Marine Boilers

M a r i n e E n g i n e e r i n g K n o w l e d g e U E 2 3 1 | Y A S S E R B . A . F A R A G18 December 2020
Marine Engineering UE231
Boilers & Evaporators

Basic Steam Power Plant
Fuel Air
Boiler
Feed water
pump
Steam
Turbine
Condenser
Super
heater
Heating
Hot well tank
Cooling water
in
Cooling water
out
Wet steam
Drysteam
Feedwater
Condensate
water
+90 C
M W
393

Steam cycle
394

Boilers Classification
 Use:
Main
Auxiliary
 Passage of flue gases:
Water tube
Fire tube
 Heating source:
Oil fired
Exhaust gas
Composite
395

Reference
SOLAS, CH. II-1, Reg. 32
396

Fire-tube boilers

Scottish boilers
Oil-fired Composite
398

Cochran boilers
is a vertical drum axis, natural circulation, natural draft, low pressure, multi-
tubular, fire tube boiler with internally fired furnace. It is the modified form of
simple vertical boiler. In this boiler, the fire tubes are placed horizontally.
Components:
1. Shell: It has a vertical axis cylindrical drum.
2. Fire Tubes: has multi tubular fire tubes. The hot flue gases from the
combustion chamber travels to the smoke box through these fire tubes.
3. Furnace: It lies at the bottom of the boiler. Furnace is the place where all the
fuel is burnt. Without furnace the working of this boiler is not possible.
4. The gas uptake (Chimney) is attached to the smoke box. It transfer smoke to
the environment. The size of chimney is small as compared with other boiler.
399

Composite Cochran boilers
• A composite boiler arrangement permits
steam generation either by oil firing when
necessary or by using engine exhaust gases
when the ship at sea.
• The amount of heat recovered from the
exhaust gases depends upon various factors,
some of which are: Steam pressure,
temperature, evaporative rate required,
exhaust gas inlet temperature, mass flow of
exhaust gas, condition of heat exchange
surfaces, etc.
400

Water-tube boilers

Water tube boiler
• The construction of water tube boilers, which
use small-diameter tubes and have a small
steam drum, enables the generation or
production of steam at high temperatures and
pressures. The weight of the boiler is much
less than an equivalent firetube boiler and
the steam raising process is much quicker.
Design arrangements are flexible, efficiency is
high and the feed water has a good natural
circulation. These are some of the many
reasons why the water tube boiler has
replaced the firetube boiler as the major
steam producer. Water drum
Economizer
Attemperator
Incoming
feedwater
Air cooled or located in
boiler drum
First stage
superheater
Steam drum
Generating
tubes
Downcomers
Risers
Second stage
superheater
Air from FDF
Burners
Water wall
headers
Exhaust
Furnace
Water wall
tubes
Wind box
Alternative Wind
box if roof fires
402

Water tube Boiler
• Air is supplied to the boiler furnace to enable
combustion of the fuel to take place. A large surface
area between the combustion chamber and the water
enables the energy of combustion, in the form of heat,
to be transferred to the water.
• A drum must be provided where steam and water can
separate. There must also be a variety of fittings and
controls to ensure that fuel oil, air and feed water
supplies are matched to the demand for steam. Finally
there must be a number of fittings or mountings which
ensure the safe operation of the boiler
403

Water tube Boiler
In the steam generation process the feed water enters the boiler where it
is heated and becomes steam. The feed water circulates from the steam
drum to the water drum and is heated in the process. Some of the feed
water passes through tubes surrounding the furnace, i.e. waterwall and
floor tubes, where it is heated and returned to the steam drum. Large-
bore downcomer tubes are used to circulate feed water between the
drums. The steam is produced in a steam drum and may be drawn off for
use from here. It is known as 'wet' or saturated steam in this condition
because it will contain small quantities of water. Alternatively the steam
may pass to a superheater which is located within the boiler. Here steam
is further heated and 'dried', i.e. all traces of water are converted
into steam. This superheated steam then leaves the boiler for use in the
system
404

Water tube boiler
The temperature of superheated steam will be
above that of the steam in the drum. An
'attemperator', i.e. a steam cooler, may be fitted
in the system to control the superheated steam
temperature.
The hot gases produced in the furnace are used to
heat the feed water to produce steam and also to
superheat the steam from the boiler drum. The
gases then pass over an economizer through which
the feed water passes before it enters the boiler.
The exhaust gases may also pass over an air
heater which warms the combustion air before it
enters the furnace
405

Advantages
• Savings in weight of about 3:1 for a comparable heating
surface area
• Possibility of using higher temperatures and pressures
without unduly increasing wall thicknesses.
• Greater mechanical flexibility due to good and rapid
circulation which prevents the problems of thermal
stressing and strains unlike tank boilers.
• Thinner tube materials allow rapid steam raising and
faster heat transfer rates
• Saving in space for same steaming rate
• Wider safety margins in case of explosions due to the
small amount of water.
• Thin tubes are easier to bend, expand and bell mouth
406

