8/10/2019 Crank case explosion.pdf

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A Recent Crankcase Explosion

Other Pages The Basics The 2 Str oke Engine The Stroke Engine Oper ation !em"ers

The story starts when the oil mist detector alarm for No 10 unit (a QMI type) on a 12 cylinder 2 stroke engine went offwhen the hief !ngineer was in the engine control room together with two of his staff"

The hief !ngineer thought that the alarm was due to a dirty detector head of the #il Mist $etector and immediately sentone of the engineers down in the engine room to check the detector heads"

The hief !ngineer noticed that the oil mist le%el was increasing in crankthrow spaces 10 and 11& so he called the 'ridgeand asked the 'ridge watchkeeper to reduce the re%olutions of the engine"

minutes later he noticed that the oil mist le%el had increased further" It was at this point that he cancelled the loadreduction programme and reduced the main engine re%olutions to rpm" *t almost the same time a hea%y e+plosionoccurred in the engine room"

The engineer sent to clean the detector heads was standing close to a relief %al%e and was se%erely 'urnt"

* fire started in the engine room and purifier room caused 'y the shockwa%e from the e+plosion 'ursting an oil pipe" Thefire was e%entually e+tinguished 'y in,ecting #2" (after 'locking off access doors that had 'een damaged in the

e+plosion)"

The ause of the e+plosion was an o%er heated main 'earing (no 1-)" .ieces of white metal were found in the crankcaseand su'se/uent in%estigations esta'lished that some of the white metal had detached due to fatigue and poor 'onding" *sthe metal detached& the load on the e+isting white metal increased& due to the now reduced area to support the crankshaft,ournal leading to 'reakdown in the lu'"oil film and wiping of the 'earing" The crankshaft ,ournal was now running on the'are steel 'acking"

hen the e+plosion occurred& doors on the safe side (the side without the e+plosion doors) 'lew off& starting the fire"

The %essel had to 'e towed to port for repairs which took 3 weeks"

The crankshaft ,ournal was 'adly scored with e+tensi%e heat cracks" It was reduced in diameter and undersi4e 'earingsfitted"

It came to light in su'se/uent in%estigations that fragments of white metal had 'een found in the 5# filters 2 weeks'efore the e+plosion" It was assumed that this was white metal from the guide shoes and no further action was taken"

It is easy to 'e wise after the e%ent" 6owe%er the oil mist detector is designed to protect& and a sophisticated set up like theQMI& which works on the light scatter principle& should 'e 'elie%ed when it indicates a high oil mist" The first mistakewas sending someone down to clean the lenses" * crankcase e+plosion is a %ery serious occurrence" The engine roomshould 'e e%acuated of all personnel not dealing with the situation from the control room"

* seemingly simple solution is as soon as the alarm sounds& the engine should 'e stopped 7ut if this is the case whyisn8t the oil mist detector linked to the engine shut downs" #n some ships it has 'een& 'ut consider this9 The ship may 'emanoeu%ering in a risky situation& or there may 'e a shaft alternator in use"

The general procedure should 'e this" #n a 'ridge control set up with the engine room in :M; mode& if alarm conditions

are reached& the au+iliary generators should run up& load transferred& and the shaft alternator isolated" *fter a 10 seconddelay the engine should immediately power down to 0< full load& 'ypassing the load control programme" This reductionin load will reduce the likelihood of a crankcase e+plosion" The delay is to gi%e the na%igating officer time to o%erride theslow down incase safety of the ship is at risk" #nce the engine has slowed down it should 'e stopped as soon as it is safeto do so"

If the engine room is manned& and on 'ridge control& the watchkeeping engineer may choose to take control of the engine&reduce the load and stop as soon as it is safe to do so" #nce the engine has stopped& the cooling and 5# must 'e keptrunning& the turning gear should 'e engaged and the engine turned continuously" The engine room should 'e e%acuated

and time gi%en (-0 minutes) for the engine to cool down 'efore opening up the crankcase for inspection"

.urifiers are fitted in separate rooms for a reason9 =ire risk" The doors should 'e closed and dogged shut when not passingthrough them"

hat a'out the white metal found in the filters> If& instead of making assumptions& the crankcase had 'een opened upthey may ha%e found the white metal in the %icinity of the damaged 'earing"

The fact that the oil mist detector alarmed for a unit not ad,acent to the o%erheated 'earing should 'e noted" The oil mistcan circulate within the crankcase" This should 'e 'orne in mind when in%estigating the cause of a oil mist alarm"

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