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IS 12560 : 1988

Indian StandardCODEOFPRACTICEFORCATHODICPROTECTIONOFHEAT

EXCHANGERSANDCONDENSERS

First Reprint NOVEMBER 1990)

UDC 621175 : 6201975

BUREAU OF INDIAN STANDARDSMANAK BIiAVAN, 9 BAHADUR SHAH ZAFAK MARG

NEW DELHI 110002October 1989 Price Group 3

(Reaffirmed 2000)

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Corrosion Protection Sectional Committee, SMDC 29

FOREWORDThis Indian Standard was adopted by the Bureau of Indian Standards on 6 October 1988, afterthe draft finalized by the Corrosion Protection Sectional Committee had been approved by theStructural and Metals Division Council.Metallic surfaces of water boxes, tube plates and tubes of heat exchangers and condensers usingcorrosive cooling water are subject to general corrosion and pitting.corrosion depends on the corrosion resistance of metals, The nature and intensity ofdesign and fabrication process of thecomponents, characteristics of cooling water velocity of cooling water and performances ofcoating, if applied to bare parts of the metal.Commonly used materials of construction for water boxes, tube plates and tubes of heatexchangers/condensers vary from design to design, Conditions. of severe corrosion leading toperforations and thinning arise, if materials possess susceptibility to corrosion-erosion attack andif they arc galvanically dissimilar in corrosive cooling water environment. Cathodic protectionin conjunction with anti-corrosive paints in water boxes can provide satisfactory corrosionprotection to corrodjng components and ensures longer life of the heat exchangers/condensers.Establishing the standard requirements for optimum corrosion control using cathodic protection is,therefore, a pre-requisite to maintain a factor of higher reliability in the maintenance of heatexchangers/condensers except these where titanium is used as a construction material. Thisstandard can also be used as a guideline for the use of cathodic protection systems as well as theselection of materials for cooling water systems of heat exchangers/condensers.

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IS 12560 1988I ndian St andard

CODE OFPRACTICEFORCATHODICPROTECTIONOFHEATEXCHANGERSANDCQNDENSERS1 SCOPE1.1 This standard deals ,with internal corrosionof water boxes and its cathodic protection ,whichcan also extend the protective currtint to tubeplates and tubes.1.2 The scope of this standard is limited to therequirements for COriosion protection againstcorrosive cooling water possessing not morethan 1 000 ohmcm resistivity.2 REFERENCESThe Indian Standards listed below are necessaryadjuncts to this stand:lrd:

IS No. TitleIS 3531 : 1983 Glossary of terms relatingto corrosion of metals( first revisionI S 8062 ( I;kl > : Code of practice forcathodic protection ofsteel structures : Part 1General principle.IS 8062 (Part 3): Code of practice for1977 cathodic protection of steelstructures : Part 3 Shipshulls.3 DEFINITIONS3.1 For the purpose of this standard, thedefinitions given in IS 3531 : 1983, and IS 8062( Part 1 ) : 1976 shall be applicable.4 MATERIALS OF COOLING WATERSYSTEM4.1 Commonly used materials for corrosivecooling water systems of heat exchangers possesscorrosion resistance in increasing order as givenbelow:

a) Water box - Cast iron,low carbon steel,gun metal, andfibre glass reinforced plastics.b) Tube plates - Admiralty brass;

muntz metal ( 60/4O brass );

c) Tubes

naval brass;aluminium bronze;cupronickel 90110, 70130;carbon steel, stainless steel,alloy steel;titanium clad brasses,bronzes and mild steel; and

titanium.Cc;y)per, admiralty brass ( arscni-

;aluminium brass, 90/10 cupro-nickel;70130 cupronickcl, monel,titanium and its alloys; andcarbon steel, alloy steel andstainless steel,

4.2 Compatibility of materials in corrosive wateris governed by their relative position in galvanicseries given in Annex A. Annex A coversmaterials generally used for the fabrication ofheat exchangers/condensers. Larger potentialdifference between members of bimetallic systemsindicates preferential corrosion tendency of thebaser material.4.3 Corrosion resistance of commonly usedmaterials of construction as described in 4.1

