58044373 Water Treatment Handbook UNITOR

WaterTreatmentHandbook

C H E M I C A L S

U N I T O R ASAMail: P.O. Box 300 Skøyen, N-0212 Oslo, NorwayOffice: Drammensvn. 211, N-0277 Oslo, Norway

Tel: +47 22 13 14 15. Fax: +47 22 13 45 00Tlx: 76004 UNTOR N

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Marine Chemicals

Water TreatmentHandbook

A PRACTICAL APPLICATION MANUAL

1st Edition

Unitor ASA, P.O. Box 300 Skøyen, N-0212 Oslo, NorwayOffice: Drammensveien 211, N-0277 Oslo, Norway

Tel: +47 22 13 14 15. Fax: +47 22 13 45 00Tlx: 76004 UNTOR N

ID. NO. 08 173 REV. NO. 00 LOBO 09.97 5K COUNTRY OF ORIGIN: NORWAY

INDEX Page

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV

1 Water Treatment Philosophy and Overview . . . . . . . . . . . . . . . . . . . . . . . 5

2 Basic Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Problems of Boiler Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4 Types of Boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5 Boiler Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

6 Unitor Boiler Water Treatment Products . . . . . . . . . . . . . . . . . . . . . . . . . 28

7 Combined Treatment for Low Pressure Boiler Water . . . . . . . . . . . . . . . 29

8 Tests for Boiler Water, Low Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

9 Unitor Coordinated Treatment Products . . . . . . . . . . . . . . . . . . . . . . . . . . 34

10 Tests for Boiler Water, Medium Pressure . . . . . . . . . . . . . . . . . . . . . . . . 38

11 High Pressure Boiler Water Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

12 Boiler Wet Layup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

13 Boiler Blowdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

14 Chemical Cleaning of Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

15 Diesel Engine Cooling Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 60

16 Reporting Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

17 Water Tests, Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

18 Evaporator Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

19 Marine Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

20 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

IIIWATER TREATMENT HANDBOOK

FOREWORDThis manual has been edited to specifically apply to Unitor’s Marine ChemicalMarket. It has been prepared to give the marine engineer basic insight intothe chemical water treatment of marine propulsion boilers, low pressure auxiliary and exhaust boilers, diesel engines, evaporators and other associated equipment.

The purpose and design of Unitor marine chemical products is to providethe marine engineer with the most environmentally-friendly products and withthe most practical and simple applications of their use.

Unitor has designed the Spectrapak test kits to accurately determinechemical concentrations of the various products and systems they are beingused to check. The Spectrapak tablet system is the most practical and economical testing system available to the marine engineer. Our water treatment programmes are designed to utilize the simplest water testing procedures along with the assistance of our worldwide service personnel andUnitor’s Laboratories which provide the technical expertise required toanswer all questions in regard to marine chemical applications.

Unitor’s products have been designed to provide the ship operator with a variety of products and systems to cover all requirements for the many different types of boiler systems and crew requirements, which will bedetailed in this manual.

Unitor has introduced the most up-to-date log review system to utilizetoday’s technology in communications and computers to provide the operatorand marine engineer with a “Rapid Response” to our log review system.

Unitor is dedicated to providing the marine operator with the most reliableproducts available in the marine chemical industry along with the many otherareas of expertise and standardisation worldwide. Our products and servicesare available 7 days a week and we are committed to maintaining this for themarine industry.

II WATER TREATMENT HANDBOOK

1 Water Treatment Philosophy and Overview

1.1 TYPES OF WATERGeneralWater could generally be described as the most important of all chemicalsubstances. Its chemical designation is H2O; the water molecule is composedof 2 Hydrogen atoms and 1 Oxygen atom.

Natural waterRaw water is the description of the water to which we have daily access. We can obtain our water from:

1. The ocean2. Surface sources (e.g. from lakes)3. Underground sources

The water will vary in composition.The natural water cycle may be as below:

While it is evaporating from the surface of a lake or the ocean into the atmo-sphere, we can designate the water vapour H2O. In the atmosphere, cloudswill form, and during suitable humidity and temperature, the clouds willdeposit water (rain). While the rain is falling towards the earth, it absorbsgases which are in the air, e.g. CO2 (Carbon Dioxide), SO2 (Sulphur Dioxide)and O2 (Oxygen).

When the water hits the earth, it absorbs additional Carbon Dioxide (frombiological degradation). The rainwater which is now slightly acid will dissolvevarious minerals from the soil.

INTRODUCTIONThis Product Applications Handbook has been designed to provide specificinformation on the variety of chemical and related products and systemsavailable from Unitor.

This handbook will give all the information required to maintain these vari-ous products, including the application of individual chemical products toproperly maintain Low Pressure, Medium Pressure and High Pressure Boilers, Diesel Engine Cooling Systems and Evaporators.

Single Function Treatment Products:1. Hardness Control2. Alkalinity Control3. Oxygen Control (Hydrazine)4. Catalysed Sodium Sulphite (Powdered & Liquid)5. Condensate Control6. Boiler Coagulant

Low Pressure Boilers, Water Treatments: 1. Combitreat (powdered)2. Liquitreat3. Condensate Control

Cooling Water Treatments:1. Dieselguard NB (powder)2. Rocor NB Liquid

Sea Water Cooling Treatment:1. Bioguard

Evaporator Treatment:1. Vaptreat

IV WATER TREATMENT HANDBOOK 5WATER TREATMENT HANDBOOK

7WATER TREATMENT HANDBOOK6 2 / BASIC CHEMISTRY

2 Basic ChemistryThe chemistry of waterIt is necessary to examine some of the basic theories in order to understandthe various problems associated with water treatment.

While rain is falling through the air, it absorbs gaseous contaminants, e.g.O2 (Oxygen), which solubility in pure water depends on temperature.

At 20 °C, 9 mg/l O2 may dissolve, and

at 50 °C approx. 5.5 mg O2/l,

and at 90 °C approx. 1.5 mg O2/l, and

at 100 °C approx. 0.0. mg O2/l,

so, the higher the temperature, the less O2 can dissolve in water.

CO2 (Carbon Dioxide) dissolves in water as follows:

CO2 + H2O > H2CO3

H2CO3 is a very weak acid. In contact with CaCO3 (ordinary lime), it is reactiveand the lime dissolves as follows:

CaCO3 + H2CO3 > Ca++ + 2HCO –3

Ca(HCO3)2 is called Calcium Bicarbonate.

SO2 (Sulphur Dioxide) is an air pollutant which stems from flue gases, so thereis usually a high atmospheric content of this gas around industrial areas.

2SO2 + O2 + 2H2O > 2H2SO4

H2SO4 is called Sulphuric Acid, and this acid also dissolves lime (CaCO3) as follows:

CaCO3 + H2SO4 > CaSO4 + H2O + CO2.

CaSO4 is called Calcium Sulphate (gypsum).

In other words, the gases dissolved in the water will increase the leaching ofthe subsoil’s minerals, so that we may have solutions in water due to:

TOTAL HARDNESS

Temporary hardness Permanent hardness

Calcium Bicarbonate Calcium SulphateCa (HCO3)2 CaSO4Magnesium Bicarbonate Magnesium ChlorideMg (HCO3)2 MgCl2

TEMPORARY HARDNESS (Alkaline Hardness) is due to bicarbonates of Calcium and Magnesium which are Alkaline in nature. They are “temporary”because when heated they rapidly break down to form Carbon Dioxide andthe corresponding carbonates which deposit as scale.

PERMANENT HARDNESS (Non-Alkaline Hardness) is due mainly to Sulphates and Chlorides of Calcium and Magnesium which are acid in nature.They are “permanent” and do not break down, but under certain conditionsdeposit to form scale of varying hardnesses.

2.1 BOILER WATER TREATMENT FUNDAMENTALSThe concept of employing water, fresh or distilled, as a power generatingsource and heat exchange medium originated and was realised with theinception of the steam generator or boiler, and has been applied most successfully and beneficially in this manner ever since.

Water has the ability to transfer heat from one surface to another, therebymaintaining the system within the correct operational temperature rangewhile generating steam to carry out work. However, water can adverselyaffect metal components under the operational conditions normally found insteam boilers and other heat exchange devices. The extent of deteriorationdepends on the specific characteristics of the water and the system in whichit is being used.

In order to counteract the detrimental properties normally attributed towater and its contaminants (dissolved and suspended solids and dissolvedgases), special chemical treatment programmes have been devised.Accepted water treatment processes and procedures are constantly beingupgraded and modernised, and new methods are being developed to complement and/or replace older ones. Unitor utilizes the most modern, practical programmes for the marine operator.

Although water from marine evaporators and boiler condensate return systems is essentially “pure”, minute quantities of potentially harmful salts and minerals can be carried by this composition and feedwater into the boiler, where they will accrue, ultimately resulting in serious problems inthe steam generating unit. In addition, the water can also contain dissolvedgases, i.e. CO2 and Oxygen, which can result in corrosion of the system.

Using unprocessed fresh water (e.g. shore water) as a makeup source canpresent some of the same problems experienced with distilled water, but inaddition, certain contaminants which are naturally present in fresh water canbe extremely destructive in boiler systems if not dealt with promptly and effect-ively. Soluble salts such as Chloride, Sulphate and Carbonate are present

as electrolytes in the untreated water, leading to galvanic and other types ofcorrosion, depending on the conditions in the system. In addition, Sulphatesand Carbonates have the potential to form insoluble, adherent, insulating“hard water” scale deposits on heat exchanger surfaces.

2.2 CONTRIBUTING ELEMENTS WHICH AFFECT BOILER WATER TREATMENT

Most dissolved mineral impurities in water are present in the form of ions.These ions contain an electrical charge which is either positive (cation) ornegative (anion). These ions can join together to form chemical compounds.

To know which ions will combine, we need to know their electrical charge.Ions of concern to us include the following:

Positive Chemical Negative Chemicalions symbol ions symbol

Sodium Na+ Chloride Cl–

Calcium Ca++ Bicarbonate HCO3Magnesium Mg++ Carbonate CO3

– –

Hydrogen H+ Hydroxide OH–

Cations will combine only with anions.

An example of this combining of ions is the action between Calcium andCarbonate. The chemical compound which forms is Calcium Carbonate.

Other impurities which will affect the boiler water treatment controlinclude Copper, Iron Oxides, oil and dissolved gases.

2.2.1 CopperCopper is introduced into a system by corrosion of Copper piping andCopper alloys. In boilers, the source of this corrosion could be dissolvedgases in the boiler water or the excessive use of Hydrazine which willcorrode Copper and Copper alloys, allowing Copper to be carried backto the boiler.

Copper in the boiler displaces metal from the tube surfaces andplates out on the tubes. This condition often occurs under existing scaleand sludge deposits, which is known as under deposit Copper corro-sion. Copper deposits are a serious problem in high pressure boilers.Waterside deposits may be submitted to Unitor for complete analysisand determination of the correct procedures to follow for cleaning.

2.2.2 OilTo prevent oil from entering condensate and feedwater systems, certain safety equipment is generally incorporated to detect, remove, andarrest such contamination.


Oil contamination may occur through mechanical failure, for example, faulty oil deflectors at turbine glands passing lubrication oil togland seal condensers and main condensers, etc., or undetected leaksat tank heating coils.

Any oil film on internal heating surfaces is dangerous, drasticallyimpairing heat transfer. Oil films therefore cause overheating of tubemetal, resulting in possible tube blistering and failure.

If oil contamination is suspected, immediate action must be under-taken for its removal.

The first corrective measure in cleaning up oil leakage is to find andstop the point of oil ingress into the system. Then, by using a Unitordegreaser, a cleaning solution can be circulated throughout the boilersystem to remove the existing oil contamination. Complete details onthis cleaning operation are covered later in the handbook.

Boiler Coagulant can assist in removing trace amounts of oilcontamination. Consult your Unitor representative for more specific recommendations.

2.2.3 Iron OxidesIron may enter the boiler as a result of corrosion in the pre-boiler section or may be redeposited as a result of corrosion in the boiler orcondensate system. Often, Iron Oxide will be deposited and retard heattransfer within a boiler tube, at times resulting in tube failure. This usually occurs in high heat transfer areas, i.e. screening tubes nearestto the flame.

When iron is not present in the raw feedwater, its presence in theboiler indicates active corrosion within the boiler system itself.

Rust, the reddish form, is fully oxidized. More often, in a boiler withlimited Oxygen, it is in the reduced or black form as Magnetite (Fe3O4).Fe3O4 is magnetic and can be readily detected with a magnet. It is a passivated form of corrosion and its presence shows that proper control of the system is being maintained.

2.2.4 Magnesium Carbonate (MgCO3)Magnesium hardness in fresh water usually accounts for about one-third of the total hardness. The remaining two thirds can normally beattributed to calcium.

Since Magnesium Carbonate is appreciably more soluble in waterthan Calcium Carbonate, it is seldom a major component in scaledeposits. This is due to the preferential precipitation of the Carbonateion by Calcium as opposed to Magnesium which remains in solutionuntil all soluble Calcium is exhausted.

Once this point is reached, any free Carbonate remaining in solutionwill combine with the Magnesium and begin precipitating out as

WATER TREATMENT HANDBOOK2 / BASIC CHEMISTRY

Besides the pure form of Silica (i.e. Silicon Dioxide), possible Silicatedeposits can form in combination with Calcium and Magnesium, whichare extremely insoluble in water and very difficult to dissolve andremove.

Besides being an extremely difficult process, the chemical removalof Silica and silicate deposits can also be very hazardous, since itinvolves the use of Hydrofluoric Acid or Ammonium Bifluoride, both ofwhich are severely destructive to human tissue by inhalation, ingestionand physical contact. In some instances, alternate acid and alkalinewashings have been used to successfully combat this problem.The only alternative to chemical cleaning is mechanical removal.

2.2.8 Calcium Carbonate (CaCO3)Calcium Bicarbonate alkalinity exists in almost all unprocessed freshwater under normal conditions. Its solubility is about 300–400 ppm at 25 °C. If heat is applied or a sharp increase in pH occurs, the CalciumBicarbonate breaks down to form Carbon Dioxide and CalciumCarbonate.

