Appendix A The Operational and Safety Aspects of Chemical ...978-81-322-2722-9/1.pdf · Appendix A The Operational and Safety Aspects of Chemical Cleaning of Thermal Power Plants

Appendix AThe Operational and Safety Aspectsof Chemical Cleaning of ThermalPower Plants

1.0 General Guidelines of Pre and Post-Operational Cleaning ofDrum-Type Boilers, Economizers, Super Heaters, Reheaters,Condensate and Feed Systems

1.1 Introduction

Damage can occur in the water/steam circuits of an operating plant ifthe internal surfaces are coated with foreign matter such as adventitiousmetal oxides, grease, oil, and dirt or have excessively thick grownoxides. These can be removed after erection and prior to commission-ing, and be controlled during subsequent operation by chemicalcleaning.

1.2 Scope

This covers the objectives and criteria for the chemical cleaning ofdrum-type/drumless boilers and surface conditioning of the water/steamcircuit of conventional power plants using suitably inhibited ammoni-ated citric, hydrochloric, sulphamic and hydrofluoric acids; it alsodetermines the protection of the plant after cleaning.

The requirements of “safety aspects”, to be applied for the pre-and post-service cleaning of boilers, economizers, super heaters,reheaters, condensate, and feed systems.

1.3 Objectives of Cleaning

The aim is to commission and operate the plant with the internalsurfaces of the water/steam circuit as free as practicable from foreignmatter, and to establish a satisfactory basis for the growth of aprotective magnetite film, by removing debris and thick oxidesaccumulated during construction and operation.

© Springer India 2016P. Chanda and S. Mukhopaddhyay, Operation and Maintenanceof Thermal Power Stations, Energy Systems in Electrical Engineering,DOI 10.1007/978-81-322-2722-9

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1.4 Criteria for Chemical Cleaning

1.4.1 Pre-service Cleaning of Boiler Furnace and Economizer TubesAlong With Condensate and Feed System

As a result of the application of clean working conditions, thecondensate and feed systems of drum boilers, super heaters, andreheaters do not require pre-service chemical cleaning. Instead, theyshall be either water flushed or steam purged. However, if the cleanconditions are not met, alkaline washing of condensate and feed systemas given in Appendix 1A.II shall be practiced.The furnaces of drum boilers still require to be cleaned and suitableprocesses, as given in Appendix 1A.-I, are an alkaline boil-out/alkalineflushing to remove grease and protective coatings followed by a citric orhydrofluoric or hydrochloric acid stage to remove oxides and otherdebris originating during construction, and finally passivation usingammonia and hydrazine or sodium nitrite and ammonia.

1.4.2 Post-operational Cleaning of Boiler Furnace Tubes (andEconomizer Where included)

Factors that need to be considered in determining the need for cleaningare:

(i) Changes in operational chemistry (e.g., the occurrence of“hide-out” or incidence of persistent condenser leakage).

(ii) The presence of large amounts of water-side debris, revealed byperiodic examination or by indirect instrumental methods.

(iii) The occurrence of on-load corrosion, particularly when there hasbeen extensive retubing.

(iv) The type of boiler-tube geometry, operating pressure, heat flux(i.e., the sensitivity of the boiler).

(v) Mode of operation-base load/cycling/number of start-ups.(vi) Lay-up practices of feed trains and boilers that have been applied.(vii) Post-acid clean history of the specific plant.

1.4.2.1 The Case for Routine Cleaning

Routine cleaning is often considered because if unduly thick oxides areallowed to accumulate, they are less easily removed and can concentratesalts which can intensify corrosion. The aim of periodic cleaning is topreempt the development of such conditions and the cleanings can becarried out on the basis of either oxide thickness or time. Severeproblems such as heavy oxide deposition would be one indication of theneed to clean. Super heaters and reheaters are not normally included inthe circuit for routine chemical cleaning.

148 Appendix A: The Operational and Safety Aspects of Chemical Cleaning …

1.4.2.2 Oxide Thickness as a Guide to Cleaning

Oxide thickness provides the most reliable guidance on the need toclean. Measurement for this purpose should be made periodically onsamples taken from the higher heat flux zones of the boiler or fromareas known to be most susceptible to deposit formation. Normal oxidegrowth rates tend to be in the range of 1–2 m/kh. A general review hasshown that for coal-fired plants (160 bar), an oxide thickness of 100 µmhas been experienced without any evidence of detrimental corrosiondamage to the underlying metal surfaces. However, the projectedinfluence of site-specific factors needs to be considered to establish anallowable maximum oxide thickness for individual units. Risks ofcorrosion beneath deposits are dependent on the heat flux experiencedby the plant and oil-fired plants typically have higher heat fluxes and alimit of 50 µm is recommended for these stations. In the absence ofreliable oxide thickness data, routine cleans should be carried out atintervals of time determined empirically, a typical frequency for160 bar plant being 4–6 years to be compatible with the plant’s majoroutage frequency.

1.4.3 Post-operational Cleaning of Super heaters, Reheaters,Condensate, and Feed Systems

1.4.3.1 Super heaters, reheaters, condensate, and feed systems are not normallycleaned for the purpose of removing iron oxide during their service life.

1.4.3.2 If an abnormal requirement for the post-service cleaning to remove ironoxide deposits from any of these plant items arises, it could probably bemet by employing a modification of Appendix 1E.

1.5 Available Cleaning Processes and Their Application

1.5.1 Process Details

Details of the on-site cleaning processes are given in the Appendices.Suitable methods of chemical analysis for controlling the cleaningprocesses are given in Sect. 4, ‘Analytical Methods’ and safetyprecautions are given in Sect. 5, ‘Safety Aspects’.Wherever pH value or conductivity is quantified, measurement at 25 °Cis implied.

1.5.2 Furnace and Economizer Tubes of Drum Boilers

1.5.2.1 Pre-operational CleaningThe specified procedure is a preliminary alkaline boilout/alkalineflushing using trisodium phosphate, followed by hydrofluoric acid/HClor ammoniated citric acid, citric acid rinse, and high temperaturepassivation, according to Appendix 1A.

Appendix A: The Operational and Safety Aspects of Chemical Cleaning … 149

1.5.2.2 Post-operational Cleaning

Selection of the chemical cleaning process should be made byreferencing Appendix 1C. The procedures are given in Appendix 1D.Hydrochloric and hydrofluoric acid are specified as alternatives toammoniated citric acid and have advantages if the boiler is especiallydirty or corroded.The choice of acids is discussed in more detail in Sect. 1.5.4.2.

1.5.3 Super Heaters and Reheaters

1.5.3.1 Pre-operational Cleaning

This area of the plant does not require being chemically cleaned iferected according to standard practices. However, the plant requiressteam purging, as specified in Appendix 1B.

1.5.3.2 Post-Operational Cleaning

Post-operational cleaning of super heaters and reheaters is covered inSect. 1.4.3.

1.5.4 Supplementary Notes

1.5.4.1 Before commissioning, removal of debris by physical cleaningprocesses such as flushing shall be used irrespective of any chemicalcleaning. Steam purging (see Appendix 1B) of the super heater,reheater, and associated pipework is used to remove material whichmay remain after erection.

1.5.4.2 Acids Available for Cleaning

The formulations conventionally used for iron removal in chemicalcleaning are 5 % hydrochloric acid, 1–2 % hydrofluoric acid, or 3 %ammoniated citric acid, each appropriately inhibited as detailed inAppendix 1F. Compared with ammoniated citric acid, hydrochloric acidis cheaper, quicker, and holds more iron, but has a greater risk ofpitting. Hydrofluoric acid is very fast and also holds more iron and canbe inhibited to reduce ferric ion corrosion, but particular care must betaken in its use and disposal. The capacities for iron of 5 %hydrochloric acid, 2 % hydrofluoric acid, and 3 % ammoniated citricacid are 2.5, 1.9, and 0.9 %, respectively. However, citric acid is quitesuitable for the majority of cleaning applications and, in some instances,is the only available option.

1.5.4.3 Choice of Acid for Iron Oxide Removal

1.5.4.3.1 Guidance on selection of chemical cleaning processes forpost-operational cleaning is given in Appendix 1C. 3 % citric acid issuitable unless the boiler is either very dirty or corroded. With dirtyboilers, extra acid can be used but where corrosion is present,


hydrochloric acid or hydrofluoric acid may be required. However,severely scabbed tubes are not susceptible to any acid cleaning processand some tube replacement is necessary. For boilers with a satisfactoryhistory of routine cleaning with hydrochloric acid, there is no goodreason to change from the reagent. However, it should be noted thatlocal corrosion of heat-affected weld zones could occur withhydrochloric acid, but to a much lesser extent, in citric acid. The effecthas occurred so far only with steels of 0.3 % carbon and while the bulkof boiler tubes are 0.18 % or less, there is an increasing tendency to usesteels with higher carbon values which tends to mitigate against the useof hydrochloric acid.

1.5.4.3.2 Work has shown that if 0.5 % formic acid is added to the conventionalcitric acid formulation, the capacity for iron is increased by about 20 %and oxide dissolution occurs more rapidly. Potentially, therefore, thismodification presents another option for iron removal.

1.5.4.4 Fluoride

1.5.4.4.1 The presence of fluoride 0.25–0.5 % ammonium bifluoride increasesthe rate of dissolution of iron oxide slightly in hydrochloric acid andmore substantially in citric acid, although in both cases, the solubility ofiron is virtually unchanged. Fluoride additions also improve thedissolution of siliceous material in hydrochloric acid but in citric acidthis effect of fluoride varies according to the form(s) of silica present.

1.5.4.4.2 Flouride/NH4HF2 should not be added to the citric or hydrochloric acidsolution until the circuit is leak free. There is no test data yet availableto demonstrate that fluoride can be used safely with austenitic stainlesssteels.

1.5.4.5 Circulation

Circulation of acid is necessary both to avoid local depletion of effectivestrength of acid and inhibitor, and to facilitate the use of analysis tocontrol the process. For drum-type boilers, the aim should be to obtainan average rate of circulation of 0.3 m/s in the generator tubes with amaximum rate of 1.5 m/s. Clearly, the target rate may be exceeded insome parts of the circuit and experimental work has shown that flowrates of 1.5 m/s double the corrosion rate found at 0.3 m/s. The effect ofvelocity is much more pronounced with inhibited hydrofluoric acid,albeit from a very low corrosion rate at the low velocity.

1.5.4.6 Copper Removal

In certain situations, economies can be introduced in the copper removalstages of chemical cleaning, for example, where local experience hasshown that only small amounts of copper are removed on cleaning. In


such cases, only one copper removal process needs to be utilized and it isadvantageous to use it after iron removal. Furthermore, it may be possibleto divide in half the chemical concentrations of sodium bromate and citricacid, the pH still, however, being adjusted to 9.5. Work has shown thatsodium nitrite is a less acceptable alternative to sodium bromate for theoxidizing agent in copper removal, despite its apparent advantage for thesecondary purpose of short-term passivation. If gas-induced circulation isbeing used, air is an acceptable medium during copper removal, but doesnot obviate the need for sodium bromate.

1.5.4.7 Passivation After Cleaning

Tominimize deterioration of the active surfaces produced by acid cleaning,a final passivation stage is an essential part of the overall cleaning process.Details are included in Appendices 1A, 1D, 1E and supplementary notesare given in Sect. 1.8, ‘Protection of Plant After Cleaning’.

1.5.4.8 Protection of Plant When the Cleaning Process is Interrupted

Special situation could arise if it were necessary at any stage to curtailor suspend a cleaning. Guidance on the available courses of action insuch circumstances is given in Appendix 1G.

1.6 Practical Considerations

1.6.1 Planning

1.6.1.1 Coordination

Experience has shown the need for full consultation between theEngineering, Design and Construction, Plant Engineering, andOperation Services before carrying out pre-operational chemicalcleaning.

1.6.1.2 Operational Water Requirements

During cleaning, there is a requirement for very large quantities ofclarified and DM water. Careful programming of the installation andcommissioning of the water treatment plant and water storage tanks is,therefore, required before commencing pre-commissioning cleaning.For post-operational cleaning, application of the complete Appendix 1Dmay use up to 12 boiler volumes of DM water.

1.6.1.3 Effluents

It is essential that all statutory requirements covering effluent disposalfrom the station are established and met. In some circumstances, citricacid waste can be disposed of by burning in an adjacent boiler.


Hydrofluoric acid waste can be disposed of in the ash lagoons byneutralizing the acid with lime and precipitating residual fluoride withcalcium chloride solution. With all chemical cleaning solutions, careshall be taken to avoid contravening Pollution Control Board dischargelimits. Where effluent removal is by tanker, adequate tanker capacitymust be available so that the cleaning program is not delayed or theplant put at risk.

1.6.2 Supervision

Supervision of cleaning processes requires suitably trained staff to bepresent at all times. In addition to the overall supervision provided bythe contractor, a complete post-operational cleaning of one boiler maytake 100–200 h depending mainly upon the rigging time.

1.6.3 Engineering Aspects

1.6.3.1 Permanent Points for Post-operational Cleaning

Recommendations are given.

1.6.3.2 Circuit Integrity

The integrity of the circuit to be cleaned must be tested by filling withwater before introducing chemicals.

1.6.3.3 Station Pumps

Subject to the manufacturer’s approval, boiler circulation pumps maybe used for pre- and post-operational cleaning, or gas-inducedcirculation. Where permanent points are fitted, the economizer isincluded in the boiler circuit for cleaning. If it is considered necessary toclean the economizer as well as the boiler furnaces when gas circulationis used, an auxiliary pump will be required. The neck weals of idlecirculation pump motors should be protected from contact withchemical cleaning solutions by back-flushing with de-mineralizedwater.

1.6.3.4 Flexible Pipework

While the use of flexible pipework is not prohibited, all temporaryconnections should be made in rigid material, wherever practicable. Allpipework, flexible or rigid, must be sufficiently reliable for the whole ofthe operation. With flexible pipework, suitably placed valves must beprovided for isolation in case of failure.

1.6.3.5 Drum Furniture

The removal of drum internals for cleaning is desirable to facilitatecirculation of reagent and inspection, and for the removal of debris, buttheir replacement is time consuming. Program considerations usually


dictate that both pre- and post-operational cleaning are carried out withmost of the drum internals in place.

1.6.3.6 Stagnant Areas

Particular attention must be given to stagnant areas, instrumentconnections, and similar items to ensure that they are properly cleanedand flushed. Temperature measurement points should be installed toshow uniformity of circulation, although an infra-red TV camera ispreferable for this purpose. Adequate sampling facilities should beavailable to check reagent strength and circulation.

1.6.3.7 Water-Plugging of Super heaters

To prevent cleaning solutions entering the super heater while only theboiler circuit is being cleaned, the super heater shall be water-pluggedbefore any circulation of cleaning solution commences andback-flushed between the various stages of the process. Care must betaken to ensure that the super heater can be adequately back-flushed. Inaddition, as discussed in Appendix 1H, a constant head overflow deviceshall be fitted to the boiler drum, and suitable arrangements made toindicate drum level during cleaning. Make-up water should be adjustedto a Ph OF 8.8–9.2, and ammonia should be used for this purpose.

1.6.3.8 Venting

While chemical cleaning operations are in progress, venting of theboiler, including the vent from the constant head overflow, should be tothe outside of the building into an area inaccessible to personnel.

1.6.3.9 Inspection

Thorough inspection of the plant, as far as practicable, shall be carriedout at the end of the cleaning process, giving due regard to theprecautions given in Sect. 5, ‘Safety Aspects’.

1.6.4 Chemical Aspects

Given that there have been problems of degradation of inhibitors instorage, it would be advisable to check the age and batch number of thechemical used. Apply the inhibitor efficiency test before use.

1.6.4.1 Chemical Requirements

As some cleanings require additional amounts of chemicals (principallyfor iron removal), a sufficient reserve should be available locally tominimize delay to the program. This is particularly important for thefirst cleaning in a boiler’s history or after a change of operating regime(e.g. from base-load to two-shifting).


1.6.4.2 Chemical Addition

All chemicals shall be added to the cleaning solution in such a manneras to avoid localized concentrations in the cleaning solution or dilutiontanks by addition at a continuous constant rate while the solution isbeing circulated. Avoiding higher acid concentration than specified isnecessary to avoid corrosion. Careful control is necessary whenammonia is being added to acid solutions containing inhibitors, to avoidany possibility of inhibitor precipitation.

1.6.4.3 Addition of Inhibitors to Cleaning Solutions

1.6.4.3.1 The approved inhibitor must be present under acid conditions at alltimes to ensure that it is fully dissolved and not subsequentlyprecipitated. It must always be added direct to an acid solution andnot be previously diluted with water or added to water to which the acidis added later. This requirement can be met by injecting the acid and theinhibitor simultaneously at the suction of the pump used for injectingchemicals into the cleaning circuit.

1.6.4.3.2 Some constituents of inhibitors have very limited solubility and,therefore, must be added to the cleaning solution in a controlledmanner, pro-rota with the acid injection. The inhibitor must be added ata constant rate over that period of time required for complete circulationof the cleaning solution, by using either a metering pump or a drip-feedarrangement.

1.6.4.3.3 The most critical of all chemical additions is that of the inhibitor which,in some instances, has a very limited solubility (e.g., stannine LTP), andits addition to the solutions must be made in accordance with Sect. 5,‘Safety Aspects’. Strict observance of these requirements, in conjunc-tion with ventilation of the plant and meeting temperature requirementsbefore entry, have enabled the breathing equipment previously requiredfor plant inspection after chemical cleaning to be waived in certaincircumstances. The precautions required under such condition are givenin Sect. 5, ‘Safety Aspects’.

1.6.4.3.4 Following the inhibitor addition and at regular intervals during the acidcleaning stage, a ‘wire wool’ ball test for inhibitor effectiveness shouldbe used. In this test, a small ball of steel wool (about 0.1 g) is degreasedand added to a sample of the iron removal solution. Inhibition is judgedto be adequate if the wire wool ball does not float after 1 min inammoniated citric acid or 2 min in hydrochloric acid. The test is rapid,but can be affected by a number of factors including temperature,therefore, the test must be carried out at the same temperature as thecleaning solution in the boiler or coupon test is done in laboratory bytaking polished metal coupon and subjecting it to test conditions oftemperature and various concentrations of acid and inhibitor.


1.6.4.4 Water Quality for Super heater Flushing

Contaminated water containing significant quantities of chloride has beenfound in the super heaters and reheaters of new drum-type boilers aftererection, presumably being present as a result of the use of unsuitablewater for hydraulic testing. To avoid any risk of stress-corrosion ofaustenitic material arising from this source, especially during thepre-commissioning alkali boil-out, flushing of the super heaters andreheaters with deionized water shall be carried out before the alkali boil.Intermittent flushing shall be used until the conductivity of the effluentwater is less than 5 us/cm and the chloride is below 1 mg/kg.

1.7 Water Flushing

Flushing of the plant with water will be required for the followingpurposes:

(i) To remove any contaminant which has entered the plant duringerection and any loose corrosion products.

(ii) To remove volatile corrosion inhibitors if used for protection ofthe plant during storage and erection.

(iii) To remove chemicals and residual sludge after site cleaningprocesses.

Notes:

1. This procedure may be unsuitable for large vessels (e.g., DC heaters) becauseof weight support limitations.

2. After water flushing has been completed, the plant shall either be dried out orput in wet storage, unless the flushing immediately precedes a further stage ofcleaning.

3. Water flushing shall be carried out using deionized water if austeniticcomponents are present or for once-through boilers. If any other plant is givena preliminary flush with filtered water, it shall be thoroughly flushed outafterward with deionized water, except where it is to be followed by a chemicalcleaning process.

