rp 039295

-9555StandardRecommended Practice

Recovery and Repassivation after Low pHExcursions in Open Recirculating

Cooling Water SystemsThis NACE International standard represents a consensus of those individual members who havereviewed this document, its scope, and provisions. Its acceptance does not in any respectpreclude anyone, whether he has adopted the standard or not, from manufacturing, marketing,purchasing, or using products, processes, or procedures not in conformance with this standard.Nothing contained in this NACE International standard is to be construed as granting any right, byimplication or otherwise, to manufacture, sell, or use in connection with any method, apparatus,or product covered by Letters Patent, or as indemnifying or protecting anyone against liability forinfringement of Letters Patent. This standard represents minimum requirements and should in noway be interpreted as a restriction on the use of better procedures or materials. Neither is thisstandard intended to apply in all cases relating to the subject. Unpredictable circumstances maynegate the usefulness of this standard in specific instances. NACE International assumes noresponsibility for the interpretation or use of this standard by other parties and acceptsresponsibility for only those official NACE International interpretations issued by NACEInternational in accordance with its governing procedures and policies which preclude theissuance of interpretations by individual volunteers.

Users of this NACE International standard are responsible for reviewing appropriate health,safety, environmental, and regulatory documents and for determining their applicability in relationto this standard prior to its use. This NACE International standard may not necessarily addressall potential health and safety problems or environmental hazards associated with the use ofmaterials, equipment, and/or operations detailed or referred to within this standard. Users of thisNACE International standard are also responsible for establishing appropriate health, safety, andenvironmental protection practices, in consultation with appropriate regulatory authorities ifnecessary, to achieve compliance with any existing applicable regulatory requirements prior to theuse of this standard.

CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and maybe revised or withdrawn at any time without prior notice. NACE International requires that actionbe taken to reaffirm, revise, or withdraw this standard no later than five years from the date ofinitial publication. The user is cautioned to obtain the latest edition. Purchasers of NACEInternational standards may receive current information on all standards and other NACEInternational publications by contacting the NACE International Membership ServicesDepartment, P.O. Box 218340, Houston, Texas 77218-8340 (telephone +1 281/228-6200).

Approved April 1992

NACE Standard RP0392Item No. 210Revised July 1995NACE InternationalP.O. Box 218340

Houston, Texas 77218-8340+1 281/228-6200

1995, NACE International

RP0392-95

NACE Int_______________________________________________________________________

Foreword

This standard recommended practice presents guidelines for preplanning for, recovering from,and repassivation after a low pH excursion in open recirculating water systems, no matter whatthe cause. The procedures presented in this standard in no way preclude the use of otherprocedures but are presented as a consensus of experience gained over the years in a variety ofplants. The provisions of this standard should be applied under the direction of qualified water-treatment personnel from water-treatment suppliers and/or consultants and plant personnel.

This standard was originally prepared in 1992 and subsequently revised in 1995 by TaskGroup T-7A-15, a component of Unit Committee T-7A on Cooling Water. The task group iscomposed of representatives from the refining, petrochemical, chemical, and water-treatmentindustries. This standard is published by NACE International under the auspices of Groupernational i

Committee T-7 on Corrosion by Waters.

This standard represents a consensus of those individual members who have reviewed thisdocument, its scope, and provisions. Its acceptance does not in any respect preclude anyone,whether he has adopted the standard or not, from manufacturing, marketing, purchasing, or usingproducts, processes, or procedures not in conformance with this standard. Nothing contained inthis NACE International standard is to be construed as granting any right, by implication orothewise, to manufacture, sell, or use in connection with any method, apparatus, or productcovered by Letters Patent, or as indemnifying or protecting anyone against liability forinfringement of Letters Patent. This standard represents minimum requirements and should in noway be interpreted as a restriction on the use of better procedures or materials.

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RP0392-95

ii_______________________________________________________________________

NACE InternationalStandard

Recommended PracticeNACE International

Recovery and Repassivation After Low pH Excursionsin Open Recirculating Cooling Water Systems

Contents

1. General..................................................................................................................... 12. Preplanning .............................................................................................................. 13. Recovery .................................................................................................................. 34. Limited or Non-Discharge Recovery.......................................................................... 55. Repassivation ........................................................................................................... 8References..................................................................................................................... 8Bibliography ................................................................................................................... 9Appendix A..................................................................................................................... 9

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RP0392-95

NACE International

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: General

process leaks, or airborne acid gases can number of serious problems. Examples of theseproblems follow:

ental problems may be present at one timewith the water from the affected system. Prob-lems such as low pH water (

RP0392-95

2

2.1.2 The volume of each cooling system should beaccurately determined (e.g., using the salt test(1) orother methods).

2.2 A decision diagram to assist the recovery planningprocess is shown in Figure 1.

Condition pH-Range Concern Procedure ReferLevel Level Number to Section:

II.

