SAFETY EQUIPMENT'S ONBOARD
HYPERMIST SYSTEM
1) CHECK THAT THE SYSTEM IS LINED UP CORRECTLY.
2) CHECK PUMP IN AUTO MODE AND NO ALARMS ON THE FIRE CONTROL PANEL IN THE MSB ROOM.
3) TRYOUT AT LEAST ONE ZONE SPRINKLER RELEASE IN CONTROLLED MODE.
4) CHECK PUMP PRESSURE WHEN SYSTEM IS TESTED.
5) CHECK SPRINKLER HEADS FOR CLARITY (NO PAINT DEPOSITS ETC..)
CO2 SYSTEM
1) CHECK KEY IS IN PLACE.
2) CHECK INTEGRITY OF ALL THE CONNECTIONS
3) CHECK ALL CO2 HEADS FOR CLARITY
4) CHECK ROOM DOORS AND CABINET DOOR.
5) BLOW THROUGH WITH AIR.
QUICK CLOSING VALVE
1) VISUALLY INSPECT THE SYSTEM.
2) CHECK THE AIR PRESSURE IN THE BOTTLE
3) TRY OUT AT LEAST ONE SECTION OF QCVS. OR INDIVIDUAL VALVE FOR PROPER OPERATION
REMOTE TRIPS
1) FUNCTION TEST ONE SECTION AT A TIME..
EM'CY FIRE PUMP
1) ENSURE PUMP IS LINED UP AND READY FOR IMMEDIATE USE
2) TRIAL RUN FOR 10MINS AND RECORD THE PRESSURE GENERATED WITH TWO FIRE HOSES RIGGED.
3) CHECK FOR LEAKAGES
EM'CY GENERATOR
1) CHECK LO, FO, COOLING WATER LEVELS
2) CHECK E/GEN ON AUTO MODE.
3) TEST RUN THE ENGINE ON BATTERY MODE AND HYDRAULLIC STARTING MODE
4) CHECK OIL LEVEL IN HYD OIL TANK
5) TEST RUN ON LOAD FOR AT LEAST 30 MIN AND CHECK AVAILABILITY OF POWER AT SERVICES PROVIDED BY E/GEN.
SCBA COMPRESSOR
1) CHECK THE CONDITION OF CHARGING HOSES AND THE CONNECTIONS.
2) ENSURE ALL SCBA BOTTLES ARE FULLY CHARGED
3) CHECK OIL LEVEL IN THE SUMP
4) CHECK THE COMPRESSOR CUT OFF FUCNTION AT 300 BAR.
LIFE BOAT ENGINE
1) CHECK LO, FO AND COOLING WATER LEVEL.
2) TEST RUN THE ENGINE IN ALL RUNNING DIRECTIONS
3) CHECK SPRINKLER PUMP DRIVING MECHANISM
RESCUE BOAT ENGINE
1) CHECK LO, FO AND COOLING WATER LEVEL
2) TEST RUN THE ENGINE IN ALL RUNNING DIRECTIONS.
VENTILATION FLAPS
1) FUCNTION CHECK.
2) CHECK FOR ANY AIR LEAKS.
FIRE HYDRANTS AND HOSES
1) CHECK THAT ALL HOSES ARE IN PLACE AND GENERAL CONDITIONS ARE SATISFACTORY
2) CHECK FOR FREENESS OF NOZZLES, AND GREASE ACCORDINGLY.
3) PRESSURE TEST ALL HOSES ONCE IN THREE MONTHS
EM’CY BILGE SUCTION
1) OPERATE AND GREASE.
S.W. RECIRC. V/V
1) OPERATE FROM REMOTE AND LOCAL
STATIONS AND CONFIRM THE OPERATION.
STEAM SMOTHERING
SYSTEM
1) CARRY OUT VISUAL
INSPECTION OF THE SYSTEM AND CHECK INDIVIDUAL
UNIT V/V FOR FREENESS
INCINERATOR
1) TRY OUT TRIPS AND ALARMS.
