Question 1. Explain The Term Water Hammer Indicating Possible Effects On The System ?
Water hammer happens when steam is admitted into a cold pipeline. The steam condenses producing each water, and a vacuum (whilst the water seals the pipeline from the steam deliver). This vacuum reasons the water plug to be drawn into the closed end of the pipe with increasing velocity generating high effect forces at the pipework. This impact pressure can be excessive sufficient to rupture the pipeline.
Question 2. State How The Risk Of Water Hammer May Be Avoided ?
Water hammer is averted via slowly admitting the steam into the cold line, and draining/venting the cold line to minimise the vacuum forming, and assist in draining the condensate.
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Question 3. State With Reasons Why The Testing And Treatment Of Boiler Water Is Essential ?
Testing of the boiler water is important to determine that:
The stage of chlorides is inside perfect limits (underneath two hundred ppm) to save you hard scale and pitting
The reserve of boiler chemicals inside the boiler water is established (P Alk above 100 ppm, and Phosphate above 20ppm)
Treatment of the boiler water with chemicals will make sure:
Alkalinity reserve in opposition to boiler water area corrosion
Scale build-up is minimised
Enough coagulant degrees exist to minimise sludge construct-up in the boiler
The power of the boiler drum is maintained.
Question 4. State With Reasons How Boiler Problems May Be Minimised If No Water Treatment Is Immediately Available And A Steam Supply Must Be Maintained ?
Boiler problems might be minimised by way of:
Reducing the steam load and demand on the auxiliary boiler to lessen firing temperatures.
Ensuring hotwell feed temperatures are on the endorsed 95°C to minimise oxygen levels inside the feed.
Minimise blowdown of boiler water, while ensuring chloride stage is not excessive, to avoid lack of the boiler chemical substances.
Question 5. Why Wear Down In Main Bearings Is Critical To The Condition Of The Crankshaft And Propeller Shaft System On Ships ?
The operational stresses present in the crankshaft is inspired by means of the bending stresses gift. If the crankshaft alignment is absolutely directly then the bending stresses are minimum, but should choppy foremost bearing wear down occur, then these bending stresses will greatly growth.
When the primary bearings wear down, the alignment of the crankshaft to the propeller shaft will change. This put on down will increase the bending stress on the propeller shaft, and the external second at the engine / shaft interface, increasing the crankshaft stresses.
When the crankshaft is subjected to those high stresses, the small defects gift in the shaft should broaden and propagate into cracks that could lead to shaft failure.
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Question 6. Why Total Reliance Is Placed On Frictional Grip In Conventional Built Up Crankshaft On Main Engine ?
Frictional grip is the usual approach of crankshaft construction for constructed-up crankshaft. This grip is subjected to the entire torque of the engine output, and subsequently subjected to excessive torsional stresses. If there are any defects at this joint, then the ensuing strain awareness would trigger a crack and viable shaft failure.
To minimise the opportunity of such defects, then handiest a frictional grip is authorized below Classification Rules for crankshaft creation, as a result pins, keys, etc are not allowed.
Question 7. Why Oil Holes Are Given Large Fillets In Crankpins And Journals ?
Defect increase from a small floor illness into a crack that propagates through the shaft cloth require excessive tiers of stress. Such degrees of stress are feasible whilst the pressure is concentrated at segment changes. The oil hole will inherently boom the local pressure tiers, and thus to minimise these will increase, the oil hollow can have a great radius at the surface. The length of this radius will significantly have an effect on the local strain ranges, and must be intently monitored at some point of crankshaft production, and feasible crankpin surface upkeep by grinding.
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Question eight. What Are The Causes And Effects Of Torsional Vibrations In Crankshaft ?
Torsional vibrations are inherent within diesel engines, due to the varying torque produced through the piston and crank arrangement from every cylinder. This torque variant is in addition compounded by way of the arrangement of the firing order of the crankshaft.
The consequences of such vibrations is to boom the shear pressure and for this reason general strain ranges carried through the crankshaft in provider, while different stresses consisting of bending and combustion loads are present.