Package Boiler
It is compact, space saving, designed for u.m.s. operation.
Feed water is force circulated through the generation coil
wherein about 90% is evaporated. The un-evaporated water
travelling at high velocity carries sludge and scale into the
separator, which can be blown out at intervals manually or
automatically. Steam at about 99% dry is taken from the
separator for shipboard use. With such a small water content
explosion due to coil failure is virtually impossible and a steam
temperature limit control protects the coil against abnormally
high temperatures. In addition the servo-fuel control protects
the boiler in the event of failure of water supply.
Performance of a typical unit could be:
Steam pressure 10 bar.
Evaporation 3000 kg/h
Thermal efficiency 80%
407

Exhaust Gas Boiler/Economizer
408

START
Auto Manual
Lockout clear
Pre-Purge 180 sec
Pilot burner ON
Flame “ON” 5 sec
Main burner
Flame “ON” 5 sec
Pilot burner “OFF”
YES
Boiler ModulatingFlame “ON”
Flame failure
NO
NO
Boiler set pressure
Fail to ignite
F.O v/v SHUTT
Post-purge Boiler Stand-by Steam cut-in pressure
Flame failure A
Fail to ignite A
High High water level A
High water level A
Low water level A
Low Low water level A
Low fuel temperature A
Low pilot fuel temperature A
Low fuel pressure A
Low steam pressure A
FDF non start A
High steam pressure A
Feed water pressure low A
Lockout
F.O v/v SHUT
Post-purge
Manual
reset
Alarm/Control panel
YES
YES
NO
Boiler starting sequence
409

Common Boiler’s Fittings

Boiler Survey
The survey covers:
1. Internal examination of the water-steam and fire side, which includes functional testing of safety valves
Guidance note: On small boilers and/or units fitted with steam generating coils / tube panels making internal
examination un-practicable, the internal examination may be substituted by hydraulic pressure testing at 1.5 times
the design pressure.
2. External examination
examination of mountings and fittings, including safety valves, pressure, level and temperature transmitters for
control and monitoring. Opening up as found necessary by he surveyor
• review of the following records since the last survey: Operation, maintenance, repair history, boiler water
management.
• verification of the safety valve setting
• examination and testing of the operation / function of safety valve relieving gear.
IACS Req. 2001/Rev.8 2018
411

Boiler Survey
• Water tube boilers used for main propulsion, including reheat boilers, all other boilers of
essential service, and boilers of non-essential service having working pressure exceeding
0.35 N/mm2 (3.5 bar) and a heating surface exceeding 4.5 m2, are to be surveyed internally.
• There is to be a minimum of two internal examinations during each 5-year special survey
period. In all cases the interval between any two such examinations is not to exceed 36 months. An
extension of examination of the boiler of up to 3 months beyond the due date can be granted in
exceptional circumstances**.
** "Exceptional circumstances" means unavailability of repair facilities, unavailability of essential materials, equipment or
spare parts, or delays incurred by action taken to avoid severe weather conditions.
412

• At each survey, the boilers, superheaters, and economizers are to be examined internally on water-
steam side and fire side.
• Boiler mountings and safety valves are to be examined at each survey and opened out as considered
necessary by the Classification Society.
Boiler Survey
413
** "Exceptional circumstances" means unavailability of repair facilities, unavailability of essential materials, equipment or
spare parts, or delays incurred by action taken to avoid severe weather conditions.

• When direct visual internal inspection is not feasible due to the limited size of the internal spaces, such as for
small boilers and/or narrow internal spaces, this may be replaced by a hydrostatic pressure test or by
alternative verifications as determined by the Classification Society.
• The adjustment of the safety valves is to be verified during each boiler internal survey.
• Boiler safety valve and its relieving gear are to be examined and tested to verify satisfactory operation.
However, for exhaust gas heated economizers, if steam cannot be raised at port, the safety valves may be set
by the Chief Engineer at sea, and the results recorded in the log book for review by the Classification Society.
• Review of the following records since the last Boiler Survey is to be carried out as part of the survey:
1. Operation
2. Maintenance
3. Repair history
4. Feedwater chemistry
Boiler Survey
414

• External survey of boilers including test of safety and protective devices, and test of safety valve using its
relieving gear, is to be carried out annually, within the window of the Annual Survey of a ship.
• For exhaust gas heated economizers, the safety valves are to be tested by the Chief Engineer at sea within the
annual survey window. This test is to be recorded in the log book for review by the attending Surveyor prior
to crediting the Annual Survey of Machinery.
• An extension may be granted by the Classification Society after the following is satisfactorily carried out:
i) External examination of the boiler
ii) Boiler safety valve relieving gear (easing gear) is to be examined and operationally tested
iii) Boiler protective devices operationally tested
iv) Review of the records since the last Boiler Survey:
Boiler Survey
415

Survey items :
1. All mountings to be opened up and surveyed.
2. Fuel oil burning system , valves and piping system
3. Pressure gauge and water level indicators
4. Safety valves
5. Collision chocks , seating stools and stay bolts to be examined. 6.
Safety devices fitted on boiler and alarm test.
Boiler Survey
416