SHIP SIDE V/V
1) OPERATE AND GREASE
FIRE AND GAS
DETECTION EQUIPMENTS
1) TEST ALL THE SENSORS
ONCE IN THREE MONTHS.
BILGE ALARMS
1) FUCNTION CHECK
BATTERIES AND
CHARGERS
2) CHECK THAT THE BATTERY IS FULLY
CHARGED.
3) EVERY QUARTER DISCHARGE ROUTINE
TO BE CARRIED OUT.
4) AFTER STARTING EM’CY GEN KEEP THE BATTERY IN
EQUALISING CHARGE
TILL BATTERY VOLTAGE
REACHED TO 27 V, THEN CHANGE OVER SWITCH TO
FLOATING CHARGE POSITION.
CRANES
1) FUCNTION CHECK THE
LIMIT SWITCHES
REF. CHAMBER ALARM
1) FUCNTION CHECK
O.W.S. 15 PPM
1) FUCNTION TEST OF
15-PPM ALARM AND CHANGING OVER OF O/B V/V
ELE. EM’CY TRIPS
1) CARRY OUT FUNCTION
TEST
2) CONFIRM ALL BREAKERS ASSOCIATED WITH THE GROUP HAVE TRIPPED.
EM’CY LIGHTING
1) FUCNTION CHECK
COMMUNICATION
EQUIPMENTS
1) FUCNTION CHECK
HAZ. AREA EQUIPMENTS
1) CHECK PHYSICAL
CONDITION OF THE EQUIPMENT
2) CHECK THE BONDING
M/E EM’CY MANOEUVRING
1) TRY OUT M/E FROM
LOCAL MANOEUVRING STATION.
EM’CY STEERING
1) TRY OUT STEERING FROM
LOCAL STATION.
MACHINERY TRIPS
1) TRY OUT TRIPS AND
ALARMS FOR MACHINERIES AS PER INDIVIDUAL SCHEDULES
BLACKOUT TEST
1) CARRY OUT BLACK OUT
TEST AND CHECK SEQUENTIAL START
EMERGENCY SHOWER
1) OPERATIONAL CHECK TO
BE CARRIED OUT.
2) OBSERVE THE COLOUR OF
WATER.
BOILER FEED WATER MANAGEMENT / CORROSION FIGHTING
CORROSION FOUND IN BOILER AND FEED WATER SYSTEM
CORROSION AND TUBE FAILURE CAUSED BY WATER CHEMISTRY
TWO PRINCIPLE TYPES OF CORROSION
Direct chemical
Higher temperature metal comes into contact with air or other gasses (oxidation, Sulphurisation)
Electrochemical
-e.g. Galvanic action , hydrogen evolution , oxygen absorption
Hydrogen Evolution (low pH attack)
CORROSION FATIGUE CRACKING
CAUSTIC CRACKING (EMBRITTLEMENT) or STRESS CORROSION CRACKING
Boiler steel is sensitive to Na OH , stainless steel is sensitive to NaOH and chlorides.
i)Departure
form nucleate boiling (DNB)
Under normal conditions steam bubbles are formed in discrete parts. Boiler water solids develop near the surface . However on departure of the bubble rinsing water flows in and redissolves the soluble solids.
However at increased rates the rate of bubble formation may exceed the
flow of rinsing water , and at higher still rate, a stable film may occur with
corrosion concentrations at the edge of this blanket.
The magnetite layer is then attacked leading to metal loss.
The area under the film may be relatively intact.
iii),
Evaporation at waterline
Where a waterline exists corrosives may concentrate at this point by evaporation and corrosion occurs.
Dissolve cupric oxide formed on copper or copper alloy tubes
Does not attack copper, hence oxygen required to provide corrosion,Hence only possibel at the lower temperature regions where the hydrazine is less effective or inactive,
CORROSION AND TUBE FAILURE CAUSED BY WATER CHEMISTRY
Metals
obtained from their oxide ores will tend to revert to that state. However , if
on exposure to oxygen the oxide layer is stable , no further oxidation will
occur. If it is porous or unstable then no protection is afforded.