While the bicarbonate salt has been shown to be moderately soluble inwater, the solubility of Calcium Carbonate at 25 °C is only about 14 ppm.This value continues to decrease as the temperature increases, becom-ing the least where the temperature is greatest. In a boiler, this would beon the surface of the furnace tubes where contact is made with thewater. The resulting insoluble Calcium Carbonate precipitate forms“building block-like” crystals which adhere not only to one another, butalso to the hot metal surfaces, resulting in a continuous, insulatingscale deposit over the entire heat exchange area.This deposit will con-tinue to grow, building upon itself to form a thick coating until all theCalcium Carbonate produced is exhausted. If suspended matter is alsopresent in the water, it can become entrained within the crystal structure, creating a larger volume of deposit than that formed by theCarbonate precipitation alone.

If this condition is allowed to continue, heat exchange efficiency at the water/tube interface falls rapidly, resulting in an increase in fuelconsumption necessary to compensate for the decline in thermal transfer and to regain design temperature as well as steam productionrequirements. This increase in the furnace-side temperature needed to run the system at optimum conditions exposes the metal surfacesto overheating which, in turn, can cause blistering fatigue, fracture, and failure of boiler tubes. In addition, if pockets of water becometrapped beneath the scale deposits and are in contact with the hotmetal surfaces, concentration of acid or alkaline materials may occur and lead to the formation of local electrolytic cells (under-deposit corrosion).

11

Magnesium Carbonate when the solubility of this salt is exceeded.Because of this latter phenomenon, where “soft” water is used for boiler structure, any Magnesium present must be removed along withthe Calcium.

2.2.5 Magnesium Sulphate (MgSO4)Magnesium Sulphate is an extremely soluble salt, having a solubility of20 % in cold water and 42 % in boiling water. It exists as the Sulphateonly in water with a low pH. Because of its high solubility, it will not normally precipitate. The Sulphate ion, however, will be precipitated bythe Calcium hardness present if no free Carbonate exists.

2.2.6 Magnesium Chloride (MgCl2)Magnesium Chloride, like Magnesium Sulphate, is soluble in fresh water.In the high temperature and alkaline conditions normally maintained in aboiler, any soluble Magnesium ions in the boiler water become extremelyreactive with Hydroxyl ions, which may be present in high concentrationsin this type of environment.

This can result in the formation of Magnesium Hydroxide precipi-tates which form insulating scale on the boiler tube surfaces. If Chlorideions are also available, they react with the Hydrogen ions previouslyassociated with the precipitated Hydroxyl ions, to form Hydrochloricacid, thereby lowering the alkalinity of the water. If this situation isallowed to continue, the pH of the boiler water will decrease until acidconditions result in corrosion of the metal surfaces. Unlike Carbonateand Sulphate ions, the Chloride ion does not precipitate in the presenceof soluble Calcium.

2.2.7 Silica (SiO2)Silica scale is not normally found in boiler systems except in minute quantities. It can be admitted to the system when severe carryoveroccurs in evaporators processing water with a high Silica content.Other sources of such feedwater may be high Silica river or raw freshwater as well as distilled/deionized or unprocessed fresh water which has been stored and taken from cement-washed or silicate-coated tanks.

Once formed, pure Silica scale is extremely difficult to remove. Itforms a tight adherent glass-like film on metal surfaces, thereby pre-venting proper heat transfer. In addition, in steam-generating devices itcan carry over with the steam coating the after-boiler sections, particu-larly the superheater.

If a turbine forms part of the system, the Silica can deposit on theblades as well as cause erosion of the finned surfaces of the blading,resulting in imbalance of the turbine, which in turn may result in turbine failure.

10

pHThe pH of a solution is a measurement of the concentration of active acid or base (alkaline constituent) in a solution.

To give a precise definition, pH is the negative logarithm of the Hydrogenion concentration.

A simpler explanation of pH is that it is a measure of relative acidity or alkal-inity of water. In other words, it reflects how acidic or alkaline the water is.

pH is the number between 0 and 14 which denotes the degree of acidity or alkalinity.

A pH value of 7 indicates neutral. Below 7 indicates increasing acidity.Above 7 up to 14 indicates increasing alkalinity.


2.2.9 Calcium Sulphate (CaSO4)Although Calcium Sulphate is more soluble in water than CalciumCarbonate, it can be just as troublesome when present in boiler andcooling water systems. Calcium Sulphate, like Calcium Carbonate, butunlike most salts, has an inverse temperature/solubility relationship inwater. As gypsum, the hydrated form in which Calcium Sulphate is nor-mally present in fresh water, its solubility increases until a temperatureof about 40 °C is achieved. At 40 °C, its solubility is 1,551 ppm; at 100 °C,which is the normal boiling point of water, its solubility decreases to1,246 ppm, and at 220 °C it falls to 40 ppm. Calcium Sulphate reacts athigh-temperature surfaces essentially in the same manner as CalciumCarbonate and with the same effects and consequences. However,whereas Calcium Carbonate deposits are relatively easy to removeusing a comprehensive acid cleaning procedure, Calcium Sulphate isessentially impervious to the effects of normal acid descaling methodsand usually must be removed by mechanical means.

2.2.10 Dissolved GasesGases such as Oxygen and Carbon Dioxide that are dissolved in distilledor fresh water, will further contribute to the deterioration of the boilersystem. Dependent upon conditions in the system (e.g. temperature,pressure and materials of construction), dissolved Oxygen can causepitting corrosion of steel surfaces, while Carbon Dioxide lowers the pH,leading to acid and galvanic corrosion. Carbon Dioxide has the addeddisadvantage of forming insoluble carbonate scale deposits in an alka-line environment when Calcium and Magnesium are present.

2.2.11 Acidity, Neutrality and AlkalinityAll water can be classified into one of these categories. Acidity,Neutrality and Alkalinity are only very general terms. We require moreaccurate methods of testing to know the degree of each condition.When testing boiler water, it is important to understand what you aretesting for.

A. ALKALINITY. The presence of Alkalinity in a water sample may bedue to many different substances. For the sake of simplicity, the presence of Bicarbonate, Carbonate and Hydroxide contributes to thealkalinity of water.

B. P ALKALINITY. Phenolphtalein (P) Alkalinity (pH values greater than8.3) measures all the Hydroxide and one half of the Carbonate Alkalinitywhich is sufficient for our purpose of control. Bicarbonates do not showin this test as they have a pH of less than 8.4.

C. M ALKALINITY. Total Alkalinity or M Alkalinity (pH values greater than 4.3) measures the sum of Bicarbonate, Carbonate and HydroxideAlkalinity.

pH is a very important factor for determining whether a water has a corrosiveor scale-forming tendency.

Water with a low pH will give rise to corrosion of equipment.

NeutralAcidic Alkaline

1 2 3 4 5 6 7 8 9 10 11 12 13 14

D. ALKALINITY RELATIONSHIP TABLEHydroxide Carbonate BicarbonateAlkalinity Alkalinity Alkalinity

P Alkalinity 0 0 Equal to= 0 total

P Alkalinity 0 2 times M Alkalinityless than P Alkalinity minus 2 times1/2 M Alkalinity P Alkalinity

P Alkalinity 0 2 times 0equal to P Alkalinity1/2 M Alkalinity

*P Alkalinity 2 times 2 times the 0greater than P Alkalinity difference 1/2 M Alkalinity minus between M

M Alkalinity and P Alkalinity

P Alkalinity Equal to 0 0equal to M AlkalinityM Alkalinity*This is the correct alkalinity relationship for boiler water

3.1.1 Pitting Corrosion“Pitting” is the most serious form of waterside corrosion and is theresult of the formation of irregular pits in the metal surface as shown inthe figure below. Evidence of pitting is usually found in the boiler shellaround the water level and is most likely caused by poor storage proce-dures when the boiler is shut down for lengthy periods, and by inade-quate Oxygen scavenging.

Pitting corrosion.

3.1.2 Stress Corrosion“Stress corrosion” cracking is the process caused by the combinedaction of heavy stress and a corrosive environment. The stages of fail-ure of the metal due to stress corrosion are shown below. Corrosion isinitiated by breakdown of the surface film followed by the formation of acorrosion pit which becomes the site for stress corrosion cracking,eventually leading to mechanical failure due to overloading of themechanical strength of the metal. This form of attack is often foundaround the ogee ring in vertical auxiliary boilers, when undue stressingis set up by poor steam-raising procedures.

Stress corrosion

15WATER TREATMENT HANDBOOK

3 Problems of Boiler WaterFeedwater produced by distillation for use in a boiler is not “pure”, even with agood distillation method. Worse still is ordinary water taken from ashore to beused as feedwater. The water will contain some of the elements (impurities)mentioned in Chapter 5.

Problems will then arise when the water is used in the boiler. The types of problem will depend on the type of impurities and in which quantities theyare present.

The most common problems are:

– CORROSION– SCALING– CARRYOVER

3.1 CORROSIONThe corrosion processes can affect boilers in the following ways:

”General wastage” is the overall reduction of metal thickness and is commonin heating surface areas, such as boiler tube walls. This “thinning” of boilertubes is often found in boilers having open feed systems (mostly auxiliary boilers) without any protective treatment. An example of wastage is given inthe figure below.

14 3 / PROBLEMS OF BOILER WATER

General wastage of a boiler tube.

3.2 SCALINGCauses and EffectsIf the inside of a boiler is scaled, there is a great risk that the boiler materialwill overheat, leading to tube failure. The efficiency of operation will also beadversely affected.

Hardness in the feedwater will usually present problems in relation to theoperation of boilers. Hardness of more than 5dH° (90 ppm as CaCO3) in thefeedwater will, as the temperature rises, cause an increase in the formationof sludge in the feedwater tank. If scale-preventing chemicals are put into thefeedwater tank, this problem will be aggravated, as nearly all precipitation ofsludge will take place in the feedwater tank. The suction pipe stub of the feedwater line will usually be placed 5–10 cm above the bottom. However, if thefeed water is not very clean, sludge will after a time be sucked into the pipingand choking may occur. In a modern centrifugal pump, the very narrow vanesmay be blocked, which will cause the pump to stop. Finally, there is a risk ofthe valves sticking and becoming blocked.

In spite of the fact that a boiler plant may be equipped with a water treatment system of some sort, there will always be a risk of hardness orother type of pollution in the feedwater, because:

1. The capacity of the water treatment system is insufficient.

2. There are defects in the water treatment system.

3. The condensate is polluted:a. By heat exchanger leaksb. By lubrication oil

Daily analysis of the quality of the feedwater will ensure that action can betaken in time to prevent irregularities.

Hardness in the boiler water will inevitably lead to the formation of scaleand the rate of this formation will depend on the composition and quantity ofthe hardness, on the temperature conditions in the boiler and on the circula-tion in the boiler.

Increased surface heating effect means increased production of steambubbles, which again will make more boiler water “pass” the spot on the heating surface (where the steam bubbles are formed) and this spot will thusalso be “passed” by the hardness-producing and corroding salts in the boilerwater. In addition, the most common hardness salts are less soluble atincreasing temperatures.

This explains why the largest amount of encrustation will always be foundwhere the temperature of the heating surface is the highest.

Scale formed just at this point means that the critical temperature of theboiler material will be reached quickly and that damage to the boiler will beinevitable.


3.1.3 Other Related Problems“Corrosion fatigue” occurs when a sufficiently high alternative stresslevel causes failure of the subjected material. It is the joint action of acorrosive environment and cyclic stressing and results in a series offine cracks in the metal. This is found in water tube boilers where irreg-ular circulation through tubes in high temperature zones induce thesecycling stresses.

”Caustic cracking” results from the contact of water of concen-trated caustic alkalinity and steel which has not been stress relieved,e.g. in riveted seams. This form of cracking follows the grain bound-aries. This is rarely observed nowadays, as both high and low pressureboilers are usually of all welded construction and are stress relieved.

Caustic corrosion takes place only in high pressure boilers (above60 bar) when excessively high concentrations of Sodium Hydroxide(Caustic Soda) cause breakdown of the magnetite layer and localisedcorrosion. This form of attack is often controlled by the coordinated PO4Treatment Programme.

”Hydrogen attack” is another form of corrosion damage that cantake place in ultra high pressure boilers.

Whichever form of corrosive attack occurs, the risk of tube failure or serious structural damage is very apparent, both often leading to con-siderable expense in the shape of repair costs.

3.1.4 Factors Affecting Corrosion

1) pH Metal oxides are more soluble as pH decreases. Corrosion is increased.

2) Dissolved solids Chloride and Sulphate can penetrate passive metal oxide film which protects the base metal from corrosion.

3) Dissolved gases Carbon Dioxide and H2S reduces pH and promotes acid attack. Oxygen promotes pitting corrosion.

4) Suspended solids Mud, sand, clay, etc. settle to form deposits, promoting different corrosion cells.

5) Micro organisms Promote different corrosion cells.

6) Temperature High temperature increases corrosion.

7) Velocity High velocity promotes erosion/cavitation.

8) Copper Copper ions plate out on steel surfaces and promote pitting corrosion.

16 3 / PROBLEMS OF BOILER WATER

3.3 CARRYOVERCarryover is any contaminant that leaves the boiler with the steam.

Carryover can be:

• Solid • Liquid • Vapour

Effects of carryover:• Deposits in non-return valve • Deposits in superheaters• Deposits in control valves • Deposits on turbine

Carryover in superheaters can promote failure due to overheating.

Turbines are prone to damage by carryover, as solid particles in steam canerode turbine parts. When large slugs of water carry over with steam, thethermal and mechanical shock can cause severe damage.

Causes of carryover:Mechanical:

• Priming • Sudden load changes • Boiler design• Soot blowing • High water level

Chemical:Foaming due to:

• High Chlorides • High TDS • High alkalinity• Suspended solids • Oil • Silica

The most common form of encrustation in a steam system stems from carryover. The boiler manufacturers stipulate a maximum allowed salinity ofthe boiler water (as a rule at 0.4° Be = 4000 mg salts dissolved per litre). If thisvalue is exceeded, there is a risk of normal bubble size being prevented; larger bubbles will be produced and the turbulence in the water surface willincrease and cause foaming. The foam may be carried over with the steam,particularly when the generation of steam is at maximum, which causes boilerwater (containing Sodium Hydroxide and salt) to pass out into the steampipes.

The content of Silicic Acid is important for boilers with high pressures.Silicic Acid in its volatile form may be carried away with the steam and bedeposited on turbine blades, for instance, on which it will form a very hard,porcelaine-like scale.

However, not only the chemical composition may cause carryover. Circum-stances such as periodic overloads, periods of a too high a water level (or morecorrectly: too small a steam volume) are two of the most common causes.

Finally, impurities from the condensate, such as oil from the preheater’scoils if they are leaking are very common causes of priming.