Question nine. What Is Meant By The Term Critical Speed And Why It Can Be A Problem On Ships ?
The vital velocity of a shaft takes place when the shaft rotational speed is at or close to resonant conditions. In this circumstance the torsional vibration of the shaft will increase greatly, and could impose very excessive shear stress on the crankshaft. These stages of stress may want to even motive crankshaft failure.
Question 10. What Is The Term Fatigue Cracking And State With Reasons Two Factors Of Crankshaft Operation Which Have The Greatest Influence On The Likelihood Of Fatigue Cracking ?
Fatigue cracking occurs whilst the number one reason of crack propagation is because of the fluctuating nature of the strain carried out to the issue.
The following factors may want to produce fatigue cracking:
High combustion pressures, growing the bending strain carried out to every crankshaft throw
Excessive crankshaft bending due to a prime bearing failure, which increases the crankshaft bending stresses.
Question eleven. How A Detuner Or Torsional Vibration Damper Can Reduce The Effects Of Torsional Vibration?
The becoming of either a detuner or vibration damper will reduce the vibration tiers of the crankshaft whilst operating in regions of excessive torsional vibration, consisting of close or inside a vital velocity variety. The detuner will trade the stiffness of the shaft and hence the natural frequency, for that reason keeping apart the excitation frequency from the thing’s herbal frequency, while the damper will soak up the vibration within the shaft, lowering the outcomes of the torsional vibration.
Question 12. Explain How A Fatigue Failure Is Identified ?
Fatigue failure is diagnosed as starting at a stress raiser or disorder, then the crack generates thru the cloth earlier than causing surprising failure. The crack progress is shown as easy, rippled formation known as striations or beach marks, even as the surprising failure is a classic brittle fracture with tough look.
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Question thirteen. Describe How A Fatigue Crack May Be Initiated ?
The initiation web page might be where the nearby stress is high sufficient to growth the minute cracks which occur on the metallic floor. The strain may be accelerated domestically through a floor illness, or even an extreme strain awareness as a result of excessive implemented pressure.
The essential causes of fatigue cracks are:
These may be decreased with the aid of ensuring a easy surface end to all location in which high pressure is implemented specifically within the internet/pin radii location
These need to be minimised on every occasion viable, and the oil hole commencing have extensive and easy radii
Fatigue power is reduced while tensile strain are present, so the radii regions are often bloodless rolled to make sure that the fatigue strength in these regions are extended.
Stress carried out on hardened substances:
Fatigue cracks can grow faster while the cloth is tougher, as the dislocations within the metal listen the strain on a smaller vicinity of the cloth shape, for this reason any hardening of the crank pins have to not be implemented to the highly burdened radii areas.
Question 14. Describe The Events Leading To A Crankcase Explosion On A Main Engine ?
The surroundings internal a crankcase is stable and will no longer permit combustion or an explosion to occur as there is no ignition or gasoline source.
Hence the first event is the production of an explosive aggregate. This will arise whilst the lube oil inside the crankcase is heated by way of a “hot spot” and lube oil coming into touch with this will be evaporated. The evaporated oil then rises inside the crankcase, and then condenses in a cooler part of the crankcase. The resultant white mist is within the explosive range, and is therefore flammable.
The 2nd occasion is the ignition of this white mist by means of both the same or some other hot spot in the crankcase. When the oil mist is ignited, a crankcase explosion will occur, so one can increase the strain within the crankcase.
Question 15. State How Overheating Might Be Indicated Other Than By Mist Detector ?
One of the common regions of overheating is the diverse bearings within the crankcase. Hence bearing temperature monitors may be used to indicate that a bearing is overheating and may be oil mist technology site.
Question sixteen. State How The Severity Of A Crankcase Explosion Is Limited ?
The rapid stress upward thrust in the crankcase can reason the engine structure to be blown apart, inflicting bodily harm, and the consequent flame journeying across the engine room area causing employees damage.