Iron+O2 --- magnetite(stable and protective) + O2----ferrous oxide (porous)
Iron+O2 --- magnetite(stable and protective) + O2----ferrous oxide (porous)
TWO PRINCIPLE TYPES OF CORROSION
Direct chemical
Higher temperature metal comes into contact with air or other gasses (oxidation, Sulphurisation)
Electrochemical
-e.g. Galvanic action , hydrogen evolution , oxygen absorption
Hydrogen Evolution (low pH attack)
Valency
= No of electrons required to fill outer shell
Pure water contains equal amounts of hydrogen and hydroxyl ions .
Impurities change the balance. Acidic water has an excess of hydrogen ions
which leads to hydrogen evolution
For hydrogen absorption
to occur no oxygen needs to be present, a pH of less than 6.5 and so an excess
of free hydrogen ions is required.
The Protective film of
hydrogen gas on the cathodic surface breaks down as the hydrogen combines and
bubbles off as diatomic hydrogen gas.
Oxygen Absorption(high O2 corrosion)
pH between 6- 10, Oxygen
present. Leads to pitting. Very troublesome and can be due to ineffective feed
treatment prevalent in idle boilers. Once started this type of corrosion cannot
be stopped until the rust scab is removed , either by mechanical means or by
acid cleaning. One special type is called deposit attack, the area under a deposit
being deprived of oxygen become anodic. More common in horizontal than vertical
tubing and often associated with condensers.
BOILER CORROSION
|
General
Wastage
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Common in
boilers having an open feed system.
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|
.
|
|
|
.
|
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Pitting
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-Most
serious form of corrosion on the waterside
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|
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-Often
found in boiler shell at w.l.
|
|
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-Usually
due to poor shape
|
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-In HP
blrs found also in screen and generating tubes and in suphtr tubes after
priming.
|
CORROSION FATIGUE CRACKING
Cases found in water
tube blrs where due to alternating cyclic stresses set up in tube material
leading to a series of fine cracks in wall. Corrosive environment aggravates.
Trans crystalline
more in depth: Occurs in any location
where cyclic stressing of sufficient magnitude are present
Rapid
start up and shut down can greatly increase susceptibility.
Common
in wall and supht tubes, end of the membrane on waterwall tubes, economisers,
deaerators . Also common on areas of rigid constraint such as connections to
inlet and outlet headers
Other
possible locations and causes are in grooves along partially full boiler tubes
(cracks normally lie at right angle to groove ), at points of intermittent stm
blanketing within generating tubes, at oxygen pits in waterline or feed water
lines, in welds at slag pockets or points of incomplete fusion , in sootblower
lines where vibration stresses are developed , and in blowdown lines.
CAUSTIC CRACKING (EMBRITTLEMENT) or STRESS CORROSION CRACKING
Pure
iron grains bound by cementite ( iron carbide).
Occurs
when a specific corrodent and sufficient tensile stress exists
Due
to improved water treatment caustic stress- Corrosion cracking ( or caustic
embrittlement ) has all but been eliminated.
It
can however be found in water tubes , suphtr and reheat tubes and in stressed
components of the water drum.
The required stress may be applied ( e.g. thermal, bending etc. ) or residual ( e.g. welding)
The required stress may be applied ( e.g. thermal, bending etc. ) or residual ( e.g. welding)
Boiler steel is sensitive to Na OH , stainless steel is sensitive to NaOH and chlorides.
A large scale attack on the material is not normal and indeed uncommon. The
combination of NaOH , some soluble silica and a tensile stress is all that is
required to form the characteristic intergranular cracks in carbon steel.
Concentrations of the corrodent may build up in a similar way to
those caustic corrosion i.e.
·
DNB
·
Deposition
·
Evaporation at water line
·
And also by small leakage
Caustic
corrosion at temperatures less than 149oC are rare
NaOH
concentration may be as low as 5% but increased susceptibility occurs in the
range 20- 40 %
Failure
is of the thick walled type regardless of ductility.
Whitish
highly alkaline deposits or sparkling magnetite may indicate a corrosion sight.
To
eliminate this problem either the stresses can be removed or the corrodent. The
stresses may be hoop stress( temp', pressure) which cannot be avoided bending
or residual weld stresses which must be removed in the design/ manufacturing
stage.
