Lay-up of Boilers

CRTD- Vol. 66

CONSENSUS FOR

THE LAY-UP OF BOILERS,

TURBINES, TURBINE CONDENSERS,

AND AUXILIARY EQUIPMENT

AN ASME RESEARCH REPORT

prepared by theTURBINE/TURBINE CONDENSER LAY-UP TASK GROUP

ANDBOILER LAY-UP TASK GROUP

for theWATER TECHNOLOGY SUBCOMMITTEE OF THE

ASME RESEARCH AND TECHNOLOGY COMMITTEEON WATER AND STEAM IN THERMAL POWER SYSTEMS

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERSThree Park Avenue n New York, New York 10016

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r PREFACE r

The Water Technology Subcommittee of the ASME Research andTechnology Committee on Water and Steam in Thermal Systems, underthe leadership of Robert T. Holloway of Holloway Associates has estab-lished a Consensus for the Lay-up of Boilers, Turbines, TurbineCondensers and Auxiliary Equipment. Since industry from time to timefaces the need to idle equipment, the importance of good lay-up practicescannot be over-emphasized. Failure to properly protect equipment hasfrequently resulted in very high maintenance costs and, in some in-stances, the need to replace badly corroded equipment. These practices,properly applied, will aid the user in protecting these critical units fromdamaging corrosion during non-operating periods.

Data compilation and preparation of the resulting consensus on oper-ating practices was performed by task groups of the subcommittee. Thetask groups consisted of a cross-section of manufacturers, operators, andconsultants involved in the fabrication and operation of industrial andutility boilers, turbines and turbine condensers. The members of these taskgroups as well as those making significant contributions to this documentare listed in the Acknowledgements section.

It is the intention of the ASME Research and Technology Committee toreview this information, revise, and reissue it as necessary to comply withthe advances in equipment design and lay-up technology. This documentsupersedes the Consensus of Current Practices for Lay-Up of Industrialand Utility Boilers published in 1985 by the Industrial Subcommittee ofASME Research Committee water in Thermal Power Systems.

It is my pleasure to commend all who generously contributed theirtime to this effort to improve the realiability of industrial steam generationequipment.

David E. Simon IIPast Chairman, ASME Research and Technology

Committee on Water and Steam inThermal Systems

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r ACKNOWLEDGEMENTS r

This document was prepared by the Turbine and Turbine CondenserLay-up Task Group and the Boiler Lay-up Task Group for the WaterTechnology Subcommittee of the Research and TechnologySubcommittee of the Research and Technology Committee on Water andSteam in Thermal Systems of the American Society of MechanicalEngineers. In addition, the former Utilities Subcommittee made significantcontributions to the preparation of this document. Recognition is herebygiven to the following members of these groups for their contributions inpreparing this document.

R. T. Holloway, Chairman

Combined Lay-up Document Task Group

W. AllmonA. AschoffA. BanwegT. BeardwoodJ. BeecherJ. BellowsW. BernahlD. M. BloomI. CottonB. CunninghamD. DanielsP. DanielD. Dewitt-DickS. B. DilcerJ. C. DromgooleA. W. FynskF. GabrielliS. GoodstineR. HackelK. W. HermanR. T. HollowayO. JonasK. Kelley

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H. KleinR. W. LaneP. J. LathamR. LongR. W. LightL. PaulT. H. PikeJ. O. RobinsonL. S. RosenzweigI. J. SchuckK. ShieldsS. ShulderJ. SiegmundD. E. Simon IIJ. TaylorK .A. TeetersP. ThomsassonT. J. Tvedt, Jr.A. WhiteheadJ. F. WilkesW. WillseyD. K. Woodman

r SAFETY PRECAUTIONS r

The following precautions are intended to assist readers, who may beinexperienced with equipment lay-up, by outlining some hazards thatmay be encountered during lay-up procedures. They do not constitute acomplete, detailed safety procedure. It is the responsibility of the person-nel planning lay-up to be aware of the hazards, all OSHA, governmentand individual company regulations, etc., and to plan accordingly

Proper handling of lay-up chemicals is essential from both a safety andan environmental standpoint. Some chemicals are flammable or explo-sive and can cause serious injury or death if mishandled. Other chemicalsare toxic. Exposure may occur through skin contact or inhalation of va-pours. All persons working with or near these chemicals must be familiarwith their hazardous properties and recommended safety precautions.

Occupational Safety and Health Administration (OSHA) regulations, orindividual company safety standards, should always be observed whenhandling nitrogen, which is an inert gas commonly used to blanket equip-ment during lay-up. It provides corrosion control when used to displaceair from equipment. Nitrogen will not support human life and special pre-cautions must be observed when it is used. Do not enter equipment laidup with nitrogen until the nitrogen supply is disconnected, the vessel ispurged, and tests show that sufficient air present and can be main-tained.

Lay-up of equipment frequently, requires confined space or vesselentry. Company procedures for testing and assuring the adequate oxygencontent and absence of flammable gases must always be observed beforeany confined space is entered even if nitrogen gas is not used during lay-up.

Material Safety Data Sheets and any other available safety precautionsmust be provided for all chemicals that are used.

Wherever hazardous or unfamiliar chemicals are used, signs should beposted to warn of the dangers involved. Attention to warnings could verywell save the lives of those entering a nitrogen-blanketed vessels. This isalso the case when these chemicals are to be discharged. Warnings needto clearly indicate the expected dangers.

Before chemicals are released, it should be made certain that they havebeen deactivated or neutralized and present no danger to the environ-ment. It may be necessary to notify the proper regulatory agencies priorto discharge.

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Hydrazine, a common volatile oxygen scavenger, has been classifiedas toxic and a suspected carcinogen. Consult the chemical suppliersMSDS sheet for further precautions when using this chemical.

Caution: When corrosion occurs in confined spaces, hydrogen isevolved creating a potentially explosive environment. Extreme cautionshould be exercised and such spaces must be checked and ventilated.

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r CONTENTS r1 r Introduction 1

2 r Factors to be Considered 3

3 r Reasons for Lay-Up 5

4 r Identification of Materials in Equipment 7

5 r Inspection of Equipment 9

6 r Cleaning of Equipment 11

7 r Use and Disposal of Lay-Up Chemicals 13

8 r Boiler Lay-Up Waterside 15

9 r Boiler Lay-Up Fireside 33

10 r Steam Turbine, Turbine Condenser, and Reheater Lay-Up 35

11 r Lay-Up of Turbine Oil System 39

12 r Lay-Up of Feedwater Heaters and Deaerators 41

13 r Lay-Up of Auxiliary Components and Pre-Boiler Systems 43

14 r Lay-Up Monitoring and Maintenance 51

15 r Start-Up After Lay-Up 53

16 r Conclusions 55

17 r Glossary of Terms 57

Tables

1 Commonly Used Lay-Up Chemicals 19

2 Boiler Water Chemical Concentrations During Lay-Up 19

Figure

1 Lay-Up Decision Tree 23

References 59

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r SECTION 1 rINTRODUCTION

Steam and water equipment systems generally employ materials thatreadily corrode or pit when exposed to air and moisture and this is a con-dition often created by poor lay-up procedures. Thus without perceivingwhat is taking place, a user can unwittingly suffer loss of unit perfor-mance, impair serviceability, extend start-up, or cause an after start-upfailure. Proper lay-up procedures can extend the useful life of a unit, re-duce repair, replacement and maintenance costs and even prevent costlyoutages.

From a stand-by corrosion viewpoint, corrosion can attack the smallsingle-stage steam turbine to the same degree as a large, multistage powergeneration turbine. Whether the plant is an industrial power facility or apower generation plant, the basic principle of keeping the combination ofmoisture and oxygen away from the metal surfaces is the same regardlessof the treatment regime. This basic principle is easy to state, however, sev-eral different procedures may be employed to reduce or prevent stand-bycorrosion. One method strives to eliminate the air while an alternatemethod strives to eliminate the moisture. For example, boilers can befilled with condensate to minimize oxygen exposure, while steam tur-bines have seals that allow leakage. Thus, steam turbines cannot hold liq-uid without modifications. Therefore, the preferred method for steam tur-bines is to minimize moisture. Steam condensers are normally laid updry. Each unit also has its own special needs and requirements, thus themany lay-up guidelines available vary in approach, timing and applica-tion.

The intent of this document is to provide a consensus of current prac-tices with resources and general guidelines, leaving development of thedetailed procedure to the user. Only the user and associated technicalsupport staff can access all the various factors such as availability, envi-ronmental constraints, atmospheric conditions, cost and other elementsthat need to be considered to arrive at the best solution with maximumbenefits and protection, at minimum cost. While this document providesmuch useful lay-up information for boilers, steam turbines and relatedequipment, qualified personnel should still be involved in the selection ofthe final lay-up procedure used.

This document addresses most components found in a steam generat-ing system for electrical power generation as well as mechanical drive ser-vices. Regardless of the lay-up method used, the basic philosophy is the

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same to keep the combination of oxygen and moisture away from partsthat can corrode. As mentioned above, there can be a basic difference inhow this may be accomplished in the static components of the system(boiler) and the rotating components of the system (steam turbine). Theboiler components can be laid up using either a wet or dry procedurewhile the rotating machinery such as the steam turbine and the steamcondenser must be laid up in a dry condition.