(delta ppm chloride as Cl) x (% purity of salt)

Vt)

pH is above 4.5 and within one Minor I 3.2

one pH unit below theeolume of system (gal) = (lb of salt added) x (72,289) x 100(delta ppm chloride as Cl) x (% purity of salII.

IV.

FIGURE 1: Decision Plan to Select Recovery Plan for Low pH Excursionsin Open Recirculating Cooling Water Systems

Note that the Concern Levels are time-dependent. The Concern Level becomes more critical as time passes and action should always be taken as quickly as possible.

2.3 A recommended checklist, chemical inventory,chemical feed rates, alkaline chemical requirements, andchemical dosage requirements are tabulated in AppendixA. The tables must be modified to be system- or site-specific. This can be accomplished by generating a titra-tion curve of a plants cooling water that will determine

the amount of alkaline material that will be required whena low pH excursion occurs. Empirical data, generated bymembers of NACE Task Group T-7A-15, indicate that theamounts of caustic/alkaline material required vary consi-derably from water to water, especially when the pH isbelow 4.5.1,2.

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(1) Salt Test: Analyzes chloride in system water. Add approximately 0.6 kg of salt (NaCl) for each 10 m3 of water (0.5 lb of salt for each 1,000 U.S.

gal of water) in the system. Test chloride content every five minutes for two hours to allow salt to be completely mixed.

Volume of system (m ) = (kg of salt added) x 607 x 1003

minimum set point

pH is between 2.5 and 4.5 Major III 3.4

pH is below 2.5 Extreme IV 3.5I. pH unit below the minimum setpoint

pH is above 4.5 but more than Mod rate II 3.3NACE International

RP0392-95

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R

Iron levels should be tested periodically duexcursion and the concentration of treatmeicals adjusted to handle the high amount of iron.

Check make-up water for pH change.

3.2.5 Look for process leaks or airborne cause(s) of

3.1.2 During recovery, pH should be monitored atreturn headers or other representative samplingpoints several times each hour, typically every 10minutes.

3.1.3 Initial dosages of alkaline materials should beabout 80% of the calculated theoretical requirementsor the empirical requirements indicated by thetitration curve recommended in Paragraph 2.3. Afterthe pH has stabilized following the initial dose, adecision can be made whether to add more material,and if so, how much. This procedure is illustrated inTables A-3, A-4, and A-5 in Appendix A.

3.2 Procedure I This procedure shall be followed whenpH is above 4.5 and within one pH unit below theminimum set point.NACE Internationallow pH.

3.2.6 Check for proper operation of acid feed pump.

3.2.7 Make necessary adjustments of blowdown andacid feed and/or notify supervisor. Recovery actionsare site-specific. Refer to Section 5 for repassivationprocedures.

3.2.8 Verify proper operation of monitoring and/orcontrol equipment and restandardize pH equipment.

3.3 Procedure II This procedure shall be followedwhen pH is above 4.5 but more than one pH unit belowthe minimum set point.

3.3.1 Verify pH reading with a recalibrated pH meter.ring a pHnt chem- 3.2.42.4 It is essential that operators be trained to recognizethe serious consequences that a low pH excursion cancause in a plant and to react appropriately. The instal-lation of corrosion probes with automatic readouts andalarms may aid in the detection of acid leaks or low pHexcursions in a cooling water system. Sudden high levelsof corrosion may alert the facility to begin correctiveaction and control damage to a system.

2.5 As part of a plants periodic review, a written inspec-tion report on the condition of all chemical feeding andhandling equipment should be made, including photo-graphic documentation, along with an inventory ofrequired recovery chemicals and testing equipment andmaterials.

2.5.1 Monitoring equipment (pH meters) and testingreagents should be checked frequently to ensure thatthey provide accurate readings.

