EffectofChlorineonCommonMaterialsinFreshWater_14049_

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(Figure 1). Details of the data collectedin this program, including informationconcerning the exposure locations andtesting methodology; were reported. 2

Figure 2 summarizes the corrosionbehavior of various alloys in raw andchlorine-treated fresh water. Theimportant findings and conclusions aregiven below.

General Corrosion The corrosion rate of cast iron

(UNS F10001) was slightly greater thanthat for carbon steel (CS) (G10100), butfollowed the same pattern. Both castiron and CS exhibited increasingcorrosion rates as chlorine increased.The maximum rates were above 5 mpy(0.13 mm/y) even at low concentrations.Materials that corrode at rates >5 mpygenerally require good protectivecoatings or inhibitors and substantialmaintenance compared to materials that

corrode at 1 mpy to 2 mpy (0.025 mm/yto 0.051 mm/y), which are generallyused bare without coatings.

The corrosion rate for aluminum6061(A96061) and 1100 (A91100) andcopper-based alloys, such as 90/10Cu-Ni (C70600), 70/30 Cu-Ni (C71500),and 8-5-5-5 red brass (C83600), wasslightly depressed up to ~2 mg/Lchlorine. The rate increased substantiallyfor aluminum 3003 (A93003) at chlorineconcentrations of 3 mg/L to 5 mg/L.Copperbased alloy specimens were not

exposed at concentrations that werehigher than 2 mg/L.

Austenitic nickel cast iron(F41002) and aluminum and copper-based alloys all had low general cor-rosion rates, allowing them to be useduncoated in most chlorinated waters.

Localized Corrosion Stainless steel (SS) and nickelbased

alloys had insignificant generalcorrosion rates of


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FIGURE 3Effect of Free Chlorine on Corrosion of Mild Steel. 3

these aluminum alloys in applicationswhere some surface corrosion andmaintenance can be tolerated, such as

slide gates.Types 304 SS (S30400) and 316 SS

(S31600) were resistant to localizedcorrosion in unchlorinated and chlo-rinated fresh waters up to 2 ppm chlo-rine. At 3 mg/L to 5 mg/L chlorine,there was incipient pitting of type 304base plate and 16-mil (0.41-mm) depthof attack in creviced areas. There was nogeneral or localized corrosion of types304 and 316 specimens in 31- to 32-dayexposure at 20 mg/L to 25 mg/Lchlorine.

These data indicated types 304 and316 and the low-carbon grades, types304L SS (S30403) and 316L SS(S31603) that are used for welded fab-rication, should resist long-term ex-posure in most chlorinated fresh waters.This is in agreement with generalexperience.

These data also indicated that forlong-term, continuous exposure towardthe high end of the 3 mg/L to 5 mg/Lrange of chlorine, type 316L would be a

somewhat more conservative choicethan type 304L.Types 317 (S31700); 17-4PH

(S17480); alloys 700 (N08700), 20Cb-3 *

(N08020), and 825 (N08825); andNi-Cr-Mo alloys C (N10002), BN10001 G N06007 and 625

*Trade name.

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film or scale could form. The INCO testrack data were for 30- to 365-dayexposures, time enough for films/ scaleto form and reduce the initial unfilmedcorrosion rates that Boffardi measured.

DisinfectionCommon practice is to disinfect

potable water systems with 25 mg/Lminimum chlorine for 24 h beforeplacing the system in service, aftermajor overhauls, or long outages.AWWA Standard C653, "Disinfectionof Water Treatment Plants, 4 requiresinjection of sufficient chlorine to pro-duce 25 mg/L minimum chlorine andtesting at the end of 12 h to ensure thatthe concentration has not dropped below15 mg/L. If below 15 mg/L, thedisinfection must be repeated.