The practices described herein have been proven in field use. Thepractices described for the boiler are in agreement with Section VII of theASME Boiler and Pressure Vessel Code. They are applicable both to newboilers before being placed in service and to operating boilers during anoutage.

Types of boilers covered are:(1) Industrial-fossil fired (2) Industrial-waste heat (3) Marine (4) Utility-fossil fired*(5) Gas turbine heat recovery steam generators (HRSG)

*This document describes procedures, etc., commonly used for drum type boilers.Procedures used for once through boilers are similar but the equipment manufacturershould be consulted.

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r SECTION 2 rFACTORS TO BE CONSIDERED

The following is a list of items which generally need to be addressedwhen preparing to lay-up a unit or system;

(1) Safety of personnel and property(2) Systems and/or equipment to lay-up(3) Condition of unit(s)(4) Estimated period of lay-up and work to be performed (5) The lay-up environment such as possibility of freezing(6) Estimated time available to start up unit(7) Availability of manpower to inspect and monitor unit(s) during lay-

up(8) Value of unit and possible financial consequences of lay-up proce-

dure selected(9) Compatibility between lay-up and operational chemical treatments(10) Disposal of lay-up solutions(11) System auxiliaries such as fuel additive feed systems, soot blowers

etc.

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r SECTION 3 rREASONS FOR LAY-UP

During any non-operating periods after initial hydrotest, boilers and re-lated equipment must be laid up properly to avoid corrosion damage.Failure to do so will reduce their availability, reliability, increase mainte-nance costs, and eventually shorten their useful life. Severe corrosioncould even lead to catastrophic failure.

After any welding is done to piping on the boiler it is often hydrostati-cally tested or "hydro" tested. It should be noted that the water used forhydro testing of boilers and related equipment should be of the same pu-rity and treated with the same chemicals used for lay-up.

Steam turbines are particularly susceptible to corrosion damage be-cause air is usually drawn into the turbine during cool down. The oxygenin the air combines with steam that has condensed in low spots and cav-ities that are not drainable, thus providing the ingredients for corrosion toquickly develop. The presence of chlorides and sulfates in the conden-sate adds to corrosivity. If deposits are present on metal surfaces, they canpromote the formation of under-deposit corrosion cells that may result inlocalized corrosion (pitting).

In boilers, both the water/steam sides and the fire/gas sides must beprotected. If the waterside of a boiler is left open to the atmosphere un-protected, corrosion will occur particularly at liquid-air interfaces.Corrosion can also occur in the pre-boiler and after-boiler sections.

In addition to the local damage that occurs, the corrosion productsgenerated in the pre-boiler section will migrate to the boiler, steam tur-bine, reheater, condenser and condensate system when the system is re-turned to service. These, along with the corrosion products generated inthe boiler, may deposit on critical heat transfer areas of the boiler, in-creasing the potential for localized corrosion and/or overheating duringoperation. If they don't deposit in the boiler, they will probably continuedownstream to damage the superheaters and steam turbines, particularlythe blading where high velocities and corrosion products can cause se-vere erosion damage in a short time.

r 3.1 Steam Turbine Steam Side and Boiler Water Side Factors The items listed below are factors that contribute to corrosion on the

steam side of steam turbines and water side of idle boilers and relatedequipment.

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(1) Moisture--Under completely dry conditions, corrosion is negligible.(2) Dissolved Oxygen--Corrosion rates are related to the dissolved oxy-

gen concentration in a moist environment. Any conditions that increasethe oxygen concentration in moisture, or allow the continued addition ofoxygen, will aggravate the corrosion process.

(3) Low pH--Low pH of water generally increases the tendency of met-als to corrode.

(4) Deposits--Presence of deposits on steam or waterside surfaces maycause the development of corrosion cells that promote localized corro-sion during lay-up periods.

(5) Contaminants--In general, the greater the contaminant levels (suchas chloride and sulfates) in water containing oxygen, the faster the corro-sion rate.

r 3.2 Boiler Fire Side FactorsThe conditions listed below are known to cause, or at least contribute

to, corrosion on the fire and gas sides of non-operating steam generators:(1) Presence of absorbent deposits;(2) Moisture absorbed in such deposits;(3) Corrodents such as sulfurous and sulfuric acids which may form

and attack steel under deposits;(4) Oxygen dissolved in moisture in deposits

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r SECTION 4 rIDENTIFICATION OF

MATERIALS IN EQUIPMENT

Identifying the materials in any system to be laid up is key to develop-ing a suitable lay-up procedure. The reader should be aware that somematerials used in the various components of steam plant equipment arenot compatible with some chemicals that may be considered for the lay-up procedure. For example, high concentrations of ammonia can causeproblems with copper alloys. The following procedures must be modifiedaccordingly.

Generally, the materials utilized should be detailed in the manufac-turer's equipment manuals but there are many variations and combina-tions of materials available. It is the reader's responsibility to determinethe metallurgy utilized in the system, identify components that might beaffected, and to consult qualified personnel to clearly establish suitabilityand/or compatibility.

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r SECTION 5 rINSPECTION OF EQUIPMENT

The ASME Boiler and Pressure Vessel Code, Section VII, RecommendedGuidelines for the Care of Power Boilers has a Subsection on Inspection(C6) that details the requirements for the boiler proper. Paragraph C6.200notes that "Most jurisdictions require that all power boilers should begiven one or more internal and external inspections per year by anAuthorized Inspector as defined in C6.100(a)." Another Subsection onControl of Internal Chemical Conditions (C8) has a paragraph onInspection (C8.570) that is quoted here in part as it adds useful informa-tion to the subject of lay-up.

"When boiler outages permit, thorough inspection should be made ofall the internal parts of the boiler to note the presence of corrosion in anyform and to permit the collection of deposits for later examination for cor-rosion products. Where any case of unusual and extensive corrosion isnoted, the services of qualified personnel may be secured to determinecauses and to suggest remedial changes in water treatment and opera-tion." This suggestion may be applied as well to the inspection of equip-ment ahead of the boiler such as feedwater heaters, deaerators and deaer-ator storage tanks.

As noted above, when equipment is out of service there is an opportu-nity to inspect, make repairs and perform routine maintenance.Equipment may also be taken out of service for economic reasons. In ei-ther case, proper lay-up is critical. Damage can occur quickly to systemsthat are not properly treated. Regardless of the circumstances, recordingwhat was inspected, what was done and what is to be monitored canidentify useful low-cost steps that can be taken to circumvent later repairs.These steps could pay large dividends in money and time if or when thesystem is returned to service.

Consequently, the recommended procedure is for a complete inspec-tion of the unit before lay-up when the waterside is breached. Then deci-sions on cleaning, repair and/or replacement can then be accurately for-mulated. As noted in the ASME Code, "a record of each inspection shouldbe kept in a uniform manner so that any change of condition can be defi-nitely noted and compared, especially with reference to the thickness ofscale, corrosion, erosion, cracks, and other unusual conditions." (ref. Sect.VII, Subsection C6.630). Using the services of a manufacturer's represen-tative should also be considered to provide technical assistance on

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equipment inspections and formulation of cleaning solutions, repairs andlay-up procedures for major system components and/or support systems.

The post-inspection report should be detailed, including photographsand deposit analyses, and should specify the condition of the equipment,comparing present condition with that during previous inspections. Thisprocedure will help determine if deposits are new or unusual. The reportmay also define the type of analyses to be performed, during future in-spections, such as soluble iron and pH, which are especially important forturbine deposits, but which are not routinely requested.

For the steam turbine, inspection is not easy, as it usually requires re-moval of the cover or top half in order to inspect the internals such asblading, diaphragms, seals and rotor. Specific disassembly proceduresand inspection criteria are normally found in the owner's manual or unit'stechnical manual.

For the turbine condenser, both the steam condensate and the coolingwater sides should be inspected. While all of these items also apply to thesteam turbine, additional items such as internal clearances, condition ofbearings, and balance of rotor should also be recorded. Properly identi-fied photos of machine deposits, blade erosion and bearing condition canalso be very useful. If deposits are unusual, chemical analysis of depositsshould be performed.

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r SECTION 6 rCLEANING OF EQUIPMENT

Boilers must be properly removed from service to minimize adherenceof suspended solids to boiler metal surfaces. Suspended solid adherencecan be reduced by immediate flushing with hot, pressurized water, whilewaterside surfaces are still moist. A boiler containing deposits that formedduring operation or because of improper removal from service may re-quire chemical cleaning at some time during the outage period.

Any chemical cleaning procedures should be designed and supervisedby trained and qualified personnel to ensure successful deposit removaland to avoid potential equipment damage. It is important that a protectivemetal oxide film be reestablished on the metal surfaces immediately fol-lowing chemical cleaning. This film can be formed most effectively afterchemical cleaning if the boiler is operated for a short period of time fol-lowing the cleaning. One recommended procedure is to operate with asolution of passivating chemicals after chemical cleaning to obtain metalpassivation before lay-up. If this cannot be done, it is recommended thatthe chemical cleaning be scheduled immediately preceding restart. It isrecommended that boiler fireside deposits be removed prior to lay-up dueto the potential for under-deposit corrosion. Samples of deposits shouldbe collected for analysis.