Avoidance
of the concentrations of the corrodents is generally the most successful. Avoid
DNB , avoid undue deposits prevent leakage of corrodents, prevent carryover.
Proper water treatment is essential.
CAUSTIC CORROSION
·
Takes place at high pressure due to
excessive NaOH
·
In high temperature, high evaporation
rates leading to local concentrations nearly coming out of solution and form a
thin film near heating surface.
·
Magnetite layer broken down
·
Soluble compound formed which deposits
on metal as a porous oxide
·
Local concentrations may cause a
significant overall reduction in alkalinity.
·
If evaporation rate reduced alkalinity
restored.
More in depth:
Generally confined to
1.
Water cooled in regions of high heat
flux
2.
Slanted or horizontal tubes
3.
Beneath heavy deposits
4.
Adjacent to devices that disrupt flow (
e.g. backing rings)
Caustic
( or ductile ) gouging refers to the corrosive interaction of concentrated NaOH
with a metal to produce distinct hemispherical or elliptical depressions.
Depression
are often filled with corrosion products that sometimes contain sparkling
crystals of magnetite.
Iron
oxides being amphoteric are susceptible to corrosion by both high and low pH
enviroments.
High
pH substances such as NaOH dissolve the magnetite then attack the iron.
The two factors required to cause caustic corrosion are;
·
the availability of NaOH or of alkaline
producing salts. ( e.g. intentional by water treatment or unintentional by ion
exchange resin regeneration.)
·
Method of concentration, i.e. one of
the following;
i. Departure form nucleate boiling (DNB)
ii. Deposition
iii. Evapouration
Under normal conditions steam bubbles are formed in discrete parts. Boiler water solids develop near the surface . However on departure of the bubble rinsing water flows in and redissolves the soluble solids.
The magnetite layer is then attacked leading to metal loss.
The area under the film may be relatively intact.
ii) Deposition
A similar situation can occur beneath layers of heavy deposition where bubbles formation occur but the corrosive residue is protected from the bulk water
A similar situation can occur beneath layers of heavy deposition where bubbles formation occur but the corrosive residue is protected from the bulk water
Where a waterline exists corrosives may concentrate at this point by evaporation and corrosion occurs.
PREVENTIONS
·
Rifling is sometimes fitted to prevent
DNB by inducing water swirl.
·
Reduce free NaOH by correct water
treatment
·
Prevent inadvertent release of NaOH
into system (say from an ion exchange column regenerator )
·
Prevent leakage of alkaline salts via
condenser
·
Prevent DNB
·
Prevent excessive waterside deposits
·
Prevent creation of waterlines in
tubes- slanted or horizontal tubes are particularly susceptible to this at
light loads were low water flows allow stm water stratification.
If the magnetite layer is broken down by corrosive action, high
temperature hydrogen atoms diffuse into the metal, combine with the carbon and
form methane. Large CH-3 molecules causes internal stress and cracking along
crystal boundaries and sharp sided pits or cracks in tubes appear.
more in depth: Generally confined to internal surfaces of water carrying tubes
that are actively corroding. Usually occurs in regions of high heat flux,
beneath heavy deposits, in slanted and horizontal tubes and in heat regions at
or adjacent to backing rings at welds or near devices that disrupt flow .
Uncommon in boilers with a W.P.of less than 70 bar
A typical sequence would be ;
·
NaOH removes the magnetite
·
free hydrogen is formed ( hydrogen in
its atomic rather than diatomic state) by either the reaction of water with the
iron reforming the magnetite or by NaOH reacting with the iron
·
This free hydrogen can diffuse into the
steel where it combines at the grain boundaries to form molecular hydrogen or
reacts with the iron carbide to form methane
·
As neither molecular hydrogen or
methane can diffuse through the steel the gasses build up , increasing pressure
and leading to failure at the grain boundaries
·
These micro cracks accumulate reducing
tensile stress and leading to a thick walled failure. Sections may be blown
out.