1.8 Protection of the Plant After Cleaning

1.8.1 The Need for Passivation

After the steel surfaces have been chemically cleaned, they are very‘active’ and subject to rapid rusting. It is, therefore, necessary to passivatethe cleaned metal surfaces to prevent their deterioration. Operationimmediately after passivation is the best means of establishing theprotective oxide film.


1.8.2. Passivation at 40 bar

Good passivation can only be achieved under high-temperature andhigh-pressure conditions (40 bar is recommended) and for preservation ofthe passive film, the boiler should be emptied while hot and at 3–5 barpressure, or if operationally acceptable, from 28 bar, to ensure that thesurfaces dry out.

1.8.3 Passivation at 7 bar and Below

In certain situations (e.g., feed systems) it is not possible to obtainhigh-pressure passivation conditions immediately after thepre-commissioning chemical cleaning. It is then necessary to resort tothe circulation of a hydrazine/ammonia solution at 95 °C which confers alimited resistance to rusting. Passivation may be carried out usingtrisodium and disodium phosphate at 70 °C. Some contractors use sodiumnitrite and ammonia solution at 70 °C for preliminary passivation and thenhydrazine and ammonia for final passivation at 90–95 °C.

1.8.4 Storage After Passivation

Where passivation at 90 °C has been utilized, it is recommended that theplant be either thoroughly dried out, which is the preferred method, orstored wet using corrosion inhibiting solutions which are specified.

Appendix 1A-I Pre-operational Cleaning of Boiler Furnace and EconomizerTubes

1A-I.1 Introduction

The following stages constitute a complete cleaning and must becarried out consecutively and with minimum delay. The steps canbe alkali flushing or alkali boil-out followed by acid cleaning andpassivation.

1A-I.2 Precautions

Precautions must be taken to ensure that the chemical cleaningsolutions used in stage 1A-I.3.3 and 1A-I.3.5–1A-I.3.8 do notenter the super heater. During stage 1A3.3, the water level shallnot be above normal working level. During stages 1AI3.5–1AI3.8, the super heater shall be filled with deionized water(treated with 200 ppm N2H4 and pH around 10) to form a waterplug and back flushing should be carried out periodically. Inaddition, during stages 1AI3.5–1AI3.8, a constant head overflowdevice should be fitted to the drum (see Appendix 1H).


1A-I.3 Sequential stages

1A-I.3.1 Hot Water Flushing

Fill and drain the boiler as far as possible using DM water toremove foreign matter and check for leakages and blockages.Flush the super heaters and reheaters intermittently usingdeionized water until the water leaving the super heater andreheater has a conductivity of less than 5 us/cm and a chloridecontent of less than 1 mg/kg chloride.

1A-I.3.2 Alkali Boil Out

Fill the boiler to working level with demineralized watercontaining 1000 mg/kg trisodium phosphate.Raise the pressure to 40 barwith intermittent blowing down for 30 sduring every hour. The final pressure should be reached in 8–10 h.Maintain the boiler at 40 bar pressure with the specified chemicalconcentration for at least 24 h. Drain while the boiler is still ashot as practicable and if possible, while under pressure.Cool the boiler drum to 90 °C metal temperature and open theboiler drum and distribution drum’s (if any) manhole forexamination/chemical addition and remove any loose deposits.

1A-I.3.3 Alkali Flushing

*The boiler is filled with a solution containing 2000 mg/kgTSP and2000 mg/kg DSP4000 mg/kg Na2CO3

and a suitable surface active agent at 90 °C.Circulate for 24 h and drain.

1A-I.3.4 Acid Cleaning

1A-I.3.5 Circulate a solution in deionized water containing one of thefollowing chemicals through the boiler

(i) 3 % W/W citric acid with an approved inhibitor (seeAppendix 1F) and ammonia to give pH 3.5–4.0.Initially, circulate at not less than 90 °C (maximum105 °C) and continue until the iron content is constant(Note 1). The concentration of free citric acid should bemaintained at not less than 0.5 % W/W during circulation,otherwise basic citrates might precipitate.

(ii) 5 % Hcl acid with 0.25 % ammonium bifluoride and 0.2 %inhibitor (Rodine-213 Sp) at a temperature of 70 °C(Appendix 1A-III).


(iii) 1 % W/W hydrofluoric acid with an approved inhibitor(Appendix 1A-IV).

Circulate at 55 °C until the iron concentration is constant (Note1). The concentration of free hydrofluoric acid should bemaintained at not less than 0.2 % W/W during circulation.

1A-I.3.6 Raise the pH to 5.0 by careful addition of ammonia added slowlyduring circulation to avoid high pH values (Note 2)

1A-I.3.7 Drain the boiler, and when using ammoniated citric acid, rinsewith a solution containing 0.2 % W/W citric acid with ammoniato give pH 3.5–4.0

1A-I.3.8 Flush the plant with deionized water until pH remains above 6.0and conductivity <20 micro Siemens/cm

1A-I.3.9 Fill the plant with deionized water containing:100 mg/kg N2H4 and with 100 mg/kg ammonia for interimpassivation.Or, 50 mg/kg hydrazine with 50 mg/kg ammonia for finalpassivation.Maintain a minimum pH of 10.0.Raise the pressure to 40 bar and maintain for not less than 24 h.No further additions of hydrazine to the boiler are requiredbecause this has been shown to be unnecessary. However,50 mg/kg hydrazine and 50 mg/kg ammonia shall be added tothe make-up water to the boiler to react with dissolved oxygen.On completion of stage 1A-I.3.9, blow the boiler empty at thehighest possible pressure, but in any event, not less than 4 bar.

Notes:

1. Experience shows that provided the system has been lagged, the temperatureshould not have fallen below 75 °C before cleaning has been completed, whenusing ammoniated citric acid, or 50 °C with hydrofluoric acid/hydrochloricacid.

2. The reasons for raising pH above 5.0 are:

(i) To minimize corrosion of the plant after cleaning, but before displace-ment of acid.

(ii) To avoid corrosion in discharge points and culverts.


Appendix 1A-II Pre-operational Cleaning of HP Feed Systems

1A-II.1 Introduction

Generally, if cleaning conditions are met during the course ofpreparation, the pre-boiler system shall be water flushed only.However, some vendors suggest an alkaline wash or alkalinewash followed by acid cleaning and passivation of the feedsystem, which are detailed below.

1A-II.2 Precautions

Precautions must be taken to ensure that all the instrumenttappings are isolated, HP heaters and BFP are blanked off,internals of all the regulating valves are removed or they arereplaced by spool pieces, all orifices and flow nozzles areremoved, and feed line connections to HP heaters are isolated orblanketed. Pipeline portions which cannot be included in theflushing operations shall be mechanically cleaned and inspectedbefore erection.

1A-II.3 Sequential Stages

1A-II.3.1 Flush the system with filtered water at an ambient temperature toremove foreign matter.

1A-II.3.2 Fill the system with DM water at 70–80 °C. Circulate the waterand drain. The process of filling, circulating, and draining iscontinued until the outlet water quality matches the inlet waterquality in turbidity and color.

1A-II.3.3 Chemical solution in demineralized water for alkali flushing oftrisodium phosphate 5000 ppm as Na3PO4 12H2O along with asuitable wetting agent are filled in the system and thetemperature is raised to 80–95 °C. Samples are taken everyhour and analyzed for oil impurities, iron, and pH values. Theprocess is deemed to be complete when there are no traces of oilimpurities when the iron content and pH stabilizes in inlet andoutlet, or after 12 h of circulation. The system is drained.

1A-II.3.4 The system is rinsed with DM water to remove alkalinity left onthe surface. Hourly samples are compared for phosphate,alkalinity content, and conductivity. When conductivity andpH are the same as that of DM water, the operation is completeand the system should be drained.

1A-II.3.5 For acid cleaning, fill the HP feed system with demineralizedwater.


1A-II.3.6 Raise the water temperature to 95 °C.

1A-II.3.7 While maintaining the circulating flow, add chemicals to givethe following final solution:3 % W/W citric Acid0.05 % W/W stannine LTP inhibitorAmmonia for a of pH 3.5–4.0.

1A-II.3.8 Circulate the solution for 6–8 h until leveling out of iron andacid concentration in inlet and outlet.

1A-II.3.9 Drain the system.

1A-II.3.10 Rinse the system with 0.2 % W/W solution of citric acidammoniated to a pH of 3.5/4.0 by filling and circulating briefly.

1A-II.3.11 Flush the system using demineralized water until the conduc-tivity is 30 us/cm or less.

1A-II.3.12 Fill the HP feed system with demineralized water.

1A-II.3.13 Raise the temperature of the circulating water flow to 95 °C.

1A-II.3.14 While maintaining the circulating flow, add chemicals to givethe following final solutions:300 ppm hydrazineAmmonia to give pH 10.

1A-II.3.15 Circulate the solution for 12 h.

1A-II.3.16 Drain the system while hot. Preserve the HP feed heater by N2

capping if not used immediately.

Appendix 1A-III Pre-operational Cleaning of Boiler Furnace andEconomizer Tubes with Hydrochloric Acid

1A-III. 1.0 Hydrochloric acid cleaning.

1A-III. 1.1 Ammonium bifluoride 0.25 % may be added to the inhibitedacid solution for the intensification of the reaction and itseffective silica removal.

1A-III. 1.2 Boiler is drained under nitrogen capping.

1A-III. 1.3 Boiler is filled with DM water at 65 °C to a level slightly higherthan the acid level and is completely drained under nitrogenpressure. The superheater is back flushed simultaneously.


1A-III. 1.4 Citric acid rinse is carried out using 0.1 % W/W citric acid witha of pH 3.5–4.0. The second rinse with citric acid is done at atemperature of 65 °C. This step is to ensure a more thoroughiron removal.

1A-III. 1.5 Drain the citric acid solution under nitrogen capping.

1A-III. 1.6 Carry out neutralization using a neutralizing solution contain-ing 8000 ppm of trisodium phosphate, (Na3PO4 � 12H2O) and4100 ppm of disodium phosphate (Na2HPO4 � 7H2O) at apressure of 7 kg/cm2. Hold the pressure for about 2 hNeutralization can also be done using 1 % soda ash solution at85–90 °C for about 6 h.

1A-III. 1.7 Switch off the fires. Allow boiler to cool gradually. Open thedrum vents when the drum pressure drops to 1–2 kg/cm2. Drainthe boiler when the drum temperature drops to below 100 °C.

Appendix 1A-IV Pre-operational Cleaning of Boiler Furnace andEconomizer Tubes–Hydroflouric Acid Cleaning

1A-IV. 1.0 Hydrofluoric Acid Cleaning

1A-IV. 1.1 Both once-through and circulating methods can be utilized forcleaning, In the once-through method, the system is filled withhot water at approximately 70 °C and the acid and inhibitor aredosed in such a way that a concentration of 0.15 % inhibitorand 1 % HF are achieved in the feed water line. The dosingshud be continued until concentration at the outlet reachesapproximately 1 % HF and the iron values are decreasing downto 2g Fe/l. All pumps are stopped and the acid remainsapproximately 2 h in the system for a static treatment.

1A-IV. 1.2 Then the acid is replaced by DM water. The super heaters areback flushed. Flushing is continued until the conductivitydifference between inlet and outlet water is less than 10 us/cm.

1A-IV. 1.3 Passivation is done by using ammonia to bring the pH up to10.2 and by hydrogen peroxide at a concentration of 0.1 % atan ambient temperature.

Appendix 1B Pre-operational Steam Purging of Super Heaters andReheaters

1B-1 Effective steam purging requires extensive temporary pipeworkand involves complex theoretical considerations which must be bestudied for each individual design. To be fully effective, it isnecessary to achieve a scouring action at least equivalent to that of


full load steam flow. ASME PTC 4.1/BS-2885 gives a method forcalculating sizes of pipework, and pressure and temperatureconditions necessary for steam purging the super heater, reheater,and steam pipework together with the necessary chart. Becausethere is now a computer program available for carrying out therequired calculations, practical guidance, based on experience onsteam purging at many stations, is also included.

1B-2 During steam blowing, there is an increased risk of water carryoverbecause the pressure drop which occurs is higher than duringnormal operation. To minimize the risk of stress corrosion, sodiumhydroxide must not be added to the boiler water during steamblowing. The boiler is initially filled with 50 mg/kg hydrazine and50 mg/kg ammonia. No further additions of hydrazine are required,but 50 mg/kg hydrazine and 50 mg/kg ammonia should be added tothe make-up water to the boiler to react with dissolved oxygen.Before commencing the steam blowing process, it must be provedthat all cleaning chemicals have been thoroughly flushed from theboiler water circuit. The boiler water should not contain more than0.1 mg/kg chloride (as Cl−) or 0.2 mg/kg sodium (as Na+).

Appendix 1C Post-operational Cleaning of Furnace and Economizer Tubes:Selection of Chemical Cleaning Processes

Principle deposition during operation of a boiler

1. Mill scale.2. Oxides of iron and copper.

Tube samples (approximately 600 mm length) to be collected from high heatflux area (around 3 m above wind box). The following criteria are considered fordepositions.

Boiler type Internal deposits

Clean surface(mg/cm2)

Dirty surface(mg/cm2)

Very dirty surface(mg/cm2)

Sub critical <15 15–40 >40

Super critical <15 15–25 >25


All measurement to be done on the furnace side of the tube samples.Criteria for deciding chemical cleaning are as follows.

Pressure (kg/cm2) Drum type Once-through type

140 140–180 180 Super critical

Quantity of deposits (mg/cm2) 50–70 40–50 30–40 20–30

Common solvent used is HCL (5 %) at 75 °C. Inhibitor used:

• Ammonium bifluoride if large amount of silica is present.• Ammonium bromate if large amount of copper is present.

Additionally, the following chemicals are also used:

• Phosphoric acid (3 %) at 100 °C• Ammonium citrate (5 %) at 105 °C• Formic hydroxyacetic acid (3 %) at 7 °C• Ammonium EDTA (3 %) at 150 °C.

Circulation speed should be between 0.3 and 1.0 m/s.

Appendix 1D Post-operational Cleaning of Furnace Tubes in Drum-TypeBoilers (And Economizers, Where Necessary)

1D-1 IntroductionThe following stages constitute a complete cleaning and must becarried out consecutively and with minimum delay (Note 1).

1D-2 PrecautionsPrecautions must be taken to ensure that the chemical solutions donot enter the super heater. The super heater must be filled withdeionized water to form a waterplug and back-flushing shall becarried out periodically. In addition, a constant head overflowdevice must be fitted to the drum (see Appendix 1H).

1D-3 Sequential Stages

1D-3.1 In some circumstances, the copper removal stage may beunnecessary (Note 2) and in others, it may be carried out atreduced strength (approximately 50 %) of the solution specifiedbelow. Otherwise, fill the boiler with a solution containing 1 %W/W citric acid with 0.5 % W/W sodium bromate and ammoniafor a pH of 9.5.Approximately 0.5 % W/W of 0.880 ammonia will be required,the bulk of which must be added before the citric acid isintroduced. Deionized water must be used for the solution.Circulate at a temperature of 50 °C, until the concentration of


copper is constant (approximately 4–6 h). Drain the boiler andback flush the super heaters with deionized water.

1D-3.2 Achoice must be made in any given case between hydrochloric,hydrofluoric, and ammoniated citric acids for iron oxide removal(see Appendix 1C). The boiler is filled with a solution of either:3 % W/W citric acid with an approved inhibitor (see Appendix 1F)and ammonia for a pH of 3.5–4.0.Or5 % W/W hydrochloric acid with 0.5 % W/W ammoniumbifluoride and an approved inhibitor (see Appendix 1H).Circulate at 90 °C (Note 3) until the iron and nickel concentrationsare constant (normally 6 h).Or1 or 2 % W/W hydrofluoric acid with an approved inhibitor (seeAppendix 1F).Circulate at 55 °C (Note 3) until the iron concentration is constant(Normally 3–4 h).Initially circulate the solution at 90 °C (Note 3) and continue untilthe iron concentration is constant (normally 6–8 h). The ironremoval solution will be drained away under nitrogen capping.

1D-3.3 Drain the boiler and when using ammoniated citric or hydrochloricacid, rinse with a solution containing:0.2 %t W/W citric acid and ammonia for a pH of 3.5–4.0.This solution will be drained under nitrogen capping.

1D-3.4 Copper removal may frequently be required at this stage unless thewater/steam circuit contains no copper alloys. The standardformulation and procedure is given in 1D3.1.The full strength solution need only be used when the boiler isknown to be heavily contaminated with copper and its oxides.Where it is judged that copper contamination is not great, a 50 %solution may be utilized.

1D-3.5 Drain the boiler and thoroughly back flush the super heaters withdeionized water which has conductivity less than 0.5 us/cm. Rinsethe boiler with deionized water to remove the cleaning solution.

1D-3.6 Interim Passivation—50 mg/l hydrazine and 50 mg/l ammonia tobe circulated at 95 °C for 24 h then drained under nitrogencapping.Final Passivation—Refill the boiler with deionized water and add50 mg/kg hydrazine and 50 mg/kg ammonia, maintaining aminimum pH of 10.0. Raise the pressure to 40 bar and maintainfor at least 24 h. No further additions of hydrazine to the boiler arerequired to maintain a reserve in the boiler water because this has


been shown to be unnecessary. However, 50 mg/kg hydrazine and50 mg/kg ammonia must be added to the make-up water to theboiler to react with dissolved oxygen.

1D-3.7 On completion of the passivation process, the boiler should beblown empty at the highest possible pressure, but in any event, notless than 4 bar.Notes:

1. No alkali boil-out is generally necessary for the post-commis-sioning cleaning of boilers, on the assumption that oil andsiliceous materials will not be present. Where this assumptionis unjustified, stage 1D3.1 shall be preceded by an alkaliboil-out as specified in Appendix 1A-I.

2. The capacity for copper of the formulation given in stage1D3.1 is 6.3 g Cu/kg. Only rarely is more than 30 % of thiscapacity required. Depending on local judgment as to theamount of copper in any boiler, it may be possible to omitstage 1D-3.1.

3. Cleaning rates fall with decreasing temperature. Experienceshows that typical temperatures at the end of the iron removalstage are 70 °C with citric acid, 60 °C with hydrochloric acid,and 50 °C with hydrofluoric acid.

Appendix 1E Post-operational Cleaning of Once Through Boilers, SuperHeaters, Reheaters, Condensate, and Feed Systems

1E-1 IntroductionThe following stages constitute a complete clean and must becarried out consecutively and with minimum delay.

1E-2 Sequential Stages

1E-2.1 Flush with deionized water at a velocity greater than 1.5 m/s in allSect. of the plant.

1E-2.2 Circulate a solution in deionized water containing:3 %W/W citric acid (Note 1) with 0.5 %W/W formic acid (Note 2)and an approved inhibitor (see Appendix 1F) and ammonia for a pHof 3.5–4.0.The solution is initially circulated at not less than 90 °C andcontinued until the iron content is constant. The concentration offree citric acid should be maintained at not less than 0.5 % W/Wduring circulation.

1E-2.3 Raise the pH to 5.0 by careful addition of ammonia, added slowlyduring circulation to avoid local high pH values (Note 3).


1E-2.4 Drain and rinse with a solution in demineralized water containing:0.2 % W/W citric acid with ammonia for a pH of 3.5–4.0.

1E-2.5 Flush with deionized water at a velocity greater than 1.5 m/s untilthe pH remains above 6.0.