Contrary to what might be expectedfrom the long-term data above,short-term exposure to 25 mg/L to 50mg/L chlorine dosages appeared to bebeneficial, not detrimental, to SSperformance. Lewus, et a1., 5 in studiesof metal pickup in potable water,reported: "A significant feature of thestatic exposure tests (at 50 ppm Cl 2 for24 h) was that the release into water wasreduced for the second exposure of thesample in the solution." An importantfinding was that for continuous exposureat 1.5 ppm to 3.0 PPM Cl 2, metal releaserates decreased markedly with exposuretime.

In other work, the beneficial effectsof short-term exposures to 25 ppmchlorine in reducing metal pickup inultra high-purity water Sys tems wereobserved. 6

An explanation is that theseshort-term exposures allow chlorine tooxidize some of the unoxidized materialin the film, enhancing its corrosionresistance. On the other hand, long-termexposures to more modest levels of chlorine are likely to be detrimental,shown by data from the test rack

program.

Other Chlorine EffectsThe principal reason chlorine is

added to potable water is for disinfection(i.e., control of bacteria harmful tohumans). Chlorine also is used in freshwaters for other effects.

(N06625), were resistant to chlorinatedwaters with up to 2 mg/L chlorine.Alloys 700, C, and 625 were resistant in

waters with 3 mg/L to 5 mg/L chlorine.(Alloys C, B, and G now have beenreplaced by improved alloys B-2[N10665], C-276 [N10276], and G-3[N06985].) Ni-Cu alloy 400 (N04400)suffered severe crevice corrosion inchlorinated fresh waters with 2 mg/L orless chlorine. Alloy 20Cb-3 suffered5-mil depth of local corrosion in the 3mpy to 5 mpy exposure.

Literature DataMany papers have been published

on the effect of chlorine on materials insaline waters, but few on the effect of chlorine on materials of construction infresh water. Boffardi found that chlorineadditions of up to 0.5 mg/L had littlesignificant effect on the normalcorrosion rate of CS in potable water in3- to 4-day tests. 3 Above 0.5 mg/Lchlorine, the corrosion rate increasedrapidly, reaching 0.63 mm/y (25 mpy) at1.0 mg/L chlorine (Figure 3). 3

The much lower corrosion ratesfrom the INCO test rack program,compared to Boffardi's data, are believeddue to the reduction in corrosion rate thatoccurs in longer exposures with scaleformation. Boffardi's data were for 3- to4-day exposures of bare steel before anysignificant

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MATERIALS SELECTION & DESIGN

Precipitation o Iron and Manganese

Chlorine is added in potable watertreatment to precipitate iron and, to alesser extent, manganese so theseelements can be filtered out.

Potassium permanganate (KMnO 4)often is added, in addition to chlorine, toprecipitate manganese more effectively.Fe(OH) 3 and manganic hydroxideMn[OH] 3 precipitates form a black deposit on pipe walls. The deposit is notharmful to SS base metal nor to SSwelds themselves. However, it has led tocorrosion in the heat-affected zone(HAZ) of welds covered by heat-tintscale in fresh waters of low chloride ioncontent, a location where under-depositcorrosion (UDC) would otherwise beunlikely to occur. 2,7 HAZ of welds that

had the heat tint removed with rotatingfiber brushes were found to be asresistant as the base metal, althoughcovered with the black deposit. 2 Thisindicated that types 304/304L and316/316L in the absence of the heattintscale are resistant to UDC-as would beexpected in low-chloride fresh waters.

Control o Microbiologically Influenced

Corrosion (MIC) The addition of chlorine to water

systems will control bacteria that areharmful to metals, and in this respect isquite beneficial to the performance of SS and other materials used for handlingfresh water. When bacteria harmful tometals are not controlled, or in specialsituations where chlorine is not fullyeffective, MIC of steel, cast iron, SS,and other materials may occur. 8 Chlorinecan enhance performance by controllingbacteria, or alter environments byprecipitating deposits that may degradeperformance, or even enter intosynergistic effects when Gallionelliabacteria are present.