19WATER TREATMENT HANDBOOK18 3 / PROBLEMS OF BOILER WATER

Illustration of Typical Conditions With

a Clean Boiler Tube

Change in Conditions When a Layer of Scale of just 3 mm

Thickness Exists

The scale causes the fuel consumption to increase by approx. 18 percent.Stress will arise in the steel as a result of the insulating effect of the scale.

Excess Fuel Consumption in %, depending on Thickness of Scale

Curve of middle values. The differences in the test results can beexplained by differences in the composition of scale (porous–hard).

Typical packaged boiler. Packaged boilers include a pressure vessel, burner, all the controls, airfans, and insulation. The boiler is tested at the manufacturer’s plant and shipped to the customer,ready for use, when the fuel lines and piping and electrical connections have been installed.

Typical Scotch Marine firetube boiler (courtesy of Orr & Sembower, Inc.).


4 Types of BoilerWhat is a boiler?

A boiler is a steel pressure vessel in which water under pressure is con-verted into steam by the application of combustion. In other words, it is simply a heat exchanger which uses radiant heat and hot flue gases, liberatedfrom burning fuel, to generate steam and hot water for heating and processing loads.

There are two types: Fire tube boilers and water tube boilers.

4.1 FIRE TUBE BOILER Hot flue gases flow inside tubes that are submerged in water within a shell.

• Pressures up to about 10 bar• Produce up to 14 tonnes of steam/hr• Can meet wide and sudden load fluctuations because

of large water volumes• Usually rated in HP

4.2 WATER TUBE BOILER Water flows through tubes that are surrounded by hot combustion gases in a shell.

• Usually rated in tons of steam/hr• Used for H.P. steam• High capacity

BOILERS HAVE SIX BASIC PARTS

1) Burner2) Combustion space3) Convection section4) Stack5) Air fans6) Controls and accessories

20 4 / TYPES OF BOILER

4.5 HIGH TEMPERATURE WATER (HTW) HEATING SYSTEMSIn recent years, interest has been revived in high temperature hot water heating systems for institutional, industrial and commercial plants. By increasing the temperature and pressure of the hot water and increasing thesize of the generators, some advantages are gained over the low pressuresteam heating systems previously used. In other cases, special forced circulation boilers have been designed, which consist of many rows of tubeswithout a steam drum. In another type, heat is supplied by steam from a standard type of boiler which heats the water in a direct contact heater.This is referred to as a cascade system.


4.3 FIRETUBE BOILERSWet back designsHave a water wall at the back of the boiler in the area where combustiongases reverse direction to enter tubes.

Dry back designsRefractory is used at the back, instead of a water wall. Internal maintenanceis simplified, but refractory replacement is expensive and overheating, gauging and cracking of tube ends at the entrance to return gas passagesoften cause problems.

4.4 CLAYTON STEAM GENERATORThe coil type generator is a vertical coil with fuel combustion taking placeinside the coil. High quality feedwater and a closely monitored chemical treat-ment programme are mandatory. The most common problem is Oxygen pitting on the inside portion of the coil near the fire. The two most commonname brands are Vapor-Clarkson and Clayton.


Medium-sized watertube boilers may be classified according to three basic tube arrangements.

WATERSYSTEM AND STEAMSYSTEM

WATER TREATMENT HANDBOOK

5.1 TYPICAL BOILER SETUP ON A MOTOR SHIP5.1.1 The Boiler SystemThis does not just consist of a boiler. As indicated by the figure above, itis a complete plant. Most motor ship boilers operate at low pressure,that is, not more than 20 bar pressure. This makes it suitable for the single treatment: the combined boiler water treatment.

The steam plant consists of the following:

Storage tankThis tank will hold the make-up water to be supplied to the various systems as they lose water through leaks and through evaporation.Normally, this water is made by a “low pressure” evaporator (this willbe described later on). The water produced in this way is normally ofgood quality if the evaporator is set up correctly. When it is introducedto the boiler, it will require the minimum amount of treatment. However,at some stage the vessel will very likely take water from ashore, andthe quality can vary considerably. This water would probably requiremore treatment to correctly condition it for use.

Hot well, observation tank or cascade tankThis has a very important function for the dosing of chemical treat-ments. This is where all the water collects on returning from the variousareas where steam has been used. It is also where water enters thesystem from the storage tank(s) to make up the quantity required in thesystem. If the steam has been used for heating fuel, the returns fromthat tank may contain oil, or if cargo heating has been used, some of

25

4.6 FIRETUBE BOILERS

Advantages:• Lower initial cost• Few controls• Simple operation

Disadvantages:• Drums exposed to heat, increasing the risk of explosion• Large water volume, resulting in poor circulation• Limited steam pressure and evaporation

WATERTUBE BOILERS

Advantages:• Rapid heat transmission• Fast reaction to steam demand• High efficiency• Safer than firetube boilers

Disadvantages:• More control than firetube boilers• Higher initial cost• More complicated to operate


5 Boiler Systems

The system described provides the more common, modern system.There are many systems where the exhaust gas boiler and the oil-firedboiler are combined (composite boiler). A diagram of one is shownbelow. One section of the tube is used for the oil-fired boiler and theother section for the exhaust gases to pass through. This unit must besituated in the funnel area because the exhaust trunking passes thatway and it is placed at a convenient point.

5.1.2 The Steam LinesThe steam comes from the steam drum of the boiler and is distributed tothe areas where it is required. That is for heating tanks, fuel, hot water,etc. No testing is required in this area under normal circumstances.Once the useful heat has been taken out of the steam, it enters thesteam return lines and comes back to the drains cooler.

5.1.3 Drains CoolerThis unit is another heat exchanger and it is there to ensure that all thereturning steam is turned to water. The returns would be a mixture ofhot water and steam before this cooler, and the cooler ensures that anyreturn steam is condensed to water.

The drains cooler normally uses sea water to cool the steamreturns, and this can be a source of contamination if there is a leak.This will show up as a high chloride level in the feedwater if it occurs.


the cargo product may be returned with the steam. That is why this tankis sometimes called the observation tank – steam returns can beinspected for contamination here. There is a series of plates and filtersin the hot well which allows the contaminating oil, etc., to be removed.Any sort of contamination is definitely not wanted in the water enteringthe boiler, as it would cause damage. Dosage of the combined productboiler water treatment is normally carried out into the hot well.

The boiler:The water is drawn from the hot well by the feed pump and pumped intothe upper drum of the boiler (this is normally called the steam drum).From here it circulates in the boiler, is heated and turns into steam.There are normally two different ways in which it is heated.

1. When the main diesel engine is running, the water is pumpedfrom the lower drum (called the water drum) and circulated through aheat exchanger in the exhaust trunking which takes the exhaust gasesaway from the engine to the atmosphere. The remaining heat in theseexhaust gases is used to generate the steam.

2. The auxiliary boiler has a burner (one or more) which uses eitherheavy oil or diesel oil to provide the heat to produce steam. If the heatavailable from the exhaust gases is insufficient, the oil fired burner(s)can be used to make the steam required by the vessel.

26 5 / BOILER SYSTEMS

Sunrod Exhaust Gas Economiser.

7 Combined Treatment for LowPressure Boiler Water

7.1 LIQUITREATLiquitreat is a combined chemical treatment product suitable for use in small,low pressure boilers. It precipitates hardness, provides the boiler water withthe necessary alkalinity, and scavenges dissolved Oxygen. Liquitreat shouldbe added when deemed necessary as shown by water analysis results.

If the boiler is open and not being fired, Liquitreat can be poured through a manhole, but when the boiler is in operation, the treatment must be appliedthrough a special dosing line. When a dosing arrangement is utilized, thechemical must be flushed to remove any residual left in the dosage lines andequipment. If dosing lines are not fitted, the chemical can be added directly to a feed tank as required. Ensure proper circulation through the feed tank to allow the chemical to enter the boiler being treated. Under low load conditions, complete changeover in the feed tank can take some time. It isnecessary to know the details of the flow pattern in the boiler for proper testing and dosing of the chemical treatment to take place.

When several boilers have a common feed tank, dosing should be carriedout through independent dosing lines to ensure the proper treatment of each boiler. Re-test within 2 hours of when the boiler water chemical treatmentwas dosed to the boiler water.

For further recommendations on product dosage and control limits, refer to the product data sheet in the Marine Chemical’s Manual.

7.2 COMBITREATCombitreat is a combined product chemical treatment similar to Liquitreat butin powder form without Oxygen scavenger, which precipitates hardness andprovides the boiler water with the necessary alkalinity.

Combitreat should be applied as a solution and added when deemed necessary as shown by water analysis results. The recommended dosagemust be dissolved in warm water, 30–60 °C in a suitable steel or plastic container, not exceeding the solubility limit of 180 grams per litre. Combitreatmust be added slowly to the water (not vice versa) and the solution being prepared must be constantly stirred.

Combitreat is best dosed by means of a bypass potfeeder directly in theboiler water feed line. It can also be dosed into the hot well after premixingwith hot water at a ratio of 1 kg per 9 litres of water.NOTE: In addition to our combined product chemicals, Condensate Control should be used in all boiler systems tokeep the Condensate pH level between 8.3–9.0. Also, the hot well temperature is of great importance when it comesto Oxygen scavenging (ref. basic chemistry at the beginning of the book). We recommend that you maintain a hotwell temperature of between 70 °C and 90 °C. For further recommendations on product dosage and control limits,refer to the product data sheet in the Marine Chemicals Manual.


6 Unitor Boiler Water Treatment Products

6.1 THE MAIN PURPOSE OF BOILER WATER TREATMENT ISA. To eliminate the total hardness of the boiler water.

B. To maintain the correct pH and alkalinity values in feedwater and boiler water.

C. To prevent corrosion, especially corrosion caused by Oxygen.

D. To prevent the formation of scale, among other things by conditioning the sludge.

E. To avoid foaming.

6.2 UNITOR PRODUCTSCombined Treatment

1. Liquitreat

2. Combitreat

Single Function Treatment

1. Alkalinity Control

2. Hardness Control

3. Oxygen Control

4. Catalysed Sodium Sulphite

5. Cat. Sulphite L

6. Boiler Coagulant

7. Condensate Control

28 6 / UNITOR BOILER WATER TREATMENT PRODUCTS

8.4 pH Recommended limits of 9.5–11.0. An additional test to determine the pH of theboiler water can be carried out to give a better overall understanding of theboiler water quality. This test is optional.

The pH of the boiler water should be maintained within the range of 9.5–11.0 to prevent any corrosion attack on the boiler metal. pH values below9.5 indicate, a greater possibility of corrosion and in such a situation, treatment levels should be increased accordingly to restore boiler water to optimum quality.

8.5 CONDENSATE pHTo control corrosion in after boiler, condensate and feedwater sections, thecondensate pH should be kept between 8.3 and 9.0. Monitoring the pH of thiswater is very important in being able to maintain a complete Boiler WaterTreatment Management Programme.

8.6 TESTING REQUIREMENTS8.6.1 Low Pressure Boiler Water Treatments:A. Unitor Combined Treatment Products

a. Combitreat – For systems up to 17.5 bar.b. Liquitreat – For systems up to 30 bar.

B. Test Equipment – Unitor Spectrapak 310 Test Kit.

C. Specification Control Limits.a. P-Alkalinity: 100–300 ppm (as CaCO3).b. Chloride: 200 ppm maximum.c. Boiler Water pH: 9.5–11.0 (optional).d. Condensate pH: 8.3–9.0.

D. Testing preparations and equipment.a. Boiler Water Sample preparation: – Cool sample to 20–25 °C.

– Filter as required.b. Sample Analysis: – Spectrapak 310 Test Kit

Reagents: – P-Alkalinity tablets – Chloride tablets.– pH strips with ranges 6.5–10.0 and 7.5–14.0. – Equipment – 200 ml sample bottles. – Test procedures.


8 Tests for Boiler Water, Low Pressure

8.1 UNITOR’S LOW PRESSURE COMBINED BOILER WATERTREATMENT PROGRAMME

The tests recommended in order to maintain boiler water within the desiredlevel of quality when treating with Unitor Liquitreat/Combitreat are as follows:

A. P-Alkalinity – Recommended Limits: 100–300 ppm as CaCO3.

B. Chlorides – 200 ppm maximum as Cl.

C. Condensate pH – 8.3–9.0.

Dosage level of Liquitreat/Combitreat is based on the P-Alkalinity value of the boiler water. However, Chlorides and condensate pH must also be controlled and maintained as recommended. Knowledge of all relevant para-meters is desirable to enable better interpretation and correct application of treatment. To increase the condensate pH, use Unitor’s Condensate Controlin conjunction with your combined product boiler water treatment. It is recommended that you dose Condensate Control on a continuous basis, tomaintain the condensate pH within the recommended range of 8.3–9.0 at all times.

8.2 CONTROLLING ALKALINITYThe alkalinity is a more accurate indicator of the boiler water condition than isthe pH. The Phenolphtalein (P) alkalinity is measured to determine whetherthe correct conditions of alkalinity exist in the boiler to:

A. Provide a suitable environment for the precipitation of hardness salts asdesirable sludge materials.

B. To help the formation of Magnetite (Fe3O4) in the presence of Oxygen scavengers (i.e. Hydrazine/Sulphite).

C. Maintain Silica in solution to prevent Silica scale formation.

8.3 CONTROLLING CHLORIDESThe Chloride value will reveal any presence of dissolved salts in the boiler. Anincrease, gradual or sudden, in the level of Chlorides is an indication of con-tamination by sea water, and Chlorides are often used as a reference pointwhen controlling rate of blowdown. Too high a Chloride level indicates thatundesirable amounts of salts are present, leading to possible foaming and/orscale and deposit formation.

30 8 / TESTS FOR BOILER WATER/LOW PRESSURE

It is essential that the condensate pH is maintained within 8.3–9.0. Test this with Unitor’s pH paper and use Condensate Control to adjust pH upwards if necessary.

8.6.5 Instructions Sulphite Test Kit(optional test for low pressure single product treatment)

8.6.6 Testing procedure:A. Take a 20 ml sample in the shaker tube supplied.

B. Add one Sulphite No. 1 tablet; shake to dissolve.

C. Add Sulphite No. 2 L.R. tablets one at a time until the sample turns blue. Note the number of tablets used.

D. Calculate as follows:Sulphite content = Number of Sulphite No. 2 L.R. tablets x 10.

E. After use, thoroughly rinse out the shaker tube before storage.

PLEASE NOTE! The Sulphite No. 1 tablet is used only to condition the sample. Do not count this tablet when calculating the Sulphite level.