1E-2.6 Circulate solution in deionized water containing:300 mg/kg hydrazine with 50 mg/kg ammonia.Raise the temperature of the solution to at least 90 °C and circulate fornot less than 24 h. Furthermore, additions of hydrazine should bemadeif necessary to maintain a concentration of not less than 25 mg/kg.

1E-2.7 On completion of stage 1E.2.6, drain the plant at the highestpossible temperature.

1E-2.8 After stage 1E.2.7, the plant should be dried out or wet stored.Notes:

1. The chloride content of the citric acidused shouldbe such that a 3 %W/W solution does not contain more than 2 mg/kg chloride as C1.

2. Formic acid is required to obtain an acceptable rate of reaction fordissolving the outer layer of duplex oxides from super heaters.

3. The reasons for raising the pH to 5.0 are:

(i) To minimize corrosion of the plant after cleaning, butbefore displacement of acid and subsequent flushing.

(ii) To avoid corrosion in discharge points and culverts.

4. In the event of the need to post-operation clean condensate or feedsystems, the processes required should be based on this Appendix.

Appendix 1F Recommended Inhibitors

1F-1 The inhibitors which are to be used during acid cleaning processesand the recommended concentrations are:

(i) For 5 % W/W hydrochloric acid, use 0.25 % W/W armohib28. or 0.1–0.2 % v/v rodine 213 (sp) or equivalent at 65 °C.

(ii) For 1 or 2 % W/W hydrofluoric acid, use 0.1 % W/Wdodigen 95 (Note 1) or lith solvent, CL-4or 0.1–0.5 % rodine 31A or equivalent.

(iii) For 3 % W/W citric acid, use, preferably, 0.05 % W/Wdodigen 95 or rodine 215 or equivalent (Note 2). If this isnot available, 0.05 % W/W stannine LTP can be used withappropriate additional safety precautions.

The inhibitor concentration selection will be based on themanufacturer’s recommendations and should have mutualacceptance.


1F-2 The approved inhibitors must be present under acid conditions atall times to ensure that they are fully dissolved and notsubsequently precipitated. They must always be added directly toan acid solution and should not be previously diluted with water oradded to water to which the acid is added later. The requirementsfor the addition of inhibitors to the cleaning solution as given inSect. 5, “Safety Aspects”, shall be strictly observed.

1F-3 Storage and handling of the approved inhibitors must be inaccordance with Sect. 5, “Safety Aspects”.Notes:

1. With hydrofluoric acid, the material must be brought onto siteas a solution (typically 15 % W/W) to which the inhibitor hasalready been added, to eliminate the need to dilute concen-trated solutions before injecting into the boiler.

2. Dodigen 95 is preferred because its chemical composition issuch that it is incapable of producing the hydrolysis productwhich has been associated with eye toxicity when usingstannine LTP.

Appendix 1F-1 Inhibitors for Acid Cleaning (For Information)

Inhibitor Type Cleaning agent Metallurgy Normalconc.

Temprange (°C)

Rodine213 Spl.

Liquid,semi-foaming

HCl Copper, Brass, M.S., S.S., admiraltymetal

1–2 %,V/V ofconc. acid

65–93

Rodine31A

Liquid HF, Chloride freesolvents

Any 0.1–0.5 %of dilutedacid

Roomtemp. to105a

Rodine212

Liquidsemi-foaming

HCl Copper, brass M.S., S.S., admiraltymetal

1–2 %, v/vof conc.acid

65–80

Rodine92B

Liquid H2SO4, H3PO4,AcOH, NaHSO4,Citric

Any 1–2 %, v/vof conc.acid

Roomtemp. to100

Rodine130

Powder Sulphamic, citric,tartaric, oxalic acidand NaHSO4

M.S., S.S., brass,copper

1–2 %,W/W ofconc. acid

Roomtemp. to 65

aVaries depending on type of acid


Inhibitor Type Cleaning agent Metallurgy Normalconc.

Temprange (°C)

Coronil 213(Spl)

Liquid HCl (also incombination with HF)etc. copper and Cualloys

Standard steel, M.S.,high carbon steels,super heated steels

0.1–0.2 %v/v ofdilutedacid

Ambientto 90 °C

Coronil-92B Liquidandpowder

Citric acid – 1–2 % v/vof conc.acid

Ambientto 100 °C

Coronil-130 Powder Sulphuric, sulphamicacid

Carbon-steel, S.S.,copper and brass.

1.5 %W/W ofacid

–

1H Constant Head Overflow and Temporary Gauge Glass

1H-1 Constant Head Overflow

1H-1.1 In addition to water plugging and back flushing the super heater, aconstant head overflow device must be fitted to the drum to ensure thatchemical cleaning solutions do not enter the super heater.The degassifying header has been placed inside the boiler drum andgenerated H2 passed through it during the acid cleaning step.

1H-1.2 The overflow device may be fitted using a temporary drum door. It is notenvisaged that the overflow would be required to take full flow of thechemical circulation pumps and a 100-mm line should be adequate.Particular care will be necessary when initially adding the acid to thewater in the boiler so as not to exceed the working level. In this context, atemporary gauge glass extending the full height of the drum should beprovided.

1H-1.3 In the event of a stoppage of the acid circulation pump, the level in thedrum may rise due to water draining back from the tubes. Thus, the heightof the overflow should be positioned 75–100 mm above the requiredworking level.

1H-1.4 The valve must be open at all times except when it is required to rinse theupper surfaces of the drum. Before such rinsing is carried out, ensure thatthe solution contains less than 2 mg/kg chloride.

1H-1.5 Provision must be made at the overflow outlet for the boiler to be ventedoutside the building in a position inaccessible to personnel and for anyliquid overflowing to be led to a convenient sump where it may beneutralized, if necessary. This may be achieved by leading the overflowoutlet into a small tank from which the liquid can be drained and thevapor vented outside the buildings.


1H-2 Temporary Gauge Glass

1H-2.1 A temporary gauge glass is required because the normal means of levelindication cannot be used.

1H-2.2 Experience shows that the boiler drum becomes slightly pressurizedduring temperature raising and with an open-ended temporary gaugeglass, a false indication of the drum level is obtained. Both links of theindicating column must be connected to the drum. It is therefore requiredthat permanent tapping points are provided for drum-level indicationduring chemical cleaning. Each tapping point must be fitted withdouble-isolating valves and a blanked flange suitable for full boilerpressure. Preferably, the lower tapping point should be from a line otherthan the permanent gauge glass impulse line (e.g., the boiler dosing orsampling line). The top tapping point may be led into a drum air releaseline before the normal air valve.

2.0 Post-Operational Cleaning of Condensers

2.1 Introduction

Adverse performance due to fouling may justify chemically cleaningthe main steam condenser-side (i.e. the cooling water [CW]) and/or thesteam side according to circumstances.At some power stations, usually those with recirculating CW systems, ithas been the practice to remove CW side (hardness) scale periodicallyby chemically cleaning.Experience has shown that deposits on the steam side of condensertubes can also cause significant efficiency losses. Improvements in backpressure of 6–12 mbar have resulted from the chemical removal of suchdeposits.Investigational work has been carried out over a number of years intovarious aspects of the chemical cleaning of both the CW and steam sideof condenser deposits. It is intended to provide general guidance topower stations on condenser cleaning, but detailed advice on anyspecific case should be sought.

The requirements given in Sect. 5, “Safety Aspects” must beapplied for the post-operational cleaning of condensers.

2.2 Objective of Cleaning

The objective of cleaning is to remove material (whether on the CWside or steam side) impeding heat transfer and restore the thermalefficiency.


2.3 Criterion for Cleaning

2.3.1 The criterion for cleaning is an unacceptable fall in condenserefficiency. If, after allowing for any air-in leakage, the losses attributedto the fouling of the CW or steam side are judged to be worth retrieving,then CW or steam side cleaning should be considered. The potentialfinancial benefit of cleaning is best judged on the basis of estimates ofthe fouling burden and the fouling resistance to heat transfer.

2.3.2 The fouling burden on individual tubes can be determined chemically.Tubes extracted from the condensers for this purpose must always beremoved by cutting between sagging plate positions and removingsections from the steam side. Extracting tubes will lead to dislodgementof the steam-side deposit.

2.3.3 In situ deposit thickness measurements on accessible tubes will give anindication of the extent of fouling. Deposit thickness can be measurednondestructively using commercially available impedance measuringinstrumentation.

2.3.4 Fouling resistance data can be obtained by externally cleaning selectedtubes, in situ, with emery cloth and comparing the cooling watertemperature rise for pairs of dirty and clean tubes. When using thistechnique on power stations where Taprogge is not installed to offsetwater-side deposit accumulation, allowance should be made forwater-side losses.

2.3.5 Fouling resistance data can also be obtained from heat transfer testscarried out, on extracted segments of tubing, by an approvedmechanical engineering laboratory.

2.4 Cleaning the CW Side of Condensers.

2.4.1 Available Cleaning Processes.

2.4.1.1 There are three distinct methods for condenser cleaning, all of whichdepend on the use of acid to dissolve he scale. The methods availableare termed ‘off-load’, ‘reduced-load,’ ‘on-load,’ and details are given inAppendices 2A–2C, respectively. Prior to chemical cleaning themechanical cleaning of condenser tubes may be carried out to removephysical debris like CT fill material, sponge balls, etc., make circulationpath clear, enhance chemical efficiency and reduce chemicalsrequirement.

2.4.1.2 In the off-load method, the acid solution is introduced into thecondenser and circulated until monitoring shows scale dissolution to beeffectively complete. The reduced-load method differs in that it isapplied to one shell of the condenser, isolated for the purpose, while theother is still operating.


2.4.1.3 In the on-load method, the pH of the cooling water entering thecondenser is decreased by acid dosage to about 2–2.5. The bufferingcapacity of the cooling water, together with the large volume of thesystem restrict the change of pH elsewhere in the circuit.

2.4.2 Choice of AcidWhile in principle any of a large number of acids may be used toremove the scales found in condensers, hydrochloric and sulfuric acidsare recommended because in addition to being inexpensive and readilyavailable, they were used satisfactorily in investigational studies of thissubject. Of these two, hydrochloric acid is recommended only when thewhole condenser is isolated, (i.e., in an off-load cleaning). Where thereis any possibility of contamination of the feed water by the cleaningsolution, as in reduced-load or on-load methods, then only sulfuric acidis to be used. For SS tubes, sulphamic acid, although costly, is alsobeing used.

2.4.3 Inhibition

2.4.3.1 The three basic methods of cleaning impose quite different requirementsfor inhibition and these are influenced by the materials of constructionof the plant and by the estimated long-term frequency of cleaning. Bythe use of inhibitors, acceptable conditions can be achieved in respect ofthe corrosion of water boxes and tubes, as well as restraint of galvanicattack and copper deposition and dezincification. The use of eitherrecommended inhibitors. Armohib 28 or Armohib 533 or equivalentsuppresses copper deposition in the water box and also counteractsgalvanic corrosion. Recommendations for inhibitor requirements aregiven in Appendix 2D.

2.4.3.2 The degree of risk to condenser integrity is related to the frequency ofcleaning.

2.4.4 Selection of Cleaning ProcessesTo aid in the selection of a suitable cleaning process, logic is given inAppendix 2E.

2.4.5 Practical Considerations

2.4.5.1 Terminal Points

Suitable terminal points can be made as branch connections, so thatrigging can be carried out on-load and subsequent flushing can takeplace without delay.

2.4.5.2 Circuitry

Where appropriate, the water boxes should be connected in series into acircuit containing a tank and pump, the water box vents being fittedwith temporary connections back to the chemical mixing tank.


2.4.6 Protection of Plant After Cleaning

In contrast to boiler plant, there are no special requirements for theprotection of condensers after cleaning provided that the cleaningsolution has been flushed away adequately.

2.5 Cleaning the Steam Side of Condensers

The process described below is not suitable for pannier condensers andeven conventional condensers may need support to take the additionalweight of the cleaning solution.

2.5.1 Available Cleaning Processes

2.5.1.1 Studies have shown that steam-side deposits which foul condensers areprincipally a porous mixture of hydrated iron oxides (nominallyFe2O3 � 2H2O) together with the corrosion products tenorite (CuO) andzincite (ZnO) formed in service. In some instances, oil has been foundincorporated into the deposit.

2.5.1.2 Even a small amount of oil will render the deposit hydrophobic, makingremoval by aqueous-based systems impracticable. Therefore, prior tocleaning, the oil content of the deposit shall be determined as this willinfluence the final formulation of the cleaning solvent and the processrequirements.

2.5.1.3 Currently, one basic cleaning process with satisfactory field experienceis available. It can be used in two modes, one for deposits which containoil and one for deposits which are oil-free. Cleaning is carried out atambient temperatures and cleaning time is typically 40 h. Details ofeach method are given in Appendices 2F and 2G.

2.5.2 Constituents of Cleaning Solutions

The available formulations contain up to five constituents which are asfollows:

(i) Reducing agent(ii) Complexing agent(iii) Approved degreasant(iv) Additional surfactant(v) Additional organic acid to adjust pH.

2.5.2. Reducing Agent

The reducing agent is oxalic acid and provides the driving force for thedissolution of ferric oxides. For both oil-bound and oil-free deposits, theconcentration of oxalic acid is 0.7 %.


2.5.2.2 Complexing Agent

2.5.2.2.1 The complexing agent which is required to hold iron, copper and zinc insolution is ethylenediamine-tetra acetic acid (EDTA). The cleaningsolution must be prepared from the tetra-sodium EDTA salt(Na4EDTA). The use of any other EDTA salt is not permitted.

2.5.2.2.2 The concentration of EDTA used, 3.6–5.5 %, determines the capacityof the cleaning solution.

2.5.2.3 Degreasant

2.5.2.3.1 The degreasant is based on C9 aromatic naptha. Two commerciallyavailable C9 naptha-based degreasants have been recommended for usein this application (see Appendix 2H).

2.5.2.3.2 For the removal of oil containing deposits, the formulation may containup to maximum of 10 % v/v degreasant. This is the maximum level ofdegreasant that can be used when butyl rubber packing is presentwithout having a permanent deleterious effect on the packing.

2.5.2.4 Surfactant

Although both approved degreasants contain some surfactants(Appendix 2H), investigations have shown that without the additionof a supplementary surfactant, separation of the emulsion can occurduring the oxide dissolution process. The supplementary surfactant islissopol and it is used at a concentration of 1 % v/v.

2.5.2.5 Additional Organic Acid

Formic acid is used to adjust the pH of the cleaning solution.

2.5.3 Selection of Cleaning Process

2.5.3.1 The choice of cleaning process will be dictated by whether oil is presentand by the estimate of the total mass of metal oxides to be removed. Oilcontent determined by solvent extraction from segments of individualtubes and the metal oxide burden found by laboratory cleaning tests.Great care should be taken to ensure that representative tube samplesare used for these tests.

2.5.3.2 Once the total metal burden is known, the concentration of EDTA to beused as such that no more than 60 % of the available capacity will beconsumed (see Appendix 2-I). Dissolution rates diminish if the solutionbecomes significantly more than 60 % exhausted. The EDTA concen-tration should be between 3.6–5.5 %.


2.5.3.3 Experience to date has shown that a solution containing Na4EDTA and0.7 % oxalic acid has sufficient capacity to cope with most of thecondenser steam side deposits encountered. If oil is present, 10 % v/vdegreasant and 1 % v/v ethomeen S25 has been found to be adequate.

2.5.4 Exclusion of Oxygen

2.5.4.1 Corrosion inhibitors are unnecessary provided air (oxygen) is excludedfrom the cleaning circuit.

2.5.5 Practical Considerations

Experience has shown the need for full consultation between cleaningcontractors, stations and if appropriate, specialist advice should besought prior to cleaning. Among the factors to be considered are:

2.5.5.1 Water Requirements

2.5.5.1.1 During the cleaning, there will be a requirement for large quantities ofhigh quality demineralized water for preparing solutions and rinsing.Water containing a significant concentration of calcium must not beused, as this would cause a precipitation of calcium oxalate and asubsequent rise in solution pH.

2.5.5.1.2 Although the clean is carried out at ambient temperatures, if possible, asupply of high quality hot water (e.g., blow-down) should be availableto facilitate more rapid dissolution of oxalic acid crystals when thecleaning solution is being prepared.

2.5.5.2 Temporary Holding Tanks

Sufficient temporary holding tanks must be provided to hold thepre-mixed solution prior to transferring it to the condenser, and to holdthe effluent when the cleaning is completed.

2.5.5.3 Mixing Procedure

2.5.5.3.1 Prior to mixing is necessary to prepare a concentrated (approx. 10 %v/v) solution of oxalic acid and to add the surfactant to the degreasant.To save process time, both these procedures may be carried out off siteby the cleaning contractor prior to the cleaning.

2.5.5.3.2 If the degreasant/surfactant mix is prepared on site, this mixture must becontinuously agitated prior to use to ensure complete dispersal of themuch denser surfactant.

2.5.5.3.3 Mixing shall be carried out in the following order:

1. Dilute Na4EDTA concentrate.2. Carefully add, with further dilution, concentrated oxalic acid

solution.


3. Carefully add, with further dilution and agitation the degreasant inwhich the required quantity of surfactant (ethomeen S25) hasalready been dissolved.

4. Dilute the solution to 95 % of required final volume. Carefully addsufficient formic acid to give a final pH of 4.5.

5. Dilute to required final volume and transfer to the condenser.

The following points shall be noted:

(i) The pH of the cleaning solution must always be maintained atmore than pH 3.8 to prevent free EDTA from precipitating out.

(ii) The surfactant must always be added to the degreasant. Directcontact with water will produce a solid precipitate.

(iii) The degreasant/surfactant must always be added to theEDTA/oxalic acid mixture. If concentrated oxalic acid solution isallowed to come into contact with the degreasant/surfactantmixture, a solid precipitate will be formed.

2.5.5.4 Quality of As-Received EDTA Solution

2.5.5.4.1 It is required that a quality control check be carried out on theas-received Na4EDTA concentrate prior to its use. The followingparameters shall be checked:

(i) Na4EDTA concentration(ii) Free sodium hydroxide(iii) Relative density

2.5.5.4.2 Experience to date has shown that some commercially available gradesof Na4EDTA are variable in quality and may contain free sodiumhydroxide which could increase the pH of the cleaning solution

2.5.5.5 Solution pH

2.5.5.5.1 The optimum pH for the dissolution process is 4.5, A solutioncontaining 3.6 % Na4EDTA, 0.7 % oxalic acid, if mixed correctly willhave a pH of 4.4–4.6. If an excess of Na4EDTA is present, pHadjustment is necessary prior to use. Formic acid is suitable for thispurpose

2.5.5.5.2 Both approved degreasants are essentially non-ionic and their presencehas little effect on the solution pH

2.5.5.5.3 It is recommended that an emergency reserve of formic acid beavailable to compensate for any adventitious rise in pH. If any pHadjustment is carried out, the pH of the solution must not be allowed tofall below 3.8

2.5.5.5.4 The pH of the cleaning solution will rise slightly during cleaning:normally the rise is not significant


2.5.5.6 Circulation, Agitation and the Exclusion of AirThorough out the duration of the clean, external pumps shall circulatethe cleaning solution. Nitrogen purging shall be used to ensure goodmixing and to exclude air. Oxygen ingress caused enhanced corrosionof brass components.