A dirty turbine should not be placed in lay-up. Cleaning of the steamturbine is usually done with the turbine open and most often by mechan-ical means (blasting). The equipment manufacturer normally recommendsa schedule for inspection and cleaning of a steam turbine. Normally, theonly cleaning required for the steam side of the steam turbine condenseris for flushing off of all accumulated matter with condensate or other highpurity water. On the other hand, the cooling water side may require ex-tensive cleaning. Flushing may be adequate, but mechanical or chemicalcleaning is often required.

It is important that equipment be placed in a fully protective lay-upafter cleaning as described in the remainder of this document.

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r SECTION 7 rUSE AND DISPOSAL OF

LAY-UP CHEMICALS

The following factors should be considered in using chemicals for lay-up:

(1) All normal safety precautions associated with using the chemical(s)should be observed.

(2) If the lay-up chemical(s) is different from the operating chemical(s),either in type or concentration, the lay-up solution may have to bereplaced or the concentration reduced before start-up.

(3) Disposal of lay-up chemical solutions must comply with all applic-able state and federal regulations. Environmental considerationsmay limit the use of concentrated solutions, or solutions with lowlevels of volatile oxygen scavenger, for wet lay-up.

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r SECTION 8 rBOILER LAY-UP WATERSIDE

r 8.1 Short-term versus Long-term Lay-up of EquipmentThe information on "Reasons for Lay-up" provided in Section 3 of this

document, is also applicable to this section.Previous documents have defined the duration of lay-up as "short" or

"long" outages sometimes defined by a specified number of days applica-ble to distinct classes of equipment. This document does not define theduration closely but allows the user to select an applicable procedurebased on plant circumstances, conditions, operating requirements, andcomplexity of the system.

Boilers in "hot standby" or "banked" are not covered by this documentas such conditions are considered to be operational. If such a conditionchanges to lay-up as the result of operating demand, the proper lay-upprocedures should be determined and implemented. Even if the boiler isin a "hot standby" condition, lay-up of steam-side of the condensers, tur-bines, and other equipment may be appropriate. These lay-up proceduresmay be found in Sections 10-13 of this document.

"Short" term lay-up is intended to cover those circumstances whereequipment must be taken off line for inspection, maintenance, repair etc.,where it is intended to place the equipment back into service as rapidlyas possible. Generally this period would not exceed one or two weeks.

"Long" term lay-up is intended to cover circumstances where it is clearthe equipment must be out of service for an extended period of time formaintenance, seasonal need, etc. A unit in a long-term lay-up will typi-cally have at least a few days notice prior to restarting.

Lay-up procedures are specified separately for simple and complexpiping systems. Simple systems are those where there is no superheater orwhere the superheater can be drained or flushed. Complex systems arethose that have a non-drainable superheater and/or reheater.

This document does not cover the condition, commonly referred to as"mothballing," where equipment is permanently removed from servicebut maintained in a preserved state for possible return to service if everrequired.

Regardless of which piece of equipment is laid up or for how long, theprimary need and concern is for isolation. This aspect cannot be overem-phasized for a variety of reasons, SAFETY being foremost. Other reasons

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include contaminant prevention, the avoidance of moisture addition, andthe overall success of lay-up in preserving the equipment. Inadequateisolation during an outage has probably contributed more to equipmentdeterioration than any other factor.

The ASME Code requires two isolation block or stop valves, with anample free-blow drain valve between them, for all boiler outlets whenconnecting to a system. The two stop valves should be closed and thedrain opened whenever the boiler is taken out of service. This effectivelyensures that the boiler is isolated from the rest of the system.

While not stated in the Code, the most probable purpose of the drainis to bleed off pressure and ensure that the boiler is not passing flow intothe system or the system is not passing steam flow into the boiler.However, this arrangement can be very effective at providing isolation inthat any leakage past the valve under pressure flows out the drain andidentifies a leaking valve, provided one can see the drain outlet.Regardless of the piece of equipment to be laid up, this principle can andshould be used.

For equipment such as steam turbines, deaerators and steam jet airejectors that are to be laid up, it is critical for the laid-up equipment to beisolated from any and all active steam systems. While blinds can be usedvery effectively, they are time consuming to install and remove. They alsoneed to be clearly marked and documented for future restart planning.From an equipment lay-up viewpoint, a small steam leak into a unit cannegate all the preparatory work and inflict substantial damage on a pieceof equipment in a very short time. In systems with condensing turbines,the condenser and steam turbine are usually considered as one block forlay-up purposes.

While the code is explicit where multiple boilers feed into a commonsystem, it does not address systems outside the boiler proper and there-fore makes no comments on valve arrangements for associated steamequipment.

A good arrangement for unit isolation is a "double block and bleed sys-tem" as previously described for the boiler outlet. This might consist ofgate valve plus globe valve main line isolators with a free-blow drainvalve between the two block valves. When the two block valves areclosed and the drain valve is open, a visual check can reveal if there isany leak across the supply side isolating valve.

This may be contrasted with "single block and bleed" arrangementsometimes used for the downstream, or exhaust side, of a turbine. Thedrain valve is trapped to remove condensate from the piping systemdownstream of the isolating gate valve. However, this arrangement doesnot allow for visual observation that the exhaust side isolator is leaking.

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Any leakage across the isolator would allow steam to flow back into theturbine. Considerable corrosion damage might result when no means ofleak detection is provided. Use of a second isolator or "block" valve be-tween the steam turbine exhaust relief valve and the turbine exhaust gatevalve isolator, combined with a free-blow drain valve between the twoisolators, would provide positive isolation and a means of checking thesuccess of isolation.

Paragraph 2.2.6 of ANSI / ASME publication, B19. 3c-1989, " SafetyStandard for Compressors for Process Industries" states important pointsregarding unit isolation and safety during lay-up. The following is para-phrased from that document and should be implemented only after theturbine is cooled on turning gear.

When maintenance or lay-up is being performed on rotating equip-ment, compressors, turbines, generators etc., precautions shall be takento ensure isolation of all energy sources from the driver or system. Theseprecautions shall include the use of blinds or double block valves andbleeder on steam and fuel gas supplies to drivers, or in the case of motorsand generators, either:

(1) Electrical load centers shall have a switching arrangement that mustbe locked in the open position, tagged and tried; or

(2) Other positive means of current interruption shall be employed.(3) In all cases, all connected equipment shall be depressurized to pre-

vent rotation of the drive shaft.

r 8.2 Boiler Lay-up WatersideThe two generally accepted lay-up methods for the waterside of the

boiler are the dry and the wet procedures. In wet procedures, the boileris left full of water with either standard boiler water or an alkaline, re-ducing solution. A pressurized nitrogen blanket is maintained, or suitablealternatives used, to prevent oxygen ingress. In dry procedures, the boileris completely dried and maintained in the dry condition during the periodof lay-up.

Often when a boiler is taken down, it is to repair something in theboiler such as a leaking tube. These cases typically require that the systembe drained to allow access to the repair area. Following the repairs, theboiler and superheater are hydro-tested. The water used for the hydro-testshould be feedwater quality, preferably deaerated, and chemicallytreated. Once the hydro-test is completed, the boiler should be laid upimmediately with one of the wet lay-up procedures described in this doc-ument.

If outage periods are to be short and/or frequent, and the boiler isknown to be relatively free of sludge and other internal deposits, draining

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and inspection may be omitted. In this case, vigorous, manual boilerblowdown should be utilized and increased several days prior to shut-down to maximize sludge removal.

The recommended lay-up procedures (dry and wet) are summarized inSections 8.2.1 and 8.2.2. In Section 8.3.4 a Decision Tree can be foundto assist the reader in determining the correct lay-up method. This is fol-lowed by detailed recommended lay-up procedures in Section 8. 4 and8.5.

The procedures are specified separately for simple and complex pipingsystems. Simple systems are those where there is no superheater or wherethe superheater can be drained or flushed. Complex systems are thosethat have a non-drainable superheater.

8.2.1 n Dry Lay-UpDry lay-up is most commonly used for simple circuitry boilers during

a long outage. The objective of dry lay-up is to keep metal surfaces freeof moisture containing dissolved oxygen. The waterside of industrial, ma-rine and waste heat boilers containing simple circuits may be laid up dry.Dry lay-up is not recommended for boilers with complex circuitry be-cause it is difficult to get and keep all internal surfaces free of moisture.

There are several methods used for dry lay-up. In one dry procedure,the boiler is vented, drained and dried as completely as possible with air.Then manholes are closed, all connections are tightly closed or blanked,and the boiler is purged and pressurized with nitrogen to prevent ingres-sion of air. The success of this procedure depends on the rapid and thor-ough drying of all boiler metal surfaces and the exclusion of air duringlay-up. An alternative and perhaps better method is to drain under nitro-gen pressure to prevent air ingress during draining. In this case, it is notnecessary to dry the boiler completely prior to establishing the nitrogenblanket. It is important to remember that when using a nitrogen blanket,the nitrogen pressure must be maintained at all times for protection to becomplete.

Another alternative for maintaining an air-dried boiler in a dry condi-tion utilizes desiccants installed in suitable locations to maintain a mois-ture-free atmosphere on the water side. Related equipment such as econ-omizers, deaerating heaters, and feedwater heaters may be laid up in asimilar manner.

A boiler containing porous moisture-retaining deposits should not belaid up dry because of the difficulty in completely drying out the depositsand the potential for subsequent under-deposit corrosion. The recom-mended dry lay-up procedures are discussed beginning in Section 8.5.