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Section 3:

3.1 General

3.1.1 This section addresses iron problems. Thewater-treatment procedure may be modified tohandle copper and other metals. Concern levels (seeFigure 1) are time-dependent and become morecritical as time increases. Procedures for recoveryfrom low pH excursions in low-carbon steel systemsare provided; modifications may be required forsystems containing other metals. High levels of ironcan ultimately reduce the effectiveness of com-ponents found in cooling water treatment programs.2.5.2 All required testing apparatus and reagentsshould be on hand for use if a low pH excursionoccurs.

2.6 Preplanning should also include a provision forhandling the composition and volume of blowdown waterthat will be discharged during the recovery period. If anin-plant wastewater treatment facility or on-site storage isnot available, a review of discharge limitations (i.e.,National Pollution Discharge Elimination System[NPDES] permit or other environmental permits) is man-datory. A working knowledge of environmental regu-lations and proper corrective action reduces the exposureto potential liability regarding environmental regulations.

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ecovery

3.2.1 Verify pH readings with a recalibrated pHmeter.

3.2.1.1 Contact water-treatment supplier. Makethe necessary adjustments in water treatment asrecommended by the supplier.

3.2.2 Look for acid leaks.

3.2.3 Determine level of acid in day or storage tankto see whether actual feed rate is as specified orwhether the specified rate has been exceeded.3

RP0392-95

43.3.1.1 Notify supervisor(s) and water-treatmentsupplier.

3.3.2 Stop all acid feed and block off acid feedsystem.

3.3.3 If environmentally acceptable, increase blow-down.

3.3.4 Stop gaseous chlorination or other oxidizingbiocide addition.


3.3.6 Determine level of acid in day or storage tankto see whether actual feed rate is as specified orwhether the specified feed rate has been exceeded.


3.3.8 Check make-up water for pH change.

3.3.9 Look for process leaks or airborne cause(s) oflow pH.


3.3.11 Slowly sprinkle predetermined amounts ofsoda ash (sodium carbonate) into recirculating pumpintake area. (This step is optional.)

3.3.11.1 Soda ash (sodium carbonate) is themost commonly used alkaline material; however,sal soda (sodium carbonate decahydrate) orsodium bicarbonate may be used. (SeeAppendix A, Table A-3.) Liquid caustic soda(sodium hydroxide) can be used only if soda ashis not immediately available, but is not recom-mended. The major disadvantage of usingcaustic soda is that iron hydroxide precipitates atthe point where relatively concentrated causticsoda meets the water and may not redissolve.

3.3.11.2 Many water-treatment personnel recom-mend that no alkaline material be fed above pH4.5, but prefer to raise the pH only by blowdownand make-up to reduce the possibility ofprecipitating iron hydroxides. This point is site-specific and is determined by the volume of thesystem, alkalinity of the make-up water, treat-ment program, etc.

3.3.12 Once pH returns to minimum control level,refer to Section 5 for repassivation procedures.

3.3.13 Resume normal blowdown controls andnormal biocide treatment program and dosage.3.4 Procedure III This procedure shall be followedwhen pH is between 2.5 and 4.5.

3.4.1 Verify pH reading with a recalibrated pH meter.


3.4.2 Stop all chemical addition and block off acidfeed system.

3.4.3 If environmentally acceptable, open blowdownto the maximum allowable rate. Overflow the sump(with fire hoses, if available) with due considerationbeing given to the handling and/or holding capacityof the wastewater treatment plant. Additional blow-down from heat exchangers and dead lines (deadlegs) is strongly recommended. Ensure that max-imum blowdown does not lower sump water belowthe level required for proper pump operation.




3.4.7 Add sufficient sequestrant and/or iron disper-sant to solubilize or disperse iron. The approximaterequirement for the iron dispersant should be prede-termined based on several estimated concentrationsof iron in the circulating water. Actual dosagedepends on the level of iron found in the water duringthe incident.

3.4.8 In raising the pH from 2.5 to 4.5, the use ofsoda ash (sodium carbonate), sal soda (sodium car-bonate decahydrate), or sodium bicarbonate ispreferred over caustic soda (sodium hydroxide).Feed predetermined amounts of soda ash as asolution or slowly sprinkle into the intake area of therecirculating pump at predetermined times, typicallyevery 10 to 15 minutes. (See Appendix A, Table A-4for dosage requirements.) Add the anticipatedrequirements in two stages to avoid unintentionaloverfeeding.