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IS 12560:1988

resistivity is not adequate for satisfactory currentthrow.5.3 Corrosivity of seawater is more aggressivewith the addition of ppm level sulphide andammonia content. Presence of sulphides andammonia in fertilizer and chemical industry, etc,are likely to cause enhanced localized pitting,enhanced crevices corrosion and render copperbase alloys susceptible to pitting as well as stresscorrosion cracking. Maximum lolerable limitsof these species in cooling seawater as given inAnnex B shall be applicable to 9015, 9OjlO and70130 cupronickel, aluminium brass, aluminiumbronze admiralty bras, muntz metal and navalbrass.6 PROTECTIVE COATINGS6.1 Application of anticorrosive coatings reducesthe magnitude of corrosion current as well asreduces the requirement of cathodic protectioncurrent.6.2 Painting of water boxes for corrosion resis-tance shall be carried out according toIS 8062 ( Part 3 ) : 1977 when fabricated out offerrous materials.7 CATHODIC PROTECTION7.1 Cathodic protection for heat exchangers/condensers is desirable, if the cumulative effectof the following factors leads to severe andunpredictable corrosion damage:a>

b)c)

Large potential difference between mate-rials of water boxes, tube plates andtubes,Cooling water possessing low resistivityand high corrosivity; andDifficulty of application and maintenancepainting of water boxes.

7.2 athodic protection cannot prevent corro-sion of metallic surfaces beyond the reach ofprotective currents. In high resistivity coolingwater, protective potential attenuation isachieved faster and, therefore, uniform potentialspread is more difficult to achieve with one ortwo anodes.7.3 Protective potential more negative than-07 Yscn may lead to hydriding of titaniumsurfaces leading to embrittlement and crackingof titanium material.7.4 Cathodic protection is best achieved whenapplied to wster boxes. installation of anodeson tube plates is not desirable from design pointof view. Such installation is likely to causeexcessive turbulence leading to erosion.7.6.1 Protective potential criterion for variousmaterials is diffcrcnt in diffcrcnt corrosivemedia. The following values arc applicable inseawater medium. These V~IU S may bc adoptedfcr ch]cridc containing waters of lower

resistivity:Plain carbon and low - 078 vscsalloy steelsBrasses and bronzes - 0550 VsceCupronickels - 0600 VSCE

7.4.2 In respect of sulphide contaminated water,protective potential shall be 100 mV morenegatives from the values given in 7.4.1.7.5 oth galvanic and impressed currentmethods of cathodic protection are applicablefor installation of cathodic protection system.Choice between the two methods depends uponthe economics, design factors, protective currentdemand and time gap between two successiveinspection schedules.8 GALVANIC ANODE SYSTEM8.1 Galvanic cathodic protection is easier forinstallation and no maintenance is required.Potential monitoring is not essential andis left to the discretion of the user. Poten-tial monitoring shall be achieved by install-ing rugged silver/silver chloride electrode onthe protected surface away from the anodelocation and taking out the cable lead throughsealed perforation. Potential difference betweenthe structure and reference silver/silver chlorideelectrode shall be measured using high impe-dance voltmeter.

8.2 Pure zinc possesses property of polarity re-versal at higher temperatures. Therefore, cautionshbuld be exercised in using zinc anodes wheretemperature is likely to increase beyond 40C. Itis desirable t indicate values of zinc anodepotentials and anode current efficiencies attemperatures beyond 40C. Magnesium basedanodes possess high driving voltage and,therefore, are not desirable for heat exchangerservice. Aluminium based composition ofcurrent etficiency better than 70 percent arcdesirable for use as galvanic anodes.8.3 Where water boxes are composed of castcopper based alloys, plain carbon unalloyedsteel anodes may be used with advantage offorming corrosion resistant layer on tubeinteriors.8.4 Purchaser of anodes shall stipulate the majorrequirements/characteristics of the anodematerial and anode design. For purpose ofguidance, the characteristics of aluminium, zinc,magnesium and iron based commonly usedcornposrtions are given in Annex C.9 DESIGN AND INSTALLATION OFGALVANIC ANODES9.1 Cathodic protection of heat exchangers/condensers is desirable on water boxes. Iubcpl:ltcs and small lengths of the tubes may rcccivcprotective current depending on the resistivityof the cooling water and contact resistancebetween water box and tube platc/tubcs. Designof the cathodic protection system shall be basedon corrosion protection aspects of both the