2.5.5.7 Duration of Clean

2.5.5.7.1 The clean should be allowed to proceed until analysis shows ironuptake has ceased or the total dissolved metal ions are equivalent to 85% of the available capacity. If the latter situation is reached, it willprobably be necessary to renew the cleaning solution to complete theclean. Details to be utilized are given in Sect. 4, ‘Analytical Methods’

2.5.5.7.2 Experience has shown that provided the correct pH is attained for thelevels of fouling, cleaning is completed in about 40 h

2.5.5.8 Effluents

2.5.5.8.1 Once the process is complete, the spent solution must be discharged tothe holding tank prior to disposal

2.5.5.8.2 It is essential that all statutory requirements covering effluent from thestation are established and met. Where tankers remove effluent,adequate capacity must be available so that the full cleaning program(e.g., rinsing down) is not delayed

2.5.5.8.3 At the planning stage consideration must always be given toincineration of the effluent in an operational boiler as an alternative todischarge via the ash lagoons or removal by tankers

2.5.5.9 Analytical Methods

During the course of the clean, it will be necessary to monitor at regularintervals, dissolved iron, copper, and zinc together with nickel in thecase of power station where cupronickel tubes are fitted. Therecommended methods are given in Sect. 4, ‘Analytical Methods’.

2.5.6 Engineering Aspects

2.5.6.1 Isolation

2.5.6.1.1 Owing to the complexity of most modern power station condensers,particular care must be taken to ensure that the condenser steam side iscompletely isolated prior to cleaning

2.5.6.1.2 If gas bags are used to seal off pipework, check shall be made to ensurethat the bag material will not be degraded by any degreasant used. Suchbags shall always be maintained under positive pressure by an inert gas(air must not be used)


2.5.6.2 Air Extraction Pumps

2.5.6.2.1 If air extraction pumps are used to draw off degreasant vapor, stepsmust be taken to ensure that the pumps do not draw over any of thechemical liquor. Any vapor must be discharged to an outside areainaccessible to personnel

2.5.6.3 Temporary Sight Glass

A temporary sight glass should be provided to indicate the level ofsolution in the condenser steam side.

2.5.6.4 Vent

A vent/overflow shall be provided just above the anticipated maximumsolution level.

2.5.6.5 Tube Plugs

Plastic tube plugs fabricated in polythene are not completely resistant toeither approved degreasant and will fail at the nose either during a cleanor on return to service. Such plugs must be replaced with brass plugsprior to cleaning.

Appendix 2A Hydrochloric Acid Process for Off-load Post-operationalCleaning of the Water Side of Condensers and SulphamicAcid Cleaning for SS Tube Condensers

2A-1 The condenser shall be made available for cleaning with all plantisolation, depressurizing and draining complete

2A-2 Circulate at ambient temperature a solution containing:1.5 % W/W hydrochloric acid with an approved inhibitor (seeAppendices 2D and 2E) until the calcium concentration is constantand an excess of at least 0.5 % W/W of acid still remains. Open thevents at intervals to release carbon dioxide liberated by thedescaling process.

2A-3 On completion of cleaning, drain the condenser and pass normalcooling water flow for 30 min. Then, drain and inspect

2A-4 For Stainless Steel Tubes7

Sulphamic acid cleaning has been successfully done, however, at ahigher cost investment.In practice, inhibited sulphamic acid (2–5 %) has been used at 65–70 °C without much pressurizing the condenser system. CO2 gasgenerated is allowed to leak off from the top vents. The acidcirculation is continued for approximately 8 h and then drained.


The system is refilled with raw water and circulated at 4–5 kg/cm2

pump pressure and drained. Mass flushing is finally done with CWpumps in service.

Appendix 2B Sulfuric Acid Process for Reduced-Load Post-operationalCleaning of the Water Side of Condensers

2B-1 The part-condenser to be cleaned shall be made available withappropriate plant isolators and drained

2B-2 Circulate at ambient temperature a solution containing:1.5 %W/W sulfuric acid with an approved inhibitor (see Appendices2D and 2E) until the calcium content is constant and an excess of atleast 0.5 %W/Wof acid still remains. The temperature of the cleaningsolution will increase as it takes up heat from the system up to amaximum of about 40 °C, depending on the particular plant.

2B-3 Open the vents at intervals to release carbon dioxide liberated

2B-4 On completion of cleaning, drain the condenser and return toservice

Appendix 2C Sulfuric Acid Process for On-Load Post-Operational Cleaningof the Water Side of Condensers

2C-1 As experience of on-load descaling of condensers is successful butlimited, this method should be considered only when off-load orreduced-load cleaning cannot be applied

2C-2 The method is, therefore, given only in outline in this directive,and detailed guidance should be sought before undertaking anon-load cleaning

2C-3 The process consists of adding sulfuric acid to reduce the pH to 2–2.5 locally within the condenser, yet restricting the total sulphateconcentration of the cooling water to less than 700 mg/kg SO4 andmaintaining the bulk pH above 6.0 to minimize the risk to theconcrete and metals in the cooling water circuit

2C-4 It has been found acceptable, at some locations, to introduce theacid via the chlorination system with the additional advantage thatthe isolating valves facilitate dosage of individual passes of thecondenser

2C-5 For any system, the practical details of on-load cleaning depend uponthe system volume, the severity of scaling, the water analysis and theindividual condenser design. The water quality is kept within therequired limits of sulphate concentration and pH by varying theduration of acid addition and by purging, when necessary


2C-6 An assessment of the probable effect of dosing on a given coolingwater chemistry shall be carried out in any situation where on-loadcleaning is being considered

Appendix 2D Recommended Inhibitors

2D-1 General

2D-1.1 If condensers are to be cleaned frequently (i.e., more than once peryear-see Appendix 2E), it is necessary to use inhibited hydrochlo-ric acid or inhibited sulfuric acid

2D-1.2 The inhibitors which are approved for use during condenser acidcleaning processes and the recommended concentrations are:

(i) For 1.5 % W/W hydrochloric acid, use 0.25 % W/WArmohib 28 or 0.025 % W/W Armohib 533 (see Note) orIndian equivalent/[0.1–0.2 % v/v Rodine 213 (sp)]

(ii) For 1.5 % W/W sulphuric acid, use 0.05 % W/W Armohib533 (see Note) or Indian equivalent

The inhibitor concentrations are based on the manufacturer’srecommendations.

2D-1.3 The approved inhibitors must be present under acid conditions atall times to ensure that they are fully dissolved and notsubsequently precipitated. They must always be added direct toan acid solution and must not be previously diluted with water oradded to water to which the acid is added later.

2D-1.4 The requirements for the addition of inhibitors to the cleaningsolution as given in Sect. 5, ‘Safety Aspects’ must be strictlyobserved.

2D-1.5 Storage and handling of the approved inhibitors must be inaccordance with Sect. 5, ‘Safety Aspects’, Appendices 5A and 5B.

2D-2 For Ferrous Metals SpecificallyHydrochloric acid inhibited with Armohib 28 or Armohib 533, orsulfuric acid inhibited with Armohib 533, may be used, selected inaccordance with the recommendations given in.

2D-3 For Ferrous Metals and Brass TogetherHydrochloric acid or sulfuric acid inhibited with Armohib 533 areto be used, selected in accordance with the recommendations.


Appendix 2E The Selection of Cleaning Process for the Water Side ofCondensers

Flow of water through condenser tubes gets obstructed mainly due to scale for-mation or fouling inside the tubes. Condenser water contains dissolved solids thatget precipitated on the inner surface of the tubes. This causes the formation of thescale. Another way of fouling is due to growth of organic bodies like algae/fungi.Various cleaning process as given below are adopted depending on the type offouling:

On-line

• Mechanical process:

– Taprogge system with sponge rubber balls

• Chemical process:

– scale and corrosion inhibition, dispersants, and biocides– Lowering pH value of the circulating water.

Off-line

• Mechanical process:

– High pressure water jet– Molded plastic cleaners/metal cleaners with controlled spring loaded cutting

edge.

• Chemical process:

– Acid or chelate dissolution.

Chemical scale removal is very effective if the scale is silica based.

Appendix 2F Cleaning Method for Removal of Oil-Free Deposits from theSteam Side of Condensers (see Note)

2F-1 The condenser must be made available for cleaning with all plantisolation, depressurizing and draining complete

2F-2 Circulate at ambient temperature a solution containing:

(i) 3.6–5.5 % EDTA (added as the Na4 EDTA salt)(ii) 0.7 % oxalic acid(iii) Formic acid to give pH of 4.5

Until the iron concentration is constant or until the total metal ionconcentration is 85 % of the available capacity, when furtherdissolution rates are minimal.


2F-3 On completion of cleaning, drain the condenser, rinse, and inspect

Note: Deposits containing less than 5 % oil.

Appendix 2G Cleaning Method for Removal of Oil Containing Deposits fromthe Steam Side of Condensers (see Note)

2G-1 The condenser must be made available for cleaning with all plantisolation, depressurizing and draining complete

2G-2 Circulate at ambient temperature a solution containing:3.6–5.5 % EDTA (added as the Na4EDTA salt), 0.7 % oxalic acid,up to 10 % v/v approved degreasant (see Appendix 2H), 1 % v/vEthomeen S25 and formic acid to give pH of 4.5.Until the iron concentration is constant or until the total metal ionconcentration is 85 % of the available capacity, when furtherdissolution rates are minimal.

2G-3 On completion of cleaning, drain the condenser, rinse, and inspect

Note: Deposits containing more than 5 % oil.

Appendix 2H Recommended Degreasants

2H-1 Commercially available degreasants suitable for use in the steamside cleaning of condensers are based on C9 Naptha. As supplied,the degreasants normally contain C9 Naptha nonylphenyl surfac-tants and dodecylbenzene sulphonate surfactants

2H-2 A number of commercially available degreasants have beenevaluated, and two have been approved for use in this applicationThere are:

(i) Industrial polyclenes.(ii) Banner slove H536.

With both these degreasants, it is necessary to add theadditional surfactant, Ethomeen S25 to obtain the requiredemulsion stability for the duration of the clean.

(iii) Non-ionic detergent (SNID-PGN) (Conc. 0.05 %).

Appendix 2-I Selection of Cleaning Process

Let: Cu = average copper burden (g/m2)Fe = average iron burden (g/m2)Ni = average nickel burden


(applicable only if cupronickeltube fitted) (g/m2)Zn = average zinc burden (g/m2)(Cu, Fe, Ni and Zn are determined by chemical cleaning tests)V = volume of solution required to fill the condenser steam side (liters)A = total surface area of condenser tubes (m2)B = total metal ion burden (moles)

B ¼ A Cu63:5

þ Fe56

þ Ni59

þ Zn65:4

� �mol

If: B < 0.048 V use 0.08 M EDTA.B > 0.048 V use upto 0.13 M EDTA (required concentration = 1.73)If B > 0.078 V seek specialist advice.The requirement for a degreasant can be established by solvent extraction and

comparative cleaning tests. Normally, even the presence of a small quantity of oilwill necessitate the use of degreasant. It is extremely important (see 2.5.3) whendetermining/fouling burden to ensure that representative tube samples are used.

When establishing the volume of solution required to fill the steam side of thecondenser, consideration should be given (subject to the design of the condenser) toblanking-off or filling with gas bags ‘dead’ areas thereby reducing solutionrequirements.

3.0 Post-Operational Cleaning of the Water Side of Feed Heaters

3.1 Introduction

Pre-operational cleaning of feed heaters was formerly carried out using anacid/neutralization/passivation sequence much the same as that currentlyavailable for boilers. However, the introduction of ‘at works’ cleaningfollowed by preservation of the heaters, by means of vapor phaseinhibition or dehumidification, largely supersedes on-site cleaning, whichwas only carried out if there were shortfalls in the performance of thenewer technique.Where post-operational chemical cleaning of feed heaters is requiredsolely for the removal of inorganic constituents, this shall be accom-plished by employing appropriate stages from Appendix 1E. The situationbecomes more complicated, however, when organic contamination ispresent due, in particular, to the ingress of turbine lubricating oil to thefeed-water. In passing through the feed system, the oil appears to undergoprogressive degradation. In the LP heaters, it is easily removed byalkali/detergent treatment, but in the HP system, the deposits maycomprise a mixture of ‘baked’ organic matter and metallic oxides andresist this treatment. A process has been developed to deal with this,which is described in Appendix 3A.


The requirements given in Sect. 5, ‘Safety Aspects’, must be appliedfor the post-operational cleaning of feed heaters.

3.2 Objective of Cleaning

The objective of feed-heater cleaning is the restoration of the thermalperformance of feed heaters by removal of contaminant material withinthe tubes.

3.3 Criterion for Cleaning

The criterion for cleaning is the loss of heater efficiency due to water-sidefouling. Examination of the samples removed provides a useful check,especially where there is a history of oil ingress into the feed system.

3.4 Available Cleaning Process

3.4.1 LP Feed Heaters

Deposits of an oily nature present in the LP feed heaters can be readilyremoved by using one of the many proprietary alkali/degreasanttreatments which are available.

3.4.2 HP Feed Heaters

3.4.2.1 The processes currently available for post-operational cleaning of HP feedheaters include:

(i) A chemical process incorporating degreasant and acid stages, fol-lowed by flushing at full feed water flow, the objective being toremove both organic and inorganic contaminates. If full feed flowcannot be achieved, then the chemical cleaning process should notbe used.

(ii) A physical process using high-velocity water jetting.

3.4.2.2 High-velocity water jetting, being a purely mechanical process, is notcovered in this directive, only details of the chemical process are given. Itshould be recognized that experience of high-velocity water jetting and itsapplication is limited and, therefore, due attention shall be given toSect. 3.5, ‘Practical Considerations’.

3.5 Practical Considerations

3.5.1 Plant to be Included

The process given in Appendix 3A has been applied to both full HP feedheater trains and single HP feed heaters. The former can give problems inensuring correct and complete circulation in all areas of the plant beingcleaned. Consequently, it may be preferable to clean HP feed heaterseither single or in pairs, if practicable, particularly if the contamination islocalized. Such an approach is justifiable on economic grounds.


3.5.2 Examination of Tubes Prior to Cleaning

The nature of deposits present on the HP feed heater surfaces will varyconsiderably according to the source and extent of contamination. Theprocess given in Appendix 3A has been formulated to deal with a widecombination of likely contaminant. However, wherever possible, tubesamples should be removed for laboratory trials to assess the effectivenessof the process, prior to its application. In extreme cases, the cleaningprocess may not be completely effective.

3.5.3 Prevention of Ingress of Cleaning Solution to other Plant Items

3.5.3.1 Care must be taken to minimize the risk to other sections of the plant bysecure isolation of the feed system from the boiler and disconnection fromthe condenser.

3.5.3.2 Care must also be taken to ensure that all the cleaning solution has beenremoved from the plant by full feed flow water flushing before it isreconnected to the condensing or boiler plant. Particular attention shouldbe paid to the boiler water analysis when returning the plant to service toconfirm the absence of contamination from the cleaning solution.

Appendix 3A Degreasant/Hydrochloric Acid Process for Post-OperationalCleaning Of HP Feed Heaters (See Note 1)

3A-1 Circulate a solution of a 50 %, v/v ‘Applied Chemicals 4–43’ (seeNote 2), at a temperature of 80–90 °C for 10 h.

3A-2 Flush to waste at a flow equivalent of full feed flow until aconductivity of <200 ms/cm is recorded.

3A-3 Circulate a solution of 5 % W/W hydrochloric acid inhibited with0.25 % W/W armohib 28 at a temperature of 75 °C for 2 h.

3A-4 Flush to waste at a flow equivalent to full feed flow until aconductivity of <200 us/cm is reached.

3A-5 Repeat 3A.3

3A-6 Repeat flush to waste at a flush equivalent of full feed flow until aconductivity of <5 ms/cm is reached.Notes:

1. If the HP feed heaters being cleaned are heavily fouled, it maybe necessary to repeat 3A.1–3A.6

2. An equivalent alkaline detergent may be used if AppliedChemical 4.-43 is not available.


4.0 Analytical Methods

4.1 Introduction

The section deals with the analytical methods required for monitoring thepre- and post-operational cleaning of boilers, super heaters, reheaters, andthe feed system described in clause 1 (4.2) and the post-operationalcleaning of condensers described in clause 2 (4.3).A list of the methods is given in Appendix 4A. There are a number ofother methods that may be required and although not fully evaluated,recommended procedures are given below.

4.2 Methods of Analysis to be Used During the Chemical Cleaning ofBoilers, Super Heaters, Reheaters, and Feed Systems

The following methods are to be utilized during various stages of thechemical cleaning. This sample must be filtered before any analysis iscarried out.

4.2.1 pH

Use method 2 given in BS 1427/ASTM/IS/

4.2.2 Concentration of Hydrochloric Acid or Hydrofluoric Acid

Take 1 mL sample and add 50 mL of demineralized water. Add pH 4.5indicator and titrate with 0.1 M NaOH.g/kg Hcl = Titre × 3.65.g/kg HF = Titre × 2.0.

4.2.3 Total Citrate

4.2.3.1 Take 2 mL sample, make up to 200 mL with distilled water and passthrough a strongly acidic cation exchange column. Discard the first100 mL and titrate the second 100 mL with 0.1 M NaOH usingphenolphthalene indicator% total citrate (as citric acid) = Titre × 0.64.

4.2.3.2 Where sodium bromate has been used, an allowance must be made for thepresence of bromic acid after cation exchange. For the addition of 0.5 %sodium bromate, the calculation becomes:% total citrate (as citric acid) = (Titre-0.3) × 0.64.

4.2.4 Free Citric Acid

The free citric acid is obtained by deducting from the total citrateconcentration the equivalent of the total iron found in solution.% free citric acid = % total citrate (3.4 × % total iron).The dimensions of a suitable ion exchange column are: internal diameter15 mm, height 200 mm. The resin is in the hydrogen form and the dilutedsample is passed through the column at a rate of about 10 mL/min.


4.2.5 Fluoride

Determine using a fluoride ion selective electrode and an epoxy bodiedreference electrode.

4.2.6 Alkalinity

Take a 100-mL sample, add pH 4.5 indicator and titrate with 0.1 M nitricacid.g/kg NaOH = Titre × 0.4.

4.2.7 Sodium

Sodium may be measured flame photometrically. Instruments giving afull scale deflection for 5 mg/kg or less of sodium will be satisfactory, andshould be operated in accordance with the manufacturer’s instruction.

4.2.8 Total Iron in Citric Acid, Hydrochloric Acid, or Hydrofluoric Acid

4.2.8.1 Dilute the sample to give a final iron concentration in the range0–60 mg/kg (3 % citric acid saturated with iron will have an approximateiron concentration of 8500 mg/kg). For most analysis, a hundred-folddilution will be adequate. With hydrofluoric acid, dilute with 2 % boricacid to protect glassware.

4.2.8.2 Determine the total iron by atomic absorption directly on the dilutedsample or take 50 mL of the diluted sample, add 0.5 thioglycollic acidand 5 mL excess of 0.880 ammonia. Make up to 100 mL. Measure thecolour using a 10 mm cuvette and a 605 filter. Read off the total ironconcentration from a calibration graph prepared under identicalconditionsTotal iron and total copper may also be determined by titration method.For iron 5 mL of filtered sample and dilute with 25 mL of DM water.Add 2 % KMnO4 solution dropwise till permanent pink colour appears.Add 15 % hydrazine sulphate solution dropwise till pink colourdisappears. Add 2 drops in excess. Add 5 g of KI crystals and stopperthe flask. Allow to stand for 5 min. Titrate the liberated iodine with 0.1 Nsodium thiosulphate solution using starch indicator.The method for copper determination is same as for iron except thatbefore the addition of KI crystals 5 g of ammonium bifluoride is to beadded and mixed well.

4.2.9 Ferric Iron in Citric Acid or Hydrochloric Acid

4.2.9.1 Take 25 mL sample and adjust the pH to 2.5 with approximately normalNa2C03 solution

4.2.9.2 Dilute the solution to 100 mL and add five drops of 5 % sulphosalicylicacid solution. Titrate with 0.1 M EDTA until the pink colour just


disappears. Add a further five drops of indicator and continue the titrationuntil the pink color disappearsg/kg Fe 3+ = Titre × 223.

