Boiler Water Treatment, Testing, and Blowdown

1. Why the boiler water must be controlled

Feedwater is never pure. Every litre carries dissolved salts, dissolved gases, suspended matter, and sometimes oil. As steam leaves the boiler, those impurities stay behind and concentrate. Without control, the concentration rises until the water starts to attack the boiler or throw solids out with the steam.

Untreated water causes four separate problems:

1. Scale and deposits — solids precipitate onto hot surfaces and insulate them.

2. Corrosion — the water chemistry becomes aggressive to steel and copper alloys.

3. Foaming and carryover — dissolved solids and oil make the water surface frothy, and water leaves with the steam.

4. Sludge accumulation — precipitated solids settle in low-velocity areas and choke circulation.

Water treatment exists to do five things:

• Keep the water alkaline so acidic attack cannot proceed.
• Precipitate or complex hardness so it leaves as removable sludge instead of hard scale.
• Remove dissolved oxygen before it pits the metal.
• Keep dissolved solids below the level at which foaming starts.
• Protect the condensate and feed system, so corrosion products do not accumulate in the boiler.

Every activity in this topic sits under one of those five aims. Dosing, testing, and blowdown are not separate rituals — they are the three controls that hold the chemistry inside its limits.

2. What is dissolved in the water

2.1 Classification of salts

Non-scale-forming or non-hardness salts

• Sodium bicarbonates, chlorides, sulphates, and nitrates.
• Very high solubility; they remain dissolved until very high density is reached.
• They do not form scale, but they raise total dissolved solids, promote foaming, and carry chloride that accelerates corrosion.
• Sodium salts can also concentrate under deposits and in crevices and produce alkaline conditions that crack steel.

Scale-forming or hardness salts

Alkaline or temporary hardness salts — bicarbonates and carbonates of calcium and magnesium:

• Bicarbonate solutions decompose when boiled. Carbon dioxide is driven off and insoluble carbonate is left behind.
• Calcium carbonate scale is porous, and less dangerous than calcium sulphate scale, but it still insulates the tube.

Non-alkaline or permanent hardness salts — chlorides and sulphates of calcium and magnesium:

• These solutions do not decompose readily on boiling.
• Calcium sulphate forms a hard crystalline ring. Its solubility falls as temperature rises, so it deposits preferentially on the hottest surface — exactly where cooling is most critical.
• Magnesium chloride is thermally unstable at boiler pressure and temperature. It breaks down to hydrochloric acid, and that acid attacks the metal. The reaction regenerates itself:

MgCl₂ + 2H₂O → Mg(OH)₂ + 2HCl

Fe + 2HCl → FeCl₂ + H₂

FeCl₂ + 2H₂O → Fe(OH)₂ + 2HCl

The acid is regenerated each cycle, so a small quantity of magnesium chloride can do a great deal of damage. This is why chloride control is treated as a hard limit, not a target.

2.2 Dissolved gases

Oxygen enters with cold feedwater and through any point in the system below atmospheric pressure. It causes pitting — local, deep, and able to perforate a tube while the rest of the surface looks healthy.

Carbon dioxide dissolves to form carbonic acid. It comes from bicarbonate decomposition in the boiler and from air ingress. It lowers pH and attacks both boiler metal and condensate lines.

Removing oxygen is easier before it reaches the boiler, so deaeration and scavenger dosing are both used. The mechanical deaerator removes the bulk; the chemical scavenger mops up the remainder.

2.3 Other sources of trouble

Oil and grease — from fuel heating coils, lubricating systems, or contaminated returns. Oil coats tube surfaces, prevents the water from wetting the metal, promotes overheating and foaming, and resists blowdown.

Treatment: the immediate response is dosing a coagulant such as sodium aluminate or a liquid coagulant, which breaks the oil out into a removable form, followed by blowdown. Find the source — usually a leaking fuel oil heater coil or an overflowing lubricating oil point.

Iron and copper oxides — corrosion products carried in from the feed and condensate system. They settle on tube plates, support plates, and in low-flow regions.

Suspended matter — sand, dirt, and debris from make-up water or from poor tank condition.