2

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IS 12560 : 1988inlet as well as outlet water boxes. Coolingwater temperature shall be taken into account.9.2 Minimum turbulence shall be effected byinstallation of galvanic anodes on the interiorof water box cover. The anodes shall have acast-in insert designed in such a way that theanode may be screwed on the interior water boxcover. Centrally located anode may give uniformspread of protective current.10 IMPRESSED CURRENT CATHODTCPROTECTION ( JCCP ) SYSTEM ANDITS INSTALLATION10.1 mpressed current cathodic protectionsystem provides protective current from externaldc source through anodes of inert nature to thecorroding structure. The system shall be capableof monitoring/measuring the protective potentialby means of reference electrode fitted on theprotected structure.10.1.1 Protective potential is closely maintainedto a preset reference value ( desired protectivepotential value ) in ICCP control equipment.Electronic circuit and design of the controlequipment shall be so constructed that dcoutput shall get automatically adjusted to avalue required to maintain the desired protectivepotential. The tolerance limits for protcctivcpotential shall be a matter decided by mutualagreement between the concerned parties.10.2 The control equipment shall have rhecapacity for continuous operation throughoutthe operating period of the condenser/heatexchanger. A pure dc output is most desirable,however, if ac ripples exist in dc output, thepeak-to-peak voltage of these ripples shall bewithin the protective potential limits. Thenature, type and dimensions of the equipmentshall be left to the disc -ction of the user

10.3 AnodesICCP anodes shall be composed of such mate-rials which do nol form anodic loose deposits.It is preferable to use platinum clad or platinizedtitanium or pure platinum wire or foil asI CCP anode material.

10.3.1 Anode construction shall incorporateproperly insulated connecting leads and insulat-ing anode backing. The insulating materialshall be water resistant and shall resist tempera-tures up to 50C.11 GUIDELINES FOR DESIGN OFCATHODIC PROTECTION SYSTEM11.1 The guidelines before adopting the cathodicprotection systems are given in 11.1.1 to 11.1.5.11.1.1 Cooling water resistivity shall be estab-lished by using conductivity meter meant forelectrolytic solutions.11.1.2 Total current requirement for cathodicprotection depends on corrosivity/resistivity ofthe cooling water and the protective coatingapplied on water boxes. Typical values ofcurrent requirements for ferrous metals are givenin Annex D, for guidance.11.1.3 Requirements for the insulating backingof the anodes shall be ascertained. Insulatingbacking is specifically rcquircd for impressedcurrent anodes to achieve better current distri-bution.11.1.4 Sclcctlon of suitable anode shall be doneby mutual agreement between the concernedpartIcs. Anode spacing shall IX decided takinginto consideration the a\~dilable space andcurrent distribution.11.1.5 Circuit resistances sllall 1)~ clctclmincd.

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IS 12560 1988ANNEX AClause 4.2 )

GALVANIC SERIES OF METALS AND ALLOYS IN SEAWATER

0 Ni - Cr- MO alloy CCZl Platinum

1 Graphite

P-1 g nes:umO0 Zinc

0 BrrylliumI Alumintum AlLoy:0 C admlum

-Mild Steel Cast Iron0 Low Alloy Steel11 Austcnitic Nlc kel Cast Iron

0 Aluminium BronzeI Naval Brass, Yellow Brass, Red Brass0 Tin0 Copper

0 Pb. Sn Solder I50/500 Adminlity Brass ALumi.niwn Brass0 Manganese Bronze

0 Silicon BronzeOTin BronteiG d, M 1Cl _ Stainless Steel -Types LlO-1160 Nickrl Silver

0 90-10 Copper Nickel0 80-20 Copper Nickel

0 m Stainless Steel -Type L300 Lead

o 70-30 Copper Nickel0 Nickel Aluminiurn Bronze

0 m Nickel -Chromium Alloys 6000 Silver Braze Alloys0 Nick21 200r] Silvrr

0 B Stainless Steel-Types 302,301,321,3LJI Nickel Copper Alloys LOO,K-500

0 N Stainless Steel Types 316-3170 Alloy 20 SPatniess Stcel,Cast and WroughtIX Nickel-Iron-Chromium Alloy 8250 Ni -Cr -Mo-Cu-Si alloy B

0 Titanium

Alloys are listed in order of the potential they exhibit in flowingseawater. Certain alloys indicated by the symbol 0 in low velocityor poorly aerated water and at shielded areas, may become activeand exhibit a potential near 05 V.