4.2.10 Nickel

Place 2 mL of the sample in a separating funnel, add four drops of 10 %hydrogen peroxide solution, and two drops of phenolphthalein solution.Then, add 5 mL of 10 % sodium potassium tartrate and mix the contents.Add 2.5 N sodium hydroxide solution drop-wise until the phenolph-thalein just turns pink and then add 0.1 N hydrochloric acid drop-wiseuntil the colour is just discharged. Add 5 mL of 0.15 %furil-alpha-dioxime followed by 25 mL of 2 N ammonia solution. Swirlthe contents of the flask to mix, and add 15 mL of the chloroform througha filter paper and measure the absorbance in a suitable size cuvette.Determine the nickel content from a calibration curve.

4.3 Methods of Analysis to be Used During the Post-operational Cleaningof Condensers

The iron, copper, zinc, and nickel content of samples of the chemicalcleaning liquor can be determined by atomic absorptionspectrophotometry/suitable equipment available at site using standardinstrument operating conditions.

4.3.1 Instrument Calibration

4.3.1.1 Prepare separate series of calibration standards by appropriate dilution of1000 mg/kg stock containing:

(i) Iron: 0, 10, 20, 30, 40 and 50 mg/kg Fe(ii) Copper: 0, 5, 10, 20, 30 and 40 mg/kg Cu(iii) Zinc: 0, 0.5, 1, 2, 3 and 4 mg/kg Zn(iv) Nickel: 0, 2, 4, 6, 8 and 10 mg/kg Ni

in 2 % v/v ‘AR’ nitric acid

4.3.1.2 Measure the absorbance of each standard, using the manufacturer’srecommended instrument conditions, at the following wave lengths:

(i) Fe: 372.0 nm(ii) Cu: 217.9 nm(iii) Zn: 213.9 nm(iv) Ni: 232.0 nm

and construct calibration curves for reference purposes.

4.3.1.3 When used in conjunction with the following analytical procedure, theabove concentrations will correspond to 0–2500 mg/kg Fe; 0–2000 mg/kgCu; 0–200 mg/kg Zn, and 0–500 mg/kg Ni in the original cleaning liquor.Two procedures are available, one for determining total metal removed in


a clean and the other for following the progress during the chemicalcleaning operation

4.3.2 Determination of the Total Amount of Iron, Copper, Zinc, and NickelRemoval in a Cleaning

Mix the final cleaning liquor sample well. Transfer 5 mL of the sample toclean dry 50 mL conical flask. Add 5 mL concentrated nitric acid (AR).Heat to boiling on a moderate hot plate and gently reflux for 15 min withoccasional swirling of the flask. Allow to cool and add approximately30 mL deionized water. Warm the solution on a hot plate and transfer thecontents of the flask quantitatively to a clean 250 mL graduated flask.Dilute to the mark with deionized water and mix the solution well.Determine the Fe, Cu, Zn, and Ni content solution by atomic absorptionspectrophotometry using the instrument operating conditions and cali-bration procedure previously described.

4.3.3 Rapid Method for Following the Progress of the Chemical CleaningOperation

Transfer 5 mL of the chemical cleaning liquor (free from suspendedmatter) to a clean 250 mL graduated flask. Add 5 mL ‘AR’ concentratednitric acid, dilute to the mark with deionized water and mix well.Determine the Fe, Cu, Zn, and Ni content of the sample by atomicabsorption using the instrument conditions and calibration proceduredescribed above.

Appendix 4A List of Analytical Methods used IN Analysis of ChemicalCleaning Solutions

Determinant Solution Method

Free citric acid Acid cleaning Selective ion electrode

Fluoride Acid cleaning Selective ion electrode

Fluoride Flushing Colorimetric

Chloride 3 % citric acid Selective ion electrode

Chloride 50 % citric acid Turbidimetric

Chloride 0.880 sg. ammonia Selective Ion electrode

Chloride Water Selective Ion electrode

Chloride Water/hydrazine Colorimetric

Chloride Flushing Selective ion electrode

Chloride Flushing Colorimetric

Silica Acid cleaning Colorimetric

Silica Acid cleaning Atomic absorption

Stannine LTP Acid cleaning UV absorbance

Active inhibitor Extract from 5A Colorimetric(continued)


(continued)

Determinant Solution Method

Armohib 28 Acid cleaning Colorimetric

Bromate/copper Alkali cleaning Titration

Nitrite Copper stripping Colorimetric

Nitrite Flushing Colorimetric

Copper Alkali cleaning Colorimetric

Trisodium phosphate Alkali boil-out Titration

Phosphate Cleaning Colorimetric

Phosphate Alkali boil-out Colorimetric

Hydrazine Water Colorimetric

5.0 Safety Aspects

5.1 Introduction

This section describes the precautions necessary for the safe handling,storage and use of chemicals used in the cleaning processes and alsodescribes the procedures for entry into the plant after cleaning anddisposal of residues. The recommendations contained in this Section shallbe considered in conjunction with the (then) CEGB Safety Rules, theNational Safety Code of Practice GS-EH162. “The implementation ofControl of Substance Hazardous to Health (COSHH) Regulation 1988”,and the other Sections of this directive.The storage used and handling of the chemicals required for the chemicalcleaning process are potentially hazardous to the personnel involved.These hazards are listed along with storage requirements, in Appendix5A. The officer responsible for the safety aspects of chemical cleaningand for ensuring that safety precautions are strictly observed shall makehimself familiar with appropriate (then) CEGB safety documentation.A summary of suitable protective equipment is given in Appendix 5B, butthis should not discourage reference to the documentation itself.Emergency provisions and first-aid treatment are given in Appendix 5C.

5.2 All Items of Plant

5.2.1 Supervision

5.2.1.1 The officer responsible for the overall safety aspects of chemical cleaningshall be the Project Site Manager in the case of pre-commissioningcleaning, and the Location Manager where post-commissioning cleaningis being carried out. In both circumstances, the Station Chemist or anominated deputy shall act as adviser to the officer responsible for safetyand shall be the Supervising Officer in so far as it is necessary to ensurethat the safety precautions are strictly observed and to ensure that suitablehygiene and first-aid facilities are available. The Supervising Officer shall


consult with the medical service (normally the Nursing Officer) withrespect to first-aid facilities. Supervision of the required safety precau-tions by the Station Chemist shall also include supervising the chemicalcleaning contractor’s employees and any failure to comply with the safetyrequirements shall be notified immediately to the Project Site Manager orLocation Manager as appropriate. The Supervising Officer or his deputyshall be present at the scene of operation whenever chemicals are beingreceived or are in the cleaning system or during subsequent inspection

5.2.1.2 The Station Chemist shall ensure that chemicals are introduced in thecorrect manner to the cleaning circuit and that the ventilation andtemperature requirements before entry into the plant for inspection orworking have been complied with (see 5.2.6)

5.2.2 General Philosophy

5.2.2.1 The manual handling of chemicals should be avoided as far as practicableand wherever possible, mechanical methods should be used fortransporting, dispensing, and transferring chemicals

5.2.2.2 Protective clothing for skin and eye protection must be worn and if notadequately ventilated, breathing apparatus must be worn when:

(i) Mixing chemicals(ii) Dealing with leaks, spillages, splashes and

accumulated vapors(iii) Approaching the plant(iv) Post-cleaning inspection is carried out

5.2.3 General Precautions and Personal Hygiene

Wherever and whenever there is danger of contact with chemicals, allpersonnel must:

(i) Be warned of the nature of the potential hazards and the necessaryprecautions and be instructed in the correct use of protectiveclothing and equipment by the Supervising Officer

(ii) Observe a high standard of personal hygiene avoiding contact withchemicals, their vapors or contaminated residues

(iii) Not eat, drink, or smoke(iv) Avoid wiping nose, eyes or face other than with clean paper tissues(v) Place all debris and chemical residues removed from the plant in

clearly labeled polythene bags for subsequent disposal(vi) On leaving the plant, remove their protective clothing for cleaning

before re-use, and clean themselves and their equipment, usingdisposable materials

(vii) Wash thoroughly as soon as possible after leaving the operationalarea (see 5.2.8)


5.2.4 Storage of Chemicals

Chemicals shall always be stored in a cool, well ventilated and securebuilding which, as far as possible, is free from fire. Because of their risk,particular properties and in some cases, their incompatibility, somechemicals require special storage precautions to be taken; these are givenin Appendix 5A. If any chemical not listed there is to be used, then theadvice of the Chief Medical Officer must be sought and the ‘Head ofIndustrial Safety Management Group’ notified so that Appendix 5A canbe accordingly modified. Chemical containers must be clearly labeled atall times.

5.2.4.2 The Supervising Officer must ensure that notices detailing the action to betaken in the event of spillage, the emergency provisions and first-aidtreatment, are prominently displayed in the chemical storage andoperating area. The notice must state the location of equipment necessaryto deal with spillage or personal contamination

5.2.4.3 An adequate water supply must be available to deal with any leakage orspillage of chemicals

5.2.4.4 Stock control shall be implemented so that there is a sequential turnoverof chemicals

5.2.4.5 The chemical cleaning contractor must provide equipment and chemicalsfor the treatment of spillages or personal contamination, which is readilyavailable and properly maintained

5.2.5 Precautions during the Cleaning Process

5.2.5.1 The chemical handling, mixing and temporarily hazardous areas must beroped off, cleared of extraneous matter, and have proper warning noticeserected and authorized by the Supervising Officer. Persons not concernedwith the cleaning process must be excluded from the area. Wheneverchemical solutions are in the plant, the entire circuit both temporary andpermanent, must be periodically examined for leaks. Any leaks should bestopped as quickly as possible and the contaminated area thoroughlysluiced down. If the Supervising Officer deems the leak to be dangerousto personnel, the process must be suspended and the affected circuitdrained and flushed prior to repair. Appropriate protective clothing mustbe worn while checking for leaks and when using appropriate equipmentfor dealing with leaks (see Appendix 5B)

5.2.5.2 Entry into any confined space into which solutions or vapor can leak fromthe cleaning circuit during the process should be avoided as far as isreasonably practicable. If entry into such spaces must be made, theprecautions given in 5.2.7 shall be observed


5.2.5.3 Whilst chemical cleaning operations are in progress, venting of the boiler,including the vent from the constant head overflow, must be to the outsideof the building, inaccessible to personnel and well away from other ventsor intakes to avoid the possibility of vapor reentering the building

5.2.6 Approach to the Plant (Excluding Bodily Entry) After any Stage ofthe Cleaning Process

5.2.6.1 When the plant is to be opened up after the passivation stage or after anyacid stage during the process, the precautions given in 5.2.6.2–5.2.6.6shall be observed

5.2.6.2 The chemical cleaning circuits must be drained to the approved disposalpoint taking care to minimize spillage, splashing of solutions oraccumulation of vapor. If chemicals are drained into a holding vessel,care must be taken that mixing of chemicals from different stages does notoccur in the vessel. It is particularly important to avoid acidifyingsolutions containing nitrite or bromate, or mixing strong acids and alkalisor strong oxidizing and reducing agents

5.2.6.3 Vapors issuing from plant openings should be dispersed by blowing cleanair through the access point using the best possible ventilation to obtain ahigh dilution rapidly. The breaking open of access points should becarried out by personnel wearing an approved type of overall and glovesand breathing apparatus incorporating a hood to give a full protection tothe head. Suitable equipment is given in Appendix 5B. Contact withsurfaces which are or have been wetted by chemicals should be avoidedas far as is reasonably practicable

5.2.6.4 Components which are contaminated with chemicals should be placed onimpervious sheets for cleaning prior to replacement

5.2.6.5 Personnel should not expose themselves to risk by making a quickobservation of the plant interior (without bodily entry) when the accesspoints are first opened

5.2.7 Entry of Personnel into Plant That has been Chemically Cleaned

5.2.7.1 The precautions given in 5.2.7.2–5.2.7.5 are necessary if entry is to bemade into the plant after any acid cleaning or passivation stage in theprocess

5.2.7.2 Entry to the plant shall be restricted to the minimum number of peoplenecessary. During the time that personnel are inside the plant, a stand-byman must be positioned at the point of entry

5.2.7.3 Before entering the plant after chemical cleaning, either after thepassivation stage at the end of the process, or after any acid stage duringthe process, or to carry out reinstatement work such as the removal offlow restrictors, there must be an absolute minimum delay of 3 h after


opening all entry points, unless full protective clothing is worn and anair-line breathing apparatus is used. During this period, ventilation of theplant should be carried out at a rate of at least ten air changes/h using afiltered air supply. It is essential that this 3-h delay period is observed,even if a higher ventilation rate is adopted. Ventilation of the plant at arate of at least 10 air changes per hour should be continued whilepersonnel are in the plant for inspection or to carry out reinstatement worksuch as removal of flow restrictors

5.2.7.4 Additionally before personnel enter plant, the temperature should beambient temperature. If the conditions above in 5.2.2 and 5.2.5 have beenfully complied with personnel can enter the plant wearing coveralls,gloves, and carefully fitted eye-goggles as detailed in Appendix 5B.Where such conditions have not been fully complied with, personnelentering the plant must wear overalls, PVC gloves, rubber boots, abreathing apparatus, and hood attachment giving full protection to thehead as detailed in Appendix 5B

5.2.7.5 Removal of debris or chemical residues from the plant must be carried outby personnel wearing full protective equipment and in such a manner asto avoid contamination of external surfaces. The residues should beextracted into impervious containers which are then passed to personswearing gloves and goggles, as detailed in Appendix 5B

5.2.8 Exit of Personnel and Materials from Plant Containing HazardousResidues After Chemical Cleaning

5.2.8.1 The personnel collecting debris and chemical residues must place them inclearly labeled polythene bags within the plant

5.2.8.2 For disposal, debris and chemical residues must be washed into a systemwhere considerable dilution can be achieved. Equipment used forhandling chemicals and the inhibitor must also be cleaned after use bywashing into a disposal system where considerable dilution can beachieved (see 5.2.9)

5.2.8.3 The same personal clothing should be used until the end of the workperiod on which a particular operator is engaged and then thoroughlycleaned. Upon leaving the plant, the operator should remove theprotective clothing for subsequent cleaning before re-use and proceeddirectly to the showers, paying particular attention to washing the handsand face

5.2.9 Disposal of Chemical Waste

Disposal of all surplus solutions and chemical waste must be by anapproved route. The appropriate waste disposal and water authoritiesshould be consulted.


Notes:

1. Where Emergency Action is Required For Dealing With Spillage OrEscape Of Chemicals, Maximum Ventilation and Water-WashingFacilities Must Be Used

2. Personnel using self-contained and air-line breathing apparatus mustbe properly trained and experienced in the use of such apparatus

3. The standard procedure outlined in documents with regard to theremoval of protective clothing must be strictly observed

4. Particular care must be exercised when opening drums of 0.880ammonia solution, particularly where these have been in a warmatmosphere, because the contents are likely to be under pressure

5.3 Boilers, Super Heaters, Reheaters, and Feed Systems

Where there is a choice, preference should be given in using inhibitorshaving a lower perceived risk.

5.3.1 In addition to the safety considerations given for all items of plant, thefollowing specific provisions apply to the chemical cleaning of boilers,super heaters, reheaters, and feed systems

5.3.2 The substituted thio-ureas present in some inhibitors specified inAppendix IF can lead to the formation of carbodiimides, which causetemporary blindness and sensitivity to light. To minimize the risk of eyetoxicity, it is essential to adhere to the recommendations in Sect. 5.2, ‘AllItems of Plant’, particularly regarding the addition of the inhibitor to thecleaning solution (5.2.5) and approach and entry into the plant (5.2.6 and5.2.7). The recommendations on supervision (5.2.1) handling, storage,and disposal of chemicals (5.2.2, 5.2.4, 5.2.5 and 5.2.9) must be strictlyobserved

5.4 Condensers

5.4.1 Cooling Water Side

5.4.1.1 The provisions given in Sect. 5.2 also apply to the chemical cleaning ofthe CW of the condensers

5.4.1.2 While it is believed that eye toxicity due to carbodiimide is not possiblewith the inhibitors currently specified for condensers in Appendices 2Dand 2E, it is nevertheless essential to flush out all traces of inhibitor usingthe full flow of the main CW pumps for at least 3 h before entering theplant. The precautions during cleaning (5.2.5) and the approach and entryinto the plant (5.2.6 and 5.2.7) must be strictly applied


5.4.1.3 The health precautions stated in the IS Safety Code of Practice on themaintenance of cooling water and other auxiliary water must be followedto minimize the risk of infection from Legionella

5.4.2 Steam Side

Inhibitors are not used in current practice for cleaning the steam side ofcondensers, therefore, no special precautions are required in this respect.

5.4.2.2 However, large volumes of acid cleaning liquids and solvents are usedand the provisions given for supervision (5.2.1). Handling storage anddisposal of chemicals (5.2.2, 5.2.4 and 5.2.9) must be applied. Somesolvents are flammable and/or toxic, and precautions must be taken toensure that no explosion hazard or toxicity risk can arise. Ventilationequipment should be selected and positioned taking into account risks topersonnel and explosion risks in accordance with ‘National Power SafetyRules Code of Practice in Confined Spaces’

5.5 Feed Heaters

The provisions given for supervision (5.2.1); the addition of inhibitors tothe cleaning solutions (5.2.5); approach and entry into the plant (5.2.6 and5.2.7), and the handling, storage, and disposal of chemicals (5.2.2, 5.2.4and 5.2.9) must be strictly observed. Solvents are also used andprecautions must be taken to ensure that no explosion hazard can ariseand that the plant is suitably ventilated to prevent risks to personnel (see5.4.2.2).

Appendix 5A Summary of Main Chemical Hazards and Special StorageRequirement

Chemicals OEL (note 1) Main hazards Special storagerequirements

Acetic acid 10 ppm Corrosive, irritant can cause severeburns flammable

Store away fromchromic and nitric acids

Ammonia 25 ppm (asNH3)

Corrosive, severe irritant Store away from acidsand/or bromate

Ammonium bifluoride Corrosive, reacts with mineral acidsto produce HF gas. Highly irritatingto skin, eyes and nose

Avoid contact withacids and fire risk

Applied chemicals 4–43 Can cause skin and eye irritation; ifswallowed gastro-intestinal irritation

Store away fromsources of heat or strongacids

C9 Naphtha degreasant Flammable (see supplier's datasheet)

Store away from firerisk in a well ventilatedarea

(continued)


(continued)


Citric acid Powder and solution can cause eyeinjury

Store away fromoxidizing agent

Chromic acid 0.05 mg/m3

(as Cr)Can cause severe burnsCan cause violentexplosion in contact with reducingagents

Store away fromoxidizing agents andany fire risk

Dipotassium hydrogenphosphate

Produces toxic, irritant fumes whenheated

Disodium hydrogenphosphate

Produces toxic, irritant fumes whenheated

Ethomean S25 – Skin and eye irritant (See Supplier'sdata sheet)

Formic acid 5 ppm Corrosive. Can cause severe burns Store in awell-ventilated area

Inhibitors (Armohib 28,Hibron armohib 533,

Can cause skin and eye irritation(some severe). Some combus-

–

Stannine LTP, Dodigen95, etc.) Rodine, Lithsolvent, coronil. etc.