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8.2.2 n Wet Lay-UpChemicals UsedChemicals used for wet lay-up are generally classified into two cate-

gories: non-volatile inorganic and volatile. Both types of lay-up chemicalsare effective when applied properly. However, lay-up chemicals usedshould typically be consistent with the operating chemical regime. Non-volatile inorganic chemicals are commonly used in low and mediumpressure boilers that either do not have superheaters or have drainable su-perheaters (simple circuits) and operate on softened water make-up.Volatile chemicals are commonly used in medium and high-pressureboilers with complex piping circuits that operate on demineralized watermake-up. Oxygen scavengers and pH control chemicals are the com-monly used materials and are shown below with their respective chemi-cal concentrations:

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Non-volatile VolatileInorganic ChemicalsChemicals

Oxygen Scavengers- sodium sulfite hydrazine - Note 1Note 2

pH control chemicals sodium hydroxide ammonia or aneutralizing amine

Table 1 - Commonly Used Lay-up Chemicals

Non-volatile VolatileInorganic ChemicalsChemicals

Oxygen 200 mg/L (ppm) 100-200 mg/L (ppm) min.Scavengers- as Na2SO3 hydrazine as N2H4-Note 1Note 2, 4

pH control 400 mg/L (ppm) min. Note 3chemicals hydroxide alkalinity as

CaCO3

Table 2 - Boiler Water Chemical Concentrations During Lay-up

Notes to Tables 1 & 2:(1) If an oxygen scavenger other than hydrazine is used, the user

should confirm the suitability and concentration of the substitutechemical with a qualified water treatment consultant.

(2) Either catalyzed or uncatalyzed oxygen scavengers may be used.(3) Sufficient chemical is required to maintain a minimum of 10.0 pH

for all-ferrous systems or a pH of 9.3-9.5 for systems containingcopper alloys. To achieve a pH of 10 in high purity water, for ex-ample, requires approximately 10.0 mg/L (ppm) of ammonia (asNH3) or 12. 4 mg/L (ppm) of cyclohexylamine (as C6H1 1NH2). Otherorganic amines will require different concentrations to achieve thedesired pH.

(4) Oxygen scavengers need not be used for lay-up if they are not usedin the normal feedwater treatment program.

Nitrogen for lay-up should contain a minimum of 99.6% nitrogen. Thispurity is typically found in commercial-grade liquid nitrogen and com-pressed nitrogen gas cylinders.

Recommended lay-up maintenance and testing practices can be foundin Section 14 of this document.

Preparation of Lay-up SolutionDeaerated water of feedwater quality should be used for laying up boil-

ers. Raw surface water or other waters containing significant suspendedmatter should not be used. For boilers with non-drainable superheatersand reheaters, utility boilers, and other high-pressure industrial boilersthat use high quality feedwater, only high quality condensate or deaerateddemineralized water and volatile chemicals should be used to preparelay-up solutions.

Preparation and Filling with Lay-up Chemical--All BoilersThe basic objective of the following procedures (14) is to achieve a

uniform concentration of the lay-up chemicals throughout the equipment. Prior to filling any boiler equipment the water temperature and metal

temperature of headers and waterwalls must typically be within 100-150oF of the water being added to prevent thermal shock to the system.Consult the OEM for specific recommendations regarding these tempera-tures. The following paragraphs, 14, outline several possible proceduresthat are suitable for the preparation and addition of lay-up solutions toeconomizers, boilers, superheaters and reheaters.

(1) Prepare the chemical solution in a separate tank. Using a suitablemetering pump, blend the lay-up chemicals at the concentrationsrequired in the boiler into the fill water as it enters the economizerand boiler.

20

(2) If condensate quality is acceptable and contamination is not acause for shutdown, an alternative method would be introductionof concentrated lay-up solutions directly into the condensate re-ceiver, with mixing to achieve the desired concentration.

(3) Prepare the chemical solution in a separate tank and add it to theboiler while filling. The solution can be added to the steam drumthrough an existing chemical feed line.

(4) After the boiler is filled and the lay-up solution has been added, firethe boiler lightly for at least 30 minutes to obtain circulation anddistribution of chemicals. The economizer must then be filled withproperly treated water when the pressure has decreased to about 5psig (34 kPag). The high water alarm should be deactivated and allvent valves operated as needed so that the boiler can be filled com-pletely. After filling, the boiler and economizer must be isolated bytightly closing the feedwater valve. If firing is not possible, the rateof addition of both the lay-up solution and the fill water must bevery carefully controlled to ensure uniform distribution of treatedwater throughout the boiler.

Boilers With Superheaters and/or ReheatersSpecial precautions are required for boilers with non-drainable super-

heaters and reheaters.(1) All chemicals used for lay-up of non-drainable superheaters and re-

heaters must be volatile to prevent deposit formation in these com-ponents when the boiler is returned to service. Superheaters shouldbe back-filled with chemically treated demineralized quality waterto minimize deposition or corrosion after firing. Preferably, volatilechemicals should also be used for laying up the economizer andboiler. If non-volatile inorganic chemicals are used in the boiler, itis essential that precautions be taken so that none of the boiler lay-up solution enters the superheater.

(2) For some steam-cooled surfaces (superheaters, reheaters), it may benecessary to fix/pin supports (as for hydro) before filling them withwater.

(3) If non-drainable superheaters and reheaters are constructed ofaustenitic stainless steel, it is recommended that the demineralizedwater used for filling have a conductivity of 1 mS/cm.

Excluding AirIn all wet lay-up procedures it is important to exclude air to eliminate

any air/water interface where the presence of oxygen could cause in-creased corrosion in a concentrated area.

To prevent inleakage of air (oxygen) during the lay-up period, pressur-ize with 5 psig (34 kPag) nitrogen through a suitable connection.

21

Where the boiler is completely filled with water instead of using a nitro-gen blanket, it may be necessary to install an expansion vessel (filled withproperly treated water) above the highest part of the boiler to accommo-date volume changes caused by temperature changes in the boiler. Thevessel should be fitted with a cover and a sight glass and connected to anavailable opening such as a vent line at the top of the boiler to create ahydrostatic head. The tank will provide a ready visual check of water levelloss or inleakage during lay-up. This tank must be disconnected prior tostart-up (see Section 15).

For boilers with complex circuitry (non-drainable superheater): Afterthe boiler, superheater, and reheater are filled with lay-up solution, allvalves on connecting piping should be tightly closed and the equipmentpressurized with 5 psig (34 kPag) nitrogen.

r 8.3 Procedure Selection

8.3.1 n Reasons for Lay-UpThe reasons for lay-up are detailed in Section 3 of this document and

it is recommended that the section be read again. The first paragraph is re-peated here for convenience.

During any non-operating periods after the initial hydrotest, boilersand related equipment must be laid up properly to avoid corrosion dam-age. Failure to do so will reduce their availability, reliability, increasemaintenance costs, and eventually shorten their useful life. Severe cor-rosion could even lead to catastrophic failure.

8.3.2 n Using Decision TreeThe reader should use the following definitions and the Glossary of

Terms, Section 17 at the end of this document, to define the lay-up para-meters. First determine whether the duration is short or long. Then deter-mine whether the boiler system will be breached or will not be breachedduring lay-up. Finally, determine if the boiler circuitry is simple or com-plex. The reader should use the definitions of these terms in the Glossaryof this document.

8.3.3 n Definition of Terms in Decision TreeBoilers in "hot standby" or "banked" are not covered by this document

as such conditions are considered to be operational. If such a conditionchanges to lay-up as the result of operating demand, the proper lay-upprocedures should be determined and implemented.

This document does not cover the condition, commonly referred to as"mothballing," where equipment is permanently removed from servicebut maintained in a preserved state for possible return to service if everrequired.

22

"Short" term lay-up is intended, in this section, to cover those circum-stances where equipment must be taken off line for inspection, mainte-nance, repair, lack of demand, etc., where it is intended to place theequipment back into service as rapidly as possible. Generally this periodwould not exceed one or two weeks.

"Long" term lay-up is intended, in this section, to cover circumstanceswhere it is clear the equipment must be out of service for an extended pe-riod of time for maintenance, repair etc. A unit in a long-term lay-up willtypically have at least a few days notice prior to restarting.

8.3.4 8.3.4 n Decision TreeDecision Tree

23

Figure 1 Lay-Up Decision TreeFigure 1 Lay-Up Decision Tree

Short LongDuration

Breach BreachYes No Yes No

Wet Dry Wet Dry Wet Dry Wet Dry

Complex Simple

Complex Simple

Complex Simple

Procedure 3 Procedure 7

Procedure 8 Procedure 8, 9 or 10



Procedure 4

Procedure 1, 2 or 6 Procedure 8, 9 or 10

r 8.4 Waterside Wet Lay-up Procedures

8.4.1 n Procedure 1 Short Outage No Breach of WatersideSystem Simple and Complex Circuits

Nitrogen Cap

This procedure is also applicable to systems following a hydro-test. Iffreezing is a problem apply auxiliary heat. Alternatively, for simple cir-cuits use a dry lay-up procedure. Caution: The boiler must not be in aconfined area such as in an enclosed building as vents or valve packingleaks could displace oxygen in the space.