Common Boiler Fittings
417

Water level
418

Burners
Pressure jet burner Rotating cup burner Steam jet burner
419

Soot Blower
420

Main steam valve
421

Direct water level indicator
422

Testing
423

Remote water level indicator
424

M a r i n e E n g i n e e r i n g K n o w l e d g e U E 2 3 1 | Y A S S E R B . A . F A R A G18 December 2020 425
Remote water level indicator

Safety valves selection
• The Safety valve must never be less than 38 mm in diameter (D), and the area (A) of
the valve can be calculated from the following formula:
H: Total heating surface (𝑚𝑚2
)
E: Evaporative rate kg/𝑚𝑚2
P: Safety valve working pressure
A: Aggregate area through the seating of the valve 𝑚𝑚𝑚𝑚2
C: Discharge coefficient whose value depends upon the type of valve.
• Ordinary valve => C=4.8, lift=𝑫𝑫𝑶𝑶𝑶𝑶𝑶𝑶/24
• High lift valve => C=7.2, lift= 𝑫𝑫𝑯𝑯𝑯𝑯 /12
• Improved high lift valve => C=9.6, lift= 𝑫𝑫𝑰𝑰𝑰𝑰𝑰𝑰 /4
• Full lift valve => C=19.2
𝑪𝑪 × 𝑨𝑨 × 𝑷𝑷 = 𝟗𝟗. 𝟖𝟖𝟖𝟖 × 𝑯𝑯 × 𝑬𝑬
𝑫𝑫𝑶𝑶𝑶𝑶𝑶𝑶 > 𝑫𝑫𝑯𝑯𝑯𝑯> 𝑫𝑫𝑰𝑰𝑰𝑰𝑰𝑰
426
Lift area= 𝝅𝝅 x D x L
Bore area = 𝝅𝝅𝑫𝑫𝟐𝟐
D
L

Safety Valves
427

Ordinary safety valve
• They are positioned on the boiler drum in the steam space.
• The ordinary spring loaded safety valve, the valve is held closed
by the helical spring whose pressurized by the compression nut at
the top. The spring pressure, once set, is fixed and sealed by a
Surveyor. When the steam exceeds this pressure the valve is
opened and the spring compressed. The escaping steam is then led
through a waste pipe up the funnel and out to atmosphere.
• The compression of the spring by the initial valve opening results
in more pressure dropping necessary to compress the spring
arrangement on the valve lid which gives a greater area for the
steam to act on once the valve is open .
• A manually operated easing gear enables the valve to be opened in
an emergency. Various refinements to the ordinary spring-loaded
safety valve have been designed to give a higher lift to the valve.
428

High lift safety valve
429

Improved High Lift Safety Valve >21 bar
The improvements to the high lift safety valve are
1. Removal of valve wings, this improves waste steam flow
and reduces risk of seizure
2. Floating ring or cylinder which reduces risk of seizure.
• A drain pipe must be fitted to the lowest part of the valve
chest on the discharge side of the valves and this pipe
should be led clear of the boiler. The pipe must have no
valve or cock fitted throughout its length. This open drain
is important and should be regularly checked, for if it
became choked, there is a possibility of overloading the
valves due to hydraulic head, or damage resulting due to
water hammer.
430

Improved High Lift Safety Valve
431

Full Lift Safety Valve
• The full lift safety valve does not incorporate a waste
steam piston, instead the valve itself operating inside the
guide acts as a piston in a cylinder.
• When the valve has lifted a small amount the escaping
steam pressure can then act upon the full area of the
valve, this increases the lift until the lower edge of the
valve just enters the guide.
• At this point the reaction pressure generated by the
escaping steam with the guide causes the valve to lift
further until it is fully open.
• When the valve is fully open the escape area is said to be
equal to the area of supply through the seating.
432
>60 bar

Comparison
Ordinary safety valve High-lift safety valve Improved High-lift safety valve
• Winged valve
• No waste steam piston
• Winged valve
• Waste steam piston
• No floating ring
• Wingless valve
• Waste steam piston
• Floating ring
Lift (L)
433

Material
• The three spring loaded safety valves, ordinary, high lift and
improved high lift, all make use of a special shaped valve
seat and a lip on the valve which gives increased valve lift
against the increasing downward force of the spring
• Materials used for the valves, valve seats, spindles,
compression screws and bushes must be non-corrodible
metal, since corrosion of any of these components could
result in the valve not operating correctly. Often the
materials used are: Bronze, stainless steel or monel metal,
depending upon conditions. The valve chest is normally
made of cast steel.
434
Valve chest
Cast steel
Valve body
Valve seat
Stainless steel, monel
Valve lid
Spindle Stainless steel
Guide/bushes Bronze
Spring Tempered steel