·
This form of damage may also occur in
regions of low pH
·
For boilers operating above 70 bar ,
where high pH corrosion has occurred the possibility of hydrogen damage should
be considered
Loss of circulation , high temperature in
steam atmosphere, or externally on suphtr tubes
Concentrated chelants ( i,e. amines and
other protecting chemicals) can attack magnetite , stm drum internals most
susceptible.
A surface under attack is free of deposits and corrosion products , it may be very smooth and coated with a glassy black like substance
Horse shoe shaped contours with comet tails in the direction of the flow may be present.
A surface under attack is free of deposits and corrosion products , it may be very smooth and coated with a glassy black like substance
Horse shoe shaped contours with comet tails in the direction of the flow may be present.
Alternately deep discrete isolated pits may
occur depending on the flow and turbulence
The main concentrating mechanism is
evaporation and hence DNB should be avoided
Low pH attack
Pure water contains equal amounts of hydrogen and hydroxyl ions .
Impurities change the balance . Acidic water has an excess of hydrogen ions
which leads to hydrogen evolution.See previous notes on Hydrogen Evolution
For hydrogen absorption to occur no oxygen needs to be present, a
pH of less than 6.5 and so an excess of free hydrogen ions is required.
The Protective film of hydrogen gas on the cathodic surface breaks down as the hydrogen combines and bubbles off as diatomic hydrogen gas.
May occur due to heavy salt water contamination or by acids leaching into the system from a demineralisation regeneration.
The Protective film of hydrogen gas on the cathodic surface breaks down as the hydrogen combines and bubbles off as diatomic hydrogen gas.
May occur due to heavy salt water contamination or by acids leaching into the system from a demineralisation regeneration.
Localised attack may occur however where evaporation causes the
concentration of acid forming salts . The mechanism are the same as for caustic
attack. The corrosion is of a similar appearance to caustic gouging
Prevention is the same as for caustic attack . Proper maintenance
of boiler water chemicals is essential
Vigorous acid attack may occur following chemical cleaning .
Distinguished from other forms of pitting by its being found on all exposed
areas.
Very careful monitoring whilst chemical cleaning with the temperature being
maintained below the inhibitor breakdown point. Constant testing of dissolved
iron and non ferrous content in the cleaning solution should be carried out.
After acid cleaning a chelating agent such as phosphoric acid as
sometimes used . This helps to prevent surface rusting , The boiler is then
flushed with warm water until a neutral solution is obtained.
OXYGEN CORROSION
Uncommon in operating boilers but may be
found in idle boilers.
Entire boiler susceptible , but most common in the superheater tubes (reheater tubes especially where water accumulates in bends and sags )
Entire boiler susceptible , but most common in the superheater tubes (reheater tubes especially where water accumulates in bends and sags )
In an operating boiler firstly the
economiser and feed heater are effected.
In the event of severe contamination of
oxygen areas such as the stm drum water line and the stm separation equipment
In all cases considerable damage can occur
even if the period of oxygen contamination is short
Bare steel coming into contact with
oxygenated water will tend to form magnetite with a sound chemical water
treatment program.
However , in areas where water may accumulate then any trace oxygen is dissolved into the water and corrosion by oxygen absorption occurs( see previous explanation )
However , in areas where water may accumulate then any trace oxygen is dissolved into the water and corrosion by oxygen absorption occurs( see previous explanation )
OXYGEN ABSORPTION
in addition to notes above pH between 6- 10, Oxygen present.
Leads to pitting. Very troublesome and can be due to ineffective feed treatment prevalent in idle boilers. Once started this type of corrosion cannot be stopped until the rust scab is removed , either by mechanical means or by acid cleaning.
Leads to pitting. Very troublesome and can be due to ineffective feed treatment prevalent in idle boilers. Once started this type of corrosion cannot be stopped until the rust scab is removed , either by mechanical means or by acid cleaning.
One special type is called pitting were
metal below deposits being deprived of oxygen become anodic . More common in
horizontal than vertical tubing and often associated with condensers.