3. What each problem does to the boiler

3.1 Scale and deposits

Scale is a poorer conductor of heat than steel. A thin layer raises the metal temperature well above the water temperature, and the tube loses its design margin.

Consequences:

• Tube metal temperature rises; strength falls.
• Bulging, cracking, and eventually rupture.
• Reduced heat transfer, so more fuel for the same steam.
• Narrowed passages and reduced circulation, which makes the deposit grow faster.
• Deposits hide crevices where corrosion concentrates.

Because deposits collect most heavily where heat flux is highest, failure happens first at the hottest tubes, not uniformly.

3.2 Foaming, priming, and carryover

Foaming is the build-up of a stable froth on the water surface. Priming is the entrainment of water droplets with the steam. Carryover is the general name for anything leaving the drum that should not — water, salt, or both.

Causes:

• High total dissolved solids, especially chlorides and sodium salts.
• High alkalinity.
• Oil or organic contamination.
• Sudden, large load change.
• Insufficient blowdown.
• Water level too high.
• Damaged or displaced steam separating equipment.

Effect: dissolved salts are carried in the steam, concentrate as the steam is used, and deposit on superheater tubes, valve seats, and turbine blades. Deposits on turbine blades change balance and reduce efficiency; deposits in superheater tubes cause overheating. Silica in particular can deposit in turbine blading and is very difficult to remove.

3.3 Corrosion mechanisms

Pitting — localised attack. Breaks through the protective oxide film in one small spot and eats downward. Oxygen and chloride drive it.

General and acidic corrosion — the whole surface thins. Low pH, carbon dioxide, and chloride are the usual causes.

Caustic attack (caustic embrittlement) — high caustic alkalinity concentrates in a crevice or under a deposit, dissolves the protective film, and causes intercrystalline cracking. The metal itself becomes brittle. Sodium carbonate in the water breaks down under heat and pressure into sodium hydroxide, which is why caustic alkalinity is measured separately from total alkalinity and limited more tightly.

Na₂CO₃ + H₂O → 2NaOH + CO₂

At the surface the sodium hydroxide attacks the steel to form sodium ferrate, and the metal loses ductility.

Corrosion fatigue — a cyclic stress applied to an already-corroded surface. Cracks start at pits or at the base of corrosion grooves.

Crevice and deposit corrosion — oxygen cannot reach the area under a deposit while the surrounding water stays oxygenated. The difference in oxygen concentration sets up a corrosive cell, and the attack continues unseen under the scale.

Dezincification — selective removal of zinc from brass fittings and tube plates, leaving a weak copper sponge.

4. Treatment chemicals and what they actually do

4.2 How the chemicals are dosed

Chemicals are normally added as a dilute solution fed by a proportioning pump, or injected from a pressure pot.

Two rules matter in practice:

• Keep the chemical usage to the minimum that holds the test results in range.
• Inject over a long period rather than in one large dose. A long, slow injection distributes the chemical evenly and avoids the local high concentration that causes foaming.

Excessive phosphate without adequate blowdown produces phosphide deposits as bad as scale. Where that risk exists, sludge conditioners such as polyelectrolytes are added as well.

4.4 Polymer, sludge, and anti-foam treatment

Polymers are large molecules built by linking simple units — polyelectrolytes, polyacrylates, polyamides. Polymer treatment prevents scale formation and minimises sludge. It can also loosen existing scale, which is a mixed blessing: a boiler converted to polymer treatment after years on phosphate can begin to leak at expanded joints that were previously sealed by scale. Polymers also absorb trace oil.

Polymer treatment suits low-pressure boilers that have no phosphate to suppress caustic alkalinity.

Sludge conditioners and coagulants — mainly polyelectrolytes. They stop precipitated particles from forming soft scale and keep oil in emulsion so it can be blown out. The water must be kept alkaline for them to work.

Anti-foams — usually polyamide-based. They lower the stability of the film around a steam bubble so the bubble collapses instead of building foam. Where contamination is severe, a separate antifoam injection point is used so the antifoam does not have to be mixed into the main treatment.