Maintenance & adjustment
1. The makers figures relating to lip clearances, seating widths and wing
clearances, etc., must be adhered to.
2. When dismantled, the parts are hung by a cord and sounded by gently
tapping with a hammer. If they do not ring true, examine for faults.
3. Check drains and easing gear.
4. Adjustment or setting of safety valves of the direct spring loaded type:
With compression rings removed, screw down compression screws, raise
boiler pressure to the required blow off pressure. Screw back compression
screw until valve blows, then screw down the compression screw carefully,
tapping the valve spindle downwards very lightly whilst doing so, until the
valve returns to its seat and remains closed.
5. When set, split compression rings have to be fitted, then hoods, keys,
padlocks and easing gear.
6. Finally check and operate easing gear to ensure it is in good working order.
D
C
A
B
E
External DIA. Of valve
SURFACE
435

Testing
Hydraulic Test
• Before 12th year (1.25xP) if P < 40
(1.20xP)+2 if P > 40
• After 12th year (1.15xP) whatever P value
436

Boiler’s corrosion

Corrosion
• The corrosion of metals may be considered as the material returning to its
original form of a metal oxide. Some Iron ore for example is an oxide of iron
that is converted into the steels and irons used in engineering.
• If conditions are correct for corrosion; moisture, acids, salts, etc., the tendency
is for the material to revert to oxide of iron by combination with oxygen
• Some metals, provide by reaction with the atmosphere, an oxide film upon their
surface which is by nature passive, and this can prevent any further corrosion.
If this film is broken or destroyed it can in the case of certain metals be very
rapidly replaced.
• Chromium, which is used in stainless steels, can form a microscopic film of
chromium oxide upon the surface of the steel which prevents further corrosion.
• Aluminium, which corrodes very rapidly, is quickly rendered non-corrosive owing
to the passive oxide film which forms.
438

Corrosion
• Formation of galvanic cells is probably the main cause of
corrosion and these can be formed in near pure boiler water,
sea water or other electrolyte.
• The galvanic elements could be provided by dissimilar metals
or mill-scale, scale, oxide film on the surface of a metal. Or
differences in surface structure, inclusion, composition of the
Metal, or salts, bacteria, oil degradation products in the
electrolyte coming into contact with the metal surface.
• Table is an extract from the galvanic series of materials in sea
water, any material in the table is anodic to those above it.
• Hence, steel is anodic to bronze in sea water, therefore, it
will corrode-we may say that the steel has given 'cathodic
protection' to the bronze.
439

Galvanic corrosion
De-zincification
Brass is an alloy of copper and zinc, in sea water the zinc is anodic to the
copper and it corrodes leaving a porous spongy mass of copper, hence de-
zincification. This should not occur to brasses in which arsenic has been
added and whose zinc content
is less than 37%.
A similar attack can occur to aluminium bronzes called de- aluminification,
4% to 5% nickel added to the bronze can avoid this problem but trouble may
still take place at welds.
440

Galvanic corrosion control
Practical points and methods of minimising galvanic effect.
1. Choose materials close to each other in the series.
2. Make the key component of a more noble metal, i.e., the metal to be
protected.
3. Provide a large area of the less noble metal, although its corrosion is
increased, it is spread over a larger area.
4. Do not use graphite grease in the presence of sea water, severe corrosion
of the bronzes and steels in contact with it may result.
Velocity of Sea Water
If the velocity of the sea water relative to the material increases the corrosion
rate increases-probably up to some limiting value. The reason for this is
twofold: (1) increased supply of oxygen; (2) erosion of protective oxide films
formed by corrosion.
441

OTHER CORROSION TOPICS
Fretting Corrosion
Can occur where two surfaces in contact with each other
undergo slight oscillatory motion, of a microscopic nature,
relative to one another. Components to which this may occur
are those which have been shrunk, hydraulically pressed or
mechanically tightened one to the other.
The small relative motion causes removal of metal and metal
oxide films. The removed metal may combine with oxygen to
form a metal oxide powder that will, in the case of ferrous
metal, be harder than the metal itself thus increasing the
wear. Removed metal oxide film would be repeatedly replaced
increasing the damage.
442

OTHER CORROSION TOPICS
Corrosion Fatigue:
• If a metal is in a corrosive environment and is also
subjected to a cyclic stress it will fail at a much lower
stress concentration than that normally required for
fatigue failure.
• This is probably due to the progressive weakening effect
of amorphous metal corrosion and stress relief.
• In boilers, microscopic examination would probably
reveal the cracks to be trans-crystalline, rather than
inter-crystalline which occurs with caustic cracking.
• The cyclic stresses may be due to the tubes vibrating or
fluctuations Fretting Corrosion in thermal conditions,
i.e. thermal pulsing.
443

BOILER CORROSION
• If however an atom gains or loses an electron or electrons there will be an excess of either positive or
negative electrical charge. It is then referred to as an ion.
• Water is basically composed of hydrogen and oxygen atoms, does also contain ions.
Hydrogen Ion
A hydrogen ion is an atom of hydrogen which has lost its electron. It would normally be written H+
indicating an excess into the boiler. It is a very dangerous form of corrosion, its rate of positive electrical
charge, or H- E indicating the loss of electron E.
Hydroxyl Ion
A hydroxyl ion is a compound of oxygen and hydrogen which has gained an electron. It would normally be
written OH indicating an excess of negative electrical charge, or OH+€ indicating a gain of an electron.
444