This stress rise is limited by way of the statutory use of alleviation doors suited for the crankcase. These doorways will open while the pressure rises above 0.02 – zero.1 bar, and prevent the over-stress of the engine shape. The doors also carry out the delivered characteristic of stopping clean air ingress into the crankcase where hot burning gases are present, through the short closing action of the relief door.
Question 17. Emission Of Flame Has In The Past Caused Severe Burns To Personnel During A Crankcase Explosion, Despite The Addition Of Flame Traps. Discuss The Procedure In The Event Of Overheating Being Indicated ?
As the explosion is an uncontrolled event, then wonderful care have to be taken to make sure the safety of the engineers inside the engine room. MAN B&W advise that:
Move faraway from the crankcase doorways immediately
Reduce pace to sluggish, and ask the bridge to forestall
When the engine has stopped, close the fuel supply
Stop the auxiliary blowers
Open the skylight and/or stores hatch
Leave the engine room
Lock engine room access doors and keep away from them
Prepare the hearth preventing system.
Do no longer open the crankcase for at least 20 mins after stopping the engine, and ensure that the oil mist detector alarm (or bearing temperature reveal) has reset
Stop the LO circulating pump. Shut the starting air, and engage the turning gear.
Locate the “warm spot” (supply of the oil overheating)
Make a permanent repair to the fault
Question 18. What Are The Problems Associated With Effective Lubrication Of The Liner And Piston Assembly Of A Large Slow Speed Engine ?
The powerful lubrication of the cylinder liner and piston assembly calls for a constant lubricant feed over the complete liner surface, and that piston motion will generate the oil pressures required to split the surfaces.
However inside the real situation the subsequent troubles arise:
The oil is injected at described factors that could cause an oversupply on the feed factors, and an below deliver faraway from these factors
The residual gas normally used incorporates acids and abrasives so as to reduce the lubrication residences of the oil
The ordinary operation of the piston will motive the piston motion to prevent at top lifeless centre, causing any oil stress evolved among the ring and liner to collapse
The high temperatures present at pinnacle useless centre reduce the effectiveness of the lubricant
The feed fee of the lubricant is regulated typically by means of the speed of the engine, so that it will purpose a mismatch among actual lube oil requirements over a huge variety of engine operation, with normally too little an quantity of oil injected at low masses and for the duration of engine load modifications.
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Question 19. Describe The Appearance And State The Causes Of Cloverleafing And Microseizure On Cylinder Liners ?
Cloverleafing can be brought on when the supply of lube oil isn't uniform across the radial bore of the lining. The regular effect is for the oil to lessen in alkalinity away from the injection factor, thus if the oil will become acidic then excessive corrosive wear costs will result.
This will reason choppy bore wear rates, with heavy put on inside the regions furthest away from the oil injection factors.
Microseizure is prompted while the liner and piston ring cloth is pressed collectively inflicting localised welding of the fabric in the absence of enough lube oil.
The reasons are insufficient oil and/or excessive cylinder pressures reasons heavy ring/liner contact forces. The look is heavy scratching/tearing inside the vertical path, collectively with a localised hardening of the ring and liner fabric.
Question 20. Describe The Composition Of A Cylinder Oil Suitable For A Main Engine Operating On Residual Fuel ?
The cylinder oil will require:
Ample viscosity to separate the surfaces beneath excessive loading situations
Sufficient alkaline reserve to neutralise the acids fashioned by combustion of residual gas oil
High stages of detergent to hold piston ring cleanliness and loose ring motion
A level of anti wear houses to minimise micro seizure
The potential to burn without residue
Question 21. With Reference To Bridge Control Of A Large Man B&w Slow Speed Propulsion Engine Explain How Starting And Reversal Are Achieved ?
For massive propulsion engines the Bridge Control is executed by means of the use of the telegraph to choose the desired pace and direction. When the bridge telegraph is placed in Stop, the gas is avoided from injecting because the gas pump puncture valves are energised. When the bridge telegraph is moved to an in advance command, the air start and gasoline cams are placed inside the required course, and the start command is given. This will admit starting air to the engine. Once the engine is turning above the starting pace, the air is closed and fuel is admitted.