8.7 TEST RESULTS – COMBINED TREATMENTA. Recording – Always use Unitor’s Rapid Response log forms to

record all readings and to keep track of all results.

1. Log form – Combined Boiler Water Treatment Log, no. 310.2. Frequency – Samples should be drawn, tested and results

logged at least every three days.

B. Reporting – The completed log sheet for the month should be distributed as shown at the bottom of the form, at the end of each month:

1. White copy – to Unitor’s Rapid Response Centre in Norway (address labels at back of log pad)

2. Pink copy – Vessel owner

3. Yellow copy – to be kept onboard

C. Evaluation

1. Logs will be reviewed at the Unitor Rapid Response Centre foradherence to recommended specifications, with the aid of Unitor’s Rapid Response staff.

2. A report letter indicating the status of the ship’s system, any problems and relevant recommendations will be issued to the ship’s operator.


8.6.2 P-Alkalinity testA. Take a 200 ml water sample in the stoppered bottle provided.

B. Add one P-Alkalinity tablet and shake to disintegrate. If P-Alkalinity is present, the sample will turn blue.

C. Repeat tablet addition until the blue colour changes to permanent yellow.

Calculation:P-Alkalinity ppm (CaCO3) = (No. of tablets used x 20) –10

For example:If 8 tablets are used, then P-Alkalinity = (8 x 20) –10 = 150 ppm.

D. Mark the result obtained on the log sheets provided, against the date at which the test was taken.

8.6.3 Chloride testA. For boilers under 30 bar, take a 50 ml sample in the stoppered bottle

provided.

B. Add one Chloride tablet and shake to disintegrate; sample will turn yellow if chlorides are present.

C. Repeat tablet addition until the yellow colour changes to orange/brown.

Calculation:Chloride ppm = (No. of tablets used x 20) –20

For example:If 4 tablets are used then Chloride ppm = (4 x 20) –20 = 60 ppm.

D. Mark this result on the Spectrapak 310 log sheet, against the date at which the test was taken.

8.6.4 pH test:For boiler water pH test, 7.5–14.0. For Condensate water, 6.5–10.0.

A. Take a 50 ml sample of water to be tested in the plastic sample container provided.

B. Using the white 0.6 grm scoop provided, add one measure of the pH reagent to the water sample, allow to dissolve – stir if required.

C. Select the correct range of pH test strip and dip it into the water sample for approximately 10 seconds.

D. Withdraw strip from sample and compare the colour obtained with the colour scale on the pH indicator strips container.

E. Record the pH value obtained on the log sheet provided, against the date at which the test was taken.

32 8 / TESTS FOR BOILER WATER/LOW PRESSURE

9 Unitor Coordinated TreatmentProducts

The use of combined product treatment for medium and high pressure boilers,is not recommended. Because higher pressures and temperatures increasethe tendency of scaling and corrosion, which makes it necessary to have thepossibility of changing the chemical conditions and test parametres individu-ally. The Unitor Coordinated Treatment Programme includes single functionchemicals which are dosed and monitored separately. This programme may ofcourse also be applied to low pressure boilers as an alternative to combinedproduct treatment.

9.1 HARDNESS CONTROLHardness Control is a Phosphate powder product used in boiler water treat-ment to precipitate dissolved calcium hardness salts and to convert thesesalts to non-adherent Calcium Phosphate sludge, which can be easilyremoved by blowdown. Hardness Control is highly effective in achieving thisfunction; minimum dosages are required. Reduced dosage of chemicals mini-mises dissolved and suspended solids in the boiler water. Hardness Controlprovides neutral reaction products in the boiler. A high level of dissolved andsuspended solids are the principal causes of carryover and priming.

Note here the term “phosphate hide-out”; as the temperature of the boilerincreases, less Phosphate can be held in solution in the boiler water. There-fore, testing and dosage of Phosphate to control hardness salts depositsshould be done when the boiler is under full load conditions. If the Phosphateresidual increases under low load conditions, this is an indication of a dirtyboiler, and increased bottom blows should be carried out to remove the sludge.The sludge holds excess Phosphate and re-dissolves when the boiler watertemperature is reduced. For further recommendations on product dosage andcontrol limits, refer to the Marine Chemicals Manual.

9.2 ALKALINITY CONTROLAlkalinity Control is used to obtain the correct pH level necessary for the Phosphate treatment to react with Calcium salts. In addition, Alkalinity Controlis used to maintain the required alkalinity in the boiler water to prevent acidcorrosion. By adopting simple testing procedures to determine thePhenolphthalein alkalinity (P-Alkalinity) and the total alkalinity (M-Alkalinity),we can determine the amount of free caustic present in the boiler water byusing the formula 2(P) – M = OH. If a positive number is obtained, free caustic(OH-Alkalinity) is present in the boiler water.

35WATER TREATMENT HANDBOOK34 9 / UNITOR COORDINATED TREATMENT PRODUCTS

The term “excess chemicals” or “reserve of chemicals” ensures thatchemicals are always readily available to perform their necessary functions.

For further recommendations on product dosage and control limits, refer tothe Marine Chemicals Manual.

9.3 OXYGEN CONTROL (HYDRAZINE, N2H4)Hydrazine is a colourless liquid at ambient temperatures, being completely miscible with water. Its solution has an odour resembling Ammonia, but is lesspungent. It is used to efficiently scavenge and remove Oxygen from conden-sate, feedwater and boiler water.

Hydrazine reacts with Oxygen, acting as a scavenger. The reaction resultsin Nitrogen and water, no solids being added to the boiler system.

Some of the Hydrazine will carry over with the steam, helping to maintainthe condensate pH in an alkaline range, which thereby helps combat acid formation. Hydrazine will also form Magnetite which will act as a protectivelayer against further corrosion.

Hydrazine should be added to the system using a separate dosing tank. Thetank should be filled daily with Hydrazine diluted with condensate or distilledwater. This solution should be dosed continuously to the storage section ofthe de-aerator. Alternatively, Hydrazine can be fed continuously to the feedpump suction or atmospheric drain tank over a 24-hour period.

It is important that Hydrazine should not be overdosed. At temperaturesabove 270 °C, Hydrazine starts to break down, creating free Ammonia.Excessive free Ammonia and Oxygen, when combined, form a corrosive condition on non-ferrous metals. This corrosive action can cause Copper to deposit in the watersides of boilers, causing additional boiler problems, as discussed earlier.

The reaction of Hydrazine in boilers is therefore threefold:

1. It scavenges any free or dissolved Oxygen.

2. It reduces red Iron Oxide to a metal-protective black oxide coating (Magnetite).

3. It raises the pH of the condensate reducing acid corrosion of the condensate and re-boiler sections of the system. For further recom-mendations on product dosage and control limits, refer to the MarineChemicals Manual.

9 / UNITOR COORDINATED TREATMENT PRODUCTS

9.4 CATALYSED SODIUM SULPHITE (POWDER) AND CAT. SULPHITE L (LIQUID)

Unitor’s Catalysed Sulphite products are used as scavengers in place ofHydrazine where economy is of importance, or used in low pressure boilerswith open feed systems where feed inlet temperatures are low. Sulphite combined with Oxygen forms Sulphate, which adds solids to the boiler water. It should subsequently not be used in boilers at pressures above 30 barswhere the TDS level is critical. Sulphite is also used as a substitute forHydrazine when rust and scale deposits are present in boiler systems onships being returned to service. Hydrazine tends to remove Iron Oxide deposits present throughout the boiler system. An amine (Condensate Control)should be used in conjunction with Oxygen scavengers to maintain the condensate pH within the desirable ranges throughout the entire condensateand feedwater system.


9.5 CONDENSATE CONTROLCondensate Control is a neutralising volatile amine recommended for use in all boiler systems to raise the pH of condensate and steam to a non-corrosive level (pH 8.3–9.0). The dosage is determined by the results of a daily condensate pH test. Condensate Control should be dosed using a continuous feed system. It can be introduced, using a flowmeter or metering pump, to the condensate pump discharge, the hot well, the conden-sate return tank, or to the de-aerator storage tank. Condensate Control can bedosed together with Oxygen scavengers. However, optimum control of condensate pH is achieved by dosing separately from the Hydrazine dosagesystem.

For further recommendations on product dosage and control limits, refer to the Marine Chemicals Manual.

9.6 BOILER COAGULANTBoiler Coagulant is a polymeric compound used in boilers contaminated withsmall quantities of oil, or as a sludge conditioner in conjunction with the useof Hardness Control when high levels of solids are experienced. BoilerCoagulant should be dosed at 250cc per day. No testing is necessary if usedregularly. Daily flash blowdown is recommended to remove precipitated solidsor coagulated oil.


37WATER TREATMENT HANDBOOK36

9.7 CHEMICAL INJECTION POINTS FOR LOW PRESSURE Boiler systems

The following diagram depicts a typical Low Pressure Boiler System. Noteinjection point for chemicals; when dosing chemicals, the recommendation toachieve the best possible results is to always dose all chemicals in the dilutedform on a continuous basis.

1 Dosage to hot well or feed tank. All chemicals can be dosed at these points.However, the recommended dosage of Alkalinity Control and HardnessControl is either no. 2 feed line or no. 3 chemical feed injection directly tothe boiler. Oxygen Control and Sulphite should preferably be dosed to thefeed tank on a continuous basis. All combined products can be dosed into the hot well.

2 Dose to injection no. 2 is required to the feed line by means of a pressureinjector or dosage pump. Dosage should be continuous, however water canbe shock treated.

3 Dosage direct to boiler no. 3. All chemicals can be dosed to this point bymeans of pressure pot injector or dosage pump. Alkalinity Control orHardness Control is best controlled at this location and and the use ofHydrazine, Sulphite or Condensate Control is recommended on a continuous basis in the condensate system.

10 Tests for Boiler Water, Medium Pressure(31–60 BAR)

In dosing medium pressure boilers, utilise Unitor’s Coordinated Boiler WaterTreatment Management Programme. This includes Alkalinity Control,Hardness Control, Oxygen Control, Condensate Control and Boiler Coagulant.The following tests are recommended to maintain medium pressure boilerwater within the desired level of quality when utilising Unitor’s CoordinatedBWT Programme are as follows:

10.1 UNITOR TESTS REQUIRED CONTROL LIMITS1. P-Alkalinity: . . . 100–130 ppm CaCO32. M-Alkalinity: . . Below 2 x P-Alkalinity3. Phosphate: . . . . 20–40 ppm as PO44. Hydrazine: . . . . 0.03–0.15 ppm as N2H45. Chlorides: . . . . . <30 ppm6. pH (boil. water): 9.5–11.07. pH (condens.): . 8.3– 9.0

10.2 UTILISE UNITOR’S SPECTRAPAK 311/312*/SULPHITE TEST KITReagentsA. Phosphate tabletsB. Chloride tabletsC. P-Alkalinity tabletsD. M-Alkalinity tabletsE. pH papers (6.5–10.0 & 7.5–14.0)F. pH reagentG. Filter paperH. Hydrazine reagent*I. Sulphite tablets*

EquipmentA. 200 ml sample bottlesB. Lovibond 2000 comparatorC. Phosphate disc 3/70D. 10 ml molded cellsE. Hydrazine disc 3/126*F. Sulphite test tube*

* Optional. Either the Hydrazine Test Kit (Spectrapak 312) or the Sulphite Test Kit must be utilised.The one to be used depends on the Oxygen scavenger in use. Please note that Sulphite is notadviceable to use in boilers above 30 bar.

39WATER TREATMENT HANDBOOK38 10 / TESTS FOR BOILER WATER MEDIUM PRESSURE

10.3 TEST PROCEDURES10.3.1 Phosphate (ppm) PO4

A. Take the comparator with the 10 ml cells provided.

B. Slide the Phosphate disc into the comparator.

C. Filter the water sample into both cells up to the 10 ml mark.

D. Place one cell in the left-hand compartment.

E. To the other cell add one Phosphate tablet, crush and mix until completely dissolved.

F. After 10 minutes, place this cell into the right-hand compartment of the comparator.

G. Hold the comparator towards a light.

H. Rotate the disc until a colour match is obtained.

I. Record the result obtained on the Spectrapak 311/312 log sheetagainst the date on which the test was taken.

10.3.2 Chloride (ppm) ClThe range of Chlorides to be tested determines the size of water sampleused. To save tablets, the use of a small water sample is recommendedwhen the Chloride level is expected to be high, i.e. for low Chloride levels use 100 ml water sample, for higher Chloride levels use 50 mlwater sample. However, it should be noted that the accuracy of the testresults increases with the size of the water sample.

A. Take the water sample in the stopper bottle provided.

B. Add one Chloride tablet and shake to disintegrate. Sample will turn yellow if Chlorides are present.

C. Repeat tablet addition, one at a time (giving time for the tablet to dissolve), until the yellow colour changes to permanentred/brown.

D. Count the number of tablets used and perform the following calculation:

For 100 ml water sample: Chloride ppm = (Number of tablets x 10) –10e.g. 4 tablets = (4 x 10) –10 = 30 ppm Chloride.

For 50 ml water sample: Chloride ppm = (Number of tablets x 20) –20e.g. 4 tablets = (4 x 20) –20 = 60 ppm.

E. Record the result obtained on the log sheet provided, against thedate on which the test was taken.

10.3.3 P-Alkalinity (ppm) CaCo3

A. Take a 200 ml water sample in the stopper bottle.

B. Add one P-Alkalinity tablet and shake or crush to disintegrate.

C. If alkalinity is present the sample will turn blue.

D. Repeat the tablet addition, one at a time (giving time for the tablet todissolve), until the blue colour turns to permanent yellow.

E. Count the number of tablets used and carry out the following calculation:P-Alkalinity, ppm CaCO3 = (Number of tablets x 20) –10 e.g. 12 tablets = (12 x 20) –10 = 230 ppm CaCO3

F. Record the result on the log sheet provided, against the date on which the test was taken.

G. Retain the sample for the M-Alkalinity test.

10.3.4 M-Alkalinity (PPM CaCO3)

A. To the P-Alkalinity sample add one M-Alkalinity tablet and shake or crush to disintegrate.

B. Repeat tablet addition, one at a time (giving time for the tablet to dissolve), until the sample turns to permanent red/pink.