3.4.9 Continue maximum blowdown and overflow, ifenvironmentally acceptable, until (1) the pH rises toat least 4.5, (2) the water clears, and (3) the total ironlevel has stabilized at an acceptable level (2 ppm and3 ppm Fe are commonly recommended values).3.4.10 Verify proper operation of monitoring and/orcontrol equipment and restandardize pH equipment.

3.4.11 Reduce blowdown and start repassivationprocedure. (See Section 5.)NACE International

RP0392-95

(with fire hoses, if availablebeing given to the handlingof the wastewater treatment plant. This water maybe hazardous to the environment and under environ-

e), or sodium bicarbonate isic soda (sodium hydroxide).

Feed predetermined amounts of soda ash as asolution or slowly sprinkle into the intake area of the

_

onmental regulations; precautions should be taken toensure proper disposal. Additional blowdown fromheat exchangers and dead lines (dead legs) isstrongly recommended. Ensure that maximum blow-down does not lower sump water below the levelrequired for proper pump operation.




3.5.7 Because of the large amounts of soda ash(sodium carbonate) that would be required to raisethe pH to about 2.5 to 3.0, the slow addition ofcaustic soda (sodium hydroxide) to the suction sideof the circulating pumps is preferred. It has beenestimated that the corrosion rate of carbon steel inthe pH range of 1.0 to 2.0 is approximately 25 mm/y(1,000 mpy). The corrosion rate drops to about 5 to10 mm/y (200 to 400 mpy) in the 2.5 to 3.0 pHrange; thus immediate corrective action is necessary

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Section 4: Limited or N

4.1 This section covers recovery of the system when thewater cannot be discharged directly from the coolingsystem due to environmental concerns.

4.2 Procedure I This procedure shall be followed whenpH is above 4.5 and within one pH unit below theminimum set point.

4.2.1 Verify pH readings with a recalibrated pHmeter.NACE Internationalrecirculating pump at predetermined times, typicallyevery 10 to 15 minutes. (See Appendix A, Table A-4for dosage requirements.) Add the anticipatedrequirements in two stages to avoid unintentionaloverfeeding.

3.5.10 Add sufficient sequestrant and/or irondispersant to solubilize or disperse iron. Predeter-mine the approximate requirement for the irondispersant based on several estimated concen-trations of iron in the circulating water. Actualdosage depends on the level of iron found in thewater during the incident.

3.5.11 Continue maximum blowdown and overflow,if environmentally acceptable, until (1) pH rises to atleast 4.5, (2) the water clears, and (3) the total ironlevel has stabilized at an acceptable level (2 ppm and3 ppm Fe are commonly recommended values).3.5.12 Verify proper operation of monitoring and/orcontrol equipment and restandardize pH equipment.

3.5.13 Reduce blowdown and start repassivationprocedure. (See Section 5.)

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-Discharge Recovery

4.2.1.1 Contact water-treatment supplier. Makethe necessary adjustments in water treatment asrecommended by the supplier.



4.2.4 Check make-up water for pH change.) with due consideration and/or holding capacity

carbonate decahydratpreferred over caust3.5 Procedure IV This procedure shall be followedwhen pH is below 2.5.




3.5.3 If environmentally acceptable, open blowdownto the maximum allowable rate. Overflow the sumpif pH is below 2.5. (See Appendix A, Table A-5 forcaustic soda dosage.)3.5.8 Monitor pH at return headers, or other repre-sentative sampling points, several times each hour,typically every 10 minutes, until pH has risen to the2.5 to 3.0 range. Do not exceed the pH range of 2.5to 3.0 when using caustic soda (sodium hydroxide)because of the possibility of overfeeding andprecipitating metal hydroxides.

3.5.9 In raising the pH from about 3.0 to 4.5, the useof soda ash (sodium carbonate), sal soda (sodium5

RP0392-954.2.5 Look for process leaks or airborne cause(s) oflow pH.


4.2.7 Make necessary adjustments of blowdown andacid feed and/or notify supervisor. Recovery actionsare site-specific; see Section 5 for repassivationprocedures.


4.3 Procedure II This procedure shall be followedwhen pH is above 4.5 but more than one pH unit belowthe minimum set point.