An interesting study was reportedconcerning severe localized corrosion of SS in a chlorinated, high manganese,fresh water in which Gallionella bacteriawere present in substantial quantities. 9

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Continuous vs intermediateInjection in Cooling WaterChlorine also is used to treat cool-

ing water for process units and airconditioning, although this use is beingincreasingly curtailed sometimes withadverse effects as the following caseshows.

Chlorine had been injected into acooling water system using type 304heat exchanger tubing for ~8 years withexcellent tubing performance. Dosagewas continuous but low, 0.5 mg/L to 1.0mg/L chlorine. Restrictions on chlorinedischarge forced a change to intermittentinjection: 12 mg/L for 6 min, decliningto 0.5 mg/ L to 1.0 mg/L at the end of anhour. Eight years later, the type 304tubing was uniformly pitted, in somecases to perforation, because of exposureto the higher chlorine residual for ex-tended times.

Chlorine Introduction

and ControlChlorine is available as liquidchlorine in steel containers, 10 as NaOCIsolution, as calcium hypochloritegranules, and sometimes as chlorinedioxide (C1O 2). Liquid chlorine is drawnfrom the bottle through gas flow metersand is normally introduced as "chlorinewater," that is, water in which 50 ppm to100 ppm of gaseous chlorine isdissolved. Liquid NaOCI also may bemetered through small metering pumpsinto water to be treated.

Chlorine water or NaOCI alsoshould be introduced into the center of the pipe to mix thoroughly with the fullvolume of the water. It should not beintroduced at the pipe wall where highconcentrations can run down the side of the pipe and cause localized corrosion. Italso is important to carefully monitorand control the addition and avoidoverdosing. Severe corro-

sion of SS water piping in severalMideast desalination plants resultedfrom chlorine overdosing.

When calcium hypochloritegranules are used, they should not bebroadcast in a manner that permitssettling on SS piping. The micro-en-

vironment around these granules restingon wet SS piping can lead to seriouspitting.

Venting of Chlorine VaporsChlorine vapors above chlori-

nated water have caused general pittingof half-full SS piping of SS ladders justabove the water line in clear wells, andon the outside of SS piping in poorlyventilated chambers. Adequate ventingis essential to prevent corrosion of SS inthe gaseous phase above chlorinated

water.

Summary and Conclusions The corrosion rate of CS and cast

iron increases significantly with aslittle as 0.5 mg/L chlorine and con-tinues to increase as the residualincreases. The rates are sufficientlyhigh to indicate that coatings or in-hibitors and maintenance are neededfor these materials in chlorinatedfresh waters.

The corrosion behavior of austenitic

nickel cast iron is not significantlyaffected up to 2 mg/L chlorine infresh water.

For copper-based alloys, corrosionbehavior is not significantly affectedup to 2 mg/L in fresh water.

Aluminum alloys suffer measurablegeneral corrosion and localizedcorrosion in raw and chlorinated rawwater, but not enough to precludetheir use for applications wherecorrosion and maintenance can betolerated.

Chlorine has beneficial effects on thecorrosion behavior types 304/ 304Land 316/316L: Additions can limit bacterial ac-

tivity that, in the absence of chlo-rine or other biocides, might leadto MIC.

Initial short-term 25 mg/L to 50mg/L dosages for 24 h for dis-infection appear to enhance theresistance of the normal protective

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Short-term exposure to 25mg/L to 50 mg/I, chlorinedosages appeared to be

beneficial, not detrimental,to SS performance.


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MATERIALS SELECTION & DESIGN

Long-term corrosion test spool data inchlorinated fresh waters with up to 5mg/L chlorine support the widespreaduse of SS in municipal waste water andpotable water treatment plants, freshwatercooled condensers and heat ex-changers, swimming pools, and othersimilar fresh-water applications.

For applications in which chlorineconcentrations are expected to be inthe 4 mg/L to 5 mg/L range for muchof the time, type 316L would be amore conservative choice compared totype 304L.

More highly alloyed SS and chro-mium-containing nickel-based alloysare not corroded in waters with up to 5mg/L chlorine. However, Ni-Cu alloy400 can suffer severe crevice corrosionin mildly chlorinated fresh water.