Dispersing agents — starch or tannin. They stop solid precipitates joining into large crystals.

4.5 Neutralising and filming amines

Neutralising amines are nitrogen-hydrogen compounds that raise the pH of the condensate. The condensate leaving a condenser is very pure and slightly acidic — often called "hungry water" — and will dissolve trace metals to satisfy that acidity. Distilled make-up aggravates this because it carries dissolved carbon dioxide.

• Cyclohexylamine (bramine) — used with hydrazine to hold feedwater alkalinity. It is stable at high temperature, so it controls steam-line alkalinity better than hydrazine, with less risk of ammonia attacking copper. It travels with the steam and condenses with the condensate, so it acts on the condensate system, and it has a gradual cleaning effect that removes the copper and iron oxide film from tube surfaces.
• Hydrazine — as a neutralising agent it breaks down to ammonia, which protects ferrous metal but attacks copper.

Filming amines — coat the pipe bore with a molecular water-repellent film. Their main job is a barrier, not neutralisation.

Where amines are injected matters:

• In the cross-over pipe between HP and LP turbines — reduces corrosion of copper alloys, but the deaerator then only works as a feed heater.
• After the deaerator — the deaerator performs correctly as both deaerator and feed heater.
• The best arrangement is a changeover: inject into the cross-over at sea, and after the deaerator when the turbine is shut down.

5. Treatment schemes by pressure

The treatment has to suit the boiler. The higher the pressure, the more sodium carbonate breaks down and the more aggressive the water becomes.

Low-pressure tank boilers, below about 14 bar

• Sodium carbonate to precipitate salts and provide alkalinity.
• Magnesium sulphate as a sludge conditioner.
• Sodium carbonate breaks down to caustic in higher-rated boilers, so the initial dose is made with sodium sulphate.

Medium-pressure tank boilers, below about 17.5 bar

• Sodium carbonate, sodium phosphate, and a sludge conditioner.
• An oxygen scavenger to allow the magnetite (Fe₃O₄) layer to form and stay intact.

Medium- to high-pressure water-tube boilers, below about 60 bar

• Sodium carbonate, disodium phosphate, and sludge conditioners.
• Oxygen scavenger in use.

Above about 42 bar

• A deaerator is required.

High-pressure boilers, about 42 to 80 bar

• Sodium carbonate decomposition becomes significant, so sodium hydroxide is preferred for controllability, together with disodium phosphate.
• Above roughly 42 bar, sodium hydroxide attacks the magnetite layer, so congruent phosphate treatment is used instead of straight caustic addition.

Congruent phosphate treatment holds the phosphate and pH in a relationship that keeps the protective magnetite layer intact. It works by keeping the sodium-to-phosphate ratio in a range where the water does not become either caustic or acidic at the tube surface.

All-volatile treatment is used where adding solids is unacceptable — the chemicals are volatile, travel with the steam, and leave no dissolved solids in the boiler.

Chelant (EDTA) treatment keeps hardness in solution so it can be removed by blowdown. It has to be fed into the feedwater, upstream of the boiler, so the hardness is complexed before it reaches the hot surfaces. Correct feed gives a chelant residual in the boiler water, but a boiler-water residual alone is not proof of correct control: the residual that matters is in the feedwater, and it has to be maintained at all times. The treatment must be fed downstream of the boiler feed pump, using a high-pressure chemical feed pump and a stainless steel injection quill. Feeding to the deaerator storage is not recommended because copper alloys in the feed pump may be attacked.

6. How to take a boiler water sample

Everything downstream depends on the sample being representative. A bad sample produces a meaningless test result, and a meaningless result produces the wrong dose.

1. Open the cooling water to the sample cooler first.

2. Open the sampling cock and drain the first portion to waste. This clears the condensate and stagnant water in the line. If you do not do this, flash-off in the line will change the concentration and the reading will be wrong.

3. Collect the sample in the container supplied with the test kit, at about 25 to 30 °C after the cooler.

Notes that matter:

• Do not take the sample from a rusty or stagnant line.
• The sample cooler is there for a reason: a hot, flashing sample gives a false, usually higher, reading and is dangerous to handle.
• Take the sample from the correct point for the test you are doing. The boiler-water sample comes from the boiler-water connection; the condensate and feed-water samples come from their own points.