4.3.2 Stop all acid feed and block off acid feedsystem.

4.3.3 Adjust blowdown flow rate and/or dischargepoint according to environmental requirements.

4.3.4 Stop gaseous chlorination or other oxidizingbiocide addition.




4.3.8 Check make-up water for pH change.

4.3.9 Look for process leaks or airborne cause(s) oflow pH.


4.3.11 Slowly sprinkle predetermined amounts ofsoda ash (sodium carbonate) into recirculating pumpintake area. (This step is optional.)

4.3.11.1 Soda ash (sodium carbonate) is themost commonly used alkaline material; however,sal soda (sodium carbonate decahydrate) orsodium bicarbonate may be used. (See Appen-dix A, Table A-3.) Liquid caustic soda (sodiumhydroxide) can be used only if soda ash is notimmediately available, but is not recommended.The major disadvantage of using caustic soda isthat iron hydroxide precipitates at the point6where relatively concentrated caustic sodameets the water and may not redissolve.

4.3.11.2 Many water-treatment personnel recom-mend that no alkaline material be fed above pH4.5, but prefer to raise the pH only by blowdownand make-up to reduce the possibility ofprecipitating iron hydroxides. This point is site-specific and is determined by the volume of thesystem, alkalinity of the make-up water, treat-ment program, etc.

4.3.11.3 Consider the use of mechanical filteringaids to reduce the possibility of contaminationand deposition of precipitated metal hydroxideswithin the cooling system. Preplanning isneeded to allow effective use of mechanicaldevices. Consider positioning and attachingequipment to the system. This may include theaddition of pipe fittings and valves to the systemto allow ease of attachment if the equipment isnot a permanent fixture of the cooling watersystem.

4.3.12 Once pH returns to minimum control level,refer to Section 5 for repassivation procedures.

4.3.13 Resume normal blowdown controls andnormal biocide treatment program and dosage.

4.4 Procedure III This procedure shall be followedwhen pH is between 2.5 and 4.5.








4.4.7 Add sufficient sequestrant and/or iron disper-sant to solubilize or disperse iron. Predetermine theapproximate requirement for the iron dispersantbased on several estimated concentrations of iron inthe circulating water. Actual dosage depends on thelevel of iron found in the water during the incident.NACE International

RP0392-954.4.8 In raising the pH from 2.5 to 4.5, the use ofsoda ash (sodium carbonate), sal soda (sodiumcarbonate decahydrate), or sodium bicarbonate ispreferred over caustic soda (sodium hydroxide).Feed predetermined amounts of soda ash as asolution or slowly sprinkle into the intake area of therecirculating pump at predetermined times, typicallyevery 10 to 15 minutes. (See Appendix A, Table A-4for dosage requirements.) Add the anticipatedrequirements in two stages to avoid unintentionaloverfeeding.

4.4.9 Begin mechanical removal of solids as soon aspossible. The removal of solids helps reduce thefouling and damage that can occur to the systemfrom the precipitated metal hydroxides.

4.4.9.1 Mechanical removal of solids can behandled by various methods. Some methodsare listed below:

(a) Use of conventional sand filters.(b) Use of sand filters with pH adjustment ofthe water prior to entering the filter. This forcesprecipitation of the solids in the filter andreduces the possibility of fouling in the coolingsystem.

(c) Filtering the water through a bed ofhydrated lime. In addition to acting as a filter,this raises the pH and precipitates any solids.This method should be used in conjunction withanother type of filter to prevent solids fromentering the cooling system.

(d) Use of lime/soda softening sludge, ifavailable, to neutralize the pH prior to a filtervessel.

(e) Use of centrifugal separators for solidsremoval.

In all cases, water flow through the solids-removal devices should constitute 1 to 5% of therecirculation rate of the system.


4.4.11 When the water quality complies with localdischarge requirements, resume blowdown.

4.4.11.1 Perform frequent water-quality checksto ensure continued compliance with dischargerequirements.

4.4.12 Begin repassivation (see Section 5).NACE International4.5 Procedure IV This procedure shall be followedwhen pH is below 2.5.








4.5.7 Because of the large amounts of soda ash(sodium carbonate) that would be required to raisethe pH up to about 2.5 to 3.0, the slow addition ofcaustic soda (sodium hydroxide) to the suction sideof the circulating pumps is preferred. It has beenestimated that the corrosion rate in the pH range of1.0 to 2.0 is approximately 25 mm/y (1,000 mpy).The corrosion rate drops to about 5 to 10 mm/y (200to 400 mpy) in the 2.5 to 3.0 pH range; thusimmediate corrective action is necessary if pH isbelow 2.5. (See Appendix A, Table A-5 for causticsoda dosage.)4.5.8 Monitor pH at return headers, or other repre-sentative sampling points, several times each hour,typically every 10 minutes, until pH has risen to the2.5 to 3.0 range. Do not exceed the pH range of 2.5to 3.0 when using caustic soda (sodium hydroxide)because of the possibility of overfeeding andprecipitating metal hydroxides.