C. Count the number of tablets used and carry out the following calculation:M-Alkalinity, ppm CaCO3 = (Number of P & M tablets x 20) –10e.g. If 12 P and 5 M-Alkalinity tablets are used,M-Alkalinity = [(12 + 5) x 20] –10 = 330 ppm CaCO3

D. Record the result on the log sheet provided, against the date onwhich the test was taken.

10.3.5 pH Test7.5–14.0 For boiler water6.5–10.0 For condensate water


A. Take a 50 ml sample of water to be tested in the plastic sample container provided.

B. Using the white 0.6 grm scoop provided, add one measure of the pHreagent to the water sample, allow to dissolve – stir if required.

C. Select the correct range of pH test strip and dip it into the water sample for approximately 10 seconds.

D. Withdraw the strip from the sample and compare the colourobtained with the colour scale on the pH indicator strips container.

E. Record the pH value result on the log sheet provided, against thedate at which the test was taken.

10.3.6 Hydrazine PPM* (Spectrapak 312)A. Take the comparator with the 10 ml cells provided.

B. Slide the Hydrazine disc into the comparator.

C. Add the water sample to both cells up to the 10 ml mark.

D. Place one cell in the left-hand compartment of the comparator.

E. To the other cell add one measure of Hydrazine powder (using theblack 1 grm scoop provided) and mix until completely dissolved.

F. Wait 2 minutes and place the cell in the right hand compartment of the comparator.

G. Hold up to the light and rotate the disc until a colour match is obtained.

H. Record the reading shown as ppm Hydrazine.

10.3.7 Sulphite PPM* (Spectrapak 312)A. Take a 20 ml sample in the shaker tube supplied.

B. Add one Sulphite No. 1 tablet; shake to dissolve.

C. Add Sulphite No. 2 L.R. tablets one at a time until the sample turnsblue. Note the number of tablets used.

Calculate as follows: Sulphite content = Number of Sulphite No. 2 L.R. tablets x 10

D. After use, thoroughly rinse out the shaker tube before storing.Please note: The Sulphite No. 1 tablet is used only to condition thesample. Do not count this tablet when calculating the sulphite level.

10.3.8 Test results – Coordinated treatmentA. Recording – Always use Unitor’s Rapid Response log forms to

record all readings and to keep track of all results.

1. Log form – Coordinated Boiler Water Treatment Log, no.311/312,or ask for special form above 30 bar pressure.

2. Frequency – Samples should be drawn, tested and results logged minimum every third day.

* This is an optional extra (to the Spectrapak 311). This test must be performed below 21 °C. A cooling coil should be fitted at the sampling point or the sample should be cooled immediately under cold running water. Cloudy samples should be filtered before testing.

B. Reporting – The completed log sheet for the month should be distributed as shown at the bottom of the form, at the end of each month:

1. White copy – to Unitor’s Rapid Response Centre in Norway (address labels at back of log pad).

2. Pink copy – vessel owner.

3. Yellow copy – to be kept onboard.

C. Evaluation1. Logs will be rewied at the Unitor Rapid Response Centre for

adherence to recommended specifications, with the aid of Unitor’s computerized Rapid Response programme and staff.

2. A report letter indicating the status of the ship’s system, any problems and relevant recommendations will be issued to the ship’s operator.


11 High Pressure Boiler Water Control

11.1 TYPES OF WATERProper control using all aspects of your chemical treatment programme forboilers operating above 60 bar is extremely important.

The high temperatures and pressures involved require your direct and constant attention to the conditions in the boiler and associated equipment in regulating the pre-treatment of the boiler water.

Unitor recommends that you test your boiler, condensate and feedwater atleast once and preferably twice a day.

The crucial aspect of controlling a high pressure boiler system is knowing the performance of your pre-treatment equipment. The evaporatorshould be producing enough high-quality distilled water to provide sufficientcomposition and to handle leaks throughout the system and blowdownrequirements.

The efficient operation of the de-areator is critical. The function of the de-areator is to:

A. Remove dissolved gases from the condensate.

B. Pre-heat feedwater.

C. Act as a storage tank for the boiler and suction head for the feed pump.

In many cases, improper operation of the de-areator heater will affect theentire control and results of your chemical treatment programme. Ensure that the Ammonia level is being kept below a maximum level in the condensate of 0.3 ppm at all times and the feedwater indicates less than 10 ppb dissolved Oxygen. Be certain to maintain proper operating tempera-tures and pressures in the de-areator. Temperature variations between the upper and lower sections of the de-areator indicate faulty operation of the unit.

To help resolve a condition where Ammonia levels exceed the allowed limit of 0.3 ppm, the de-areator should be vented to the atmosphere.Controlled venting is critical to ensure that excess water and heat are not lost to the atmosphere to reduce your Ammonia level below the maximum allowable level. At times, the efficiency of the gland exhaust condenser re-dissolves the gases which are intended to be vented off to theatmosphere and which continually attributes to the build-up of the Ammonia

levels in the condensate. Of course, precise control and dosage of Hydrazineis critical in controlling this factor. Overdosage of Hydrazine will greatly affectthe build-up of Ammonia in your system. Always dose enough Hydrazine toreact with the trace amounts of Oxygen left in your feedwater after deaeration. Unitor recommends a 0.05 ppm residual of Hydrazine in your boilerwater. However, theoretically, any test results above 0.03 ppm will indicate the presence of Hydrazine and this is an adequate residual to assure Oxygen-free boiler water.

Controlling the pH and Phosphate coordination of the boiler water is alsovery critical. The coordination of the dosage of these products will prove tomaintain your internal boiler surfaces free from caustic embrittlement corrosion and deposition.

Unitor’s high pressure coordinated pH-Phosphate boiler water treatmentprogramme is designed to maintain your boilers in optimum condition. If youexperience any difficulties in controlling the programme prescribed herein, contact your local Unitor representative.

Lastly, a routine for set periodic blowdown will enhance the results of thisboiler water treatment programme. Even if test results are within good rangeof the recommendations, sludge is forming in the boiler at all times. This is a normal reaction of the chemicals you are treating. Plan a schedule that will fit into the vessel’s normal operating procedures to allow a completeblowdown procedure, including a bottom blow and a blow of each header and to remove the sludge build-up. Unitor recommends that this routine beperformed twice a day. Of course, if conditions warrant it, additional blowsshould be performed.

11.2 TREATMENT PROGRAMME FOR BOILERS OPERATINGIN THE RANGE OF 60–83 BAR

Unitor recommeds the use of coordinated Phosphate/pH water treatment control.

The following high pressure boiler programme is based on the pressures, temperatures and operating conditions of boilers operating in the range of60–83 bar. Maintaining the chemical concentrations and parameters prescribed will protect your boiler system. The following are specific controlparameters and products required.

45WATER TREATMENT HANDBOOK44 11 / HIGH PRESSURE BOILER WATER CONTROL

SPECTRAPAK TEST UNITOR TREATMENT

Water to be Spectrapak Control Unitor analysed water analysis limits treatment

products

Feedwater Hardness 0Oxygen (optional) < 10 ppb Oxygen ControlChlorides < 5 ppm –

Boiler water P-Alkalinity Reference Alkalinity ControlM-Alkalinity Reference Alkalinity ControlpH (coordinate) 9.6–10.2 Alkalinity ControlPhosphate (coordinate) 10–25 ppm Hardness ControlHydrazine 0.05–0.10 ppm Oxygen ControlChlorides < 20 ppm –Silica < 3 ppm –Cond. < 300 µS/cm –

Condensate pH 8.3–9.0 CondensateControl

Chlorides < 5 ppm –Ammonia < 0.3 ppm –

11.3 TESTING HP – BOILER WATER TEST KIT PC 22 PHOTOMETERPC 22 LED filter photometers are micro-processor controlled and have beenspecially designed for this purpose. Production using the most modern SMDtechnology, ergonomically-styled housing and the robust character of theinstruments guarantees high precision in analysing in laboratories as well asusing the instruments in the field.

The four-line display enables the clear indication of the complete date setting and an exemplary user’s direction.

System Specifications The PC 22 Photometer combines the sum of experience, determined by thedaily experience which establishes precise measurement results within a short period.

The aspects of compact measurement, ergonomical operation, moderndesign and a high measure of spraywater protection were taken into accountin designing the housing.

The foil keyboard, which incorporates an acoustic feedback via a beeper, is scratch-resistant and acid/solvent-resistant. The electronic componentsare sealed to provide maximum protection against corrosion.

Delivery Contents of SPEKTRAPACK PC 221 Ph-meter Reagents1 PC 22 Photometer in a case Ammonia 1 9 V-Battery Silica 1 12 V-Mains adapter P-Alk4 Cells M-Alk1 Conductivity meter Hardness4 Stoppers Phosphate1 Measuring cylinder 100 ml Hydrazine1 Test tube brush Chloride1 Stirring rod1 Cleaning kit1 Manual1 Guarantee-Certificate

Optional dissolved Oxygen test. The set is very easy to use and gives a quickaccurate answer. The test results given can easily be compared with similar equipment in a lab.

(Unitor recommends using the Chemetrics dissolved Oxygen test. Consultthe Unitor office to arrange availability.)

11.3.1 SparesStandard spares are available from your local Unitor Marine Chemicalrepresentative. Order all spares from the on-going supply list providedwith these test instructions. A Replacement Tablet Reagent Pack.Estimate 3-monthly requirements.

11.3.2 SafetyReagents are for chemical testing only; not to be taken internally. Keepaway from children. Wash hands after use.

11.3.3 High Pressure Procedures A. Phosphate.

B. P-Alkalinity.

C. M-Alkalinity.

D. Chloride (Boiler and Condensate Water).

E. Hydrazine.This test should not be performed at a temperature above 21 °C. A cooling coil should be fitted at the sampling point or the sample should be cooled immediately under running water. Cloudy samples should be filtered before testing.

F. pH (Boiler and Condensate Water). The electronic pH meter is the most accurate and reliable method of testing high purity boiler and


condensate water. High pressure boiler water using the co-ordinated Phosphate-pH control method should always be tested using the pH meter for accuracy and the best results. Note: Never touch the pH electrode sensor. Always rinse the sensor in untreated distilled water after use and keep the sensor damp. Store in distilled water. To use, follow the manufacturer’s instructions provided with the instrument. Calibration and slope adjustment can be checked using pH 7 and pH 10 buffers.

G. Conductivity Meter.Note: Existing pH and conductivity meters can be used if onboard. Also verify test reults by standard solutions, pH buffer solutions or laboratory verification.

H. Ammonia.

I. Hardness.

J. Dissolved Oxygen (optional). Testing feed water for dissolved Oxygen entering the boiler may be conveniently analyzed by insert-ing Oxygen ampoule into a flowing stream of the sample. Feedwatershould be allowed to flush from sample line for a minimum of 10 minutes before taking sample. When the ampoule tip is snapped, vacuum inside the ampoule pulls the sample in where it mixes with the pre-measured reagent inside. A deep reddish/violet colour forms proportional in intensity to the dissolved Oxygencontent of the sample. After inverting the ampoule several times to mix the contents, compare that colour with the liquid colour standards in the kit to determine the concentration of Oxygen.

K. Silica.

L. Boiler pH.

M. Condensate pH.

11.4 TEST RESULTS – HIGH PRESSURE BOILER WATER TREATMENT11.4.1 RecordingAlways use Unitor’s Rapid Response log forms to record all readingsand to keep track of all results.

A. Log form – Ultra High Pressure Boiler Water Treatment Log, no. 314.B. Frequency – Samples should be drawn, tested and results logged at

least once per day.

11.4.2 ReportingThe completed log sheet for the month should be distributed as shownat the bottom of the form, at the end of each month:

11 / HIGH PRESSURE BOILER WATER CONTROL

A. White copy – to Unitor’s Rapid Response Center in Norway (address labels at back of log pad)

B. Pink copy – Vessel owner

C. Yellow copy – to be kept onboard

11.4.3 EvaluationA. Logs will be reviewed at the Unitor Rapid Response Centre for

adherence to recommended specifications.

B. A report letter indicating the status of the ship’s system; any problems and relevant recommendations will be issued to the ship’s operator.

11.5 INTERPRETING TEST RESULTS11.5.1 Hydrazine testing and controlFor reasons of economy, try to minimise the quantity of Hydrazineemployed to scavenge Oxygen as well as reducing the amount ofAmmonia that will be formed by the breakdown of Hydrazine. Ammoniain the presence of Oxygen is corrosive to Copper and Copper alloys(non-ferrous alloys).

It will be necessary to test the Hydrazine residuals in the boiler dailyin order to obtain complete protection with minimum doses of Hydrazine.

If the Hydrazine residual in the boiler is over 0.1 ppm, reduce the dosage of Hydrazine until the boiler Hydrazine residual falls below the recommended maximum of 0.1 ppm. If the Hydrazine residual does notimmediately drop below the 0.1 ppm level, the boiler should be blowndown to reduce the Hydrazine level. New boilers, or those recentlyopen for inspection and repair, may take several weeks to achieve anormal boiler Hydrazine residual due to oxides. This is normal, and untila Hydrazine residual is obtained in the boiler water, test the feedwaterfor the Hydrazine content. Maintain the Hydrazine reading in the feed-water between 0.02 and 0.03 ppm. No Oxygen is entering the boiler withthe feedwater when Hydrazine is present in the water. However, be certain not to exceed the max. level of 0.1 ppm in boiler water.

Hydrazine may be dosed into the feed pump suction, or preferably, to the storage section of the de-aerator, which will maximize the residence and reaction time of Oxygen control.

A separate dosing tank and pump set should be used for dosingHydrazine to the system. (Condensate Control may be fed with theHydrazine.)

The estimated daily dose should be mixed with condensate and thepump should be set to deliver the daily dosage over an entire 24-hour period.

49WATER TREATMENT HANDBOOK48

11.5.2 Coordinated phosphate/pH treatment system

If a pump and tank set is not available, Hydrazine (and Condensate Control) can be added to the system through a tank and flowmeter intothe atmospheric drain tank, with injection point well below the waterlevel of the tank.

Most boiler treatments use Sodium Hydroxide to produce therequired alkalinity in the boiler water. This procedure is often called“The Free Caustic Regime”, which means that if a sample of the boilerwater were evaporated to dryness in an inert atmosphere, the remain-ing solids would contain Sodium Hydroxide.

High concentrations of Sodium Hydroxide can cause inter-crys-talline cracking and, in high pressure boilers operating with a high heatflux, caustic gouging can occur. Caustic gouging is a reaction betweenSodium Hydroxide and iron to form Sodium Ferrate. Nascent Hydrogenis liberated by this reaction and can cause Hydrogen embrittlement ofthe steel; often the embrittlement occurs simultaneously with the loss of boiler metal due to gouging. To prevent this from occurring, a coordi-

nated phosphate to pH ratio method is used to produce the alkalinityrequired to protect the boiler steel from corrosion.