Tible/toxic/corrosive

Hydrazine 0.1 ppm Strongly caustic. IrritantMay cause damage to liver andkidneys

Store separately. Seenational safety code ofpractice GS-C1 0.15

Hydrochloric acid 5 ppm Corrosive and irritant. Store in awell-ventilated area

Hydrogen peroxide 1 ppm Oxidizing and corrosiveCan cause severe damage to eyesand skinMay explode in contact with dust

Store separately, andaway from allcombustible materials ina cool area

Hydrofluoric acid 3 ppm Toxic and corrosive. Can causesevere burns

Store in awell-ventilated area

Nitric acid 2 ppm Oxidizing and corrosive can causesevere burns

Store away from aceticacid, ammonia andcombustible materials

Oxalic acid 1 mg/m3 Corrosive. Avoid breathing dust orvapor

Store away fromoxidizing agents

Potassium hydroxide(caustic potash)

2 mg/m3

(Note 2)Highly corrosive. Irritant. Inhalationof dust or mist causes intenseirritation

Severe store away fromacids

Potassium or sodiumdichromate

– Eye/skin irritant, with acid solutionstoxic gases can be produced

Store away from acidsand combustiblematerials

Possible explosion hazard on contactwith organic materials

(continued)


(continued)


Potassium or sodiumbromate

– Oxidizing agent. Eye/skin irritant.With acid solutions toxic gases areproduced

Store away from acids,combustible materialsand ammonia

Possible explosion hazard withammonia and contact with organicmaterials

Potassium or sodiumchromate

– Eye/skin irritant. With acid solutionstoxic gases can be produced.Possible explosion hazard on contactwith organic materials


Potassium or sodiumnitrite

Eye skin irritant with acid solutionsnitrons fumes are produced. Possibleexplosion hazard on contact withorganic materials


Sodium carbonate (sodaash)

Skin irritant. Dust or mist, irritatingto upper respiratory tract

Store away from acids

Sodium fluoride 2.5 mg/m3

(as F)If heated or in contact with acids,emits highly toxic fumes


Sodium hydroxide(caustic soda)

2 mg/m3 Highly corrosive. (note 2) irritant.Dustor mist can cause irritation to upperrespiratory tract

Severe store away fromacids

Sulphamic acid – Emits toxic fumes when heated.Irritant

Store away from heat

Sulphuric acid 1 mg/m3 Extremely irritant and corrosive.Cause severe burns

Store away from alkalis

Tetra sodium ethylenediamine tetraacetate

– Concentrated solution is caustic.Skinand eye irritant

Store away from acids

Tripotassium phosphate – Skin irritant. If heated highly toxicfumes

–

Trisodium phosphate – Skin irritant. If heated emits highlytoxic fumes.

–

Wetting agents(Dissapol, Teepol, etc.)

– May cause eye and skin irritation –

Notes1. OEL—Occupational Exposure Limit (8-h TWA value)2. Confirm by reference to the most recent HSE Guidance Note eH 4016


Appendix 5B Summary of the Protective Equipment to be Used WhenHandling Chemicals

Conditions Protective equipment

B-1 Normal handling of the following chemicals:

Ammonia a. Chemical safety goggles.

Ammonium bifluoride b. PVC apron.

Applied Chemicals 4–43 c. PVC gloves.

Armohib 28 d. Rubber boots (molded).

C-9 Naphtha degreasant

Citric acid In addition, for particulate chemicals

Diaminetetra acetic acid

Ethomeen S 25 e. Dust respirator

Formic acid

Hydrazine In addition, for formic acid, hydrochloricacid and sulfuric acid

Hydrochloric acid

Hydrofluoric acid

Lissapol C

Lissapol N f. Vizor.

Oxalic acid

Sodium bromate

Sodium hydroxide

Sodium nitrite

Stannine LTP

Sulfuric acid

Tetra sodium ethylene

Trisodium phosphate

5B-2 (i) For entry into plant chemical cleaningin which the requirements for inhibitoradditions and ventilation and temperaturehave been fully complied with

a. Chemical safety goggles

b. One-piece cotton/polyester overall withhood or one-piece disposable overall inPE-coated tyrek

c. PVC gloves

d. Rubber boots (molded).

(ii) For handling debris and chemicalresidues removed from chemical cleanedplant

As for 5B.2(i) above.

(continued)


(continued)

Conditions Protective equipment

5B-3 (i) For entry into plant after chemicalcleaning in which the requirements forinhibitor additions and ventilation andtemperature have been fully complied with

a. Compressed air-line breathing apparatus

b. One-piece cotton/polyester overall withhood or one-piece disposable PE-coatedtyrek

c. PVC gloves

d. Rubber boots (molded)

(ii) When breaking open access pointsafter chemical cleaning

a. Compressed air-line breathing apparatus(if entry also required).

b. Open-circuit self contained breathingapparatus (if entry not required)

c. One-piece cotton/polyester overall withhood or one-piece disposable Tyrek

d. PVC gloves

e. Rubber boots (molded)

(iii) Where contact with vapor andmerging from drains or vents during achemical process is unavoidable

As per 5B.3 (ii)

(iv) Where severe spillage or escape of thefollowing chemicals has taken place:Sodium bromate, Nitrous fumes,Stannine LTP and Armohib 28

a. Open-circuit self-contained breathingapparatus

b. Compressed air-line breathing

c. PVC gloves

d. Rubber boots (molded)

e. One-piece cotton/Polyester coverallwith hood or one-piece disposable overallin PE-coated tyrek (alternatively, PVCchemical splash suit)

Appendix 5C Emergency Provisions and First-Aid Treatment

5C-1 Emergency Provisions

Flushing and washingwater supplies

(i) Ample supplies of tepid flushing and washing water shall be providedat all possible points of discharge, spillage or escape of chemicals

(ii) Adequate provision shall be made for emergency treatment of theeyes, comprising eyewash bottles, located conveniently to places wheredischarge, spillage, or escape of chemicals can occur

First-aid room A suitable first-aid treatment room with outside telephone facilities shallbe provided within a reasonable distance of the place where chemicalsare being used

Store room A suitable room shall be provided for housing the protective clothing andapparatus required for emergency use


5.C-2 First-Aid Treatment

Injury Chemicals Treatment

Splashes inthe eye

All chemicals (i) Immediately flood the eye with water. To be effective,the eye must be opened

After a quick preliminary swill to wash away fluidaround the eye, the eyelids should be pushed apart usingthe thumb and index finger of the left hand. The casualtywill probably not be able to open the eye themselvesbecause of painful spasms

If an eyewash bottle is used, the jet would not be directedat the front of the eye but should be directed in from theside, so that flow is over the surface of the eye

(ii) Irrigation should be continued for 5−10 min, afterwhich the casualty should be taken to the first-aid room

(iii) Irrigation should be continued in the first-aid room.Remember, vision is saved by thorough irrigation, noother treatment can prevent damage if this is omitted

(iv) After thorough irrigation, the eye should be coveredwith a pad: the patient should be referred for medicalopinion

Irritation ofthe skin

All chemicals If signs of skin irritation occur, the person should beremoved from contact and referred for medical opinionIn the event of splashing of the skin with chemicals, theaffected area should be washed thoroughly avoidingspreading contamination to the face and eyes

Gassing All chemicals Bring person to fresh air, remove contaminated clothing,cover with blanket and keep person still and underobservation. Refer for medical opinion

Ammonia ornitrogen. Brominefrom sodiumbromate. Nitrogen

In addition to the above, if breathing is distressed, giveoxygen. If breathing fails, give artificial respiration.Summon doctor to site. dioxide from sodium nitrite

N.B. Oxygen can only be issued by a doctor or an occupational first-aiderholding the appropriate certificates

Appendix 5D Inhibitor Efficiency Test Procedure

5D-1 The selected inhibitor for acid cleaning of pre-boiler and boilerparts is to be checked for its efficiency. This can be done in twoways. The first is the laboratory test method, which confirms theefficiency of the inhibitor and also helps in arriving at the desiredconcentration of inhibitor required for effective results. The secondis a field test method which can be used during acid cleaning atintermediate intervals so that necessary changes, if any in theinhibitor concentration may be made from time to time


5D-2 Laboratory Test Method

The relative corrosivity of inhibited solutions used for chemicalcleaning can be checked in laboratory under static conditions attemperature of 65–70 °C. The test can be conducted on metalcoupons, preferably water wall tube samples, under clean condi-tions. The test consists of exposing metal coupons to cleaningsolvent under controlled conditions. The coupons are weighedbefore and after the test and the corrosion rate is calculated fromthe weight loss method. Reagent grade chemicals and DM watershould be used in all tests.

5D-2.1 Metal Coupon Preparation

A convenient metal coupon dimension is 13 × 100 × 3 mm(0.5 × 4.0 × 0.125 in.). Other shapes and sizes of test coupons areacceptable provided the total area is about 2600 mm2 (4 in2) orgreater. The principal requirement is to keep the flat surface arealarge when compared with the edge area. The surface finish of themetal coupons should be carried out with No. 120 abrasive paperor cloth of the equivalent grit grade unless the surface is to betested in the mill finished condition.

5D-2.2 Surface Area-Volume Ratio

Specific coupon surface area to solution volume ratio is to bemaintained for the test. For comparative results, a recommendedratio of surface area to solution volume (S/V) is 0.35 cm2/cm3.Other S/V ratios may be used to match the S/V ratio of a test to aspecific application for which the cleaning solution is intended. Forexample, chemical cleaning solutions may also be tested at a typicalS/V ratio of 0.6 cm2/cm3 for drum-type boilers or 1.3 cm2/cm3 foronce-through boilers. The S/V ratio for specific equipment can becalculated by the examiner. It is important that the test S/V ratio berecorded and maintained during the test.

5D-2.3 Test Procedure

5D-2.3.1 Prepare a sufficient quantity of solution to conduct all the plannedtests for one day. Place the solution in individual glass or plastictest vessel (plastic test vessels must be used if the solvent containsfluoride). The test vessel should be resistant to both the chemicalcleaning solution and the test temperature. Note that the corrosioninhibitor should be added to the solution just prior to testing.

5D-2.3.2 Add the amount of solution to the test vessel and record the S/Vratio and maintain it during the test.


5D-2.3.3 Place the test vessel in a constant temperature bath and allow it toequilibrate to the test temperature.

5D-2.3.4 Weigh the coupon to the nearest tenth of a milligram. The couponshould not be added to the test vessel containing the solution untilthe solution reaches the test temperature. Totally immerse thecoupon in the test solution. Any supports or hangers used shouldbe electrically nonconductive material.

5D-2.3.5 The duration of test should be 6 h.

5D-2.3.6 Duplicate tests must be performed to confirm results and tominimize the possibility of random errors. Duplicate tests shouldbe conducted separately so that any errors made in one test will notbe repeated in duplicate.

5D-2.3.7 After completion of the test, rinse the coupons in DM water andthen rinse them with acetone or methanol to remove the inhibitorfilm. Scrub the test coupons using a nylon brush and soap solution.Rinse with DM water and follow with an acetone or alcohol rinseto replace the water and dried in oven at a temperature of about105 °C for about 15 min. Store the coupons in a desiccator for aminimum period of 1 h prior to re-weighing.

5D-2.3.8 Calculation of Corrosion RateAfter cleaning, the coupon should be re-weighed to the nearesttenth of a milligram. The corrosion rate, as on average penetration,based on weight loss should then be calculated in the units ofmg/cm2/h.

5D-2.3.9 Criteria for AcceptanceThe weight loss should not be more than 0.1 mg/cm2/hr at 65 °Cfor carbon steel and mild steel sample.

5D-3 Field Test Method

A small ball of steel wool (about 0.1 gm) is degreased withacetone and added to a sample of inhibited acid solution in the acidtank solution during cleaning process.

5D-3.1 CriteriaInhibitor efficiency is judged to be adequate if the wire wool balldoes not float after 1 min in ammoniated citric acid or after 2 minin hydrochloric acid.


5D-4 Notes:

1. The expiration date of the inhibitor is to be checked beforestarting use.

2. In the event that the test fails, the test is to be conducted at ahigher concentration so as to conclude at what concentrationthe efficiency is acceptable and accordingly concentration ofinhibitor in acid cleaning procedure is to be adopted.


Appendix BFire Protection of Power Stations

1.0 Introduction

Plant is exposed to onerous operating conditions and the combinations offlammable material in large quantities and ignition sources which can lead tothe incidence of fires. This Guidance Note applies the principles and givesspecific recommendations to achieve a satisfactory level of protection,methods to prevent fires, and routine checks/maintenance jobs for operationalstation at risk from fire.

2.0 Any previous Guidelines

Nil

3.0 Scope

This Guidance Note is specifically geared at fixed fire detection andprotection systems. The provision and use of portable equipment, such ashose pipes/reels and extinguishers by a fire fighting team is covered by theTAC/CISF Fire Manual.Recommendations are made for prevention/detection/protection against fire,for inspection, for testing and maintenance, and for operational needspertaining to the fire detection and protection equipment.

4.0 Fire Hazards and Prevention

The various hazards in a power station and the methods to prevent these aregiven in the following table.


205

S. No. Area Fire hazard Fire prevention

4.1 Coal stockyard Self-ignition due to coal airinteraction (dry coal-wet airfrom the period of March toJune is the most criticalcombination and moist coal-dryair the most favorablecombination)

1. Coal to be visible as wet whilestacking2. Fresh coal not to be stacked overold coal3. Coal to be stacked layer by layer(each of 1–1.5 M height) withcompaction of each layer4. Regular spray of water over coalyard to be done5. Stacking to be done intrapezoidal stockpile and not inconical form6. Proper records of period ofstacking to be maintained and theprinciple of FIFO (First In FirstOut) to be adopted

4.2 Bulldozers,pay-loaders, etc.

Coal dust and oil depositscombined with hot exhaustpipes, fuel oil tank, fuel oilleakages, cables

Regular cleaning of enginecompartment, inspection to checkfor any fuel leakage

4.3 Coal conveyors 1. Maintenance activitiesinvolving welding/gas cuttingleading to weld spatter oncoal/conveyor2. Friction caused by

(a) Belt with steel frame(b) Jammed idler(c) Jammed conveyor belt

due to choking of chute butpulley rotating3.Fluid coupling failures4. Overfilled gear box5. Self-ignition of accumulatedcoal dust at concave contours ofconveyors6. Loosely laidwires/cables/welding cableswith exposed joints

1. Regular cleaning and inspectionof all areas of CHP2. Chute block switches to be keptin service to alarm chute choking3. Pulley, idlers, gear boxes, fluidcouplings not to be overgreased/over filled4. System of hot work permit to befollowed during welding/cutting jobin bunker floor. CISF man to bepresent along with portableextinguishers, ready hose, etc5.Only fire retardant (FR grade) beltto be used including bunker sealingbelt, ILMS belt6. Belt not to rub steel work7. While welding any chute/hopperlined with rubber/polymer liners,special care to be taken to cool theliner8. Adequate illumination in all areasof CHP9. Coal dust accumulation onmagnets and its cleaning belt to beavoided as temperatures are highthere10. Loose wires/cable/weldingleads with open joints to be avoided11. Belt flapping to be avoided byinstalling rollers mounted oncarrying side

(continued)

206 Appendix B: Fire Protection of Power Stations

(continued)


4.4 Coal bunkers 1. Feeding of hot coal fromstockyard, which may be aboutto burn2. Residual coal sticking tobunker walls for a long periodsresulting in self-ignition3. Any draught of air throughthe coal in bunkers, particularlycompressed air from air blastequipment4. Low bunker level coupledwith unsatisfactory isolationfrom feeder/mill withsubsequent pressurization offurnace causing hot gases topass through the bunker5. Bunker conveyor fires

1. Residual, compacted coal shouldbe avoided in bunkers and bunkersshould be emptied and cleanedthoroughly during overhaul of unit2. Bunker gates to be maintained toensure that they close properlywhen bunker is not in use3. Hot coal should not be fed intothe bunkers from stockyard4. System of hot work permit to befollowed during welding/cutting jobin bunker floor5. Availability of bunker levelindication along with annunciationfor low bunker level to be ensured

4.5 Coal feeders 1. Hot or burning coal passingfrom coal bunkers2. Fires in mills particularlyduring start-up or shut-downperiods3. Friction due to mechanicalfailure4. Welding/gas cutting etc.5. Residual coal in pockets offeeder

1. Routine cleaning of feeder frominside to reduce extent of residualcoal left compacted in dead spaceswithin the feeder2. Bunker gates and mill dampers tobe maintained to prevent passage ofcombustion products from fires intothe feeders or elsewhere in thesystem3. The system of hot work permit tobe strictly followed duringwelding/gas cutting jobs4. Periodic checking of feederprotection on “No coal on belt” tobe ensured

4.6 Coal mills and P.F. piping

1. High mill outlet temperaturedue to coal flow interruption2. Low level of coal in ballmills

1. Appropriate fire detection systemto be maintained in both runningand standby mills2. Instrumentation ofmeasuring/maintaining level of coalin ball mills and of measuringsound level to be maintained3. Proper start-up and shut-downprocedures to be maintained4. Mill inerting system to always bekept in service5. Auto closing of HAG from milloutlet temperature high protectionis to be kept in service

(continued)

Appendix B: Fire Protection of Power Stations 207

(continued)


4.7 Boiler burnerfronts

1. Ignition of preheated fuel oilon hot boiler casing/steam pipes2. Rupture of flexible hoses3. Leakage of PF pipes4. Faulty ignitors coupled withleaking oil

1. Steam pipes for oil atomizationare to be thoroughly insulated2. Prompt attention to defects onburner connecting hoses and pipework3. No spillage of oil around burnerarea during removal of burnercarrier for tip cleaning. In case ofoil leakage, soaked insulation to beremoved and re-insulation to becompleted4. Minimum electricalequipment/cables/junction boxesnear burners to be located5. Ignitor faults to be immediatelyattended6. Oil waste, rag, and combustiblematerials should not to be allowedto accumulate7. Periodic checking of ignitereffectiveness to be done

4.8 Fuel oil storagetanks

1. Greater risk during venting,gassing, and filling operationsof light fuel oil2. Leakage of tank3. Dry grass around tanks4. Oil spillage5. Unclean surroundings6. Soaked insulation7. Electrical tracing

1. Precautions to be taken duringtank emptying, cleaning, tankinspections, vent inspections, andother maintenance work (includingelectrical/lighting work).Welding/cutting to be avoided. Ifcarried out, all precautions must betaken2. Entry to bunded area to berestricted to authorized personsonly3. Filling lines to be purged androad tanker connections should bekept secure when not in use4. Recycled oil to be cooled tobelow the flash point beforereturning to storage tanks5. Excess temperature safetysystems and alarms to be installedon heater banks6. All areas within the bund wallsmust be free of vegetation and othercombustible materials

(continued)


(continued)


4.9 Fuel Oil unloadingand transfer pumphouse

1. Oil spillage or leakage due tofailure of joints or of ventingdue to overheating orrestrictions in system2. Heaters3. Loosely laid electricalcables/welding cables4. Drain oil stagnant inunloading pipe trenches andsurface drains

1. There should be adequateventilation in the enclosed pumphouse to keep the concentration ofoil vapors within safe levels2. Proper smoke vents andadjustable louvers at high and lowlevel3. Proper earthing of all electricalsystems4. Use of flame prooflighting/electrical appliances onlyin the pump house5. Trenches to be filled with sandand PCC on top to preventcontamination with oil6. Oil waste, rag, other combustiblematerials not to be allowed toaccumulate7. No spillage of oil8. Prompt attention to defects on oilpipes and heaters etc.9. If used, oil absorbing granulesshould be removed immediatelyafter use. Wood dust not to be usedas it is an oil-absorbing medium