PH value
Water contains the previously defined hydrogen and hydroxyl ions, the relative concentration of these ions
is important. The product of the hydrogen and hydroxyl ion concentration in water at approx. 25C must
always equal 𝟏𝟏𝟏𝟏−𝟏𝟏𝟏𝟏 gm ion/litre of solution. If the hydrogen ion concentration exceeds the hydroxyl
concentration the water is acidic. If the concentrations are equal the water is neutral. When the hydroxyl
ion concentration is greater than the hydrogen, the water is alkaline.
example: 𝟏𝟏𝟏𝟏−𝟓𝟓 (H+) x 𝟏𝟏𝟏𝟏−𝟗𝟗 (OH-) solution Acid
𝟏𝟏𝟏𝟏−𝟕𝟕(H+)x 𝟏𝟏𝟏𝟏−𝟕𝟕 (OH-) Neutral
𝟏𝟏𝟏𝟏−𝟗𝟗(H+) x 𝟏𝟏𝟏𝟏−𝟓𝟓(OH-) ,, Alkaline
Note the product of the concentrations is always 𝟏𝟏𝟏𝟏−𝟏𝟏𝟏𝟏 and the powers 5, 7 and 9 for the hydrogen ion
concentration serve to indicate the degree of acidity or alkalinity of the solution. Hence the pH values
now becomes apparent, p (for power), H (for hydrogen ion)
445

Electro Chemical Corrosion
Hydrogen, which has formed on the surface of the
metal due to the combination of the hydrogen ion and
metal electron may form a polarising layer upon the
metals surface. This will prevent further corrosion. If
however, dissolved oxygen is present in the water, it
will combine with the hydrogen to form water and no
polarisation will occur and corrosion will continue.
Also, if the water is acidic enough, the hydrogen can
leave the surface of the metal in the form of hydrogen
gas, again preventing polarisation and continuing
corrosion. Hence the need for boiler water to be
alkaline and with little or no dissolved oxygen content.
446

Causes of Boiler Corrosion
1- Oils
Lubricating oils may contaminate the feed system and find their way into the boiler, this could be caused due
to over
lubrication of machinery and inefficient filtering of the feed. Oil can decompose in the feed water boiler
liberating their fatty acids, these acids can cause corrosion. Hence it is advisable to use pure mineral oil for
lubrication of machine parts where contamination of feed can result, but oil of any description should never
be allowed to enter the boiler as it can adhere to the heating surfaces causing overheating. It can also cause
priming due to excessive ebullition.
2- Mechanical Straining
Mechanical straining of boiler parts may be due to mal-operation of the boiler, raising steam too rapidly from
cold, missing or poorly connected internal feed pipes, fluctuating feed temperature and steaming conditions.
Grooving is caused through mechanical straining of boiler plates, and where a groove is present there is
always the danger of corrosion resulting in the groove.
447

3- Galvanic Action
When two dissimilar metals are present in a saline solution galvanic
action may ensue, resulting in the corrosion of the more base metal.
Zinc for example would serve as an anode to iron and iron would
serve as an anode to copper. Sacrificial anodes are frequently used to
give cathodic protection. In Scotch boilers zinc plates are sometimes
secured to furnaces and suspended between tube nests, these act as
sacrificial anodes giving cathodic protection to the steel plating, etc.,
of the boiler.
Corrosion of non-ferrous metals in steam and condensate systems may
result in deposits of copper on boiler tube surfaces (known as 'copper
pick up'), which due to galvanic action can lead to boiler corrosion.
448

4- Caustic Embrittlement
The phenomena of caustic embrittlement (or intercrystalline fracture)
is believed to be caused by high concentrations of caustic soda
(Sodium hydroxide NaOH) and the material under stress. The stress
corrosion cracks follow the grain or crystal boundaries of the material
and failure of the affected part could result. Concentrations of sodium
hydroxide required for embrittlement to occur vary with operating
conditions, roughly about 102.7 kg/m3 at 300°C is a guide to the
amount of concentration required. Normally such concentrations
would never be found in a boiler, but, leakages at rivet heads,
seams and boiler mountings, etc., whereby water is flashed off to
steam, leaving behind the solids locally, can cause the high
concentrations required.
449

Caustic Embrittlement
450

Sodium hydroxide depresses the solubility of sodium sulphate, and sodium
sulphate can therefore be made to precipitate. Use is made of this fact to
give protection against caustic embrittlement. When concentrations of
sodium hydroxide are high and sodium sulphate is present, the sodium
sulphate can precipitate and form a protection for the material.. It is
recommended that the ratio of sodium sulphate to caustic soda should not
fall below 2.5 at all times. Other substances that have been used as
inhibitors against caustic embrittlement are, quebracho tannin and sodium
nitrate. Caustic corrosion in high pressure boilers is usually indicated by
gouging of the tubes and is caused by excess sodium hydroxide and a
concentrating mechanism. This phenomenon results in the destruction of
the protective magnetic oxide of iron film (Fe04) and the base metal is
then attacked by the concentrated sodium hydroxide.
451
Caustic Embrittlement

