367
1 INTRODUCTION
These main propulsion engine which propels the
vesselsatseahavetobehighlyreliableandsafeatall
times, whilst sailing athigh seas, transiting through
canals and manoeuvring in ports.It is imperative
that the maintenance regime on board the vessels
have to be very well structured, with utmost
considerat
ion to safety and reliability of the main
propulsionsystem.
The Reliability of the main propulsion system is
interdependent on the reliability of its subsystems,
whicharelistedbelow.
MainEngineLubricatingoilsystem
MainEngineJacketCoolingWatersystem
MainEngineFuelOilsystem
MainEngineScavengesystem
MainEngineAirStartsystem
MainEngineSafetySystem
Thi
s paper discusses the methodology adopted to
quantify reliability of one of the vital sub-system viz. the
lubricating oil system, (Mollenhauer & Tschöke 2010),and
development of a model thereof.
On large two strok eengines the lubricating oil sump
capacity may be as high as 30,000 litres. The lube oil pump
stariner is a wire mesh type located in the sump, from
where the pumps draw the Lube oil and delivers it through
a fine mesh 25 microns discahrge filter, to the Main Engine
Lube Oil plate type highly efficient cooler, the medium of
cooling being sea water. There is a Temperature Control
Valve as shown in Fig. 1 below, which controls the Lube
Oil flow through the cooler as per the required temperature
to the engine inlet. Normally the Lube Oil inlet temperature
to the engine will be 40 -42 degs C. The function of the
lubricating oil is to lubricate the main bearings, cross-head
bearings (the connecting rod top end ) and the big end
bearings ( connecting rod bottom end). It also supplies oil
to the piston crown and cools the crown to acceptable
working temperature in the engine. Failure of the Main
ABSTRACT: Effective and efficient maintenance is essential to ensure reliability of a ship's main propulsion system,
which in turn is interdependent on the reliability of a number of associated sub- systems. A primary step in evaluating the
reliability of the ship's propulsion system will be to evaluate the reliability of each of the sub- system. This paper discusses
the methodology adopted to quantify reliability of one of the vital sub-system viz. the lubricating oil system, and
development of a model, based on Markov analysis thereof. Having developed the model, means to improve reliability of
the system should be considered. The cost of the incremental reliability should be measured to evaluate cost benefits. A
maintenance plan can then be devised to achieve the higher level of reliability. Similar approach could be considered to
evaluate the reliability of all other sub-systems. This will finally lead to development of a model to evaluate and improve
the reliability of the main propulsion system.
A Step by Step Approach for Evaluating the
Reliability of the Main Engine Lube Oil System for a
Ship's Propulsion System
M.Anantharaman,F.Khan,V.Garaniya&B.Lewarn
A
ustralian Maritime College, University of Tasmania, Australia
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 8
Number 3
September 2014
DOI:10.12716/1001.08.03.06
368
Engine Lubricating oil system could lead to major damages
to engine components, resulting in expensive repair and
replacement costs, (Gupta 2012).
Figure1.MainEngineLubricatingoilsystemforalargetwo
strokeengine
Analysis(FTA),forthesystemwillbeconsidered.
This will be followed by a critical component
identification (CCI) and then a Reliability Block
Diagram shall be developed (RBD). A model to
evaluate the reliability for each of the system
componentisdevelopedandtheoverallreliabilityof
thesystemcanbe
determined.
Weshallnowlookintothevariouscomponentsof
the Main Engine Lubricating oil system, (Cicek &
Celik 2013), and determine the reliability of the
system.Thefollowingstepsarefollowed:
TheFaultTreeAnalysis(FTA)fortheMainEngine
LubeOilsystem,(Zhu2011)
Developa
ReliabilityBlockDiagram(RBD)forthe
Main Engine Lube Oil sysstem.(Bhattacharjya &
Deleris2012)
Look at the individual components in the Main
Engine Lube Oil system and draw the state
diagramforthesecomponents
CarryoutaMarkovAnalysisforthesecomponents
,(Gowid,Dixon&Ghani2014).
Carry
outarelaibilityanalysis.
Consider measures for improving the system
reliability.
Drawcomclussionsbasedontheanalysis.
2 THEFTADIAGRAMFORTHEMAINENGINE
LUBEOILSYSTEM
Therearefive(5)maincomponentsoftheM.E.Lube
Oilsystem,failureofwhichwillleadtothefailure
of
themainpropulsionengine.
Figure2.FaultTreediagramforM.E.LubeOilsystem
IntheabovediagramSrepresentstheMainEngine
Lube oil pump strainer, P represents the pumps, F
represents discharge filter, and TCV is the
temperaturecontrolvalveandCLRtheMainEngine
LubeOilcooler.
The next step in the analysis of evaluating the
Reliability of the Main engine Lube Oil sysytem is asshown
below:
CCThefollowingfive(5)casessareanalysed:
FailureofsuctionstrainerS
FailreofpumpsP
FailureofdiscahrgefilterF
FailureofTemperatureControlValveTCV
FailureofcoolerCLR
3 RBDFORTHEMAINENGINELUBEOIL
SYSTEM
Thefollowingpointsintoconsideration.
1 Each block represents the maximum number of
componentsinordertosimplify
thediqgram.
2 Thefunctionofeachblockiseasilyidentified
3 Blocksaremutuallyindependentinthatfailureof
oneshouldnot affect the probability of failure of
another.(Anantharaman2013;Xu2008).