4.5.9 In raising the pH from about 3.0 to 4.5, the useof soda ash (sodium carbonate), sal soda (sodiumcarbonate decahydrate), or sodium bicarbonate ispreferred over caustic soda (sodium hydroxide).Feed predetermined amounts of soda ash as asolution or slowly sprinkle into the intake area of therecirculating pump at predetermined times, typicallyevery 10 to 15 minutes. (See Appendix A, Table A-4for dosage requirements.) Add the anticipatedrequirements in two stages to avoid unintentionaloverfeeding.

4.5.10 Add sufficient sequestrant and/or irondispersant to solubilize or disperse iron. Predeter-mine the approximate requirement for the irondispersant based on several estimated concen-trations of iron in the circulating water. Actual7

RP0392-95

8

dosage depends on the level of iron found in thewater during the incident.

4.5.11 As the pH of the system nears 4.5, beginmechanical removal of solids by methods discussedin Paragraph 4.4.9.1. Flow to these units should be1 to 5% of the recirculating rate of the tower. Ideallythese units are placed off the return risers to thetower to capture solids from the system. When the

4.5.11.1 Perform frequent water analyses toensure compliance with discharge requirements.


4.5.13 Reduce blowdown and start repassivationprocedure. (See Section 5.)

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5.1.1 Protective corrosion-inhibiting films maystripped from metal surfaces in contact with lowrecirculating water. After control of a low pH excur-

Applicable environmental and wastewater treatmentictions may necessitate adjusting dosages of repas-

sivation treatment programs.

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e

2. A.E. Feltzin, Unpublished Data, March 22, 1990.

3. NACE Standard RP0182 (latest revisConditioning of Cooling Water Equipment (Houston, TX:N

Treatment Programs, CORROSION/87, paper no. 158 NACE, 1987).ACE International).

ion), Initial

(Houston, TX:sion has been regained and the pH has returned toits normal range, the metal surfaces requirerepassivation to ensure optimum long-term corrosionprotection. This is normally accomplished by in-creasing the concentration of the corrosion inhibitorhigher than normal for some period of time or byadding specific pretreatment inhibitors. Failure toincrease inhibitor dosage may either prevent or delayattaining adequate control of corrosion.

5.1.1.1 During the first few days of repassiv-ation, inorganic inhibitors (e.g., polyphosphate,ortho phosphate, nitrite, zinc, or others) should

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Refer

1. G. Engstrom, Unpublished Data, April 9, 1990.5.3 Careful control of chlorine or other oxidizing biocideduring the early stages of repassivation is recommended.The use of a nonoxidizing biocide should be consideredduring repassivation.

5.4 Whenever possible, the progress of repassivationshould be monitored with a linear polarization resistance(LPR) probe or corrosion coupons.5.5 Refer to NACE Standard RP0182,3 Initial Condi-tioning of Cooling Water Equipment, and Recovery fromLow pH Excursions in Cooling Water Systems Using All-Organic Treatment Programs.4

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nces

4. R.K. Fuller, J.W. McCarthy, Recovery From Low pHExcursions in Cooling Water Systems Using All-Organic be pH

5.2restrwater quality complies with local requirements,resume blowdown.

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Section 5: R

5.1 History, experience, and site specifics in a plantdetermine the specific repassivation procedures.___________________________________

epassivation

be used to help in quickly reestablishingpassivation or corrosion-inhibiting films.NACE International

RP0392-95

NACE International

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Bibliography

Bridgeport Tube Handbook. Bridgeport Brass Company,1964.

Brooke, J. M. Unpublished data from Puckorius &Associates, Sweeney, TX, 1987.

Cohen, A. Copper in Potable Water Systems. Heating,Piping, and Air Conditioning 50, 5 (1978): pp. 81-87.

McCoy, J.W. The Chemical Treatment of Cooling WNew York, NY: Chemical Publishing Co., 1974.