The method of control, in practice, is to determine the pH of the boiler water and the Phosphate ppm level. These figures are thenchecked against the graph. If the intersection of Phosphate/pH valuesfalls within the parallelogram zone or below the curve, no free SodiumHydroxide will be present, which is the desired situation.

If the pH is high according to Phosphate/pH chart, blow down toreduce it to the appropriate range, which also reduces the Phosphatelevel. If the pH is low and the Phosphate reading is in the proper range,add Alkalinity Control. If the Phosphate reading is below the recom-mended limits, add Hardness Control only. This procedure will alsoreduce the pH. If the Phosphate reading is high, blow down to the correct level. The correct balance of Phosphate to pH, to eliminate freeCaustic, is easily achieved with the use of quality distilled feedwater.When both Alkalinity Control and Hardness Control are required, raisethe Hardness Control before the Alkalinity Control.NOTE: Balance of Phosphate/pH to eliminate free caustic is easily achieved with the use of

distilled (evaporated) feedwater. If raw or contaminated water is employed, it may be difficult or impossible to achieve a proper balance.

11.6 UNITOR TREATMENT CHEMICALS – DOSAGE GUIDES11.6.1 Hardness Control – Dosage GuidePhosphate test Hardness controlResult ppm gr/ton0– 5 20.775–10 16

10–15 1115–20 No Dose20–25 No Dose25 and above Blow down

11.6.2 Alkalinity Control – Dosage GuidepH test Alkalinity controlresult ppm ml/tonne8.4 188.6 178.8 179.0 169.2 169.4 159.6 139.8–10.2 Satisfactory

10.3 and above Blow down


11.6.3 Oxygen control – Dosage guideHydrazine test results Oxygen control AdjustmentLess than 0.05 ppm Increase dosage 25 %0.05–0.10 ppm Maintain dosage more than0.10 ppm Decrease dosage 25 %

Note: Bear in mind that variations in plant loads and the efficiency of the de-areateor will affect the actual dosage of Hydrazine.

11.6.4 Condensate control – Dosage chartLitres per 10 tonnes Boiler Water CapacityCondens. pH Less than 8.3 8.3–9.0 over 9.0Dosage Increase by 25 % Maintain daily Reduce by 25 % everyltr/day every 72 hours dose 0.75 ltr 72 hours

11.6.5 Initial dosage for each ton capacity boiler waterHARDNESS CONTROL 23 gr/tonneALKALINITY CONTROL 180 ml/tonneOXYGEN CONTROL 120 ml/tonneCONDENSATE CONTROL 0.75 ltr/day

Note: All dosage recommendations given above are estimations only, will vary depending on local conditions as makeup water quality, type of boiler and boiler load.

Water treatment on-going supply list – 6 months estimate

11.7 RECOMMENDED DOSAGE POINTS FOR MEDIUM PRESSUREAND HIGH PRESSURE CONDENSATE ANDFEEDWATER SYSTEMS11.7.1 HydrazineContinuous to the storage section of the de-aerator.

11.7.2 Condensate ControlShould be dosed to the condensate system on a continuous basis.

Note: The testing point for Condensate pH should be up-stream (before) from the dosage point of Condensate Control.

For steam vessels, separate dosages of Oxygen Control andCondensate Control are recommended for better individual control ofeach chemical. However, if only one dosing unit is available, bothOxygen Control and Condensate Control can be dosed together.Hydrazine and Condensate Control are compatible with each other.

11.7.3 Recommended Sampling PointsPoint (A) Condensate pH, Ammonia, Chlorides.Point (B) Feed Water Dissolved Oxygen, pH, TDS, Chlorides.

Note: Testing can be done at the discharge from the feed pump. However, if high dissolved Oxygen residuals are found, water in the storage area of the de-aerator should be checked to ensure no air is leaking into the feed pump.


12 Boiler Wet LayupBoilers are likely to suffer more from corrosion during periods when not in useor laid up. They must be protected. Proper layup procedures are essential.

Corrosion will occur if :A. Low pH conditions occur.B. Oxygen is present in the boiler water.

The procedure starts 2–3 days before the layup date

1 Test the boiler treatment levels and blow down the boiler at regular inter-vals to reduce potential sludge. The boiler should not be laid up dirty.

2 Raise the treatment levels for alkalinity to the maximum allowable level forthat boiler pressure.

3 The boiler should then be treated with a high level of Oxygen Control afterit has been isolated from the main steam line. Gentle firing of the boilershould be used to fully circulate the treatment with the boiler vented.150–200 ppm Hydrazine is dosed into the boiler. (This works out at 1.25 litres/tonne of water.)

NB! Full water capacity must be used to calculate this – not working capacity.

4 The vent cock on top of the boiler should be opened and the boiler filledwith feedwater that is as hot as possible (90 °C).

5 The boiler should be given a “head”of water to ensure that the boiler is keptfull of water. This is achieved by connecting a hose of a drum of treatedwater to the boiler vent cock to make up for any losses due to leaks.

6 Where super heaters are in place, the manufacturer’s instructions must be followed.

7 This principle of wet layup can be used for exhaust gas economisers, etc.8 “Wet” layup of boilers is for the short term. A different procedure should

be used for a long term layup .

Returning to ServiceDrain the boiler of excess Hydrazine, refill with water and warm through in thenormal way.

13 Boiler BlowdownBlowdown is the mechanical process employed to remove and lower excessive concentrations of dissolved and suspended solids in boiler water.This procedure must be exercised on a regular basis to prevent solids frombuilding up which in turn can result in steam carryover leading to contamina-tion of the after-boiler system. In addition, the consequential concentrationand accumulation of sludge and scale in the boiler can cause heavy depositsto collect on heat exchange surfaces. Once formed, these deposits reduceheat transfer and restrict water circulation, causing the boiler to operate atless than its optimum design efficiency. In order to compensate for the loss in thermal transfer, the fuel consumption must be increased to raise the temperature on the furnace-side of the boiler. This in turn can cause overheating and tube failure.

In general, most feedwater and makeup water is processed and monitoredprior to entering the boiler to ensure that the concentrations of naturally-occuring solids are at a minimum. If done properly, only small amounts ofthese contaminants are allowed to get through. These, however, will concentrate in the system and therefore must be dealt with by the addition of water treatment chemicals.

Solids concentrations in boiler water are usually determined by a conductivity meter which displays a visual readout of the ability of the boiler water to transmit an electrical current. This characteristic, called the specific conductance, is directly related to the solids content of the solution being measured. The greater the solids concentration, the higher the reading. The scale on the meter usually measures the results in units of electrical conductance as either siemens or microohms per centimeter at 25 °C. This value can be multiplied by a specific factor to determine the dissolved solids concentration. Some meters have scales that read directly in parts per million of total dissolved solids. Thus, these devices are called both conductivity and TDS meters. In some systems, these meters are permanently installed to continuously monitor boiler, condensate and feedwater. Understand and know the conductivity meter you are using.

An upper limit for the maximum allowable concentration of dissolved solids is usually specified for a system based on the characteristics of that system. Operational temperature and pressure are normally given primary consideration. The higher the value of these parameters, the lower the tolerance of the system for dissolved and suspended solids andtherefore the lower the specification limit. Once this value has been reached or exceeded, the system must be blown down to reduce the solidscontent as much as possible without sacrificing other aspects of the system operation.

55WATER TREATMENT HANDBOOK54 13 / BOILER BLOWDOWN

The Chloride residue is used as a reference value for the TDS level, and isused to determine blowdown requirements. An upper Chloride concentrationlimit is prescribed for the system being monitored.

Blowdown as percent is expressed as:

Cl in feedwater x 100 = % Blowdown

Cl in boiler.

A bottom blowdown may be done to rapidly remove high solids content inthe boiler water. Continuous or intermittent surface blowdown may be used toachieve controlled reduction of TDS. The method used is usually dictated bythe severity of the contamination and the conditions of the specific systeminvolved. Observe all manufacturers’ recommendations for blowdown procedures as improper procedures can be detrimental to the boiler.

Therefore, the process used must be implemented and performed judiciously, bearing in mind all parameters of the system (i.e. available makeup water, available chemicals, boiler load requirements, etc.).

EXCESSIVE BLOWDOWN WASTES WATER, HEAT & CHEMICALS.

Dumping the BoilerOccasionally it may be necessary to remove the entire contents of the water-side of the boiler system, or to prepare the unit for dry layup when it is to bedecommisioned for an extended period of time. The boiler must never be emptied while the system is still hot, as this can cause solids to bake onto thehot surfaces, forming deposits which are extremely difficult to remove. Sincethe boiler internals retain heat for a considerable period of time after the system is taken off line, a wait of at least twenty-four hours is recommendedfrom when the unit is shut down before commencing the dumping process.

14 Chemical Cleaning of BoilersMany different types of contaminants can be found in the waterside of a boiler system. These can originate from impurities naturally found in oradded to the water or from extraneous materials which have gained entrancedue to faulty, worn or defective equipment associated with the system. Thiscontamination can be in the form of hardness scale, oil, metallic oxides,sludge and various combinations of these as well as other miscellaneousmaterials. The procedure(s) required to clean the system will thereforedepend on the nature and condition of the substances to be removed.

The best initial approach to chemical cleaning is to inspect the fouled systemas thoroughly as possible to determine the nature and extent of contamination.If possible, samples of the offending materials should be taken for examinationand if necessary sent in for laboratory analyses. Once the results of this pre-liminary investigation and/or lab analysis are known, the appropriate cleaningprocedure or procedures can be determined and implemented as follows.

14.1 BOILING OUT PROCEDURE14.1.1 ParametersA. Pre-commission cleaning of new systems to remove preservatives,

mill scale and other contaminants of construction.B. Subsequent to major system repairs, prior to returning to service.C. Removal of trace amounts of oil contamination.

14.1.2 ProcedureA. Mechanically remove as much oily matter and as many other loose

contaminants as possible.B. Fill the boiler to about one half its capacity with hot fresh water.C. Add Unitor Alkleen Safety Liquid at the rate of 15 litres/tonne of

boiler capacity.D. Secure manhole openings and fill boiler to normal steaming level.E. Open drum vents and drains on superheater outlets.F. Carefully and slowly commence firing while maintaining below

operating conditions.G. When steam begins to appear at vents, close vents and superheater

inlet drain. Leave outlet drain or outlet vent slightly open.H. Allow pressure in the system to increase at a rate no greater than

7 kg/cm2 per hour until one half of normal operating pressure or maximum 21 kg/cm2, whichever value is lower, is reached.

I. Maintain this condition for at least twenty-four hours, if necessary by intermittent firing of the boiler. Do not exceed originally-detemined cleaning pressure.

57WATER TREATMENT HANDBOOK56 14 / CHEMICAL CLEANING OF BOILERS

J. During this period, make short blowdowns from drums and headers, adding water as necessary to maintain the initial level.

K. After twenty-four hours, shut down the boiler and allow to cool until the pressure drops to zero.

L. Open all vents and drains and allow boiler to drain.

M. While draining, or as soon as possible after draining, flush the boilerwith high-pressure, hot, fresh water.

N. Inspect the system, removing any sludge or scum which may haveaccumulated during the cleaning process.

O. If results of the cleaning are unsatisfactory, repeat the procedure.

P. Secure boiler and return to service.

Q. If system is to be laid up, do so in accordance with recommended wet or dry procedure.

14.2 DEGREASING PROCEDUREFor removal of light to heavy contamination resulting from ingress of oil due todefective machinery, equipment seals, or bunker or cargo tank heating coils.

A. Determine the source of oil contamination and take appropriate steps toeliminate the problem prior to initiating the cleaning operation.

B. Inspect boiler interior as thoroughly as possible to determine the approxi-mate degree of contamination (i.e. light, moderate, heavy). While boiler isopen, muck out as much oil and oily sludge found in boiler as possiblebefore closing the boiler up. You are also recommended to plug down comers, if present, to allow circulation through main tubes of boiler. Installexternal circulation pump to circulate cleaning solution from water drumback to steam drum. Make all necessary connections.

C. Secure inspection access openings and introduce the appropriate amountof Tankleen Plus and fresh water based on the estimated degree of conta-mination as follows. Ensure all boiler internals needed to be cleaned.

Degree of % by Volume of Contamination Tankleen Plus in WaterLight 1–2 %Moderate 2–3 %Heavy* 3–5 %* If contamination is particularly heavy, Tankleen Plus can be substituted

by Carbon Remover at the rate of about 10 % by volume.

D. If circulation pump is being used, start circulating solution. Fire the boiler for about 5 minutes, then secure for 15–20 minutes. Continue this process until the water temperature reaches 50–60 °C. Do not allow the temperature to go above 60 °C. Continue this operation for about 12 hours.

E. Drain the boiler.F. Rinse thoroughly with high-pressure water (with heat if available).G. Drain and inspect as thoroughly as possible.H. If necessary, repeat steps 3 through 7.I. Secure all access openings and fill with feedwater. Remove plugs from

down comer if this method was employed.J. Startup initial dosage of treatment chemicals and initiate boiler operation.K. Monitor treatment residuals and adjust as necessary to bring boiler

water treatment programme employed into proper specification.L. Add 250 ml Unitor Boiler Coagulant every 12 hours and increase blowdown

to remove any excess oil that remains for at least one week after the unitis returned to service.

14.3 DESCALING AND DERUSTING PROCEDUREA. Inspect boiler interior as thoroughly as possible to determine degree of

contamination (i e. light, moderate, heavy).B. If deposits are covered with an oily or greasy film, degrease as outlined in

steps 1 through 8 of Unitor’s degreasing procedure (previous, this section).C. Subsequent to degreasing or, if not required, construct a circuit for

recirculating the acid cleaning solution through the boiler, being certain toby-pass all sections of the system containing non-ferrous metals. Ensurethis circuit is vented at its highest point to allow the release of gases produced during the cleaning process.

D. Introduce a solution containing the appropriate amount of Descalex orDescaling Liquid mixed with fresh water, based on the estimated degree ofcontamination as follows:

Degree of Descaling Liquid DescalexContamination in Water in Water

Light 5–10% 3–5%Moderate 10–15% 5–10%Heavy 15–20% 10–15%

E. The descaling process can be accelerated by controlled heating of thecleaning solution. This must be done with great care, never allowing thesolution temperature to exceed 60 °C.

