10% Sn) 0.02 15 3 1 8 4 1 1Cu 2Cu 1Cu 1MS 3MS 7MS 2Al 20Al 100Al

*Gun metal LG4 0.035 10 2 1 6 3 1 1Cu 1Cu 1Cu 1MS 3MS 7MS 2Al 20Al 100Al

*Hiduron 501 0.02 25 5 1 6 3 1 2 1 1 1MS 3MS 7MS 2Al 20Al 100Al

90/10 Cupro-nickel (1% Fe) 0.02 15 3 1 5 2 1 2 2 2 1MS 3MS 7MS 2Al 20Al 100Al

70/30 Cupro-nickel (1% Fe) 0.02 10 2 1 5 1 1 1Cu 1Cu 2Cu 1MS 3MS 7MS 2Al 20Al 100Al

CNNS Cupro-nickel 0.02 10 2 1 5 1 1 1Cu 1Cu 2Cu 1MS 3MS 7MS 2Al 20Al 100Al

IN732 Cupro-nickel 0.02 10 2 1 5 1 1 1Cu 1Cu 2Cu 1MS 3MS 7MS 2Al 20Al 100Al

+Monel 400 0.005 3 3 1 3 2 1 1Cu 1Cu 10Cu 1MS 3MS 7M 2Al 20Al 100Al

+Stainless steel Type 316 0.005 3 3 1 3 2 1 1Cu 2Cu 10Cu 1MS 3MS 7MS 2Al 20Al 100Al

*/+Ferralium 40V 0.005 3 3 1 3 2 1 1Cu 2Cu 10Cu 1MS 3MS 7MS 2Al 20Al 100Al

Titanium 0.001 2 1 1 1 1 1 1Cu 5Cu 10Cu 1MS 2MS 5MS 2Al 30Al 30Al

Carbon (Acheson YAV Graphite) 1Ti 1Ti 2Ti 1Cu 8Cu 40Cu 2MS 4MS 10MS 10Al 85Al 200Al

NOTE: ** Results based on 100 hour tests for materials which can undergo polarity reversals.++ Acceleration Factors are subject to change due to variable complex microstructure.+ These materials are subject to crevice corrosion.* Materials in case formothers in wrought form.

The box indicates where copper is the base metal in the couple material.

TABLE 1.3 ACCELERATION FACTORS FOR CORROSION DUE TO DISSIMILAR METAL COUPLING IN FLOWING SEAWATER(ACCELERATION FACTOR FOR COUPLED MATERIAL UNLESS INDICATED BY SUFFIXES OF THE APPROPRIATE SYMBOL FOR THE

OTHER MATERIAL)

NES 704Part 5

Issue 3 (Reformatted)

1.5

TABLE 1.4 COMPARISON OF POTENTIALS USING ZINC, COPPER/COPPER SULPHATEAND SILVER/SILVER CHLORIDE, REFERENCE ELECTRODE

NES 704Part 5Issue 3 (Reformatted)

1.6

NES 704Part 5

Issue 3 (Reformatted)

A.1 ANNEX A.

ANNEX A.

RELATED DOCUMENTS

A.1 Reference is made to:

Referred to inClause

BS CP1021 Code of Practice for Cathodic Protection Foreword

DEF STAN012

Guide to Engineering Alloys used in NavalService (Data Sheets)

1.a.

BR 1254 Corrosion of Sea Water Cooling systems inHM Ships

1.f.

BR 3008 Manual of Materials and Processes(Mechanical Engineering)

1.a.

NES 704Part 5Issue 3 (Reformatted)

A.2ANNEX A.

NES 704Part 5

Issue 3 (Reformatted)

B.1 ANNEX B.

ANNEX B.

DEFINITIONS AND ABBREVIATIONS

B.1 For the purpose of Part 5 of this NES the following definitions apply:

Galvanic Series (TABLE 1.2) Order of nobility of various metalsused to determine which of two metalswill sacrifice if coupled to the other inan electrolyte.

Table of Potentials (TABLE 1.1) This table relates various metals andalloys to a Saturated Calomel Electrode(SCE) in Sea Water (carried out inlaboratory conditions).

Bi-metallic corrosion The corrosion which takes place whentwo dissimilar metals are coupledtogether in sea water or a seaenvironment. The corrosion is causedbecause one of the metals is moreelectro-negative and an electricalcharge flows from one to the other;metal atoms pass into solution.

Table of Acceleration factors anduncoupled corrosion rates (TABLE 1.3)

This table summarizes some of thework carried out on bi-metalliccorrosion and shows also the uncoupledcorrosion rates of various metals andalloys.

NES 704Part 5Issue 3 (Reformatted)

B.2ANNEX B.

NES 704Part 5

Issue 3 (Reformatted)

INDEXINDEX.1

ALPHABETICAL INDEX

BBi-metallic couples, iii

GGalvanic series, 1.1

inclusions, 1.1

LLaboratory, B.1

OOpen circuit potentials, 1.1

PPollutants, 1.1

SSacrifice, 1.1, B.1

Sulphides, 1.1

NES 704Part 5Issue 3 (Reformatted)

INDEX INDEX.2

Inside Rear Cover

Crown Copyright 2000

Copying Only as Agreed with DStan

Defence Standards are Published by and Obtainable from:

Defence Procurement AgencyAn Executive Agency of The Ministry of Defence

Directorate of StandardizationKentigern House65 Brown Street

GLASGOW G2 8EX

DStan Helpdesk

Tel 0141 224 2531/2 Fax 0141 224 2503

Internet e-mail enquiries@dstan.mod.uk

File Reference

The DStan file reference relating to work on this standard is D/DStan/69/02/704.

Contract Requirements

When Defence Standards are incorporated into contracts users are responsible for their correctapplication and for complying with contractual and statutory requirements. Compliance witha Defence Standard does not in itself confer immunity from legal obligations.

Revision of Defence Standards

Defence Standards are revised as necessary by up issue or amendment. It is important thatusers of Defence Standards should ascertain that they are in possession of the latest issue oramendment. Information on all Defence Standards is contained in Def Stan 00-00 Standardsfor Defence Part 3 , Index of Standards for Defence Procurement Section 4 Index of DefenceStandards and Defence Specifications published annually and supplemented regularly byStandards in Defence News (SID News). Any person who, when making use of a DefenceStandard encounters an inaccuracy or ambiguity is requested to notify the Directorate ofStandardization (DStan) without delay in order that the matter may be investigated andappropriate action taken.

CONTENTSTITLE PAGESCOPEFOREWORDSponsorshipConditions of ReleaseGeneralMOD Tender or Contract Process

Related DocumentsHealth and SafetyWarning

1. GENERAL INFORMATION AND TABLESTABLE 1.1 POTENTIALS IN SEA WATER (AGAINST ICE)TABLE 1.2 GALVANIC SERIES IN SEA WATERTABLE 1.3 ACCELERATION FACTORS FOR CORROSION DUE TO DISSIMILAR METAL COUPLING IN FLOWING SEAWATER (ACCELERATION FACTOR FOR COUPLED MATERIAL UNLESS INDICATED BY SUFFIXES OF THE APPROPRIATE SYMBOL FOR THE OTHER MATERIAL)TABLE 1.4 COMPARISON OF POTENTIALS USING ZINC, COPPER/COPPER SULPHATE AND SILVER/SILVER CHLORIDE, REFERENCE ELECTRODE

ANNEXESANNEX A. RELATED DOCUMENTSANNEX B. DEFINITIONS AND ABBREVIATIONS

ALPHABETICAL INDEX