Silicate
452

Auxiliary Boiler defects
Deformation
With cylindrical furnaces, this can be determined by sighting along the furnace or by use of a lath swept
around the furnace or by furnace gougings. The causes of deformation are: scale, oil, sludge or poor
circulation, resulting in overheating of the furnace and subsequent distortion. Local deformations could be
repaired by cutting through the bulge, heating and pressing back the material into the original shape, and
then welding. By cutting through the bulge prior to heating and pressing facilitates flow of metal during
pressing. Alternatively, the defective portion could be cut out completely and a patch welded in its place. If
the furnace is badly distorted then the only repair possible may be renewal
Wastage
The causes of wastage are corrosion and erosion. If it is great in extent then renewal of the furnace may
be the only solution. Localised corrosion could be dealt with by cutting out the defective portion of furnace
and welding in a new piece of material.
453

Cracks (Grooving)
Circumferentially around the lower part of the connecting
necks cracks may be found. These cracks are caused by
mechanical straining of the furnace and the defect is generally
referred to as grooving. If the groove is shallow compared to
plate thickness (depth can be ascertained by drilling or by
ultrasonic detection) it is usual to cut out the groove and
weld. However, if the grooving is deep the material is cut right
through and welded from both sides. Cracks, due to
overheating, may be found where deformation has occurred,
these must be made good in the manner described above.
Auxiliary Boiler defects
454

Refractory
• A refractory material is one that retain its strength and not fuse at
high temperatures.
• “non-metallic materials having those chemical and physical properties
that make them applicable for structures, or as components of
systems, that are exposed to environments above 538 C.
• Example: Fire clay, Silica, Chromite magnesite
• Refractory bricks are bricks that can withstand high temperatures
• A block of refractory ceramic material
• Should not spall under rapid temperature change, and their strength
should hold up well during rapid temperature changes.
• Dense firebricks are used in applications with extreme mechanical
chemical or thermal stresses
• In other, less harsh situations, more porous bricks are used.
455

Refractory failure
SPALLING ‫اﻟﺘﻜﺴﯿﺮ‬
This is the breaking away of layers of the brick surface. It can be
caused by fluctuating temperature under flame impingement or
firing a boiler too soon after water washing or brick work repair.
May also be caused by failure to close off air from register outlet
causing cool air to impinge on hot refractory.
SLAGGING ‫اﻟﺨﺒﺚ‬
This is the softening of the bricks to a liquid state due to the
prescience of vanadium or sodium ( ex sea water ) in the fuel. This
acts as fluxes and lowers the melting point of the bricks
Flame impingement may lead to carbon penetrating refractory.
456

SHRINKAGE CRACKING
Refractories are weaker in tension than in
compression or shear thus, if compression takes place
due to the expansion of the brick at high temperature
, if suddenly cooled cracking may occur.
Failure of brick securing devices
Refractory failure
457

out of service
• When boilers are taken out of service for short or long periods, they must be protected from corrosion.
• In case of water tube boilers out of service for a short period of time (e.g. 2 days), the boiler can be fired in intervals to keep the
boiler pressure above about 3.5 bar and the boiler water must be maintained in composition as required for the boiler when under
normal steaming conditions.
• Alternatively the boiler could be filled while hot, with hot de-aerated alkaline feed water at about 0.5 kg of sodium sulphite (It is
used in water treatment as an oxygen scavenger agent, to treat water being fed to steam boilers to avoid corrosion
problems) added for each ton of water in boiler. The boiler must be topped up periodically and any air in the system must be got
rid of.
• With Fire-tube boilers out of service for short periods, the only action that needs to be taken is to ensure that the alkalinity is not less
than the recommended value, or completely fill the boiler with alkaline water.
• If the boiler is to be taken out of service for long periods, it should be drained completely, then dried out by means of heater units.
Next, trays of quicklime should be placed internally in suitable positions throughout the boiler before it is sealed up. Blanks should be
fitted to the pipe connections in the event of steam being maintained in other boilers and the blow-down should be blanked in any case.
The lime should be renewed at least once every 2 months.
458

Boiler Fires
Good combustion conditions will minimise the risk, deposits allowed to accumulate in this area are a fire
risk and, should fire take hold undetected.. There is plenty of evidence of soot fires leading on to
hydrogen fires.
1. Soot Fires:
The ignition of an accumulation of soot, rich in carbon, caused by poor combustion either in
ort or when operating at low power for prolonged periods, can when supplied with the
necessary oxygen be the source of a fire sufficiently intense to melt and burn steel.
2. Hydrogen Fires:
When overheating of a superheater due to insufficient steam circulation is very severe, the
tube material may ignite at about 700°C and, burning in the steam, produce free hydrogen. The
iron will continue burning independently of any supply of oxygen from the air, and the hydrogen
produced by the reaction will burn on coming into contact with air. This means that once such a
fire has started there are likely to be two fires burning simultaneously, one, iron burning in
steam and the other, hydrogen burning in air, the combined fire being self supporting and
probably lasting until the supply of steam is exhausted.
459