4.10 Naphtha tanks andpiping

1. Leak in the system, whetherfrom bulk storage, thedistribution network, controlvalves, or naphtha pipelines atcombustion chambers2. Venting or leaking Naphthagas getting ignition due todischarge of static electricityduring tank filling

1. Gas leak detection system to bekept operational2. Entry to storage areas should berestricted to authorized personsonly3. Areas around tanks to be keptfree of vegetation and any othercombustible materials4. Earthing of tanks, otherequipment to be checked regularly5. Filling lines to be purged androad tanker connections to be keptsecure when not in use6. Prompt attention to leakagedefects

4.11 Regenerative AirHeaters

1. Carry over of unburnt liquidfuel onto the internal heatexchanger surfaces during coldstart-up2. Slow build-up of deposits ofunburnt fuel in the absence ofsoot blowing for a period oftime

1. Frequent inspection and waterwashing of air heater2. Soot blowing of air heatersspecially during start-upimmediately after bringing boilerinto service and cleaning regularlyat least once per shift at a minimum3. Oil to be burnt with maximumattainable efficiency in the furnaceby appropriate cleaning andadjustment of burners to minimizethe quantity of unburnt particles,elimination of tramp air, andconsequent chilling of the flame and

(continued)


(continued)


by ensuring that combustionchambers are gas tight4. Air heaters can be put underobservation during light up with thehelp of digital camera5. Regular cleaning, maintenanceand testing of oil burners6. Thermo-couple type firedetection system which has beenfound to be more reliable to be keptin service for monitoring air heatertemperatures7. Infra-red fire detection system,wherever provided, also to bemaintained for prompt hot spotdetection8. Burner flushing and testing fortheir sprayer leakage andatomization to be done

4.12 Turbine-generator 1. Minor leakage of lubricatingand control fluids intoinaccessible areas, lagging,drain trenches and coming incontact with hot surfaces2. Heavy oil leakage in the formof spray onto bare hot metalcaused by bursting ofpipe/flange3. Leakage of hydrogen toatmosphere4. Leakage of hydrogen intobus duct coupled with chokingof vents of bus duct5. Cables laid near hotequipment6. Looseness of current carryingbolts, carbon brushes

1. Oil leaks, if any, should becollected nearest to the leak2. Prompt attention to oil leakages3. Good housekeeping.Accumulation of rubbish should beavoided4. Dispensing point of flammableliquid to be kept away from turbinehall5. Seepage of oil into insulationshould be avoided6. Any increase in consumption ofhydrogen to be thoroughlyinvestigated and rectified7. Adequate ventilation of TG hall8. Any welding/gas cutting work tobe done only after issue of hot workpermit9. Steam pipes to be thoroughlyinsulated10. In case of oil leakage, soakedinsulation to be removed andre-insulation to be done

4.13 Mineral oil filledtransformers

1. Electrical faults inside thetransformers including tapchanger failures2. Oil leakage fromtransformers3. Bushing failure4. Rupture of transformer tankbody caused by internal faults

1. Oil leakages to be promptlyattended to2. Vegetation, rags, etc. should notbe allowed around transformer3. Routine checking of cooling fansand pumps, operational parameters4. Soaking pit to be inspectedregularly and cleared as necessaryso as to avoid saturation5. DGA (dissolved gas analysis) tobe done regularly for transformers,

(continued)


(continued)


and any defect indicated should beattended to as early as practicable6. Condition monitoring oftransformers by thermo-visioncameras, acoustics methods shouldbe done

4.14(a)

Cablegalleries/vaults

1. Overheating of cables/cablejoints up to temperatureconditions high enough to bringthe plasticizers of PVCcompound into a volatile state2. Short-circuit creatingsufficient heat3. Accumulation of coal dust,flammable debris, cardboardpackages, fuel and lubricatingoils4. Welding/cutting inside cablegallery5. Heating during installation ofheat-shrinkable cable joints

1. Cable galleries/vaults to be keptclean and free of all extraneouscombustible materials and not to beused as storage and office areasRegular inspection of cablegalleries2. Access to cable galleries to berestricted3. Proper ventilation to be provided.4. All cable entry points to cablegallery to be fire sealed5. Fire barrier walls to be providedbetween cable tunnels of units andfire doors to be kept closed6. Loosely laid wires to be avoided7. Lighting fittings, lighting wires tobe inspected regularly8. No welding work to be done incable galleries9. Any leakage of fuel/lubricatingoil into cable gallery to beimmediately attended10. Ingress of coal dust from boilerside must be avoided11. Any overheated joint should berepaired at the earliest12. Proper illumination in the cablegallery to be maintained

4.14(b)

Cables in trays inboiler area

1. Accumulation of coal dust,flammable debris, cardboardpackages, fuel, and lubricatingoils2. Welding/cutting inside cablegallery3. Hot flue gas/ash from boilerfurnace during furnacepressurization4. Heat radiation/hightemperature due to vicinity offurnace, p.c. pipes, hot air ducts

1. Cable trays to be covered withaluminum sheet from top2. Cable trays to be regularlyinspected and cleaned3. Loosely laid wires to be avoided4. Care to be taken during gascutting/welding near/above cabletrays5. Any leakage of fueloil/lubricating oil on cables to beimmediately attended

(continued)


(continued)


4.14(c)

Cables in traysnear bottom ashhoppers

1. Accumulation of coal dust,flammable debris, cardboardpackages, fuel, and lubricatingoils2. Welding/cutting inside cablegallery3. Hot flue gas/ash from boilerfurnace during furnacepressurization4. Heat radiation/hightemperature due to vicinity offurnace, p.c. pipes, hot air ducts5. Hot bottom ash falling oncables during abnormaloperation

1. Cable trays to be covered withaluminum sheet from top2. Cable trays to be regularlyinspected and cleaned3. Loosely laid wires to be avoided4. Care to be taken during gascutting/welding near/above cabletrays5. Any leakage of fueloil/lubricating oil on cables to beimmediately attended6. Cables trays can be insulatedwith refractory material for limitedlengths keeping in view deratingfactors as per cable manufacturers(Cables may have to be replaced byhigher size)

4.15 Switch-gears 1. Insulating oil of circuitbreakers2. PVC cables, epoxy resinbased and paxolin/melamineinsulating material, PVCwiring, solenoids, and plasticencased relays

1. Switchgear rooms to be keptclean and free of flammable debris2. Regular inspection of switchgearrooms to be done3. Switchgear rooms not to be usedas storage areas or office space4. Proper maintenance ofswitchgears and regular testing ofprotection relays5. Proper ventilation of switchgearrooms

4.16 Gas turbines 1. Leakage of gas, Naphthafrom joints, covers etc.2.Improper burning of liquidfuel leading to its accumulationin the duct3.Leakage oflubricating/jacking oil

1. Gas leak detectors to be kept inservice always and to be regularlytested2. Gas/liquid fuel leak should bepromptly given attention3. Lubricating oil/jacking oil leakshould be attended at the earliestpossible time4. No flammable materials shouldbe allowed to be stored in theturbine hall5. Liquid fuel should be fired tomaximum attainable efficiency6. Good housekeeping.Accumulation of rubbish to beavoided7. Dispensing point of flammableliquid to be kept away from turbinehall8. Any welding/gas cutting work tobe done only after issue of hot workpermit9. Seepage of oil into insulation tobe avoided10. Adequate ventilation of TG hall

(continued)


5.0 Fire Detection and Protection Systems

Power stations must be provided with fire detection and protection systems inall hazardous areas. There are certain variations with regard to the type ofsystems due to change of technology from time to time. Common types of firedetection and protection systems are described in the following table

Fire Detection and Protection System

SN Area Detection system Protection system Remarks

5.1 Main plant TG building/block

a. Unit Turbine lube oiltanks, coolers andpurifiers

Quartzoid bulb typeheat detectors (withhydraulic detectionpipe network)

Automatic HVWspray system and fireextinguishers

b. (i) Gas turbine enclosures(If any enclosures areprovided)(ii) Gas turbinecombustion chambers

Heat detectors andvapor detectors asper manufacturer’spractice

Automatic carbondioxide gasextinguishing systemor automatic inert gasextinguishing system

(continued)

(continued)


4.17 Diesel Generatorsand DieselEngines DrivenFire Pumps

1. Leakage of fuel oil2. Lubricating oil gettingoverheated and leaked3. NRV of diesel return line totank not working

1. Permanent natural ventilationshould be provided in the dieselengine room at high and low levelsto disperse vapors and fumes2. Exhaust pipes should be suitablyinsulated to prevent ignition offlammable materials3. Fuel, lubricating oil leakagesshould be immediately attended to4. Fuel tanks should preferably bepositioned outside the building5. Instrumentation and controls ofdiesel engine to be regularlychecked and maintained6. Overloading should be avoided7. NRV of diesel return line to tankto be checked regularly8. Engine oil sample to be testedregularly9. Battery and diesel tank should besufficiently apart


(continued)


c. (i) Unit Turbine lube oiltanks, coolers, andpurifiers(ii) Turbine lube oil tankassembly in auxiliarycompartment of gasturbines (design withoutGT enclosure)



d. Central lube oil tanksassembly and purifiers

- do - - do -

e. Turbine lube oil pipes (inoil canal)

- do - (optional) Automatic HVWspray system(optional)

Feasibility to bechecked as perlayout for eachproject

f. Lube oil system (tanks,piping if any) of TD-boiler feed pump

- do - Automatic HVWspray system and fireextinguishers

g. Generator seal oil system - do - - do -

h. Cable galleries/cable vault (a) Linear heatsensing cable typeheat detectors;ionization andphotoelectric typesmoke detectors(b) - do - plus TEStypesprinkler bulbs (forlocal/auto spray)

(a) Automatic MVWspray system and fireextinguishers(b) TES type waterspray system

(b) Not beingprovided in newprojects

i. Cable vault (above falseroof and below falseflooring of unit controlrooms)

Linear heat sensingcable type heatdetectors; ionizationand photoelectrictype smoke detectors

Fire extinguishers;automatic carbondioxide gasextinguishing systemor automatic inert gasextinguishing system

Indicator of thephoto-electricand ionizationtype smokedetectors to bemounted at falseroof

j. Battery rooms (C&I andelectrical)

Electrical spot typeheat detector andionization typesmoke detectors

Fire extinguishers

k. Steam turbine bearinghousing, turbineenclosure

(a) Quartzoid bulbtype heat detectors(with hydraulicdetection pipenetwork) (optional)(b) Flame detectors,gas detectors

(a) Manual HVWspray system and fireextinguishers(optional)(b) Automatic inertgas extinguishingsystem

To be provided inconsultation withmanufacturer

(continued)


(continued)


l. All MCC and Switchgearrooms (LT/HT)

Ionization typesmoke detectors

Fire extinguishers

m. UCB and its adjoiningoffice space, Controlequipment rooms, UPS,inverter rooms,marshalling cabinet area

Ionization and photoelectric type smokedetectors

Automatic Inert gas(‘INERGEN’ or‘ARGONITE’)extinguishing system;automatic inertsystem

n. SWAS rooms – Fire extinguishers

o. Service building/facilitiesbuilding

Smoke detectionsystem

Sprinkler system, fireextinguishers

p. Along the periphery – Hydrant system Hydrant valvesand individualhose boxes/hosereels

q. Stair cases – Hydrant system andfire extinguishers

Landing valvesand individualhose boxes

5.2 Main plant boiler/WH RB block

a. Electro-static-precipitator – Hydrant system,water monitorsaround ESPs andWHRB

Landing valvesand individualhose boxes, hosereels

b. Gas turbine fuel syst.skids(gas/Naphtha/NGS/HSD)for metering/filtering etc.



c. Boiler burner front Quartzoid bulb typeheat detectors (withpneumatic detectionpipe network) orelectrical spot typedetector


d. All control rooms, MCCand switchgear rooms(ESP/VFD, ash handlingplant and other buildings)


Fire extinguishers

e. Cable galleries (ESP andVFD building)


Automatic MVWspray system and fireextinguishers

f. Boiler staircases – Hydrant system,water monitors oneither side of boilersand fire extinguishers


(continued)


(continued)


g. Coal Bunkers – Bunker inerting byCO2/inert gas/steam(optional)

h. Along the periphery – Hydrant system Hydrant valvesand individualhose boxes

5.3 Transformer yard area

a. All transformers Quartzoid bulb typeheat detectors (withhydraulic/pneumaticdetection pipenetwork)

Automatic HVWspray system hydrantsystem and fireextinguishers

Hydrant valvesand individualhose boxes

b. Along the periphery – Hydrant system Hydrant valvesand individualhose boxes

c. DG set/black start DGarea


Automatic MVWspray system and fireextinguishers

d. All control rooms, MCCand switchgear rooms(compressor house, DGset area or any other localMCC/switchgear rooms)


Fire extinguishers

5.4 Coal handling plant

a. Coal Conveyors (a) -(b) LHS cable typeheats detectors andinfrared type heatdetectors(c) Linear heatsensing cable typeheat detectors,quartzoid bulb typeheat detectors (withhydraulic/pneumaticdetection pipenetwork) andinfra-red type heatdetectors

(a) Hydrants/monitors(b) (i) Sprinklersystem(ii) Solenoid operatedautomatic MVWspray system andhydrant system(c) Automatic MVWspray system andhydrant system

Hoses to beprovided incentral hosehouses

b. Transfer points andcrusher houses

Quartzoid bulb typeheat detectors

(a) Automatic MVWspray/sprinklersystem and hydrantsystem (landingvalves and/or watermonitors)(b) Hydrants

(continued)


(continued)


c. Coal handling plantcontrol rooms, MCC andswitchgear rooms


(a) Fire extinguishers(b) Hydrants (outside)

d. Cable galleries in CHPcontrol/switchgear rooms(if any)


(a) Automatic MVWspray system and fireextinguishers(b) Hydrants (outside)

e. Transformers of rating 10MVA and above withinthe plant premises

Quartzoid bulb typeheat detectors (withhydraulic detectorpipe network)

Automatic HVWspray system and fireextinguishers hydrantsystem


5.5 Fuel oil handling

a. Fuel oil tanks(NAPTHA/NGL/HSD)HFO/LDO

Linear heat sensingcable type heatdetectors, quartzoidbulb type (withpneumatic detectionpipe network) heatdetectors

Foam injectionsystem andautomatic/manualMVW spray system(for uninsulatedtanks)

b. Fuel oil dyke – Hydrant system(hydrants and watermonitors);foam waterhydrants/monitors


c. Fuel oil pump houseequipment

‘Quartzoid bulb’type heat detectors(with hydraulicdetector pipenetwork)

(a) AutomaticMVW/foam spraysystem(b) Fire extinguishers,foam hydrants

d. Control rooms,MCC/switchgear rooms ifany


Fire extinguishers

e. Transformers of rating10 MVA

Quartzoid bulb typeheat detectors (withhydraulic detectorpipe network)

Automatic HVWspray system and fireextinguishers hydrantsystem


5.6 All Other off site area

a. All pumphouses/permanentstructure such as WTP,PT Plant etc. (other thancooling towers)

– Hydrant system(hydrants and/orwater monitors) fireextinguishers


(continued)


(continued)


b. Miscellaneousswitchgear/MCC andcontrol rooms


Hydrant system(hydrants and/orwater monitors) andfire extinguishers

c. Transformers of rating 10MVA and above withinthe plant premises

Quartzoid bulb typeheat detectors (Withhydraulic detectorpipe network)

Automatic HVWspray system, hydrantsystem and fireextinguishers


d. Administration building(periphery)

– Hydrant system Hydrant valvesand individualhose boxes

e. Administration building(staircases)

– Hydrant system andrire extinguishers


f. Communicationbuilding/SATCOMbuilding if any switchgearroom, control/cubicleroom


Fire extinguishers

g. Communicationbuilding/SATCOMbuilding (periphery)

– Hydrant system Hydrant valvesand individualhose boxes

6.0 Inspection, Testing and Maintenance Requirements of Fire Detectionand Protection SystemsThe recommended inspection, testing, and maintenance requirements for firedetection and protection systems are given below.

6.1 Inspection, Testing and Maintenance Requirements for Hydrant Systemand Fire Water Pump House

Frequency Checks

Daily 1. Check and record discharge pressure of each electric and diesel driven pump(including booster pumps) after running it at least for 5 min daily2. Check and record pressure gauge reading of firewater header3. Check and record pressure gauge readings of hydrant system at the highestand farthest points and other strategic points. These should be 3.5 kg/cm2

(minimum)4. Check level of water in the priming tanks to ensure that the foot valve of thepump is not leaking5. Check main firewater header, pipes in the pump house for anyleakage/damage

(continued)


(continued)

Frequency Checks

Weekly 1. All hydrant valves and monitors to be examined systematically to ensure thatall valves and spring catches are maintained in good condition along withhand-wheels, couplings, lugs, etc.2. Inspect hydrants for any obstruction of approach to these due to vehicles, etc.3. Open randomly selected valves one by one and observe flow of water for ashort time. Close the valves. The whole operation of valves should be smoothand there should not be any leakage4. Inspect all hose boxes to ensure that these contain the required number ofhoses, branch pipes, and nozzles5. Open air release valves on the main pipes in order to expel trapped air6. Inspect hose reel installations and ensure that their isolating valves are closed7. Inspect isolating valves for valve position and for any leakage8. Check valve pit for proper cleanliness and ensure that it is not flooded and isin good repair, readily operable condition

Frequency Checks

9. Check level and specific gravity of electrolyte in the batteries of dieselengines10. Check that automatic start sequence of diesel engine-driven pump isoperative. Run each diesel engine for about 30 min under load (not less than60 % operating load) until the time operating parameters such as exhausttemperature, closed circuit water temperature, lubricating oil temperature,lubricating oil pressure, etc. are stabilized. Check whether operating parametersare within recommended rangeCheck exhaust pipes of each diesel engine for leakage, chokage, andoverheating when the pump is running11. Check battery charger panels for proper functioning12. Check fire pumps control-cum-annunciation panel for proper functioningand alarm/annunciation13. Check temperature of pump house14. Check all auxiliary equipment such as battery charger, compressor, waterpumps, and diesel fuel level15. Carry out flow test as detailed below:(a) Select hydraulically most remote hydrant and place a pressure gaugemounted on a blank cap adjacent to it(b) Connect two or more hose pipes with nozzles each 30 m long athydraulically most remote hydrant and adjacent valves(c) With a pump running at its maximum pressure, with other hydrant valvesclosed, flow water through the hose reels with valves fully open. Note downreadings of pressure gauges mounted adjacent to hydraulically most remotehydrant valve and in the pump house. The running pressure should be between3.5–5 kg/cm2. This test should be repeated with different pump next week byrotation. (Alternatively, the pressure gauge can be mounted at the hydraulicallymost remote hydrant also instead of adjacent one). Test should be rotated fordifferent locations which are hydraulically far or are hazardous16. Change over to other pumps as per ‘Change Over Schedule’

(continued)


(continued)

Frequency Checks

Monthly 1. Clean strainers of spray pumps (in case of clarified fire water site may changethe frequency of cleaning the strainers)2. Check that connectors of battery are clean and free from corrosion andproperly connected. Smear a little petroleum jelly on them and on the batteryterminals3. Top up cells with distilled water, if required4. Carry out monthly maintenance of diesel engine as per manufacturer’srecommendation5. Measure vibrations of pumps and gear boxes

Quarterly 1. Clean and examine pump coupling for signs of wear, general damage,looseness, and misalignment2. Carry out quarterly maintenance of pump and motor and diesel engine as permanufacturer’s recommendations3. Inspect fan belts of diesel engine for slackness and wear. Adjust/replace ifnecessary4. Clean crankcase breather (use clean fuel for cleaning) by using air

Frequency Checks

5. Remove air filter element and shake out excess dirt by gently tapping on a flatclean surface6. Inspect exhaust pipe work for any damage, leakage, or choking and clean itthoroughly.7. Check and clean terminals of electric motors. Tighten connections, if required8. Reassemble air compressors using new gaskets9. Inspect compressor delivery filter10. Carry out quarterly maintenance of air compressors as per manufacturer’srecommendations11. Adjust the gland assembly by tightening the gland adjusting nuts on eitherside of split gland collar. Replace gland packing if it has hardened

Yearly 1. Overhauling of pump and motor to be performed per manufacturer’srecommendation2. Yearly maintenance of diesel engine to be done per manufacturer’srecommendations including:(a) Inspection and cleaning of fuel injectors(b) Thorough checking of diesel engine cooling system for leaks, blockages(flushing, if required, to be done with clean water)(c) Inspection of starter motor and replacement of carbon brushes, if necessary(d) Inspection and cleaning of engine exhaust manifolds and pipes andreplacement, wherever necessary(e) Inspection of air filter and replacement of air filter element, if required3. Painting of stand posts, overground pipes, and risers is recommended4. Carry out hydraulic test of pipelines to detect leakages5. Remove suction filter, cylinder head and valve plate assembly of aircompressors and clean. Inspect valve plates and counter plates. Replace, ifnecessary

Every 2years

1. All isolating valves to be dismantled and thoroughly overhauled2. Various pressure/temperature switches/gauges to be calibrated

Every 5years

Drain, clean, repair, and return to service all pump suction tanks for the systems


6.2 Inspection, Testing and Maintenance Requirements for SprinklerSystem

Frequency Checks

Weekly 1. Check water pressure gauge to ensure that requiredpressure is maintained2. Check that sluice valves are strapped to their normaloperating mode3. Check that alarm(s) is operative4. Check alarms function correctly

Quarterly (in addition toweekly requirements)

1. Check that water supply arrangements (including back-upsupplies) are in order. Operate valves and carry out a valvedischarge test2. Operate main stop and zone isolating valves over fullrange. A non-hardening packing should be used in valveglands. Restart valves3. Check back pressure valves for correct function. Inspect allsprinkler heads for freedom from corrosion and correctorientation4. Painted sprinkler heads should be replaced

Annually 1. Replace a few sprinklers by opening nozzles to start spray.Measure the runningpressure at the hydraulically most remote point. It should bemore than 1.4 kg/cm2

2. Carry out hydraulic test of pipelines to detect leakages3. Various pressure/temperature switches/gauges to becalibrated.