Monette, J., D. Hunter. Unpublished data from DrewChemical Co. Ltd., Ajax, Ontario, Canada, 1986.

Mullins, M.A. Unpublished data from Drew IndustrialDivision, Boonton, NJ, 1986.

Nalco Chemical Co. The Nalco Water Handbook. 2nded. New York, NY: McGraw-Hill Inc., 1988.

1979, Houston, TX.

Uhlig, H.H., ed. Corrosion and Corrosion Control. 2nd

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e__________________________________

App

The general guidelines and checklists in Tables A-1through A-5 have been developed from the input of usersand water-treatment vendors, almost all of whom havehad direct experience with low pH excursions. Thus,most of the factors required to recover from a pHexcursion have been covered.

Each plant should review its individual requirements,capabilities, lines of communication, procedures, etc.,during the planning phase (which must include both plantand water-treatment supplier personnel) so that recoveryprocedures are:ed. New York, NY: John Wiley and Sons Inc., 1971.

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ndix A

- in compliance with environmental permits,- site-specific,- cover all contingencies,- ensure recovery in minimum time, and- minimize damage to the cooling water system.

These procedures should be completed prior toexperiencing a low pH excursion.ater.DeGroof, J.E., E.W. Biggers. Unpublished data fromExxon Company, Baytown, TX, 1985.

Drew Principles of Industrial Water Treatment. 11th ed.Boonton, NJ: Ashland Chemical Co., Drew IndustrialDivision, 1994.

Handbook of Industrial Water Conditioning. 7th ed.Trevose, PA: Betz Laboratories Inc., 1976.

Kunz, R.G., et al. Cooling Water Calculations. Chem-ical Engineering (1977): p. 61.Nathan, C.C., J.R. Scheiber. Statistical Aspects ofCorrosion Inhibition Measurement and Control inIndustrial Systems. Materials Performance 17, 4(1978): p. 24.

Scott, W.J. Handling Cooling Water Systems During aLow pH Excursion. Chemical Engineering (February22, 1982): p. 121.

Townsend, J.R. Handling Upsets In Cooling WaterSystems TP-196-A. Presented at the Cooling TowerInstitutes Annual Meeting held January 22 to 24,9

RP0392-95

TABLE A-1(A)Checklist to Prepare for a pH Excursion

Name Daytime Phone Nighttime Phone to be Notified(B)Plant Personnel

Water-Treatment Supplier Personnelto be Notified(C)

Warehouse

DemineralizerPlant

Vacuum Truck

WastewaterTreatment Plant

Retention Timeof System(D)

Volume of System(see Para-graph 2.1.2) Maximum Blow-down Rate

MaximumMake-up Rate

Circulation Rate

Half-lifeof System(E)

Desired pHControl Range

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(A) Most supplies can be stored in a shelter near the cooling tower for easy accessibility.

(B) Supervisors, laboratory, waste treatment, utilities, environmental, safety, and others as specified by company policy.

(C) District representative (office, home), district manager (office, home), other.

(D) Retention Time (days) = volume of system (m or U.S. gal)

blowdown / day (m / day or gal / day)3

3

(E) Half life (days) = 0.693 x volume of system (m or U.S. gal)[blowdown (m / day or gal / day) + windage (m / day or gal / day)]

3

3 3-10 NACE International

RP0392-95TABLE A-2Minimum Inventory and Maximum Feed Rate for Maximum Excursion below pH 2.5 (A)

Identification Minimum MaximumWarehouse Supply Number Inventory Rate Feed or Use

CORROSION INHIBITORS

Organic

Organic

Inorganic

Inorganic

DISPERSANTS AND DEPOSIT INHIBITORS

Dispersant

Dispersant

Dispersant

Specific Iron Dispersant

Non-OxidizingBiocide

Non-OxidizingBiocide

Soda Ash(B)(sodium carbonate) Caustic Soda(C) (%)(sodium hydroxide) ____________________________

(A) The following formulae can be used to estimate nonalkaline chemical requirements:

SLUG: kg of product = Desired product concentration (ppm) x system volume (m ) 1,000

3

lb of product = Desired product concentration (ppm) x system volume (U.S. gal)120,000

CONTINUOUS: kg of product per day = Desired product concentration (ppm) x make - up (m )cycles of concentration x 1,000

3

lb of product per day = Desired product concentration (ppm) x make - up (gal / daycycles of concentration x 120,000