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IS 12560 1988

ANNEX B( Chse5.3 )

TOLERANCE LIMITS OF HARMFUL SPECIES IN COOLING WATER

B-l Tolerance limits of harmful species in Species Tolerance L imi t s i ncooling water as applicable to 9515 CuPronickel, 90110 cupronickel, 70/30 cupronickel, Cooling Wateraluminium brass, aluminium bronze, admiralty Free ammonia, mg/l, Mnx 01brass, muntz metal and naval brass shall be Biochemical oxygen demand 200( 5 days at 20C ) ( mg/l )as follows: Sulphide as S- mg/l, MUX 10

ANNEX C( lause 8.4)

RECOMMENDED CHEMICAL COMPOSITIONS OF ANODE MATERIALAND THEIR PROPERTlESC-I Chemical composition of typical zinc anode alloys and their properties are as follows:Composition/Property No. 1 No. 2 No. 3 No. 4

cu OOO S M ax 0005 M UX 0005 M UX 0002 MuA l 030-050 010-050 04-06 -Si 0003 M ax 0125. Max 0125 M UX -Fe 0 002, ax 0005 Max 0001 Max 0001 M axPb 0005, Max 0006 Max 03 M ax -Cd 0025-0100 0025-015 0075-0125 -Hg - - 010-015Zn Remainder Remainder Remainder RemainderEfficiency 95 percent 95 percent 95 percent 95 percentPotential (V) - 105 vs -105 vs - 105 vs - 105 vs

AglAgCl AglAgCl AglAgCl AglAgClCapacity( Ahkg- ) 780 780 780 780

C-2 Chemical composition of typical aluminium anode alloys and their properties are as fol]ows:Composition/Property No. 1

Si 01 l-O.21Fe 000, MaxZn 0.35-050Sn -Hg 0035-050In -Mg -cu 0006, MaxAl RemainderEfficiency 95 percent,

averagePotential -105 vs

Ag/AgClCapacity( Ahkg- ) 2 830 ;IVerage

No. 2010, MUX013 M ax050-50-

-0005-005-001, MaxRemainder90 percent,Max-115 vsAgiAgCl2 700, i2fux

No. 3010, MUX-500-

-00208000 I ) MaxRemainder95 percent

approx-115 vsAs/A&l2 700 approx

No. 4-

013, Max400-5.0001 -

--

0 01, MaxKemainderSO-80

pcrccn t- I 1 vsAg/AgCIVariable

No 5--

70001---

001, MNXRemainder50-80percent- I IO v.sAg/AgCIV:irrilblc

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IS 12560 : 1988ANNEX D

Clause 11.1.2 )TYPICAL VALUES OF CURRENT REQUIREMENTS FOR PLAIN CARBON STEELIN VARIOUS ENWRONMENTS

D l Typical current densities for cathodic protection of plain carbon steels in various environ-ments are given below for guidence:

Stationary fresh waterMoving fresh waterHighly turbulent fresh water with entrained airHot water

Environi, ent

Polluted estuarine waterCondensers boxes having contact with tube plates

Current Density folAdequure CathodicProtectionmh/m2

54054 to 6565 to 16054 to I6054u to I 6101 3.50 overail

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Standawl Mark

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Boreao of Indian StandardsBIS is a statutory institution established under the Bureau of I ndian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification ofgoods and attending to connected matters in the country.CopyrightBIS has the copyright of all its publications. No part of these publications may be reproduced inany form without the prior permission in writing of BIS. This does not preclude the free use, inthe course of implementing the standard, of necessary details, such as symbols and sizes, type orgrade designations. Enquiries relating to copyright be addressed to the Director (Publications), BIS.Revision of Indian StandardsIndian Standards are reviewed periodically and revised, when necessary and amendments, if any,are issued from time to time. Users of Indian Standards should ascertain that they are in possessionof the latest amendments or edition. Comments on this Indian Standard may be sent to BISgiving the following reference :

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