F. Circulate for 4–12 hours depending upon the degree of contamination.

59WATER TREATMENT HANDBOOK58 14 / CHEMICAL CLEANING OF BOILERS

G. Continually check temperature and pH of the solution at regular intervals.Maintain temperature as previously indicated. If pH goes above 4, addadditional Descaling Liquid or Descalex. When using Descalex, take sample of original solution to compare with later samples. If solutionchanges to a yellowish colour, additional Descalex is required.

H. When the circulation period is complete, drain the system and rinse thoroughly with fresh water to remove any excess debris.

I. Neutralise any remaining traces of acid by circulating a 0.5 % solution of Alkalinity Control through the circuit for 2–4 hours.

J. Drain the neutralizing solution, checking the effluent to ensure it has a pH of 7 or greater. If not, repeat steps 9 and 10.

K. Re-inspect system interior and if necessary repeat steps 2 or 3 through 11 as indicated.

L. Remove by-pass connections, secure all access openings and fill withfeedwater.

M. Add start-up dosage of treatment chemicals and initiate boiler operation.N. Check for proper treatment residual levels, adding additional chemicals if

necessary to bring within proper specification limits.

Refer to Descalex and Descaling Liquid Product Data Sheet for additionalinformation.

15 Diesel Engine Cooling Water Treatment

15.1 PROBLEM AREASThere are four key areas which must be considered when treating dieselengine cooling water systems.

15.1.1 ScaleScale results when a compound precipitates from the water phasebecause its solubility has been exceeded. Scale is a dense, adherentdeposit of minerals and is tightly bonded to itself and to metal surfaces.Scale forming on metal surfaces requires four simultaneous factors:

A. Exceeding the solubility of the compound in water.B. Formation of small nuclear particles.C. Adequate contact time for crystal growth.D. Scale re-deposition exceeds the rate of dissolution.

One primary factor influencing scale adherence is surface roughness. The rougher the surface, the greater the probability of adherent scaleforming. Also, scale forms more readily on corroding surfaces than onnon-corroding surfaces. Easily corroded metals (mild steel) result in significantly more scale than metals that do not corrode (stainlesssteel).

In addition to the four primary factors influencing scale deposition,there are other factors that offset the formation of scale. Wildly fluctuating pH is a significant cause of scale deposition in closed loop systems. Unitor uses Borates to buffer and control this fluctuating pH.As the pH of the system increases, so does the scaling potential foralmost all common scale. This would include Calcium Carbonate,Calcium Sulphate, and Iron Oxide. Low pH extrusions can acceleratecorrosion, provide nucleating sites and increase the potential for someforms of Silica scale.

Scale formation in diesel engine cooling water systems can be controlled by various methods. Removing scale-forming Ions from thewater before that water enters the cooling system is the most effectivemethod. Almost all engine manufacturers recommend the use of distilled water. Distilled water is free of minerals. However, it is aggressive water and, if untreated, can lead to corrosion.

15.1.2 CorrosionCorrosion is the phenomenon that returns metals to their native statesas chemical compounds or minerals.

61WATER TREATMENT HANDBOOK60 15 / DIESEL ENGINE COOLING WATER TREATMENT

In diesel engines containing dissimilar metals, our concern is galvanic corrosion. When exposed to water, one metal becomes anodicand the other cathodic, setting up a galvanic cell. For example, whenCopper and Mild Steel are connected in water, the Mild Steel becomesthe Anode, because it will give up electrons more readily than theCopper. The metal loss occurs at the anode, so the Mild Steel corrodes.Unitor recommends the use of a corrosion inhibitor containing Nitrite,Borate and Azole. Nitrite protects Mild Steel and Iron, while Azole protect Copper from corrosion. Nitrite acts by forming a protectivemetal oxide (passivating film) on the metal to be protected.

15.1.3 FoulingFouling is different from scaling in that fouling deposits are formed frommaterial suspended in the water, while scale deposits are formed fromminerals in solution. Materials that cause fouling in cooling water systems are suspended solids and oil leaking into the system. We mustcontrol fouling in a diesel engine cooling water system, as it interfereswith the effectiveness of corrosion inhibitors.

15.1.4 Microbiological activityNitrites act as a food source for some types of bacteria. While the presence of bacteria is not as widespread in diesel engine coolingwater systems as in other cooling water systems, it is a potential problem. The problem becomes apparent when conducting chemicaltests of the cooling water. If the personnel on the vessel are dosingNitrites and do not get a reading and the pH begins to fall, there is apossibility of microbiological activity. This can be verified by simple testmethods (“dip slides”), or by sending a sample of the water to Unitor.

15.2 UNITOR COOLING WATER TREATMENT PRODUCTS Diesel engines have almost completely replaced turbines as the main propulsion unit in ships. These engines need to be cooled and water is usedfor this purpose. This water must be conditioned to ensure that scale does notdeposit on the heat transfer surfaces in the cooling system.

15.2.1 The SystemThe water is circulated around the engine and any loss due to leaks,etc. is made up from the expansion tank. As it circulates through theengine cooling spaces, the water picks up the engine heat, and this hotwater goes to a heat exchanger where it is cooled.

The steam heater is used to warm the engine up from cold. An airseparator is normally installed to get rid of entrained air in the system.

The water added to the expansion tank is termed “make-up” water.Distilled water shall preferably be used for these cooling systems.

This is normally made onboard by a fresh water evaporator (or generator). A useful way of increasing the plant efficiency is to utilisethe heat taken from the engine to provide a heat source to the evaporator.

If evaporated water cannot be used for make-up, then fresh shorewater will have to be used. This is normally much higher in impurities.

The engine water temperature is in the region of 65 °C to 75 °C at theinlet to the engine. It is maintained at this temperature by controllingthe cooling. The cooler is bypassed if the temperature drops.

15.2.2 CorrosionAs mentioned above, this is the main problem in diesel engine coolingsystems. The water contains some Oxygen, and if it is untreated, anideal environment will exist for all types of corrosion.

15.3 DIESELGUARD NB AND ROCOR NB LIQUID15.3.1 How do they work?All the information is contained in the relevant product data sheets butcan be summarised as follows:

They provide a very thin coating to all metal surfaces to prevent thecorrosion from starting. The water is also made alkaline by the treat-ment to ensure that there is no acid corrosion.

It is important that there is an excess of treatment in the system toreplace any breakdown in the coating and to treat the makeup water asit enters the system.

The testing for this is quickly carried out by the Spectrapak 309Cooling Water Test Kit.

Some points to note:– All cooling water treatments must be approved by accepted

Government bodies for use where the water is used as a heat source for an evaporator making drinking water.

– The treatments must also be accepted by the engine manufacturer. The Unitor products are covered in these areas.

15.3.2 Dieselguard NB dosage chartUnitor Dieselguard NB

– Initial dosage for an untreated system is 2 kg/1,000 liters of makeup water. This will bring the treatment level up to a minimum level of 1000 ppm.


– The chart below can be used to determine the dosage requirement necessary to achieve a nitrite residual level between the minimum and maximum specification range limits.

Nitrite (as ppm NO2) 0 180 360 540 720 900 1080 1260 1440 1620–2400

Dieselguard NB Kg/1000 L 2.88 2.52 2.16 1.80 1.44 1.08 0.72 0.36 0 0

15.3.3 Rocor NB liquid dosage chartUnitor Rocor NB LiquidA. Initial dosage for an untreated system is 9 litres/1,000 litres of

distilled water. This will bring the treatment level up to a minimumlevel of 1000 ppm.

B. The chart below can be used to determine the dosage require-ment necessary to achieve a Nitrite residual level between the minimum and maximum specification range limits.

Nitrite (as ppm NO2) 0 180 360 540 720 900 1080 1260 1440–2400

Rocor NB Liquid L/1000 L 13.0 11.3 9.7 8.1 6.5 4.9 3.3 1.7 0

Note: When initially dosing a cooling water system, it is typical that the initial dosage may vary from vessel to vessel, or system to system.Total passivation of the cooling water system will consume more product than when making Nitrite up as mainte-nance dosages. The quality of make-up water will also affect initial dosage rates.

15.4 TESTS FOR DIESEL ENGINE COOLING WATER TREATED WITHDIESELGUARD NB/ROCOR NB LIQUID

The following tests are recommended to maintain cooling water within theprescribed limits when using Dieselguard NB/Rocor NB Liquid:

1. Nitrite 1000–2400 ppm as NO2

2. pH 8.3–10.03. Chlorides 50 ppm maximum

15.4.1 Nitrite – Recommended Limits 1000–2400 ppm as NO2

The Nitrite concentration should be maintained within the above recommended limits to effectively inhibit any corrosive or scaling action within a closed cooling system. Over-concentration should be avoidedto minimise the cost of maintaining the system. Under-dosage can setup a condition where accelerated corrosion can occur in areas whichbecome unprotected. Dieselguard NB/Rocor NB Liquid is dosedaccording to the recommended nitrite level.

15.4.2 pH – Recommended Limits 8.3–10The effectiveness of a corrosion inhibitor is restricted to within a certain pH range. Treatment with Dieselguard NB/Rocor NB Liquidensures that this pH range is observed when the Nitrite level is sufficiently maintained to prevent corrosion. Under certain conditionsbecause of external contamination, the pH may not fall into the rangeusually found with the correct Nitrite dosage. In such cases, Unitor recommends dosing 50 ml of Unitor’s Alkalinity Control per tonne ofcooling water to raise the pH value when the pH is below 8.3. Re-testpH after dosage to prove that the pH value is being maintained between8.3 and 10.0.

15.4.3 Chlorides – Recommended limit max. 50 ppmThe Chlorides value of the cooling water should be kept as low as possible. Any increase in value whether sudden or gradual, will be anindication of sea water contamination. Check with the engine manu-facturer for other specified limits.

If the Chloride level exceeds 50 ppm, the possibility of corrosion inthe system increases because Chlorides have a negative effect on thepassivation film created by nitrites. Therefore, until corrective actionhas succeeded in bringing the Chloride level back down below 50 ppm,the nitrite level should be kept close to the upper limit (2400 ppm).

15.4.4 Sampling and testing of cooling waterSamples should be drawn, tested and results logged for each system atleast of once per week and if possible six times per month.


15.5 SAMPLING OF DIESEL ENGINES:Accessible sampling cocks should exist on all cooling systems for each dieselengine. This including, but not limited to, main jacket water, piston cooling,fuel oil valve, auxiliary engines, low temperature systems, etc. A representa-tive sample must be taken from each cooling water system to be tested.To minimise the effort in obtaining cooling water samples, a sample cocklocated in a position to draw a sample/having access to draw the samplequickly and easily will make the task of drawing samples a simple one.

In each case of drawing a sample, the container should be filled with thewater to be tested, then sealed and labelled. It is advisable to conduct theappropriate tests within 30 minutes of drawing the sample, although this timelimit can be extended when sample container is completely filled and sealed.

15.5.1 Sampling Procedure: The suggestion is for one sample bottle for each system to be tested.Mark each bottle clearly for each system.

A. Provide a clean bottle for each sample drawn:

The bottle should contain 0.5 litre, should be made of glass or plastic, have a screw cap that seals air-tight and a label indicating pertinent data:

a. Nature of water sample:1. High temperature system2. F.O. valve 3. Piston 4. Auxiliary 5. Low temperature system

b. Sampling point/location

B. Allow effluent to flush through sampling line a minimum of three to five minutes.

C. Cool effluent to less than 25 °C before commencing to draw sample.

D. Rinse bottle at least three times with sample water.

E. Secure cap on bottle air tight.

F. Be sure sample is representative of total coolant in system.

G. Draw sample from same point in the system each time.

H. Sample should be analysed as soon as possible after securing.

15.6 TEST EQUIPMENT – UNITOR SPECTRAPAK 309 TEST KIT TEST PROCEDURES15.6.1 Sample preparation:A. Cool sample to 21–25 °CB. Filter if necessary to clarify.

15.6.2 Spectrapak 309 content:A. Reagents:

a. Nitrite No. 1 tabletsb. Nitrite No. 2 tabletsc. Chloride tabletsd. pH test strips (6.5–10.0)

B. Equipment:a. Syringeb. Plastic sample container

15.6.3 Test methods: A. Nitrite test

a. Take a 5 ml water sample with the syringe and put into the container provided.

b. Make the sample up to 50 ml using distilled water.c. Add two Nitrite No. 1 tablets and shake to disintegrate (or crush

with the rod provided). Sample will be white.d. Add one Nitrite No. 2 tablet and shake to disintegrate.e. Continue adding the Nitrite No. 2 tablets one at a time until a pink

color persists for at least one minute.

Calculation:Nitrite(ppm) = number of No. 2 tablets x 180For example: If 9 tablets are used Nitrite = 9 x 180 = 1620 ppm.f. Mark the result obtained on the log sheets provided against the

date on which the test was taken.

B. Chloride testa. Take a 50 ml water sample in the container provided.b. Add one Chloride tablet and shake to disintegrate; sample should

turn yellow if Chlorides are present.c. Repeat tablet addition one at a time until the yellow colour

changes to orange/brown.

Calculation:Chloride ppm = (number of tablets used x 20) –20For example:If 3 tablets are used, Chloride ppm = (3 x 20) –20 = 40 ppmd. Mark the result obtained on the log sheets provided, against the

date on whichthe test was taken.


C. pH testa. Dip one of the test strips into the water sample so that the colour

zone is completely immersed.b. Compare the colour obtained with the reference, and read off the

printed pH value.c. Mark the result obtained on the log sheet provided, against the

date on which the test was taken.

15.7 TEST RESULTS15.7.1 RecordingThe test results should be recorded on the Spectrapak 309 RapidResponse log forms.

15.7.2 ReportingCompleted monthly log should be distributed as shown:

A. White copy – Send to Unitor Rapid Response Centre.

B. Pink copy – Vessel’s head office.

C. Yellow copy – Retain for ship’s records.

15.7.3 Evaluation

A. Logs will be reviewed for adherence to specification requirements by Unitor’s computerised RAPID RESPONSE system and staff.

B. A log review indicating the status of the system, problems and recommendations will be issued to the ship’s operator.

15.8 DESCALING LOW SPEED MARINE DIESEL ENGINECOOLING WATER SYSTEMS

Note: Be careful – use protective glasses and glovesConnect a thin (1/3”–1/2”) transparent hose to some low point of the systemand run it up to the level of the top of the expansion tank. You now have alevel indicator for the system.