7. How to perform each test

Where possible, use the ship's test kit. The methods below are the standard titration and comparator procedures. The kits supplied on board may use different reagent concentrations and different multipliers, so always read the kit instructions and use the multiplier printed on the kit.

7.1 Alkalinity to phenolphthalein (P-alkalinity)

What it measures: the alkalinity due to hydroxides and half the carbonates. It is the warning against excessive caustic concentration and the risk of caustic embrittlement.

Method:

1. Take 100 ml of cooled boiler water sample.
2. Add 1 ml (about 10 drops) of phenolphthalein indicator.
3. The sample turns pink. Phenolphthalein is a weaker alkali than hydroxide or carbonate, so a pink colour means those are present.
4. Titrate with N/50 sulphuric acid until the pink colour just disappears and the sample is clear.
5. Record the millilitres of acid used.

Calculation:

ppm of CaCO₃ = ml of N/50 acid used × 10

Why it works: the acid first neutralises the hydroxides, forming salts, then reacts with the carbonate to form bicarbonate. Bicarbonate is less alkaline than phenolphthalein, so when all the hydroxide and carbonate has been dealt with, the pink colour is gone. Two carbonate molecules produce one bicarbonate molecule, so the acid used represents the hydroxides plus half the carbonates.

7.2 Total alkalinity (T-alkalinity)

What it measures: hydroxides, carbonates, and bicarbonates together.

Method:

1. Continue directly from the P-alkalinity sample — do not start again.
2. Add 10 drops of methyl orange; the sample turns yellow.
3. Titrate with N/50 sulphuric acid until the colour changes to pink.
4. Record the total acid used for both stages.

Calculation:

ppm of CaCO₃ = ml of N/50 acid used in both tests × 10

Interpretation: methyl orange is less alkaline than phenolphthalein and less alkaline than bicarbonate, so it only changes when the bicarbonates have also been neutralised.

Two practical conclusions come out of the relationship between the two results:

• If no yellow colour appears when methyl orange is added, there are no bicarbonates — so there were no carbonates either — and the whole of the P-alkalinity was due to hydroxides.
• Hydroxides and carbonates can exist together in solution, but hydroxides and bicarbonates cannot. Getting both in a single result means a sampling or titration error.

7.5 Phosphate test

What it measures: the phosphate reserve. Phosphate must be present to deal with any hardness that reaches the boiler, but too much phosphate causes foaming and priming and, on highly rated boilers, thick phosphide coating.

Method using a comparator:

1. Take 25 ml of filtered boiler water sample.
2. Add 25 ml of vanadomolybdate reagent.
3. Fill the comparator tube with this solution and place it in the right-hand compartment of the comparator.
4. In the left-hand compartment place a blank made by mixing equal volumes of vanadomolybdate reagent and de-ionised water.
5. Allow the colour to develop for at least three minutes.
6. Compare with the disc and read the phosphate reserve.

Calculation:

Phosphate reserve in ppm (mg/l) = disc reading

Method using the drop-count technique (some kits):

1. Take the sample. Do not cool it. Filter it.
2. Add 4 crystals of potassium.
3. Cool it.
4. Add 5 ml of ammonium molybdate, which makes the sample cloudy.
5. Time how long the cloudiness takes to appear.

Reading the drop-count result:

• Cloudy within about 2 minutes → approximately 70 ppm phosphate.
• Cloudy within about 5 minutes → approximately 20 ppm phosphate.

Filtering matters: suspended matter produces a false cloud or a false colour.

7.6 Hardness test

What it measures: the calcium and magnesium hardness remaining in the water, expressed as ppm calcium carbonate. It is the direct check that the treatment is coping with hardness ingress.

Method:

1. Take 100 ml of filtered boiler water sample and cool it.
2. Add 2 ml (about 20 drops) of ammonia buffer solution. This holds the sample at the pH at which the indicator works correctly.
3. Add 0.2 g of mordant black 11 indicator (also supplied as Eriochrome Black T) and stir until dissolved.
4. If hardness salts are present, the solution turns wine red.
5. Titrate with EDTA solution until the colour changes to purple, and then to blue.
6. Record the millilitres or drops of EDTA used.