Figure3. DetailedRBDfor M.E. LubeOil system,with all
systemcomponents
369
4 STATEDIAGRAMFORTHEMAINENGINE
LUBEOILSTRAINERS
ThefirstcomponentsuctionstrainerSisabaskettype
strainer, located before the lubricating oil pumps,
(Khonsari & Booser 2008).This is a duplex type of
filterwith a change over cock for isolationof filters.
One of the
filters is in use, the second one being a
standby.Cloggingofthestrainercanresultinpump’s
inabilitytodrawsuctionfromthesump,whichmay
sound a low pressure alarm. This provides time for
changingovertothestandbystrainer.Failureofthis
standbywillresult inpump
failure,finallyresulting
inanenginefailure.Thesefilterswillbeidenticalas
shown in Fig. 4 below. The state diagram for the
filters is shown in Fig. 5 below. The reliability
functionisanexponentialfunctionoftimetandthe
failure rateλexpressed as number of failures per
running
hours.
Figure 4. Lube oil suction strainers for the Main Engine
Lubeoilsystem
Figure 5. Markov Model analysis for the M.E. Lube oil
StrainerS
Table1
_______________________________________________
StateofLubeoilstrainerS Strainer1 Strainer2
_______________________________________________
1CleanClean
2Clooged Clean
3Clogged(Failed)Clogged(Failed)
_______________________________________________
From the table 1 above we see that there are 3
states. In this case the two M.E. Lube Oil Pump
Strainersareidenticalstandbyunits,onofwhichis
on line and the other standby.The reliability of the
two identical systems isderived as,
1
0
!
i
t
s
i
t
Rt e
i
.
In this case
1
t
s
R
te t
and MTTF
(Meantimetofailure)=2/λ
.
5 RELIABILITYOFTHEMAINENGINELUBEOIL
SYSTEM
The stae diagrams for all other components of the
systemareanalysedonthesamelines,asdoneforthe
suction strainer S. Markov analysis(Smith 2011;
Troyer 2006), carried outto determine the reliability
ofthesystemcomponents.Finally
therelaiilityofth
Lubricatingoilsystemisdetermined.
..
L O s p F TCV CLR
R
t R tR tR tR tR t,
p
where R t
is the reliability of the Pumps
F
R
t is the relaibility of the Filter
TCV
R
t is the reliability of the temperature control valve
CLR
R
t . is the reliability of the cooler.
6 IMPROVINGRELIABILITY
Reliability of the system can be improved by
improving the componnet reliability as seen in the
aboveequation.ForinstanceinthecaseoftheStrianer
SshowninSection5above,physicalintroduction
ofanadditionalfilterwillincreasethereleiability.This
cost for improvement ofreliability
need to be
assessed and the cost benefit for the incremental
reliability to be determined.If the original value of
Reliability
O
R
at cost x is improved to Reliability
I
R
at cost y, then the incremntal reliability for the
differential cost
IO
R
R
y
x
should be compared with
thebase relaibility to cost ratio which in thiscase is
O
R
x
.Forcostbenefit
IO
R
R
y
x
>
O
R
x
.
This could be a feasible proposition for some
components,bitnotforallcomponents.Similarstudy
needstobedoneforallothercomponentsandacost
beneficialCBMmodelcouldbedeveloped.
Fig. 6 below shows the Reliability for two (2)
identical suction strainers s and Fig. 7 shows
the
expected improved Reliability, when an additional
suction filter is utilised. On similar lines means for
improvingReliabilityforothercomponentscouldbe
considered. Fig. 8 shows the improvement in
reliabilitywhenaredundantfilterisusedandtoFig.
11 shows the reliability improvement when an
370
additional control valve is installed after the
lubricating oil cooler.No additional redundancies
wereprovidedforthepumpsandthecooler.Thiswas
obtainedbassedonapplicationofMarkov’sprinciple.
ThustheoverallReliabilityfortheMainEngineLube
oil system could be evaluated, and improvement in
thereliabilityisshown,
asseeninFig.12.
Figure 6. Base Reliability vs running hours for two (2)
Strainers
Figure7.ImprovedReliabilityvrunninghoursforthree(3)
Strainers
Figure8.ChangeinreliabilityoadditionofLubeoilfilter
Figure9.ReliabilityforLubeoilpumps
Figure10.ReliabilityforLubeOilCooler
Figure 11. Changein reliability by additionof Temp Cont
Vlave
371
Figure12.ImprovedReliablityfortheLubeoilsysytem
7 CONCLUSION
InthispapertheMainEnginelubricatingoilsystem,
which is a very vital part of the Main propulsion
system was analyzed Failure of the Main Engine
lubricating system may result in serious damage to
the engine components and failure of the Main
Engine. A step by step approach
for evaluating the
reliability of the Main engine lube oil system was
presented. Also it was shown that use of additional
components in the system, could provide
improvement in the component reliability and
contribute to overall reliability of the Main Engine
lubricating oil system. Similar process could be
looked at
to evaluate the reliability of other sub
systems of the main propulsion engine. Next steps
will involve a development of a reliability centered
condition based maintenance model for the main
propulsion system and determine the cost of
improvedreliability.Havingdonethatamaintenance
plancouldbedevisedleadingtoa
finaldevelopment
of a cost beneficial CBM model for the ship’s
propulsionsystem.
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