Drain the system and fill up with clean tap water to the lowest level in theexpansion tank sight glass.

Connect the pressure side of the chemical cleaning module to the coolingwater inlet manifold. Make return connection from the bottom of the expan-sion tank to the mixing tank of the module.

The ship’s fresh cooling water pump should be isolated from the systemand not used for circulation, i.e. suction and pressure valves closed. The sameapplies to auxiliary machinery such as evaporators, generators, etc. Theseshould be boiled out separately if necessary.

Sufficient Descalex to mix up a 5–10 % solution is gradually filled into themixing tank, well dissolved and fed into the inlet manifold.

Take a sample of the solution for later colour comparison.The solution should be heated to 60 °C using the engine’s cooling water

pre-heater.Circulate the system for 1/2 hour, then close the shut-off valves on all

cylinders except one, and circulate for 15 minutes. Continue to circulate onecylinder at a time for 15 minutes each, over a period of 4 to 6 hours, checkingthe solution colour and temperature regularly. If the solution colour changesfrom red to orange or yellow, indicating acid neutralisation, add sufficientDescalex to the solution to return it to its original colour (usually 25 g per literof solution). This reinforcement of the solution should not be done more thantwice. If after two reinforcements the acid is still neutralised, the solutionshould be drained off and the process started again with a fresh solution. Thiswill usually only be necessary when dealing with very thick deposits.

When the cleaning solution retains its red colour for one hour, the cleaningoperation may be considered complete and the solution can be drained off.

Fill up the engine with clean fresh water and circulate each cylinder forten minutes. Then drain each cylinder separately in order to get the highestpossible dumping speed.

Open all inspection covers and check that all debris that has formed duringdescaling is flushed out. Close covers. Fill up the engine again and add 0.5 %Alkalinity Control.

Circulate the solution to remove any remaining acidity and passivate steelsurfaces. Circulation must be maintained until sufficient level of pH value isobtained. This should be tested through the whole engine. Drain the engine.

Adding the inhibitor – DIESELGUARD NB – ROCOR NB LIQUID.Refill the engine with fresh water produced by the evaporator to the lowest

level in the expansion tank sight glass. Add sufficient cooling water treatmentfor the initial dosage through the cleaning module.

Disconnect the cleaning module.Put all valves in normal operating position and circulate the system with

the main cooling water pump for 15 minutes. Vent the system thoroughly during this time.

Check the treatment concentration and adjust to 1500 ppm nitrite content.Fill the expansion tank to the normal operating level using water from the

evaporator production.Check the acid content of the system lubricating oil directly after the

descaling operation and repeat after 24 hours.Virtually the same procedure as above can be followed when descaling

4 or 2 stroke trunk engines. However, this kind of engine seldom has shut-offvalves on the individual cylinders and therefore all cylinders must be circulated simultaneously.

Medium-speed engines of this kind often have a drain bore “Tell Tale Bore”


from the space between the upper (water) and the lower (oil) cylinder liner O-ring. This is to check for leakages.

The bores should be inspected when the engine is running. If leaks areindicated, NO descaling should be performed unless the engine can be dismantled and the cylinder liners pulled out immediately after the descalingoperation. Otherwise, you cannot be sure that all acid is flushed out/neutralised, and corrosion of the sealing surface may occur.

15.9 DEGREASING MARINE DIESEL ENGINE COOLING WATER SYSTEMS

When diesel engine cooling water systems become contaminated with oil andand grease, the system should be cleaned to remove oily deposits, as theycan interfere with the cooling water corrosion treatment.

In Service CleaningThis method may be undertaken with engine running at normal speed.

1) Take a 0.25 litre cooling water sample for future comparison and let itstand in a clear glass container.

2) Calculate the amount of Tankleen Plus required for solution of 0.5 % i.e. 5 litres per 1000 litres cooling water. Drain off similar amount of coolingwater from engine if necessary. Slowly and intermittently add the cleanerto the cooling system via either the expansion or return tank.

3) After 5 hours, take a 0.25 litre cooling water sample. This should be allowedto stand in a clear glass container until any oil has risen to the top. Theprogress of the cleaning operation can be gauged by comparing thicknessof this oil level with that of the first sample. A sample should be taken after5–6 hours to monitor cleaning progress.

4) The cleaner can be left in the engine for a few days until a convenient portis reached where the engine can be drained.

5) Drain off the complete engine cooling system and flush thoroughly withclean water prior to re-filling with water of the required quality, to whichan appropriate anti-corrosion treatment such as Dieselguard NB or Rocor NB Liquid should be added.

Out of service CleaningThis method may be used when engine is stopped.

1) Take a 0.25 litre sample of cooling water for future comparison and allow itto stand in a clear glass container.

2) Drain the cooling system and flush out with water – then refill the system.

3) Calculate the amount of cleaner required for a solution strength of 2 % i.e.20 litres per 1000 litres cooling water. Drain of similar amount of coolingwater from engine if necessary. Add Tankleen Plus to the expansion tankor return tank.

4) Circulate the solution through the system and heat until the water reachesa temperature of about 60 °C.

5) Continue circulation of the solution through the system for a minimum of 5 hours.

6) Take a sample of cleaning solution from the system after a minimum of 5 hours.

7) When cleaning is completed, drain off the cooling water system, and thoroughly flush with clean water prior to refilling and adding an anti-corrosion treatment such as Dieselguard NB or Rocor NB Liquid.


16 Reporting Analysis ResultsOne important aspect of a good water treatment management system is toensure that analysis results and any action taken are recorded as the eventstake place and the reports are properly maintained for future reference.

As mentioned earlier, special log forms are supplied separately for bothboiler water treatment and diesel engine cooling water treatment. Theseshould be completed by the water treatment officer responsible. Attentionshould be paid not only to recording the results of various water analyses, but to reporting any changes in circumstances that may have a direct or an indirect influence on the results, including any major cleaning or repairs to the system.

In order that Unitor may keep a watchful eye on water treatment pro-grammes onboard individual vessels, it is essential that the instructions forour Rapid Response programme are followed and logs sent promptly to ourRapid Response Centre for review and comment.

Unitor will monitor the progress and performance of the onboard watertreatment programme and liaise with the vessel’s head office and shipaccordingly.

Examples of how to complete the report logs are given overleaf. Make sureyou use the correct log form in conjunction with your treatment programme.

Picture page 72, 73, 74, 75, and 76, shows log examples.

73WATER TREATMENT HANDBOOK72 16 / REPORTING ANALYSIS RESULTS

Unitor ASAChemical Business UnitP.O. Box 300 SkøyenN-0212 OsloNorway

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17 Water Tests, Summary

17.1 SPECTRAPAK TEST KITS309 Test Kit: – Nitrite

– pH– Cl

310 Test Kit: – P-Alkalinity– Cl– pH

311 Test Kit: – P-Alkalinity– M-Alkalinity– PO4– Cl– pH

312 Test Kit: – Hydrazine/Sulphite

PC 22 Test Kit: – P-Alkalinity– M-Alkalinity– PO4– Cl– pH– Conductivity– Hardness– Ammonia– Hydrazine– Silica

Samples to be tested: – Boiler water– Feed water– Condensate return– Make up water– Engine cooling water

17.2 TESTINGBoiler water: – P-Alkalinity

– M-Alkalinity– Cl– PO4– pH– Hydrazine/Sulphite– Conductivity– Silica– Appearance

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79WATER TREATMENT HANDBOOK78 17 / WATER TESTS, SUMMARY

Feed water: – Cl– Conductivity

Make up water: – Cl– Hardness– Silica

Condensate return: – Cl– pH– Ammonia

Engine cooling water: – Nitrites– Chlorides– pH– Appearance

Testing is mandatory to make sure the water treatment programmes are effective.

BOILER WATER – TEST DAILYFEED WATER – AS REQUIRED

CONDENSATE – TEST WEEKLYENGINE COOLING WATER – EVERY FOUR DAYS

MAKE-UP WATER – AS REQUIRED

Record all chemical tests on the Rapid Response logs.

17.3 TROUBLESHOOTING17.3.1 Boiler water tests

Fault Action

P-Alkalinity Too high BlowdownToo low Dose Alkalinity Control to the boiler

M-Alkalinity Too high Blowdown

Chlorides Too high Blowdown

pH Too low Dose Alkalinity Control to boilerToo high Blowdown

Phosphate Too high BlowdownToo low Dose Hardness Control

Hydrazine/Sulphite Too high BlowdownToo low Check for source of Oxygen leakage

Increase chemical dosage

Conductivity Too high Blowdown

Other actions in conjunction with previously mentioned:

AlkalinityIf P-Alkalinity test results are above limits even after not dosing chemicals,check the P-Alkalinity of the make-up water.

ChloridesIf high Chloride readings exist after blowdown, check for sources of saltwater leaks:

A) Drain cooler B) Condenser C) Heat exchangers

Always check the Chlorides of the feedwater, condensate return and make-upwater when Chloride readings in the boiler continue to be above maximumlimits. If you have steam on deck, check the return lines.

pHCheck pH of condensate. If too low, increase dosage of Condensate Control. If too high, decrease dosage of Condensate Control.

PhosphateIf unable to maintain a Phosphate reading after dosing Hardness Control,check the make-up water for Chlorides.

Hydrazine/SulphiteCheck temperature of feedwater. In most cases, the higher the temperature of the feedwater, the lower the dosage of Oxygen Control or Sulphite.

ConductivityIf conductivity readings remain high after blowdown, check for:

A) Chloride levels/leaks B) Condensate return C) Phosphate level

17.3.2 Cooling water tests

Fault Action

Nitrites Too low Dose Dieselguard NB or Rocor NB Liquid.

Too high Stop dosing of chemical until the Nitrite level is back down below the max. limit.

pH Too low Check for salt water leaks and combustion gas leakage.

Chlorides Too high Check for leaks. Increase the chemical dosage to bring the Nitrite level close to the upper limit (2400 ppm).

81WATER TREATMENT HANDBOOK80 17 / WATER TESTS, SUMMARY

NitriteIf Nitrite readings remain low after dosing Dieselguard NB or Rocor NBLiquid, you may have a bacteriological problem. The cooling watershould then be analysed with appropriate test “dip slides” which can beordered from Unitor. Unitor also has available an effective biocide calledMAR-71, which is specially developed for bacteriological problems.

pHIncrease chemical dosage. If Nitrite level is within recommended limits,dose Alkalinity Control to increase the pH.

17.3.3 Sea water cooling treatmentTo avoid fouling in sea water systems, Unitor has developed a veryeffective Amine-based dispersant of marine growth such as ShellfishAlgae and micro-organisms in order to prevent the a.m. problem.Because of its filming properties, the product also acts as a corrosioninhibitor.

Bioguard can be used in both static and flowing systems such asballast tanks and looped cooling systems.

The diagram on the previous page shows the typical dosage layout.This can be modified to suit a particular situation. Although the

product will gradually clean fouled systems, treatment should preferably be started on a clean system.

Dosage for sea water cooling systems:Dose 0.6 ltr Bioguard for every 100 m3 of seawater flowing through thesystem per hour. The system throughput is to be determined either fromthe rating of the pump(s) or from the system specifications. Treatment isnecessary in coastal waters and should commence three days beforeentering these waters and continue for three days after leaving coastalwaters. The calculated dose should be given over a one-hour periodand repeated every 48 hours.

Dosage for static ballast tanks:Dose one litre of Bioguard per 100 m3 of water prior to ballasting, followed by a monthly dose of 2 litre per 100 m3.

NB! Bioguard should only be diluted with fresh water prior to dosing if necessary.

83WATER TREATMENT HANDBOOK82 18 / EVAPORATOR TREATMENT

18 Evaporator TreatmentTHE FRESH WATER EVAPORATOR (OR GENERATOR)

There are two main types:THE VACUUM or FLASH EVAPORATORandTHE STEAM HEATED EVAPORATOR

18.1 THE VACUUM EVAPORATORVacuum is maintained in the evaporator, considerably reducing the boilingpoint of the water.

The heat source used is the engine jacket water. The jacket water is circulated through the lower section of the evaporator where the heating section is. This heating section is a series of vertical tubes surrounded by theheating water. Sea water is pumped into the vertical tubes from below to beheated by the jacket water. The water vapour produced rises to the top of theevaporator where it comes into contact with cooling tubes and condenses.The condensate is then taken off for storage. The system is very efficientwhen correctly set up, but there are several points to consider:

A. 3 percent of seawater is dissolved minerals.

B. Evaporators of this type have a tendency to allow the seawater to foamand so salt is carried over with the distilled water.The treatment is to be fed continuously. The evaporator vacuum will pullthe treatment in and it will enter the evaporator with the seawater.

Sufficient treatment should be mixed for 24 hours operation. Treatment isessential to keep the evaporator operating efficiently for longer periods of time. It works in the following ways:

a. Some of the dissolved solids may form scale and the treatment will help prevent the solids from adhering to the heating surfaces and keep these scale formers in solution.

b. The sludge will be conditioned to make extraction of the concentrated sea water (brine) easier.

c. The foaming tendency of the brine will be suppressed by anti-foaming agents.

Unitor treatment is: Vaptreat.Average dosage: 0.3 l/10 tonnes of distillate produced.This is calculated on a standard brine density of 1.038 kg/l.

85WATER TREATMENT HANDBOOK84 18 / EVAPORATOR TREATMENT

FRESH WATER GENERATORType AFGU 1-E-10/1-E-15

19 Marine Equipment19.1 SOME COMMON MARINE EQUIPMENT

19.1.1 High Pressure Boilers > 30 bar• Babcox & Wilcox • Combustion Engineering• Foster Wheeler • IHI

19.1.2 Low Pressure Boilers < 30 bar• Sunrod • Aalborg • Cochran • Osaka • Kawasaki • MHI

19.1.3 Slow Speed Diesel Enginees < 120 rpm• Mitsubishi • Sulzer • MAN B & W • Gøtaværken • Fiat GMT

19.1.4 Medium Speed Diesel Engines 120–900 rpm• Wartsila • Sulzer • Pielstick • Enterprise • MAN B & W• MaK • Deutz • Bergen Diesel • Daihatsu

19.1.5 High Speed Diesel Engines > 900 rpm• Hitachi • Yanmar • EMD • Cummins • Caterpillar

19.1.6 Evaporators• Alfa-Laval Desalt • Atlas (bought by Alfa-Laval) • Nirex• Maxim • Weir


Notes:

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Notes:

88 20 / NOTES

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58044373 Water Treatment Handbook UNITOR

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