Boiler Failure- Case study
460

461

462

463

464

465

466

467

468

469

470

Water Treatment

Water Treatment
Boiler water treatment
Chemical
Anti
scales
Oxygen
scavengers
Corrosion
prohibitors
Cleaning heat
transfer surfaces
Natural
Cleaning heat
transfer surfaces
Blowing
down and
Scumming
Hot well
temperature
Removal of
oil
472

Water Chemistry
• Dissolved solids in fresh waters vary considerably depending on the source of the water
• The various solids listed above will react in different ways when subjected to heat and
pressure within a boiler.
473

• Temporary Hardness salts: these are alkaline salts: i.e.,
hydroxides, carbonates and bicarbonates of calcium and
magnesium. These salts will decompose when the water is heated
to boiling point, liberating carbon dioxides and leaving
carbonate scales.
• Permeant Hardness salts: These are non-alkaline salts i.e.
chlorides, sulphates, nitrates and silicates. Permanent hardness is
not removed by heating the water to boiling point but will cause
problems with scale and acidity as the water is further heated.
• Total Hardness: the sum of temporary and permanent hardness
salts. It’s an indication of the total scale forming potential in the
water.
474
Water Chemistry

Hardness salts
Temporary
Alkaline salts
Hydroxides, Carbonates and Bicarbonate of
calcium and magnesium
With heating to boiling point it
will decompose and liberating
CO2
Permanent
Non-alkaline salts
Chlorides, Sulphates, Nitrates
and Silicates
When heated to the
boiling temperature, will
cause acidity
Scales
Corrosion
Corrosion
475
Water Chemistry

Type Impurity Problem caused
Gaseous
Dissolved Oxygen Pitting Corrosion
Carbon Dioxide Condensate Corrosion
Soluble
Calcium / Magnesium Scaling
Sodium / Potassium Corrosion
Chloride / Sulfate Corrosion
Carbonates /
Bicarbonate
Scaling / Foaming
Hydroxides Scaling / Foaming
Silica Scaling / Deposition
Insoluble Suspended solids Fouling
Others Oils / Organics Foaming / Carryover
476
Water Chemistry

Scaling
477

Oxygen / low PH Corrosion
478

High Alkalinity Corrosion
479

Carbon dioxide
480

Carry over
481

Conclusion
Fuel Air
Boiler
Feed water
pump
Steam
Turbine
Condenser
Super
heater
Heating
Hot well tank
Cooling water
in
Cooling water
out
Wet steam
Drysteam
Internal>>
Corrosion /
Scaling/Fouling/Foaming/Cracks/
Grooving/Caustic embrittlement
External>>
Overheating/Deformation/Wastage/
Cracks/Corrosion
Carryover
Corrosion
Corrosion
Feedwater
Condensate
water
CO2O2 + Oil
• Oxidation
• Acidity/PH
• Hard Salts
• Galvanic corrosion
• Na(OH)
• Soot, Poor
combustion/Circulation
• Thermal stresses
• Mechanical strain
• Oil
• Metal
• Water
• TDS
+90 C
482

Boiler water treatment
Chemical
Anti scales Oxygen
scavengers
Corrosion
prohibitors
Cleaning heat
transfer
surfaces
Natural
Cleaning heat
transfer
surfaces
Blowing down
and Scumming
483

Lime and Soda treatment
484

Phosphate – Sodium hydroxide treatment
485

Combination treatment
486

Conclusion
Boiler Water chemical treatment
Lime & Soda
 CaOH3
 Used for Low pressure boilers
 Calcium hydroxide removes
the temporary hardness
 High TDS in water => foaming
and carry-over => constant
blow-down is necessary =>
uneconomical
Phosphate – Sodium Hydroxide
 Can be used for all group of boilers
 The end result is insoluble sludge
(calcium phosphate & magnesium
phosphate) and soluble sodium chloride
and sodium sulphate
 TDS should be monitored and regular
blow-down to maintain TDS levels.
 Sludge may build up in headers which
will impede thermal circulation =>
overheating => tube failure
Combination treatment
• A chemical mixture
• Simple and convenient
• Precise and simple instructions to use
• Consists of sodium carbonate and
sludge conditioning agents
• Antifoam
• Hydrazine and oxygen scavengers
added to condensate water
• Chemical supplier provide test kits
• Also provide limits for different
parmeters
487

Water limits
1 2 3 4 5
PH
6 7 8 9 10 11 12 13 14
Corrosion of steel vs
boiler water PH
Relativecorrosionattackmm/yr
488
09-11