Calculation:

ppm of CaCO₃ = ml of EDTA used × 10

or, for drop-count kits:

ppm of CaCO₃ = drops of EDTA × 10

Why the colour changes: the indicator combines with the hardness ions to give the wine-red colour. EDTA has a stronger affinity for those ions than the indicator does, so as it is added it strips the ions away from the indicator. When all the hardness has been taken up by the EDTA, the indicator returns to its free blue colour. The purple stage is the transition.

Note that some waters give a greyish end point rather than a clean blue. Read the end point consistently, and use the same judgement each time so the trend remains meaningful.

7.8 pH value

pH can be obtained by three methods:

1. Litmus paper — quick, but only tells you whether the water is acidic or alkaline, and rough at that. Blue means alkaline, red means acidic.
2. Colourimetric — comparator with indicator, reasonably accurate.
3. Electrolytic — a pH meter with glass electrode, the most accurate of the three.

For routine watchkeeping the colourimetric method is normal; the pH meter is used where accuracy matters or where results are being disputed.

7.9 Salinometer and hydrometer

On low-pressure boilers such as the multitubular Scotch, vertical Cochran, and thimble-tube types, a salinometer is still used as a quick check on density.

• The scale normally runs from 0 to 1/32nd.
• Floating in pure water at 93 °C, with relative density of unity, the reading is zero.
• Floating in common salt solution at 93 °C with a relative density of approximately 1.025, the reading is about 1/32nd, representing roughly 32,000 ppm.

For low-pressure boilers using sea water as make-up, the boiler density is held as close as possible to about 1/32nd, which is approximately 125,000 ppm, by blowdown. Using sea water as make-up should be avoided; where it cannot be avoided, soda ash provides some protection.

The salinometer is a rough indicator only. For accurate work it is inadequate, and the titration tests in the sections above must be used.

8. What the test results tell you

8.1 Reading the trends, not the numbers

A single result tells you what the boiler water is doing right now. A trend tells you where it is going.

8.2 Why you treat the cause, not the reading

If chloride is rising, the answer is not more blowdown forever. The answer is to find the seawater leak. If phosphate is falling, the answer is not an unlimited dose — the answer is to find what is consuming it. The test results are evidence, and the evidence points at a physical fault somewhere in the plant.

9. Blowdown and Scum Blowdown Procedures

Blowdown is the controlled discharge of boiler water to remove accumulated dissolved solids, precipitated sludge, floating grease, or oil contamination, and to empty the boiler for internal inspection and maintenance. Boiler blowdown is categorized into surface (scum) blowdown and bottom blowdown.

9.1 Overview of Blowdown Types

A marine boiler employs three distinct operational forms of blowdown:

9.2 Scum Valve & Surface Skimming Procedure

The scum valve is a specialised boiler mounting fitted to the steam drum or upper shell. On the inside of the drum, it connects to a shallow scum collector pan or funnel located just beneath the normal working water level.

Warning: MARPOL Annex I Crucial Restriction: Never Discharge Oily Scum Overboard!

When scum blowdown is performed to clear oil ingress or surface grease, the discharge MUST be routed to the engine room bilge holding tank or oily bilge, NEVER OVERBOARD. Discharging oily boiler surface foam through the ship-side overboard cock directly violates MARPOL Annex I regulations and results in heavy port-state fines, vessel detention, and legal prosecution. The oily bilge effluent must subsequently be treated through the 15 ppm Oily Water Separator (OWS) with a certified Oil Discharge Monitoring and Control System (ODME) or retained for shore disposal.

Step-by-step scum blowdown execution (What valve, in what manner):

1. Raise the boiler water level slightly: Bring the water level to roughly 70–75% (high normal) in the gauge glass so that surface froth and floating oil spill easily into the lip of the internal scum pan.