(1) As a minimum, maintain the same oxygen scavenger and pH con-trol chemical concentrations as those present during normal opera-tion. Any additional water added to the boiler as it cools must bedeaerated and chemically treated.

(2) Establish a 5 psig (34 kPag) nitrogen cap on the superheater and thesteam drum through the drum vent and superheater outlet headerdrain/vent as the unit is cooled and before a positive pressure is lost.Boiler vents should not be opened to atmosphere. Avoid the ad-mission of air into any water-containing circuit during lay-up.Once the nitrogen blanket is established, it is critical that it is con-stantly maintained or corrosion can result.

(3) Complete lay-up of the steam cycle requires lay up of auxiliaryequipment such as feedwater heaters, condensers and deaearators.Lay-up procedures for this equipment can be found in Sections 10and 12.

8.4.2 n Procedure 2 Short Outage No Breach of WatersideSystem Simple Circuits Only

Water Cap

This procedure is also applicable to systems following a hydro-test. Iffreezing is a problem apply auxiliary heat. Alternatively, for simple cir-cuits use a dry lay-up procedure.

(1) Maintain the same oxygen scavenger and pH control chemical con-centrations as those present during normal operation.

(2) Fill boiler completely with feedwater up to the vent. Drainable su-perheaters should be backfilled with deaerated feedwater contain-ing volatile oxygen scavenger. To accommodate volume changescaused by temperature changes, connect an expansion vessel filled

24

with properly treated water to the drum vent. The vessel should belocated above the highest part of the boiler and connected such thata hydrostatic head can be maintained on the boiler at all times. Thevessel should be fitted with a cover and a sight glass. The tankshould be monitored regularly and will provide a ready visual checkof water level loss or inleakage during lay-up. This tank should bedrained to waste prior to startup.

(3) Complete lay-up of the steam cycle requires lay-up of auxiliaryequipment such as feedwater heaters, condensers, and deaearators.Lay-up procedures for this equipment can be found in Sections 10and 12.

8.4.3 n Procedure 3 Short Outage Breach of WatersideSystem Simple and Complex Circuits

Nitrogen Cap

Since the system will be breached, dry lay-up is the appropriate lay-upprocedure for all affected equipment, until maintenance is complete.When complete, the boiler can be left in a dry lay-up condition or filledpreparatory to start-up. If filled, the following wet lay-up procedure ap-plies. If freezing is a problem apply auxiliary heat. Alternatively use a drylay-up procedure. Caution: The boiler must not be in a confined areasuch as in an enclosed building as vents or valve packing leaks could dis-place oxygen in the room.

(1) Drain and open only those sections requiring repairs.(2) Isolate remainder of unit under 5 psig (34 kPag) nitrogen pressure

where it can be done safely. Avoid the admission of air to isolatedareas.

(3) Maintain the same oxygen scavenger and pH control chemical con-centrations for water remaining in the cycle as those present duringnormal operation.

(4) Once maintenance and the hydrostatic test are complete, the boilershould be filled to the normal operating level with treated anddeaerated boiler feedwater and a 5 psig (34 kPag) nitrogen blanketestablished on the steam drum. If deaerated water cannot be used,higher concentrations of oxygen scavenger and amine (or other pHcontrol chemical) must be added to the boiler fill water as specifiedin Procedure 4.

(5) Complete lay-up of the steam cycle requires lay-up of auxiliaryequipment such as feedwater heaters, condensers, and deaearators.Lay-up procedures for this equipment can be found in Section 12.

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8.4.4 n Procedure 4 Long Outage No Breach of WatersideSystem Complex Circuits

Chemical Protection with Nitrogen Cap

If freezing is a problem apply auxiliary heat to areas of the boiler proneto freezing. Caution: The boiler must not be in a confined area such as inan enclosed building as vents or valve packing leaks could displace oxy-gen in the room.

(1) Add sufficient volatile oxygen scavenger and volatile neutralizingamine or ammonia to the waterwalls, economizer, and associatedpiping to protect it against oxygen. The recommended level for hy-drazine is 200 mg/L (ppm) for an all-ferrous system and 100 mg/L(ppm) for feedwater piping that contains copper. The amine or am-monia concentration should be such that the pH of the water is 10for an all-ferrous system and 9.3-9.5 for mixed metallurgy systems.If other oxygen scavengers and amines are used, consult the chem-ical vendor for the proper dosage.

(2) Volatile oxygen scavenger and volatile neutralizing amine or am-monia should be added in a manner that results in a uniform con-centration throughout. They may be added to the system in severalways, for example:(a) Pump concentrated solutions through the chemical feed equip-

ment and blend-fill to achieve the desired concentrations.(b) If condenser leakage is not a cause for shutdown, concentrated

solutions can be introduced directly into the hotwell where theycan be mixed to achieve the desired concentration and pumpedforward. If ion exchange condensate polishers are employed,they must be bypassed during this operation.

(3) It is important to have the water temperature in the boiler below204oC (400oF) before addition of volatile oxygen scavenger. If thistemperature is exceeded, some volatile oxygen scavengers, such ashydrazine, will start to decompose. Also, temperature differentialbetween the metal temperatures and the added water temperaturecannot exceed the manufacturer's recommendations.

(4) The tube side of copper alloy feedwater heaters should be filledwith condensate-quality water containing volatile neutralizingamine or ammonia to adjust the pH to 9.5 and 50 to 100 mg/L(ppm) of volatile oxygen scavenger.

(5) The superheater can be simply blanketed with nitrogen empty orback-filled with condensate quality water containing 200 mg/L(ppm) of volatile oxygen scavenger or performance equivalent and10 mg/L (ppm) of volatile neutralizing amine or ammonia. Add the

26

fill water to the outlet of the non-drainable section allowing thewater to fill the superheater completely as indicated by a rise indrum level.

CAUTION: Steam-cooled surfaces (superheaters, reheaters) will typicallyrequire additional structural support prior to being filled with water.

(6) Establish and maintain a 5 psig (34 kPag) nitrogen cap on the su-perheater and steam drum. Nitrogen cap the shell side of the feed-water heaters. Nitrogen blanket should be applied through thedrum vent and superheater outlet header drain/vent as the unit iscooled when pressure drops to 5 psig (34 kPag). Avoid admissionof air to all water-containing circuits throughout the duration of thelay-up.

(7) Test lay-up solution weekly for the first month and then monthlythereafter. If the volatile oxygen scavenger concentration decreasesby more than 33% of the original level or if the pH of the boilerwater drops to below 9.0, additional chemicals must be added tothe boiler to re-establish the desired concentrations. Refer to sec-tion 14 for additional instructions on monitoring.

(8) Complete lay-up of the steam cycle requires lay-up of auxiliaryequipment such as feedwater heaters, condensers, and deaerators.Lay-up procedures for this equipment can be found in Section 12.

8.4.5 n Procedure 5 Long Outage Breach of Waterside System Complex or Simple Circuits

Chemical Protection with Nitrogen Cap

Since the system will be breached, dry lay-up is the appropriate lay-upprocedure for all affected equipment, until maintenance is complete.When complete, the boiler can be left in a dry lay-up condition or filledpreparatory to start-up. If filled, the following wet lay-up procedure ap-plies. If freezing is a problem apply auxiliary heat. Caution: The boilermust not be in a confined area such as in an enclosed building as ventsor valve packing leaks could displace oxygen in the room.

(1) Drain and open only those sections requiring repairs.(2) Fill the remainder of the boiler with the recommended concentra-

tions of the appropriate pH control and oxygen scavenging chemi-cals consistent with the normal feedwater chemical treatment. (a) For complex circuits this is typically a volatile oxygen scavenger

such as hydrazine (or equivalent) and volatile neutralizing amineor ammonia such that the concentration in the waterwalls,econ-omizer and feedwater heaters (tube side) and associated

27

piping are 200 mg/L (ppm) and 10 mg/L (ppm), respectively forall ferrous systems and 100 mg/L (ppm) and pH of 9.3-9.5 formixed metallurgy systems.

(b) For simple circuits, where non-volatile chemicals are used foroperation, the lay-up chemicals should be sodium hydroxideand sodium sulfite such that the concentrations in the boiler are400 mg/L (ppm) hydroxide alkalinity as CaCO3, and 200 mg/L(ppm) as Na2SO3, respectively.

(3) Lay-up chemicals should be added in a manner that results in a uni-form concentration throughout. They may be added to the systemin several ways, for example:(a) Pump concentrated solutions through the chemical feed equip-

ment and blend-fill to achieve the desired concentrations.(b) If condenser leakage is not a cause for shutdown, concentrated

solutions can be introduced directly into the hot well wherethey can be mixed to achieve the desired concentration andpumped forward. If ion exchange condensate polishers are em-ployed, they must be bypassed during this operation.

(4) It is important to have the fluid temperature in the cycle below204oC (400oF) before addition of volatile oxygen scavenger. If thistemperature is exceeded, some scavengers, such as hydrazine, willstart to decompose. Also, temperature differential between themetal temperatures and the added water temperature cannot ex-ceed the manufacturer's recommendations.

(5) The superheater can be blanketed with nitrogen or back-filled withcondensate-quality water containing 200 mg/L (ppm) of volatileoxygen scavenger or performance equivalent and 10 mg/L (ppm) ofvolatile neutralizing amine or ammonia. The pH of the solutionshould be approximately 10.0. Add the fill water to the outlet of thenon-drainable section allowing the water to fill the superheatercompletely as indicated by a rise in drum level. A nitrogen cap of5 psig (34 kPag) should be established on the steam drum of theboiler to prevent air inleakage.