New Technology/ELYSATOR
The function of the Elysator is based on the anodic/cathodic principle, i.e., letting a less noble metal
(magnesium) be sacrificed (corroded)instead of the system itself, related to galvanic series/elements. During
the process the oxygen in the water will be absorbed creating H2O and magnesium hydroxide. When the
Elysator is installed, the entire system will be protected from corrosion. Even aluminium and aluminium
alloys are protected.
Dilution of magnesium
Anode:
Mg(s) → Mg2+
(aq) + 2e-
Cathode:
½O2 + H2O + 2e- → 2OH-
Total reaction:
Mg(s) + ½O2 + H2O → Mg (OH)2
489

ADVANTAGES
• No chemicals
• Minimum maintenance
• Self regulating
• Kills and prevents growth of bacteria
• Savings in cost of chemicals and prevention of corrosion
related failures
• Fast "Pay back"
• Improved water quality due to sludge and deposits removal
• Environmentally safe and meets ISO 1400 requirements https://www.iwtm.com/index.php/en/articles/articles/elysator-how-it-works
New Technology/ELYSATOR
490

P-Alkalinity test
The Alkalinity Test is carried out in two stages:
1. Phenolphthalein Alkalinity Test
• Purpose:
1. It gives the alkalinity of the sample due to Hydroxides and Carbonates.
2. It gives warning against high concentration of sodium hydroxides and
subsequent damage to the boiler from caustic embitterment.
• Procedures:
1. Take a 200 ml water sample in the stopped bottle.
2. Add one P- Alkalinity tablet and shake or crush to disintegrate.
3. If P-Alkalinity is present the sample will turn blue.
4. Repeat the tablet addition, one at a time (giving time for the tablet to
dissolve), until the blue colors turns to permanently yellow.
5. 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 CaCO3
6. Record the result obtained on the log sheet provided, against the date on
which the test was taken.
7. Retain the sampler for the M-Alkalinity.
491

M-Alkalinity test
• Purpose:
1. It gives alkalinity due to bicarbonates, includes the bicarbonates formed during the P-
alkalinity test.
2. The result warns us against possible formation of carbonic acid inside the boiler as
well as in the steam condensate lines, due to high concentration of bicarbonates.
• Procedures:
1. To the P-Alkalinity sample add one M. Alkalinity tablet and shake or crush to
disintegrate..
2. Repeat tablet addition, one at a time (giving time for the tablet to dissolve), until the
sample turns to permanent red/pink..
3. Count the number of tablets used and carried out the following calculation: M-
Alkalinity, ppm CaCO3= (Number of P. & M. Tablets x 20) – 10 e.g. If 12 P. 5 M.
Alkalinity tablets is used.
4. Record the result obtained on the log sheet provided, against the date on which the
test was taken.
492

PH Test
• Purpose:
1. To give warning on acidity or alkalinity of boiler water sample.
2. Result help to establish the dosage of boiler compound to fight against corrosion.
• Procedures:
1. Take a 50 ml sample of the water to be tested in the plastic sample container
provided.
2. Using the white 0.6 gram. Scoop provided, add one measure of the pH reagent to
the water sample, allow dissolving – stirring if required.
3. Select the correct range of pH test strip and dip it into the water sample for one
minute.
4. Withdraw the strip from the sample and compare the color obtained with the
color scale on the pH indicator strips container.
5. Record the pH value obtained on the log sheet provided, against the date on
which the test was taken.
493

Chloride ppm CI Test
• Purpose:
1. Gives warning against any seawater contamination of the Boiler Feed System.
2. Help to establish an effective blow down control of the boiler.
• Procedures:
1. Take the water sample in the stopper bottle provided.
2. Add one Chloride tablet and shake to disintegrate. Sample should turn yellow if chlorides are present.
3. Repeat tablet addition, one at a time (giving time for the tablet to dissolve), until the yellow color changes to permanent
red/brown.
4. Count the number of tablets used and perform the following calculation:
For 100 ml Water Sample: Chloride ppm = (Number of tablets x 10) - 10 e.g 4 tablets = (4 x 10) – 10 = 30 ppm chloride
For 50 ml Water Sample: Chloride ppm = (Number of tablets x 20) - 20 e.g 4 tablets = (4 x 20) – 20 = 60 ppm chloride
For small steps of ppm chloride use a larger sample.
For larger steps of ppm chloride use a smaller sample.
5. Record the pH value obtained on the log sheet provided, against the date on which the test was taken.
494

Phosphate ppm Test (PO4)
• Purpose:
It helps to maintain a phosphate reserve in the boiler to counter any possible contamination of the boiler water by corrosive and
scale forming salts. However, too much phosphate in the boiler may also contribute to foaming and priming.
• Procedures:
1. Take the comparator with the 10 ml cells provided.
2. Slide the phosphate disc into the comparator.
3. Filter the water sample into both cells up to the 10 ml mark.
4. Place one cell in the left hand compartment.
5. To the other cell add one Phosphate tablet, crush and mix until completely dissolved.
6. After 10 minutes place this cell into the right hand compartment of the comparator.
7. Hold the comparator towards a light.
8. Rotate the disc until a color match is obtained.
9. Record the result obtained on the log sheet provided, against the date on which the test was taken.
495

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