2. Line up the discharge route to bilges / oily drain: Open the bilge line isolation valve (Valve 1 in the scum circuit schematic) to verify that the path to the bilge well or oily bilge holding tank is completely open and unpressurised.

3. Open the boiler scum isolation valve (Valve 2): Open this primary isolation valve mounted on the drum fully. This ensures the valve seat is completely out of the flow path.

4. Crack and throttle the intermediate scum control valve (Valve 3): Open the throttling valve carefully to control the skimming flow rate. Observe the boiler steam pressure and keep a sharp continuous watch on the water gauge glass. Maintain scum blowdown for only 1 to 2 minutes.

5. Shut the intermediate throttling valve (Valve 3) tightly: Once floating oil and foam have cleared, shut Valve 3 firmly. Then close the boiler root scum valve (Valve 2).

6. Shut the bilge isolation valve (Valve 1): Close the downstream line valve. Verify water level has recovered to normal steaming level via automatic feed control.

7. Verify zero valve leakage (thermal check): Feel the scum discharge pipe downstream after 10–15 minutes. It should cool down to engine room ambient temperature. A warm or hot pipe indicates that the scum valve is passing steam and water continuously.

8. Isolate the contamination root cause: Surface scumming removes only the floating film. Immediately investigate fuel oil heating coils, lube oil cooling jackets, or contaminated drain observation tanks, dump suspect condensate, and dose coagulants (e.g. sodium aluminate) to agglomerate remaining oil particles for bottom purging.

9.3 Bottom Blowdown Valve Construction & Mechanical Safety Features

Bottom blowdown discharges from the bottom of the water drum or shell under full operating boiler pressure and temperature. The valve configuration is engineered with specific safety features to protect personnel and prevent mechanical damage.

Two valves in series arrangement:

• The boiler bottom blowdown branch utilizes two valves in series: a primary (boiler-side root) valve and a secondary (intermediate throttling) valve.
• Purpose: When opening, the root valve is opened fully before the secondary valve is cracked. All high-velocity wire-drawing and erosive wear from gritty sludge occurs across the secondary valve seat, leaving the primary valve seating surfaces pristine. This guarantees 100% leak-tight isolation when both valves are secured.
• On water-tube and medium-to-high pressure boilers, parallel-slide valves with rack-and-pinion drive are widely used.

Ship-side blowdown valve / cock:

• Mounted directly on the ship's bottom shell plating with studs screwed into the hull plating and riveted over.
• Constructed as a taper plug cock with an engineered safety guard.
• Safety slotted gland guard: The gland cover is arranged with a special slot or guard that matches a projection on the box spanner/handle. The handle can ONLY be engaged or removed when the cock is in the 100% FULLY CLOSED position. This physical interlock prevents the watchkeeper from accidentally removing the spanner or walking away while the overboard cock is left open.

9.5 Essential Oral Exam Questions & Practical Rules

Class 4 / MEO Oral Exam Questions & Answers

Q1: Why is the ship-side blowdown cock opened FIRST and closed LAST?

• Safety of Personnel (Line Integrity): The external blowdown pipe running between the boiler and ship side is exposed to harsh bilge environments and may suffer internal/external corrosion. If the boiler valve were opened first, this line would be charged with full boiler pressure (e.g. 16–30 bar at 200 °C) while the ship-side cock was still shut. If the pipe ruptured, scalding steam and boiling water would blast across the engine room, killing or severely burning the watchkeeper who stepped down to open the ship-side cock. Opening the ship-side cock first ensures the line is never dead-ended under pressure.
• Prevention of Cold Sea Water Ingress: On completion of blowdown, closing the boiler valve first ensures that condensing steam inside the boiler cannot draw cold seawater back into the boiler drum under vacuum. Closing the ship-side cock last provides secondary isolation.

Q2: Why is the ship-side cock fitted with a safety slotted guard on its gland?

• The guard ensures that the box spanner/handle can only be engaged or withdrawn when the taper cock is in the fully shut position. This prevents watchkeepers from accidentally leaving the ship-side discharge open or walking away while the vessel is exposed to the sea.

Q3: Why must bottom blowdown be performed in short 5–10 second bursts rather than one continuous blow?