CAUTION: Any steam-cooled surface (superheater, reheater) will typi-cally require additional structural support prior to being filled with water.

(6) Establish and maintain a 5 psig (34 kPag) nitrogen cap on the super-heater and steam drum. Nitrogen cap the shell side of the feedwaterheaters. Nitrogen blanket should be applied through the drum ventand superheater outlet header drain/vent as the unit is cooled whenpressure drops to 5 psig (34 kPag). Avoid admission of air to allwater-containing circuits throughout the duration of the lay-up.

28

(7) Once the chemical concentrations are established, regular testingmust be performed to ensure that treatment levels are maintained.Test lay-up solution weekly for the first month and then monthlythereafter. If the volatile oxygen scavenger concentration decreasesby more than 33% of the original value, or if the pH of the boilerwater drops to below 9.0, additional chemicals must be added tothe boiler to re-establish the desired concentrations.Recommendations on testing can be found in Section 14.

(8) If chemical additions are made, it is important to ensure sufficientmixing so that the concentration of the scavenger and amine areuniform. This can be achieved by firing the boiler lightly or by anexternal circulation pump. Attention should be directed to valvemaintenance that may cause treated water loss or the addition ofuntreated water into the boiler and auxiliaries causing dilution ofproperly treated lay-up solutions.

8.4.6 n Procedure 6 Short Outage No Breach of WatersideSystem Simple Circuits Only

Steam Cap

This procedure is not applicable to boilers with superheaters. Air (oxy-gen) ingress can be prevented by keeping the waterside of the boilerunder slight constant pressure. The pressure must remain above atmos-pheric at all times for this procedure to be successful.

(1) The continuous blowdown water from a properly treated operatingboiler can be piped into a mud drum header on the idle boiler, al-lowing the water to overflow from the steam drum vents to an ac-ceptable disposal location.

(2) Steam-heated coils can be installed in the mud drum to maintaintemperature in the boiler or the boiler may be intermittently fired tomaintain a positive pressure. An oxygen-free, treated feedwatersource is necessary to replenish the water lost through steam pro-duction.

r 8.5 Waterside Dry Lay-up Procedures There are a number of methods for creating and maintaining a dry lay-

up condition in a boiler. These procedures discuss the use of a continu-ous nitrogen purge, dehumidified air, and chemical desiccants as dry lay-up methods.

An alternative for small industrial boilers is use of silica gel as a staticdehumidifier in a sealed boiler. The procedure for the Use of Desiccants

29

(p.31) can be used to determine the amount of silica to be used and pro-vides a recommended inspection schedule. If metal corrosion is ob-served, correct problem of moisture ingress. If desiccant is exhausted, dryout boiler again, replace with fresh silica gel.

8.5.1 n Procedure 7 Long or Short Outage No Breach ofWaterside System Simple and Complex Circuits

Nitrogen Drain and Blanket

Caution: The boiler must not be in a confined area such as in an en-closed building as vents or valve packing leaks could displace oxygen inthe room.

(1) Generally remove boiler from service, drain the boiler under a ni-trogen overpressure before the boiler pressure dissipates com-pletely (e.g., at 10 psig). Liquid water must be drained from all sec-tions of the steam/water circuit. Check all low point drains to en-sure removal of as much moisture as possible.

(2) Maintain a nitrogen overpressure of 5 psig (34 kPag) throughoutdraining and subsequent storage. All circuits must be pressurizedwith nitrogen to exclude air (oxygen) ingress. The safety precautionsdiscussed at the beginning of this document must be given carefulattention.

8.5.2 n Procedure 8 Long or Short Outage Breach of WatersideSystem Simple and Complex Circuits

Nitrogen Drain and Blanket

Caution: The boiler must not be in a confined area such as in an en-closed building as vents or valve packing leaks could displace oxygen inthe room.

(1) Drain and open only those sections requiring repairs. Some sec-tions may not be able to be drained completely nor blanketed withnitrogen during maintenance activities and some corrosion mayoccur. Therefore it is important that repairs be made quickly andthat the nitrogen blanket be re-established as soon as possible.

(2) Where it can be done safely, isolate remainder of unit under 5 psig(34 kPag) nitrogen pressure. Avoid the admission of air (oxygen) toisolated areas.

(3) Once maintenance and the hydrostatic test are complete, drain allwater-filled equipment under a nitrogen overpressure of 5 psig (34kPag). Liquid water must be drained from all sections of thesteam/water circuit. Check all low point drains to ensure removal of

30

as much moisture as possible.(4) Maintain a nitrogen overpressure of 5 psig (34 kPag) throughout

draining and subsequent storage. All circuits must be pressurizedwith nitrogen to exclude air (oxygen) ingress. The safety precautionsdiscussed at the beginning of this document must be given carefulattention.

(5) Complete lay-up of the steam cycle requires lay-up of auxiliaryequipment such as feedwater heaters, condensers, and deaerators.Lay-up procedures for this equipment can be found in Section 12.

8.5.3 n Procedure 9 Long Outage Breach of Waterside System Simple Circuits Only

Recirculating Dry Air

Note: Waterwall surfaces must be clean to use this lay-up procedure.

(1) To facilitate drying of surfaces, it is preferable to drain the boilerhot, while the pressure is still 10 psig (68 kPag).

(2) While the boiler is still hot and before condensation can occur,(typically within 8 hours), begin circulating filtered dehumidifiedair through the boiler.

(3) Piping and dehumidification systems must be designed for the specificboiler layout. The system must be instrumented and inspected to assurereliable operation. This should include monitoring of the relative hu-midity of air leaving the boiler. The direction of flow and the bleedpoints are not important so long as the flow is through the entire sys-tem. The airflow should be sufficient to dry the system out in less thanone week, i.e., the faster, the better.

(4) For the equipment to be considered dry, the air leaving the equipmentshould have a maximum dew point of -10oF (-23oC). After this dewpoint is reached on all the bleeds, the flow can be reduced to approx-imately 1% of the system volume per hour.

(5) Inspect the dehumidification equipment and boiler at regular intervals.

Use of Desiccants This procedure is an alternative for small industrial package-type boil-

ers with no superheater.(1) To facilitate drying of surfaces, it is preferable to drain the boiler

hot, while the pressure is still 10 psig (68 kPag). (2) When boiler is cool, and after observing all safety practices for con-

fined-space entry, install bags of a desiccant, in trays, at all availableopenings. Either silica gel or quicklime can be used, however thepreferred desiccant is silica gel. The amount of desiccant used de-

31

pends on the boiler size and is shown below

Silica gel ( 5.0 lbs/100 ft3 (2.7 kg/m3) of boiler volume. Thisis available with a color indicator to show the degree of mois-ture absorption.

Quicklime 2.0 lbs/100 ft3 (1.1 kg/m3) of boiler volume. (3) Close all manholes and blank or close all connections on the boiler

as completely as possible to prevent ingress of moist air. (4) Check the desiccant daily for the first week, then weekly for the

next 7 weeks. Replace as necessary. All work should be performedas quickly as possible to minimize entry of moisture.

(5) Inspect the waterside of the boiler every three months for evidenceof active corrosion.

Note: Spilled desiccant may cause corrosion where it comes in contactwith metal surfaces. See Section 16 (10) for corrective actions to be taken.

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r SECTION 9 rBOILER LAY-UP FIRESIDE

When boilers are to be laid up, the fireside must be considered as wellas the waterside. Two common methods used for fireside lay-up are iden-tified as cold and hot. The preferred method for each installation will de-pend on local conditions.

The primary objective in fireside lay-up is to keep the metal surfacesdry. If appreciable amounts of deposits are present, the fireside should becleaned before lay-up. This is especially true where fuels containing highconcentrations of sulfur have been used.

r 9.1 Hot Lay-upThe following items should be considered where hot lay-up is planned.

(1) Since certain boilers cannot be effectively cleaned on the gasside without extensive dismantling, a hot lay-up may be neces-sary.

(2) The hot lay-up method may not be practical for extended peri-ods because of energy costs.

(3) To prevent moisture absorption by deposits on the gas side, thetemperature of the metal surfaces must be kept at 170oF (77o C)or higher, depending upon the sulfur content of the fuel.

(4) Fireside metal temperatures can be maintained at a safe level bycontrolled light firing with low sulfur fuel or by the use of elec-tric hot air blowers.

(5) The circulation of hot blowdown water through the boiler water-side may not be sufficient to assure metal temperatures of 170oF(77o C) or higher in all parts of the boiler because of the parallelcircuits involved and cooling resulting from air infiltration.However, the installation of a steam coil in the lower drumshould provide sufficient heat input and circulation to produceadequate metal temperatures throughout the boiler.

r 9.2 Cold Lay-upThe following items should be considered where a cold lay-up is

planned.(1) If fuel containing high concentrations of sulfur has been used,

fire the boiler, if practical, on natural gas or number 2 oil for oneweek prior to the shutdown. This technique may help remove

33

corrosive deposits, but its effectiveness should be verified bysubsequent inspection of the fireside surfaces.

(2) Before removing the boiler from service, operate all soot blow-ers starting with the blower farthest from the stack.