The ensuing pitting not only causes trouble
due to the material loss but also acts as a stress raiser
The three critical factors are
i. the prescience of water or moisture
ii. prescience of dissolved oxygen
iii. unprotected metal surface
The corrosiveness of the water increases
with temperature and dissolved solids and decreases with increased pH
Aggressiveness generally increases with increased O2
The three causes of unprotected metal surfaces are
i. following acid cleaning
ii. surface covered by a marginally or non protective iron oxide such
as Hematite (Fe2O3)
iii. The metal surface is covered with a protective iron oxide such as
magnetite (Fe3O4 , black) But holidays or cracks exist in
the coating, this
may be due to mechanical or thermal stressing.
During normal operation the environment
favours rapid repair of these cracks. However, with high O2
prescience then corrosion may commence before the crack is adequately repaired.
FEED SYSTEM CORROSION
Graphitization
Cast iron , ferrous materials corrode
leaving a soft matrix structur of carbon flakes
Dezincification
Brass with a high zinc content in contact
with sea water , corrodes and the copper is redeposited. Inhibitors such as
arsenic , antimony or phosphorus can be used , but are ineffective at higher
temperatures.
Tin has some improving effects
Tin has some improving effects
Exfoliation (denickelfication)
Normally occurs in feed heaters with a
cupro-nickel tubing ( temp 205oC or higher)
Very low sea water flow condensers also susceptible.
Nickel oxidised forming layers of copper and nickel oxide
Very low sea water flow condensers also susceptible.
Nickel oxidised forming layers of copper and nickel oxide
Ammonium corrosion
Ammonium formed by the decompositin of hydrazineDissolve cupric oxide formed on copper or copper alloy tubes
Does not attack copper, hence oxygen required to provide corrosion,Hence only possibel at the lower temperature regions where the hydrazine is less effective or inactive,
The copper travels to the boiler and leads to piting.
BOILER'S SAFETY VALVE REGULATION
BASED ON ABS RULES
NUMBER OF SAFETY VALVES FOR BOILER
Each boiler (including exhaust gas boiler) and steam generator is to be fitted with at least one safety valve and where the water-heating surface is more than 46.5 m2 (500 ft2), two or more safety valves are to be provided. The valves are to be of equal size as far as practicable and their aggregate relieving capacity is not to be less than the evaporating capacity of the boiler under maximum operating conditions.
SAFETY VALVES - SIZE RESTRICTIONS
In no case,
- is the inlet diameter of any safety valve for propulsion boiler and superheaters used to generate steam for main propulsion and other machinery to be less than 38 mm (1.5 in.) nor more than 102 mm (4 in.).
- For auxiliary boilers and exhaust gas economizers, the inlet diameter of the safety valve must not be less than 19 mm (3/4 in.) nor more than 102 mm (4 in.).
SAFETY VALVES - FOR SUPERHEATER & ECONOMIZER
Superheater
Each superheater, regardless of whether it can be isolated from the boiler or not, is to be fitted with at least one safety valve on the superheater outlet.
Economizers
Each economizer, where fitted with a bypass, is to be provided with a sentinel relief valve, unless the bypass arrangement will prevent a buildup of pressure in the economizer when it is
bypassed.
bypassed.
MINIMUM RELIEVING CAPACITY FOR BOILER SAFETY VALVE
In all cases, the safety-valve relieving capacity is to be determined on the basis of the boiler heating surface and water-wall heating surface along with the fuel-burning equipment, and is not to be less than that given in the table (see later).
Where certification by the boiler manufacturer of the evaporative capacity of the boiler under maximum operating conditions indicates a higher capacity, the higher capacity is to be used.
MINIMUM RELIEVING CAPACITY FOR SUPERHEATER SAFETY VALVE
Where a superheater is fitted as an integral part of a boiler with no intervening valve between the superheater and the boiler, the relieving capacity of the superheater safety valve, based on the reduced pressure, may be included in determining the total relieving capacity of the safety valves for the boiler as a whole.
In such a case, the relieving capacity of the superheater safety valve is not to be credited for more than 25% of the total capacity required.
The safety valves are to be so set and proportioned that, under any relieving condition, sufficient steam will pass through the superheater to prevent overheating the superheater.