• Sludge is dense and rests in stagnant pockets. A short, violent blast creates maximum flow acceleration that scours and dislodges settled mud. A long, slow blow merely channels water through the centre of the drum, wastes tons of expensive heat and chemically treated water, destabilises water level, and risks tripping the burner on low water.

Q4: How do you detect a passing blowdown valve, and what are its consequences?

• Detection: Feel the blowdown pipe downstream of the valve during routine watchkeeping rounds. If the valve is tight, the pipe will be cold (ambient engine room temperature). If the pipe is scalding hot, the valve is passing.
• Consequences: Continuous loss of hot demineralised water, severe fuel wastage from heating replacement make-up, rapid exhaustion of chemical reserves (phosphate and alkalinity drop rapidly), and frequent false alarms of boiler tube leakage.

10. Protecting the boiler when it is not steaming

10.1 Short periods out of service

Water-tube boilers, about two days: either fire the boiler at intervals to hold pressure above about 3.5 bar with the water maintained at its normal steaming composition, or fill the boiler while hot with hot deaerated alkaline feed water with about 0.5 kg of anhydrous sodium sulphite per tonne of water. If the second method is used, top up periodically and remove all air from the system.

Fire-tube boilers, short periods: ensure the alkalinity to phenolphthalein is not below the recommended value, or fill the boiler completely with alkaline water.

The logic in both cases is the same: exclude oxygen and keep the water alkaline. A boiler sitting partly full of aerated water corrodes faster than one that is steaming.

10.2 Long periods out of service

1. Drain the boiler completely.

2. Dry it out with heater units.

3. Place trays of quicklime internally at suitable positions throughout the boiler.

4. Seal the boiler up.

5. Fit blanks to pipe connections where steam is being maintained in other boilers. Blank the blowdown in every case.

6. Renew the lime at least once every two months.

10.3 Chemical cleaning of a new boiler

Before a new boiler is commissioned, it carries surface rust, mill scale from manufacture and erection, dirt, and traces of oil. Pre-commission cleaning is carried out in this order:

1. Boil out at atmospheric pressure with an alkaline solution to remove oil and dirt.
2. Wash out with a heated acid solution to remove rust and mill scale.
3. Rinse with a weak acid solution.
4. Flush repeatedly to remove debris.
5. Passivate under pressure with hydrazine. The feed system is treated the same way, except that the alkaline boil-out is omitted and the passivation is done at atmospheric pressure.

11. The routine

EVERY ROUND
- Read and record water level, and check both gauge glasses
- Confirm dosing pump running at the correct stroke
- Look at the sample for colour, oil, or suspended matter

DAILY
- Take samples correctly: cool the line, drain first, collect at 25-30 C
- Run the tests required by the ship's programme
- Record results and compare against the previous readings, not just the limits
- Adjust dosing and blowdown in small steps
- Carry out surface blowdown as required and bottom blowdown at the scheduled interval

WHEN A RESULT IS OUT OF RANGE
- Repeat the test before acting: confirm sample and reagents are correct
- Compare against the trend to see how fast it is moving
- Look for a physical cause: condenser leak, dosing fault, level problem, oil ingress
- Correct the cause; use dosing and blowdown only to hold the situation until the cause is fixed
- Record what you found and what you did

12. Handling the chemicals safely

The treatment chemicals are hazardous and the test reagents are worse.

Danger: Handle with the correct PPE

• Hydrazine is toxic and a suspected carcinogen. Use gloves, eye protection, and avoid vapour. Never pipette by mouth.
• Sodium hydroxide and strong alkalis burn skin and eyes severely. Flush with copious water and get medical help.
• Sulphuric acid and other acids burn and splatter. Add acid to water, never water to acid.
• Silver nitrate stains skin and clothing and is an oxidiser. Keep it away from organic material.

• Store all chemicals in their labelled containers, in the correct compartment, with the safety data sheets available.
• Use the correct PPE and the correct eye-wash and emergency shower arrangements.
• Never mix chemicals unless the procedure requires it.
• Dispose of test samples and waste reagents according to the ship's procedures, not down the sink.