Water mist systems are extensively used as fire protection of machinery spaces onboard passenger ships, and have almost taken over as fire extinguishing systems after IMO standardized such systems. Water mist systems are documented through full scale fire testing of the manufacturers' solutions. In practice it has been shown that in spaces with a ceiling height above approximately 10m it is necessary with more water mist nozzles to extinguish low seated fires. The IMO-method that describes the test procedures requires that all nozzles are mounted at ceiling level, and gives no opportunity to extrapolate results from fire tests to spaces with higher ceiling heights.
Conventional merchant vessels have large machinery spaces with ceiling heights above 10m. Therefore it is still common to install CO2-systems in these ships, since no alternative extinguishing systems are approved for this application area. Until now several manufacturers of water mist systems have documented that it is possible to extinguish fires in machinery spaces with height up to 10m and a volume exceeding 3,000m3. A research project initiated by IWMA (International Water Mist Association) resulted in a change of IMO's regulations. That means that the test results will be valid also for spaces up to twice the tested volume, but there was not given any possibility to increase the ceiling height.
If it can be shown through testing that water mist systems have sufficient ability to fight fires in larger machinery spaces, such systems will challenge and replace CO2-systems. In practice this means that fire extinguishing can start immediately after a fire has been detected. Today the start of extinguishing may be delayed with 10-15 minutes because CO2 represents a toxic hazard to persons in the machinery space. The CO2 cannot be released before people are evacuated from the engine room and all air supply is stopped and all openings are closed. Every minute with a fire in the machinery space increases the damage to equipment and cables; it has been indicated that the damage increases with €12,000 per minute.
Water mist systems can be released immediately after fire detection, and will quickly cool down the machinery space. Most fires will be extinguished after 10-15 minutes. In addition water mist systems have become popular among engineers and crew because they, besides being possible to use without hazard to people, are easy to test regularly. Water mist systems on passenger ships are often tested every week, and are simultaneously used for cleaning the machinery space. The costs connected to refilling the water reservoir are negligible in contrast to replacement of CO2-bottles after release of a CO2-system.
SINTEF NBL is now working to start projects that can open up for use of water mist system in large machinery spaces, and for this purpose we have the possibility to utilize our large test hall. The test hall is over 20m high and has a total volume of approximately 14,000m3.
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..)
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
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
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.
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.
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
CORROSION AND TUBE FAILURE CAUSED BY WATER CHEMISTRY
Iron+O2 --- magnetite(stable and protective) + O2----ferrous oxide (porous)
TWO PRINCIPLE TYPES OF CORROSION
Higher temperature metal comes into contact with air or other gasses (oxidation, Sulphurisation)
-e.g. Galvanic action , hydrogen evolution , oxygen absorption
Hydrogen Evolution (low pH attack)
Common in boilers having an open feed system.
-Most serious form of corrosion on the waterside
-Often found in boiler shell at w.l.
-Usually due to poor shape
-In HP blrs found also in screen and generating tubes and in suphtr tubes after priming.
CORROSION FATIGUE CRACKING
CAUSTIC CRACKING (EMBRITTLEMENT) or STRESS CORROSION CRACKING
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.
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.
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.
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.
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.
Entire boiler susceptible , but most common in the superheater tubes (reheater tubes especially where water accumulates in bends and sags )
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 )
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.
Tin has some improving effects
Very low sea water flow condensers also susceptible.
Nickel oxidised forming layers of copper and nickel oxide
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,