Every statutory outage Pressure vessels should be examined internally and theopportunity taken to repaint with rust-resisting paint

Every 5 years Drain, clean, repair and return to service all pump suctiontanks for the systems

6.3 Inspection, Testing, and Maintenance Requirements for High- andMedium-Velocity Systems

Frequency Checks

Weekly 1. Check main water and air/water detection line pressure gauges toensure that required pressure is maintained2. Check that sluice valves are strapped to their normal operatingmode3. Open air line drain valve and blow out condensate4. Check tank water level5. Check that alarm(s) is operative6. Test alarms7. Operate drains and main vent valves8. Check for any leakage of air/water from detection/main lines9. Check for correct position of local/manual selector switch

(continued)


(continued)

Frequency Checks

Monthly 1. Check for proper functioning of solenoid valves forremote/manual operation and local/manual operation by energizingsolenoid valves but not allowing spray to take place2. Check quartzoid bulbs and spray nozzles for properpositioning/orientation

Quarterly (in addition toweekly requirements)

1. Check that water supply arrangements (including back-upsupplies) are in order and operate valves and carry out a valvedischarge test2. Operate main stop and zone isolating valves over full range.A non-hardening packing should be used in valve glands. Restartvalves. Trip and reset deluge valves3. Test the deluge system by doing actual spray. Where plantoperations prevent routine testing of fixed water sprays,consideration should be given to conducting a trial of the equipmentduring a plant overhaul4. Check back-pressure valves for correct function. Inspect allsprays and nozzles for freedom from corrosion and correctorientation. Painted detector heads should be replaced5. Examine piping to ensure that it is corrosion free, is properlysupported and is painted6. All electrical and hydraulic alarms and their initiation devicesshould be checked7. Check spray nozzles for proper orientation8. Operate water spray system by releasing pressure from detectionline after taking precautionary measures. Observe the spraycoverage and nozzles for any choking, wrong directional mountingIn the case of spray system of transformers, check that the top ofspray cones are below turret of bushings. Reset deluge valve9. Clean strainers after the spray

Annually 1. Overhaul all control valves, isolating valves and deluge valves2. Alarm valves, isolating valves to be dismantled and overhauled3. Various pressure/temperature switches/gauges to be calibrated4. Flush detection and spray lines and clean all nozzles5. Carry out hydraulic test of pipelines to detect leakages

Every statutory outage 1. Pressure vessels should be examined internally and theopportunity taken to repaint with rust-resisting paint2. Test the deluge system by doing actual spray. Where plantoperations prevent routine testing of fixed water sprays,consideration should be given to conducting a trial of the equipmentduring a plant overhaul3. Carry out a full flow pump test for a minimum of 6 h4. Adequate steps should be taken to prevent vulnerable itemssuffering damage from water ingress and to ensure that spraypipework is completely drained afterward

Every 15 years Drain, clean, repair and return to service to service all pump suctiontanks for the system


6.4 Inspection, Testing, and Maintenance Requirements for Foam Systems

Frequency Checks

Weekly 1. Check level of foam in tanks2. Check position of valves3. Check for any leakage etc. of foam4. Check yard foam spray hydrant valves for hand wheel, coupling and itslug etc.

Quarterly 1. Check all pressure gauges register properly. All control valves shouldbe properly set and access to valves, pumping in points and proportioningequipment is maintained. Manipulate and repack valves2. Inspect and clean strainers, check alarms auto control valves, indicators,manual tripping devices, vapor seals, piping, level of foam liquid and levelof liquid and level of liquid in any gas cylinders3. Inspect external surfaces of the foam concentrate tank for signs ofleakage and corrosion

Every 6 months 1. Sample and test foam concentrate2. Withdraw a sample of foam concentrate from the foam tank and test it3. Turn foam maker by 180° so that the foam will come out on ground andopen the isolating valve of foam/water line for 5 min. Observe the qualityof foam being made and the rate at which foam is being sucked byventuri/pump4. Compare it with designed value

Annually 1. Replace the foam concentrate as and when the life guaranteed bysupplier or as per test, expires2. Inspect internal surface of foam concentrate tank before replacement offoam tank concentrate to ensure that it is free from dirt or foreign materialsand the epoxy coating is intact. If required, touch up amounts of epoxy(not the ordinary paint) may be applied3. Clean and service all valves, pipes, in-line inductor/pump4. Carry out hydraulic test of pipelines to detect leakages5. Various pressure/temperature switches/gauges to be calibrated

Every statutoryoutage

Discharge test, flush, and reinstate

6.5 Inspection, Testing, and Maintenance Requirements for CO2 Systems

Frequency Checks

Quarterly Check pressure gauges register properly, all control valves are properly set andaccess to valves is not obstructed. Examine cylinder contents level and replacecylinders as necessary

TwiceAnnually

Check that correct number of cylinders are in service; piping, alarms, lock-offsmanual and emergency releases drop curtains etc. are properly located andfunction correctly, also that any interlocks operate properly

At 10 Years Deluge test, return cylinders for stretch test and refill


6.6 Inspection, Testing and Maintenance Requirements for Halon Systems

Frequency Checks

Quarterly Check pressure gauges register properly, all control valves are properly setand access is not obstructed. Examine cylinder content level and replacecylinders as necessary

Twiceannually

Check that correct number of cylinders are in service; piping alarm lock-offsmanual and emergency releases, drop curtains, etc., are properly located andfunction correctly, also that any interlocks function correctly

5 times a year Withdraw and pressure test cylinders

Dischargetesting

Consult Industrial Safeguards Branch

6.7 Inspection, Testing, and Maintenance Requirements for DetectionSystems

Frequency Checks

Monthly 1. Functional test of detection system, if required, as part of the protectionsystem. Testing in a particular area2. Inspect physical position of LHS cable, IRD type detection systems for anydamage and test these by simulation and observe annunciation. In case of IRD,a moving heat source can be used to generate fire signal

Quarterly 1. Functionality test2. Check better condition, where applicable3. Check and test all control/annunciation panels, i.e.,

- Main fire alarm panels- Local fire alarm panels- Fire station repeater panel- Coal conveyor belt stooping panel- Cable gallery TES/Zone operating panel.

Annually 1. Check detectors (except once only detectors) by an in situ test using heat orsmoke as appropriate. Withdraw air heater poles for this test2. Check system integrity

Every 4Years

Carry out electrical checks as specified in IEE regulations


Appendix CSystem for Plant Modifications

1.0 Purpose

The directive specifies the system for modifications in plant/equipment atthe power station.

2.0 Scope

2.1 This directive shall be applicable to all modifications (or design change)to plant/equipment/systems/components of existing power stations afterthe date of issue of the directive. For modifications made prior to issue ofthis revision, procedure described at clause no 5.7 should be followed

2.2 In the case of power stations set up after the date of issue of this directive,the directive shall apply from the date the PG test is conducted or date ofcompletion of warranty of the contractor, whichever is later

2.3 The directive shall not be applicable to modifications/design change to becarried out under contractual obligations of the contractor under thecontract irrespective of the period when such modification is carried out.However, in such cases where modification is necessary to be carried outbefore expiry of the warranty period or before PG Test, whichever is later,written consent of the contractor for such proposed modification shouldbe obtained before carrying out the modification. In all such cases, anapproval from the Engineering Department must be obtained, which shallbe routed through Operation Services (OS)

2.4 The reference design or datum for each plant/equipment/system/component of the power station shall be as per the last documentapproved by Engineering or the original design drawings

2.5 The directive shall not be applicable to ‘defects’ or ‘repairs’ which requireequipment to be reinstated to the original condition

2.6 For the purpose of this directive, system, or component shall also includeload-bearing structures


225

3.0 Previous Guidelines

If any

4.0 Records of Revision

The entire document has been redrafted after review by the SystemReview Group

5.0 Process

5.1 Definition

5.1.1 For the purpose of this directive, the term modification or design changeshall have the following meaning or interpretation:

5.1.1.1 ‘Modification’ shall include

(i) A repair or replacement of a system/equipment/component where itinvolves a change to its reference design or datum, geometry, ormaterials.

(ii) Any change to the settings, or mode of operations, of a componentin a control, interlock or protection system (including computersoftware).

(iii) Any addition or deletion of a system, component, or of a completesystem or complete equipment.

5.1.1.2 The following shall not be construed as modifications for the purpose ofthis directive:

(i) The repair/replacement/modification of minor components orequipment as may be specified by the Head of the Station in theLocation Management Instruction issued for implementation of thisdirective. However, details of these shall be intimated to COS.

(ii) The overriding of any interlock (protection by pass) or any change tothe settings or mode of operation of any component in a control,interlock, or protection system (including computer software) whichis authorized, implemented, and recorded in accordance with aLocation Management Instruction, provided that no such override orchange remains in place for a period exceeding 72 h. If it is toexceed 72 h, it will be treated as a modification and will requireregistration and assessment in accordance with this directive.

5.2 Need for Modification

The need for modification or design change may arise from:

• Recommendations of an enquiry report/audits.• Proven best practice elsewhere in the utilities known globally.• Improvement in efficiency/commercial parameters.• Statutory/legal requirements.

226 Appendix C: System for Plant Modifications

• Feedback from major failures/trip analysis.• Constraints faced during plant operation.

5.3 Proposal

5.3.1 In order to maintain a record of all modifications or design changes toplant/equipment/systems/components, all proposals for modificationsshall be registered with the Station Planning department. Furthermore,to ascertain the suitability of the modifications, all proposals will beassessed technically as per the system laid down hereunder:

5.3.2 A format for registration of all proposals for modification or design changeis given in Appendix I (Modification Registration Performa/DesignChange Request).

5.3.3 The proposal for modification/design change may be initiated by theconcerned department at station/engineering/research and developmentothers, and sent to Incharge O&M of the station for formal initiation. Theproposal shall give sufficient details of modification i.e., name of theplant/equipment/component/system, its location, name of thesupplier/manufacturer, reasons for modification, approving authority, etc.The details of modification shall be maintained by the Head of Planningdepartment of the power station in the Performa (request for design change)given in Appendix 1. A flow diagram showing the process of the system forplant modification/design change is shown in Appendix 2.

5.4 Categorization of Modifications

The category of technical assessment required i.e., internal or external tothe station, shall be approved by the appropriate authority based on the notegiving details of modifications received from the head of the power station.

5.4.1 For the purpose of this directive, technical assessment of proposals shallbe of two types, i.e., Category A (requiring external assessment) andCategory B (requiring internal assessment).

5.4.2 Category A assessment will be required in case of all proposals which, ifinadequately conceived or executed, could lead to the following:

• A major safety/environmental implication.• A major plant failure (boiler, turbine, generator, transformer, cooling

water system, ash disposal system, coal handling plant, switch yard).

Appendix C: System for Plant Modifications 227

Category A assessment will also be required in case of

• Any change in the protection scheme for main equipment i.e., boiler,turbine, or generator.

• Modifications related to improvement of efficiency commercialparameters of major equipment.

5.2.3 Category A assessment may not be required:

(i) If repair/replacement of any system or component or equipment iscarried out without changing the original design or datum and usingapproved procedures relevant to such repair.

(ii) If replacement of any system or component or equipment is beingdone due to age or obsolescence by a modern equivalent with nochange in original design or datum, materials or operatingenvironment.

5.5 Category A Assessment

The proposals for modification of all Category A proposals as definedabove will be submitted for technical approval to the Engineeringdepartment by the power station. Engineering may seek the comments ofother departments of Corp. Centre e.g., R&D, Safety, etc. Technicalapproval from Engineering will be sent to the station. Thereafter, theproposal should be submitted for approval of Competent Authority by thepower station as per DOP. If required, detailed engineering will be doneby the Engineering department and sent to the station for implementationof the modification.

5.6 Category B Assessment

Proposals which do not qualify for category A assessment will becategorized as Category B. The proposals involving category Bassessment will be scrutinized and assessed by a team comprisingrepresentatives of O&M, FQA, and Technical Services departments at thestation in consultation with Operation Services & Engineering, andapproved in accordance with DOP if any costs are involved. After themodification has been completed, a post facto approval will be sought bythe station in charge from the Engineering department detailing therequirement for the modification, implementation status, etc. Anyrecommendations from Engineering shall be implemented by the Station.


5.7 Modification Made Prior to this Directive

The station will compile the modification with relevant details made priorto the issue of this document. For all the modifications which have notbeen vetted or approved by Engineering, the station will be required tointimate the same to Engineering with the relevant details, pre- and postmodification assessment and amendment to documents and drawingswherever applicable. Any recommendations from Engineering shall beimplemented by the station.

5.8 Implementation of the Directive

Each head of the power station is responsible for ensuring that thedirective is implemented at the power station by issuance of locationmanagement instructions (LMI).

5.9 Amendment of Station Documentation

All relevant drawings, operation and maintenance instructions, details inthe stores catalog, and other requirement for modifiedequipment/system/component will be amended before the first modifiedsystem or component is commissioned. The amended documentation asbuilt drawings must be approved by the same authority that initiallyapproved the documentation/drawing. The master list of documents anddrawings must be revised accordingly. The issue of these modifieddocuments as stated above shall be controlled and the old version will bestamped as superseded. Where the modification is to be progressive,covering various areas of the power station, then care must be taken toclearly identify the system or component or equipment to which theamended documentation applies. The necessary records will be updatedin the Modification Register Performa.

5.10 Execution of the Plant Modification

After the receipt of the detailed Engineering report, the Planningdepartment will find out whether any procurement is required. Ifprocurement is required, then the Maintenance department will initiatethe procurement. After receipt of the material, the Maintenance depart-ment will execute the modification with relevant quality checks by theField Quality department. Commissioning will be done by the Operationsdepartment. Reports, as required, will be generated and given to thePlanning department for consolidation.


5.11 Post Modification Assessment

After the system or component has been commissioned, an assessmentshall be carried out by the head of O&M of the power station to determine

(i) that the modification has been implemented in accordance with theapproval.

(ii) the resulting change in performance as compared to that proposedoriginally.

(iii) that the integrity of plant safety has not been impaired.

5.11.1 Where appropriate, this assessment shall include such tests and trialsspecified in the approval.

5.11.2 A report shall be generated by the head of O&M of the station stating theimprovement after the modification with respect to pre-modification statusand shall be sent to the head of Operation Services (OS). Final acceptanceof the modification shall be given by OS in association with Engineering.In case of non-acceptance of the modification, necessary analysis shall bedone by Planning along with the concerned department(s). Eithercorrective action is taken and post modification assessment is carriedout or pre-modification status is restored. The site may also initiate a freshproposal for modification.

5.11.3 The Modification Register Performa should then be updated completelyand shall be circulated to all concerned.

5.12 Compliance of Directive

Compliance of this directive shall be verified during the course of internaland external LMI audits and a technical audit of the station by OS.

5.13 Records

The following records shall be maintained by the Planning department atthe station:

• Records of modifications as per Modification Registration Proforma.• Records of approval of modification.• Reports of post modification Assessment.

6.0 Review

The head of Corporate Operation Services will be responsible forreviewing the document on a 3-year basis or as necessary.


Appendix 1 Modification Register Proforma/Design Change Request

MODIFICATION REGISTER Serial No.:

For Plant, Apparatus and Structure Date Proposed:

1. PROPOSED FOR MODIFICATION AT POWER STATION

Station Code:Purpose of Modification (State justification)Component / System:

Manufacturer :

Details of Proposal (including time schedule):a) Whether the modification suggested is for phasing out

an obsolete item, if so, details.b) Whether the modification suggested is for

indigenisation, if so, details.

Effect on interchangeability

Any identified safety hazard / Environment impact on account of the Plant Modifications

Requirement for amending documents Yes No

Pre-modification Condition (e.g. Operational Performance, Emissions, Plant Life. etc.):

Approval of Head of O&M Date:

Approval Head of Power Station Date:

2. REVIEW BY APPROPRIATE AUTHORITY & CATEGORIZATION

Category of modification as per note ref. no. received.

Date


3. APPROVALS

Final approval from Engineering Note Ref. Date:

i) Not Approved Note Ref. etc. Date:

4. IMPLEMENTATION

(After work has been completed, record the means by which modification has been achieved. State Contract Number, etc.)

Signature:Concerned Dept. I/CDate:

5. COMMISSIONING

Confirm that commissioning has been done as per procedure and the relevant protocol; has been filled up.

Signature:Operation Dept. I/CDate:

6. AMENDMENTS TO DOCUMENTATION

Confirm the completion of amendments to operating/maintenance Instructions, station manuals, plant status records, stores records, drawings, training programmes, etc.

Signature:Concerned Dept. I/CDate:

7. POST MODIFICATION DATA

Date of modification

Signature of Initiator of Proposal: Date:

Confirm completion of commissioning and state the condition after modification compared to the original data recorded in Section 1

Relevant Report Ref. etc

8. CIRCULATIONTO DATE SIGNATURE

Note:1. This Directive applies only to modifications; it does not apply to `defects' or

repairs which require equipment to be reinstated to the original condition.2. Section 2 `Categorization'-The selection of Assessment Category is the

responsibility of the Appropriate authority.


Appendix 2 Flow Diagram for Process of Modification/Design ChangeAppendix II


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