The quantity of fuel admitted will depend on the placement of the telegraph take care of, i.E. Sluggish ahead, full beforehand, and so forth. When the bridge telegraph is moved to an astern direction, the air begin and gas cams are reversed. Once the air begin is reversed, the engine will begin as special for the in advance start.
Question 22. Describe The Investigation And Remedial Action Required If The Engine Fails To Turn On Air ?
If the engine fails to start on air the following points would be investigated, and remedial action taken.
No air strain at engine manifold. The valves from the air receiver could be checked, and opened if observed close.
Low air stress at engine manifold. This ought to suggest that the air compressors are either no longer operating or excess air is getting used. All air compressors would be started, and air usage limited to engine manoeuvring best.
Turning gear engaged. The turning tools position and the interlock switch would be visually checked. The gear would be removed if discovered engaged.
Question 23. Describe The Investigation And Remedial Action Required If The Engine Turns On Air But Fails To Fire On Fuel ?
If the engine fails to fireplace on gas the subsequent factors might be investigated, and remedial motion taken.
Check for any shut-downs nonetheless energetic. The close down panel could be examined, and if a ride is active the motive might be investigated and device made operational. Following this the journey reset button could be pressed.
Low gas pressure on the engine manifold. The gas system might be investigated, and all valves checked to be opened, and all booster and deliver pumps checked for running.
Sticking gasoline linkage. The motion of the gasoline linkage could be checked throughout the start collection. The gas linkage must admit a “beginning degree” of fuel after the engine begin collection has been completed. The physical movement of the gasoline linkage could be checked, and any mechanical friction reduced via lubrication.
Question 24. Describe The Investigation And Remedial Action Required If The Engine Fails To Reverse ?
If the engine fails to opposite the following points might be investigated, and remedial motion taken.
Air start distributor now not reversing. The engine controls would be moved beforehand and astern at the same time as watching the movement of the air start distributor. If the distributor is not moving, then the air servo cylinder would be checked to make sure that it's miles unfastened to move, and that air is being admitted and vented as required to attain the movement required.
Air begin valve now not commencing. It is feasible that the air distributor does reverse as anticipated, but that the desired air begin valve could no longer open to rotate the engine inside the new course. This might be investigated through turning the engine inside the ahead course in order that it stops in a new position. The engine might once more be examined inside the astern direction to test if a beginning air valve has did not open. Any valve determined defective could be removed, freed and refitted.
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Question 25. Why Self Closing Sounding Pipes Are Used Onboard?
It may also likely regulatory but I sincerely recognize the United States Coastguard pick out up on it. It is for the reality a tank can be overfilled. A self remaining sounding pipe will prevent overflow.
Question 26. How Ships Are Flooding?
Ships can be flooded due to rupture of its hull because of several reasons inclusive of collision, grounding, and or terrible hull upkeep by way of which corrosion may additionally eat away the hull. Also for warships it is able to be of conflict related trade of firing.
Question 27. What Is Specific Fuel Consumption And How Fuel Calculate?
Generally it check with the fuel consumtion rate, there are several deferent way to catlculate the precise fuel consuption, including volumetric method and float method. But those techniques may be taken simplest in lab. No viable do it on the sea.
Question 28. What Is High Temperature Corrosion And What Is Center Priming?
When material uncovered to excessive temperature atmospehic situation like excessive degree of oxygen presence, sulfer presence and special type chemical presence reason matrial worsening . This sort of cloth corrosion is called High temperature corrosion.
Question 29. What Is The Purpose Of O-ring, Wearings In The Centrifugal Pumps?
O-ring : to prevent leakage among metallic components while permitting some motion between them.
Wear ring : normally a softer cloth than the discern cloth , hired to wear down quickly than the discern metallic thereby avoiding loss of discern metallic.
Question 30. What Is The Different Between Gate Valve And Globe Valve?
Gate valve is non regulator method full close or full open positions simplest, at the same time as globe valve is regulator.