See Tables A-3, A-4, and A-5 for alkaline chemical requirements.(B)

Sal soda (sodium carbonate decahydrate) or sodium bicarbonate can be substituted for soda ash (sodium carbonate).(C)

Usually available at the boiler make-up water demineralizer plant. Can be transported by a caustic soda tank trailer or a vacuum truck.NACE International 11

RP0392-95TABLE A-3Estimated Alkaline Chemical Requirements to Raise pH to 7.0 from 4.5

Anhydrous Soda Ash (Sodium Carbonate)

From pH per 100 m3 of water per 10,000 U.S. gal of water

Initial Dosage (80%of total) (kg)

Total Requirements(kg)

Initial Dosage (80%of total) (lb)

Total Requirements(lb)

4.5 0.48 0.60 0.40 0.505.0 0.16 0.20 0.16 0.205.5 0.050 0.060 0.040 0.0506.0 0.016 0.020 0.016 0.0206.5 0.0050 0.0060 0.0040 0.0050

TABLE A-4(A)Estimated Alkaline Chemical Requirements to Raise pH to 4.5 from pH 1.0 and Above

Anhydrous Soda Ash (Sodium Carbonate)

From pH Free MineralAcidity (FMA) as

CaCO3

per 100 m3 of water per 10,000 U.S. gal of water

Initial Dosage(80% of total)

(kg)

TotalRequirements

(kg)

Initial Dosage(80% of total) (lb)

TotalRequirements

(lb)

1.0 4,500 160 200 190 2401.5 1,500 53 66.5 64 802.0 450 16 20 19 242.5 150 5.3 6.6 6.4 8.03.0 45 1.6 2.0 1.9 2.43.5 15 0.50 0.66 0.64 0.804.0 4.5 0.16 0.20 0.19 0.24

(A) Chemical requirements for operating systems with buffered waters may be somewhat different from these values that are based on theoretical

calculations for unbuffered water and on unpublished empirical data from cycled systems. These alkaline requirements were calculated for sulfuricacid and may vary for other mineral or organic acidic contaminants. These data are approximate and need to be quantified, as recommended inParagraph 2.3. Sodium carbonate is most commonly available commercially in the 99% pure, anhydrous form (soda ash). However, it is also available as thesesquicarbonate (trona), the monohydrate, septahydrate, and decahydrate. The latter is commonly called sal soda or washing soda and issometimes used because it dissolves faster than soda ash. Treatment requires 2.7 times as much sal soda as it does anhydrous soda ash.12 NACE International

RP0392-95

TABLE A-5(A)Estimated Fresh Caustic Soda Requirements to Raise pH to 2.5 from pH 1.0 and Above

NaOH (50% Solution)(B)


Initial Dosage (80%of total) (L)

Total Requirements(L)

Initial Dosage (80%of total) (U.S. gal)

Total Requirements(U.S. gal)

1.0 950 1,200 95 1201.5 450 550 45 552.0 150 200 15 20

(A) Chemical requirements for operating systems with buffered waters may be somewhat different from these values that are based on theoretical

calculations for unbuffered water and on unpublished empirical data from cycled systems. These caustic requirements were calculated for sulfuricacid and may vary for other mineral or organic acidic contaminants. These data are approximate and need to be quantified as recommended inParagraph 2.3.(B)

49.9% NaOH by weight, 762.7 g/L (6.365 lb/U.S. gal), specific gravity of 1.5253.NACE International 13

RP0392-95

TABLE A-5(A)

Estimated Fresh Caustic Soda Requirements to Raise pH to 2.5 from pH 1.0 and Above

NaOH (50% Solution)(B)


Initial Dosage (80% oftotal) (L)

Total Requirements(L)

Initial Dosage (80% oftotal) (U.S. gal)

Total Requirements(U.S. gal)

1.0 950 1,200 95 120

1.5 450 550 45 55

2.0 150 200 15 20

(A) Chemical requirements for operating systems with buffered waters may be somewhat different from these values that are based on theoreticalcalculations for unbuffered water and on unpublished empirical data from cycled systems. These caustic requirements were calculated for sulfuricacid and may vary for other mineral or organic acidic contaminants. These data are approximate and need to be quantified as recommended inParagraph 2.3.(B) 49.9% NaOH by weight, 762.7 g/L (6.365 lb/U.S. gal), specific gravity of 1.5253.NACE International 13

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