(3) When the unit is off line and the water temperature has droppedsufficiently, wash down the gas side of the boiler, economizer,air heater, and the flue gas side of the ID fan. Use a five percentsolution of an alkaline chemical such as soda ash to neutralizeacidic deposits. Be sure that all wash water is completelydrained from the equipment.

(4) After this procedure, all of the areas contacted by wash watershould be dried by some technique such as firing with sulfur-freefuel.

(5) Moisture should not be allowed to remain in the refractory or in-sulation. The relative humidity of the air should be kept as lowas practicable. Seal the furnace as completely as possible to min-imize entry of moist air. Keep the metal surface dry by the use ofheat lamps, dehumidification with desiccants along with air cir-culation, circulation of dry warm air, or a combination of these.Thicker deposits may require removal by mechanical cleaning.

(6) Make provisions to keep rainwater from entering the boilerthrough the stack.

(7) Inspect the fireside once per month for evidence of active corro-sion and, if found, take corrective measures as previously dis-cussed.

34

r SECTION 10 rSTEAM TURBINE,

TURBINE CONDENSER, ANDREHEATER LAY-UP

This procedure is not applicable to air-cooled condensers. Consult thecondenser manufacturer for specific procedures for lay-up of this equip-ment.

r 10.1 Steam SideThe steam turbine, turbine condenser and reheater are considered as a

unit because they are normally interconnected with no reasonable meansof isolating them from each other. If the reheater can be isolated from thehigh and intermediate pressure stages of the turbine, the steamturbine/condenser and the reheater can be laid up separately. Unlike theboiler, the steam side of the steam turbine can normally only be laid updry. The steam turbine shaft rests in bearings, which are oil-lubricated andseparated from the steam side by seals. These seals come in variousarrangements but are generally not positive isolators nor designed for liq-uid, therefore the steam turbine should be laid up dry.

All potential sources of moisture intrusion such as from the extraction,backpressure or auxiliary sealing steam connections, must be eliminatedby blanking or double-blocking and bleeding. Any moisture that entersthe system will likely remain in the system and combine with other im-purities to attack metal surfaces.

The steam turbine should be shut down as recommended by the man-ufacturer. Depending on the system and the manufacturer's recommen-dations, it is desirable to start lay-up procedures prior to complete cool-ing of the unit and turning off the turning gear (if unit is so equipped). Assoon as practical after removing steam supply from the unit, the steam tur-bine/condenser should be drained and dried as completely as possible.

Carry out the drying process by flowing either filtered, dehumidified airor nitrogen through the system. The direction of flow and the bleed pointsare not important so long as flow is through the entire system. If air isused, the quantity should be sufficient to dry the system out in less than

35

one week, i.e., the faster, the better. If nitrogen is used the time can beconsiderably longer, as the oxygen content in the system should be neg-ligible after a short time. For the equipment to be considered dry, the gasleaving the equipment should have a maximum dew point of 10oF(23oC). After this dew point is reached on all the bleeds, the airflow canbe reduced to approximately 1% of the system volume per hour.

CAUTION: Nitrogen will not support human life and special precau-tions must be observed when it is used. Do not enter equipment laid upwith nitrogen until the nitrogen supply is disconnected, the vessel ispurged, and tests show that sufficient air is present and maintained.Ensure that nitrogen is not vented into an enclosed room or area.

If the system is going to be down for more than two weeks, the lubri-cation system should be operated and the unit rotor turned, using theturning gear, or manually rolled. When rolling the shaft, the starting pointshould be marked to ensure that the rotor comes to rest at a new point ap-proximately 90o from the previous resting point. This procedure should berepeated every two weeks.

If the steam turbine has not been inspected for some time and the tur-bine is going to be laid up more than two (2) months, the turbine and tur-bine condenser should be inspected and cleaned before lay-up proce-dures are implemented. It is also suggested the condenser shell side be in-spected at the same time for steam impingement, corrosion at tube sup-ports and the integrity of the baffles and the drain lines entering the unit.If the turbine or condenser is suspected of being dirty, inspection andcleaning, if necessary, is recommended regardless of the outage duration.

After the system has been opened and cleaned, long-term lay-up pro-cedures can make use of either filtered, dehumidified, dry air or pressur-ized dry nitrogen. If filtered dry air is used, then a continuous flow mustbe maintained through the system. If dry nitrogen is used and it is possi-ble to pressurize the system, a small positive pressure must be main-tained. For this to be successful, the turbine rotor seals will probably re-quire some modifications. Nitrogen for turbine lay-up should contain aminimum of 99.6% nitrogen. This purity is typically found in liquid nitro-gen and compressed nitrogen gas cylinders.

If the rotating equipment is going to be laid up for an extended periodof time and monitoring manpower is limited and the rotors are flexibleshafts, consideration should be given to removing the rotors from theequipment. This would eliminate the need for periodic rotation of therotor and/or complete sealing of the system. For long-term flexible shaftrotor storage many maintenance engineers prefer vertical hanging in acontrolled atmosphere (low humidity). While this method of lay-up re-

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duces the need for frequent monitoring of the equipment, it does increaseboth the time and labor to recommission the system and its cost.

r 10.2 Waterside of Turbine Condenser

10.2.1 n Short-Term Lay-UpTwo procedures are commonly practiced:

(1) Cooling water is continuously circulated through the condensertubes. Care must be taken to ensure that the cooling water con-tains an adequate concentration of corrosion inhibitors, bio-cides, and, if needed, dispersants. In most cases, the normalcooling water treatment program for microbiological and corro-sion control can be continued; however the chemical vendorshould be consulted. It is important to avoid stagnation in anyareas of the cooling water system.

(2) The condenser tube side is filled with cooling tower water con-taining the appropriate concentrations of treatment chemicals,and then isolated. If the recirculating cooling water has very highconductivity, it may be desirable to use water with lower TotalDissolved Solids and Specific Conductance for filling theCondenser. Higher than normal concentrations of non-oxidizingbiocide and corrosion inhibitors might be considered. Caremust be taken to ensure that adequate protection is providedfrom corrosive and microbiological attack. A possible disadvan-tage of this method is that suspended solids can settle on metalsurfaces and promote the formation of under-deposit corrosioncells. Problems associated with high suspended solids can beminimized by increasing the cooling tower blowdown rate priorto filling the condenser, thus purging much of the suspendedsolids from the cooling system. Procedure (2) is not suitable forsystems using once through cooling water unless the source haslow Total Dissolved Solids.

10.2.2 n Long-Term Lay-UpFor long-term lay-up, the water side of the turbine condenser should be

inspected and cleaned, if necessary. It should then be dried by using fil-tered, dehumidified air. Drying is considered complete when the air leav-ing the condenser has a maximum dew point of 10oF (23oC). Whendrying is complete, either the condenser should be pressurized with ni-trogen to prevent air inleakage or the circulation of dehumidified airshould be continued.

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r SECTION 11 rLAY-UP OF TURBINE OIL SYSTEM

The turbine oil, including that in the reservoir, should be cleaned priorto lay-up. The cleanup must remove water and suspended matter sincethese impurities can support microbiological activity. The cleaned oilshould be treated with a corrosion inhibitor and a biocide recommendedby the oil manufacturer, then circulated for about a day to obtain goodmixing of these materials with the oil and to establish a good protectivefilm on the metal surfaces. During the lay-up period, the oil should thenbe circulated for several hours and tested on a scheduled basis, at leastmonthly. Tests should include moisture content, microorganism counts,contaminant levels, inhibitor level, particle count, and wear metals. Ifproblems are found, corrective action must be taken.

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r SECTION 12 rLAY-UP OF FEEDWATER HEATERS

AND DEAERATORS

r 12.1 Lay-up of Feedwater HeatersThe tube side of feedwater heaters should be treated the same as the

boiler during lay-up periods. The shell side normally is steam blanketedor dried and pressurized with nitrogen during lay-up. However, the shellside may be flooded with treated condensate or condensate-quality water.All-steel systems should be laid up with condensate containing 200 mg/L(ppm) volatile oxygen scavenger or equivalent, and ammonia or suitableamine such as cyclohexylamine as needed to maintain the pH at 10.0min. For copper or copper alloy systems, use 50 to 100 mg/L (ppm) ofvolatile oxygen scavenger and adjust the pH to 9.5.

r 12.2 Lay-up of Deaerator and DA Storage TankA number of methods may be used to properly lay up the deaerator

and deaerator storage tank. It is preferred to maintain a steam blanket onthe equipment as this ensures some hot deaerated water for the subse-quent startup. If steam is not available then the deaerator and storage tankmay be:

(1) Blanketed with a small continuous flow (30 SCFH) of nitrogen (2) Drained while hot and maintained dry with dehumidified air or

desiccant(3) Filled to the vent with water containing volatile oxygen scav-

enger and either ammonia or amine, as previously described forfeedwater heaters

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r SECTION 13 rLAY-UP OF AUXILIARY COMPONENTS

AND PRE-BOILER SYSTEMS

r 13.1 ScopeThe protection of the auxiliary components of a power plant during

stand-by is equally as important as the protection of the boilers and/or tur-bines. However, it may be impractical to protect all auxiliary equipmentduring a shutdown. For example, it may require more time to protectsome auxiliary parts than the length of time of the shutdown. In othercases, the cost of treatment may approach the cost of replacement, inwhich case stand-by treatment would not be cost effective. Plant person-nel must decide which components are critical.