Specially designed full-flow superheater valves, pilot-operated from the steam drum, may be used.
PRESSURE RISE DURING RELIEVING
For each boiler, the total capacity of the installed safety valves is to be such that the valves will discharge all steam that can be generated by the boiler without allowing the pressure to rise more than 6% above the maximum allowable working pressure.
PRESSURE SETTING - BOILER DRUMS
At least one safety valve on the boiler drum is to be set at or below the maximum allowable working pressure.
If more than one safety valve is installed, the highest setting among the safety valves is not to exceed the maximum allowable working pressure by more than 3%.
The range of pressure settings of all the drum safety valves is not to exceed 10% of the highest pressure to which any safety valve is set In no case is the relief pressure to be greater than the design pressure of the steam piping or that of the machinery connected to the boiler plus the pressure drop in the steam piping.
PRESSURE SETTING – SUPERHEATERS
Where a superheater is fitted, the superheater safety valve is to be set to relieve at a pressure no greater than the design pressure of the steam piping or the design pressure of the machinery connected to the superheater plus pressure drop in the steam piping.
In no case is the superheater safety valve to be set at a pressure greater than the design pressure of the superheater.
In connection with the superheater, the safety valves on the boiler drum are to be set at a pressure not less than the superheater-valve setting plus 0.34 bar (0.35 kgf/cm2, 5 psi), plus approximately the normal-load pressure drop through the superheater.
SAFETY VALVE - EASING GEAR
Each boiler and superheater safety valve is to be fitted with an efficient mechanical means by which the valve disc may be positively lifted from its seat.
This mechanism is to be so arranged that the valves may be safely operated from the boiler room or machinery space platforms, either by hand or by any approved power arrangement.
SAFETY VALVE - CONNECTION TO BOILER & SUPERHEATER
Safety valves are to be connected directly to the boiler, except that they may be mounted on a common fitting.
However, they are not to be mounted on the same fitting as that for the main or auxiliary steam outlet.
This does not apply to superheater safety valves, which may be mounted on the fitting for the superheater steam outlet.
SAFETY VALVE - ESCAPE PIPE
The area of the escape pipe is to be at least equal to the combined outlet area of all of the safety valves discharging into it.
The pipe is to be so routed as to prevent the accumulation of condensate and is to be so supported that the body of the safety valve is not subjected to undue load or moment.
SAFETY VALVE - DRAIN PIPE
Safety valve chests are to be fitted with drain pipes leading to the bilges or a suitable tank.
No valve or cock is to be fitted in the drain pipe.
SAFETY VALVE - PRESSURE ACCUMULATION TEST
Safety valves are to be set under steam and tested with pressure accumulation tests in the presence of the Surveyor.
The boiler pressure is not to rise more than 6% above the maximum allowable working pressure when the steam stop valve is closed under full firing condition for a duration of 15 minutes for firetube boilers and 7 minutes for watertube boilers.
During this test, no more feed water is to be supplied than that necessary to maintain a safe working water level.
The popping point of each safety valve is not to be more than 3% above its set pressure.
SAFETY VALVE - PRESSURE ACCUMULATION TEST (WAIVER)
Where such accumulation tests are impractical because of superheater design, an application to omit such tests may be approved, provided the following are complied with:
- All safety valves are to be set in the presence of the Surveyor.
- Capacity tests have been completed in the presence of the Surveyor on each valve type.
- The valve manufacturer supplies a certificate for each safety valve stating its capacity at the maximum allowable working pressure and temperature of the boiler.
- The boiler manufacturer supplies a certificate stating the maximum evaporation of the boiler.
- Due consideration is given to back pressure in the safety valve steam escape pipe.
CHANGES IN SAFETY VALVE SETTING
Where, for any reason, the maximum allowable working pressure is lower than that for which the boiler and safety valves were originally designed, the relieving capacity of the valves under lower pressure is to be checked against the evaporating capacity of the boiler.
For this purpose, a guarantee from the manufacturer that the valve capacity is sufficient for the new conditions is to be submitted for approval, or it is to be demonstrated by a pressure accumulation test, conducted in the presence of a Surveyor.