Heat-tint scale from welding SS shouldbe prevented or removed. Chlorineinjection into raw water results inprecipitation of insoluble Fe(OH)3 andmanganic and other metallichydroxides. Crevice UDC or MIC canoccur in HAZ of welds that arecovered by heat-tint scale in lowchloride waters in which ironmanganese deposits cover the weldarea.

Other precautionary measures as-sociated with chlorine additions in-

clude injecting in the center of thepipe, avoiding overdosing, and ventingmoist chlorine vapors from confinedareas.

AcknowledgmentThe authors, consultants to the

Nickel Development Institute (NiDI),Toronto, Ontario, Canada, thank NiDI forits support in the preparation of thisinformation.

References1. Water Supply Operations, Water Treatment(Denver, CO: AWWA, 1995).2. A.H. Tuthill, et al., "Effect of Chlorine on CommonMaterials in Fresh Waters," CORROSION/98, paperno. 708 (Houston, TX: NACE, 1998).3. B.P Boffardi, "Corrosion and Deposit Control in MillWater Supply," Proceedings of the 1992 TAPPIEngineering Conference (Atlanta, GA: TAPPI, 1992),p. 953.4. AWW Standard C653, "Disinfection of

Water Treatment Plants" (Denver, CO: AW WA).5. M.O. Lewus, et al., "A Study of the Potential for theMigration of Metals from Stainless Steel Systems intoChloride and Hyprochlorite Bearing Waters,"Proceedings of the International Congress onStainless Stainless 96, held June 1996 (Dusseldorf,Germany), p. 236-243.6. A.H. Tuthill, Private Communication.7. R.E. Avery, et al., MP 35, 9 (1996): p. 59.8. A Practical Manual on Microbiologically Influenced

Corrosion, ed. G. Kobrin (Houston, TX: NACE,1993).9. J. Tvreberg, et al., "The Role of Manganese FixingBacteria on the Corrosion Resistance of StainlessSteel," CORROSION/90, paper no. 151 (Houston, TX:NACE, 1990).10. Materials Selector for Hazardous Chemicals,Vol. 3: Hydrochloric Acid, Hydrogen Chloride andChlorine, eds. C. P. Dillon, W.I. Pollock, MTIPublication MS-3 (St. Louis. MO: MTI, 1999).

This article is based on CORROSION/ 98

paper no. 708, presented in San Diego,California.

Arthur H. Tuthill, FNACE is a corrosion consultantwith Tuthill Associates, Inc. He has more than 50years of experience as a materials and corrosionspecialist. He won the NACE Technical AchievementAward in 1994 and has won several TechnicalAssociation of the Pulp and Paper Industry (TAPPI)awards, and is a Fellow of TAPP[ and NACE. He hasa Masters Degree in metallurgy from the CarnegieInstitute of Technology, and has authored more than20 publications.

Richard E. Avery of Avery Consulting Associates is a

consultant to the Nickel Development Institute. Hespecializes in welding, metallurgy, and corrosion ofnickel-containing alloys. He was previously employedby INCO Alloys international, Inc., where he worked inthe technical services and market development areas.He has a Bachelors degree in metallurgicalengineering from Rensselaer Polytechnic Institute andis a NACE member.

Stephen Lamb is president of Specialized ResourcesCorp. He worked at [NCO Alloys International, Inc. for30 years in the areas of market development andstrategic planning. He has been a consultant for thepast 5 years, specializing in welding, corrosion, andstrategic and market planning. He has a Bachelorsdegree in metallurgy and a Masters degree in financeand is a Fellow of the Institute of Metallurgists.

Gregory Kobrin is a consultant in materialsengineering. He worked for the DuPont Company fornearly 40 years. He is editor of the NACE book, APractical Manual on Microbiologically-Influenced Corrosion, and is a NACECertified CorrosionSpecialist.

56 Printed in the U.S.A. MP/November 1998

EffectofChlorineonCommonMaterialsinFreshWater_14049_

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