Depending upon the nature of the equipment and the anticipatedlength of shutdown, the equipment can be stored wet or dry. In eithercase, the objective is to prevent damage of the auxiliary equipment dueto corrosion and/or by freezing.

Whenever a specific piece of equipment is removed from service,where available, the manufacturer's instructions should be followed.

Electrical equipment should be isolated and locked out as required forsafety purposes. Where equipment is outdoors, precautions should betaken to prevent freezing.

r 13.2 Inspection of EquipmentIt is desirable that all critical equipment be inspected before being

placed into lay-up. The inspection should include the integral parts of theequipment including both sides of heat exchange equipment. Wheneverpossible, detailed photographs of the equipment should be taken and arecord made of the condition of the equipment. When the outage is short-term, inspection may be impractical.

r 13.3 Lay-up Term Definition for Auxiliary EquipmentFor the purpose of protecting the auxiliary equipment, short-term lay-

up is very generally defined to mean that it is expected that the equipmentwill be restarted soon (no longer than two weeks) and it is desired tomaintain a state of readiness while minimizing any possible damage. Forsome equipment, "short-term" may represent a different time period thanfor other equipment.

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Long-term lay-up implies no state of readiness and the main concernis for prevention of corrosion damage.

As stated in Section 8.1, this document does not cover the condition,commonly referred to as "mothballing," where equipment is permanentlyremoved from service but maintained in a preserved state for possible re-turn to service if ever required. Many auxiliary components, such as listedbelow, are not normally subjects of either "short" or "long" term lay-upprocedures except under special circumstances such as "mothballing."

Motors and generators Pumps Fans Induced draft fans Piping Air receivers, inert gas tanks and other similar tanks Tanks Ejectors, chillers, etc. Switch gear, circuit breakers, control cabinets, relay cabinets, etc. Conveyors, hoppers and other handling equipment

r 13.4 Chemical Feeding Equipment The equipment manufacturer's instructions should be followed where

available. Every chemical feed system is different. The following sug-gested procedure may not cover every situation and should be regardedonly as a guide.

13.4.1 n Solution Feeders Excluding Demineralizer RegenerationSystems

(1) Flush chemical day tanks, pumps, piping, valves, injection linesand instruments associated with the chemical feed systems withcondensate quality water. Drain and allow to dry.

(2) Chemicals may remain in bulk tanks. However, plant personnelshould review each chemical for storage suitability.

(3) Dry chemicals may remain in storage in accordance with the stor-age suitability.

(4) Solution (Dissolving) tanks should be drained and the contentsstored in marked drums or disposed of in accordance with govern-ment guidelines. The tanks should be flushed with condensate qual-ity water and the tanks dried and sealed for a very long lay-up.

13.4.2 n Dry Feeders(1) Close the isolating valves of slide gates between the dry chemical

hoppers and run the dry chemical out of the feeder.

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(2) The chemical day tanks, pumps, piping, valves, instruments, etc. as-sociated with the chemical feed systems should be flushed withclean water and drained before lay-up.

(3) Dry chemicals may remain in the bulk tank during short-term lay-up in accordance with the storage instructions for each chemical.

(4) Solution (Dissolving) tanks should be drained and the contentsstored in marked drums or disposed of in accordance with govern-ment guidelines. The tanks should be flushed with condensate qual-ity water and the tanks dried and sealed for a very long lay-up.

13.4.3 n Pretreatment EquipmentFrequently, there is not enough manpower available to carry out a de-

tailed short-term lay-up procedure for pre-treatment equipment. As a re-sult, most plants do little or nothing with regard to short-term shutdown.However, there are some things that must be considered with each shut-down.

Wherever available, the manufacturer's instructions should be con-sulted and followed. In lieu of specific manufacturer's instructions, thefollowing suggestions may apply. However, keep in mind that few pre-treatment systems are the same type or configuration depending on influ-ent water quality and the required effluent purity. The following sugges-tions cannot cover every situation and should be regarded only as aguide.

Ion Exchange Equipment(1) Ion exchange resin should be kept wet, protected from freezing,

and should not be subjected to temperatures greater than 95oF(35oC). After ion exchange resins have been in service, they mayalso be subject to biological growths and should be protected frombiological action by a micro-defouling cleaning procedure prior tostorage. The resin or equipment vendor can supply a cleaning pro-cedure.

(2) If lay-up is expected to be greater than two weeks, all ion exchangeresins should be regenerated normally prior to shutdown.

(3) Although the stability of strong acid cation resins in the regeneratedhydrogen form is greater than that of strong base anion resins in theregenerated hydroxide form, for long-term chemical stability reasons,consideration should be given to conversion of strong acid cationresins to the sodium form for storage. Similarly, strong base anionresins should be converted to a more stable form such as the chlo-ride, sulfate or carbonate form. Detailed and recommended conver-sion procedures should be obtained from the resin manufacturers.

(4) The following is a rough guideline applicable to sodium or chloride

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conversion only. Exhaust the resin using a 5% to 10% by weightsodium chloride solution. The quantity of sodium chloride solutionrequired for this is four times the total volume of the ion exchangeresin.

(5) If the planned lay-up will extend beyond twelve months, consider-ation should be given to converting the resin to the sodium andchloride form as in 3 above, unloading and wet-storing the com-plete resin charge. When returning resins to service, stored ion ex-change resin requires double or triple regenerations before normaleffluent quality can be achieved. Depending on the resin volumeand value, it might be more cost effective to consider disposal of theresin following the appropriate governmental regulations and thepurchase of new resin when the equipment is to be placed backinto service. It may be advantageous to purchase resin in the re-generated form so that the unit can be put back into service quickly.

(6) Ion exchange vessels may be drained, dried, and stored in place ifindoors and not subjected to extreme temperatures. Ion exchangevessels that must be stored outdoors and/or in direct sun should becovered with tarps and stored full of water. In this case, a ventshould be left open to prevent pressure from building up from heatand the water level in the vessel should be checked and re-estab-lished periodically. Care must be taken to prevent freezing as thiscan destroy vessel internals.(a) Empty lined ion exchange vessels should not be stored in direct

sun nor in areas in which the temperatures can become greaterthan 95oF (35oC).

(b) Ion exchange vessels with stainless steel internals that have beenused to prepare ion exchange resin for storage as outlined above,should be rinsed with water with a low chloride content beforeeither wet or dry storage.

(c) Lined ion exchange vessels should not be returned to serviceafter an extended lay-up without the integrity of the lining beingconfirmed by spark testing.

(7) Acid and caustic storage tanks associated with the demineralizerwill require proper lay-up and storage. Consult the bulk chemicalsupplier for proper procedures.

Reverse Osmosis (RO) Equipment"Short-term" lay- up, with RO membranes in place in pressure tubes, is

defined as more than 5 days and less than 30 days out of operation."Long-term" lay-up, with RO membranes in place in pressure tubes, is de-fined as more than 30 days out of operation.

Before undertaking any "short" or "long" term lay-up operation, the

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membrane manufacturer should be contacted for specific instructions re-lated to the specific equipment and local environments.

For thin film composite (Polyamide) membrane elements(1) Short-term lay-up

(a) Flush the RO system with feedwater, while simultaneously vent-ing any gas from the system.

(b) When the pressure tubes are filled, close the appropriate valvesto prevent air from entering the system.

(c) Reflush as described at 5-day intervals.(2) Long-term lay- up

(a) Clean the RO membrane elements in place.(b) Flush the RO section with a solution of permeate that contains

an appropriate, approved biocide.(c) When the RO section is completely filled with this solution,

close the valves to retain the solution in the RO section.(d) Repeat steps b and c with fresh solution every 30 days if the tem-

perature is below 80oF (27oC) or every 5 days if the temperatureis above 80oF (27oC).

(e) When the RO system is ready to be returned to service, flush thesystem for approximately 1 hour using low-pressure feedwaterwith the product dump valve open to drain; then flush to drainat high pressure for 5 to 10 minutes. Before returning to service,ensure there is no residual biocide in the product water.

For cellulose acetate blend membrane elements(1) Short-term lay-up

(a) Clean the RO membrane elements in place.(b) Flush the RO section with acidified water (pH 5.06.0) that con-

tains a free chlorine residual of 0.10.5 mg/L (ppm) when mea-sured at the brine outlet.(i) When the RO section is completely filled with this solution,

close the valves to retain the solution in the RO section.(ii) Repeat steps b and c every 2 days.(iii) The membrane manufacturer may provide identification of

other approved biocides that do not require such frequentflushing.

(2) Long-term lay-up (a) Clean the RO membrane elements in place.(b) Flush the RO section with a solution of permeate that contains an

appropriate, approved biocide with the pH adjusted to 5.0-6.0.(c) When the RO section is completely filled with this solution, close

the valves to retain the solution in the RO section.(i) Repeat steps b and c using fresh solution every 30 days

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if the temperature is below 80oF (27oC) or every 5 days if thetemperature is above 80oF (27oC).

(ii) When the RO system is ready to be returned to service, flushthe system for approximately 1 hour using low-pressure feed-water with the product dump valve open to drain; then flushto drain at high pressure for 5 to 10 minutes. Before returningto service, ensure there is no residual biocide in the product.

Dry storage o

Lay-up of Boilers

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