MEO Class 2 Orals Function 4 & 6 Q & A

Q.When we changeover ME from HFO to DO ... why the rpm is reduced ??? At same fuel index, more mass of HFO will be injected as compared to DO as the density of HFO@ 130 deg is higher than that of DO at normal temp. And also the main engine is matched for running on HFO like ignition lag, vit operation which may be changed by FQS. Fuel plunger and barrel is made for running on hfo,incase of DO the leakage through the plunger and barrel comparatively increases.

Q. What is the crank pin oil hole position? When the piston is at TDC the crank pin oil hole position is horizontal, this done to reduce the stresses which could have generated if otherwise, this position is the only position allowed. Q. Why thrust pad is in pieces, y not single piece? By being in pieces each pad can generate its own hydrodyn film.....so as compared to a normal journal bearing more area can be utilized for the film and taking load... the.wedge.formed...using.a.single.piece.wud.make.it.tilt.in.such.a.manner.causing.huge.clearances.at.one.end...if.u.break.it.do wn.to.smaller.pieces.u.get.a.more.or.les.even.oil.distribution. Q. How many stern tube bearing are there and how are they connected with stern tube?Material of bearing and why white metal does not rotate with shaft? Stern tube bearings generally consists of two ( fwd & aft ) bearings which r pressed in and secured to the stern tube the bearing sleeves r made of high strength ductile iron and centrifugallylined with high tin base babbitt. the bearing bore is normally finish machined to fit the propeller shaft and outside diameter is semi finished for final machining in shipyard Two procedures are commonly used for fitting stern tubes 1.the stern frame is finish machined.the stern tube is pressed in and secured by bolting or welding .the stern tube is bored and bearings are then pressed into stern tube 2.In the second procedure, the stern tube is bored in the shop and fitted with its bearings then the entire assembly is pressed into the stern frame at shipyard. Boring of stern tube to provide an interference fit Q. Why piston rings are positioned in a lower place in a marine engines as compared to piston rings positioned at a higher place in AC compressors? Piston rings are down in IC engines as the temperature above will be higher and may cause LO particles to break down and hence loss of lubrication while in case of AC compressors temp is not so high as no combustion of fuel is there and hence less temp are experienced Q. PS (As in power) 735.5 W. Q. REMOVING LOWERHALF MAIN BRG.IT IS STUCK WHAT WILL YOU DO? If the lower half is getting struck and or there is less than 0.1mm clearance between the shell and the bearing on both sides then u change the position of the cross bar u have put for jacking the adjacent web there can be 50~150mm adjustment in the position of the cross bar. IF this does not solve ur prob then u have to arrange a 0.5T chain block between the web and the casing of the exhaust side and u will get the required clearance. U shld note down all the pressures u have applied as u wil need them while boxing them. The procedure is as per MAN B&W manual Q. Floating ring and blow down ring Floating ring acts as a cylinder for waste steam piston........while blow down ring is on the valve seat and used to adjust the blowdown of the valve. Q. The changes in the power card between an engine with and without vit. The difference in power card is that the peak pr rises but the the curve thins down towards the top so power remains same.(Refer A.J.Wharton) Q.Function of motor on governor A wattmeter senses alternator output Kilowatt load. This load feedback is sent to power management system. As load increases or decreases, especially sudden gradients, a signal is sent to the motor on the governor. This motor is bi directional and its rotation adjusts the spring tension that the flyweights have to work against.This changes the speed setting of the generator. Speed of motor for ug governor is 72 rpm for 60 hz & 60 rpm for 50 hz.

Q.What's is the meaning of 15w40? The oil weights in a multiviscosity oil refer to thickness of the oil. In a 15W40, the 'w' stands for winter weight, the oil has a viscosity of 15 ., but has an additive in the oil, called a viscosity inducer, which causes the oil to thicken as it heats up. When the oil reaches operating temperature, it will thicken to a viscosity of 40. It's important to realise that these SAE specifications only tell us about viscosity, not Quality. Here 40 is SAE number. SAE number like SAE 10, SAE 20 corresponds to that having kinematic viscousity at 100°C. Likewise W denotes the winter grade for cold start. Thus SAE 15W40 denotes that the lube oil of this grade has kinematic viscousity of 40 cst at 100°C and its winter grade is 15W ie, the cranking and pump ability of this lube oil grade has passed tests of 20W and 15W but failed test of 10W at below zero temperatures.

Q.Why Negative cam or Inward cam used in Air distributor of the MAN B&W Starting Air System. Why not a positive cam? The cam for the air distributor serves its purpose only while starting the engine, reversing and again starting. Actually if you see there is no other requirement of this particular cam while the Engine is in continuous operation. Therefore if a cam ( normal positive ) is used then the wear of this particular cam will be obviated and will be expensive to repair/replace this cam. So when the engine has started, and the vessel is en-route a voyage, then this particular cam turns without any running gear touching it. It comes into play only while starting. Q. Advantages of using Wasted studs for securing main bearing top keep in MAN B&W.Why not jacking bolts? Previously, you might be knowing that the main bearing keeps were held down by Jacking bolts (eg. Sulzer RND ). The reason behind that was the the kind of construction of the bed plate itself. When a cylinder fires, the pressure not only forces the main journals down but there is also a component of force which pushes the cylinder head up. Now the Cylinder Head, entablature and the bed plate is tied and precompressed by the TIE RODS. Now when the firing forces come, then there is a couple formed- a) One component of force tries to push the journal down and b) the other component tries to Push the Tie Rods up. Now at the bottom, the tie rods are bolted to the bed plate so a couple thus formed will try to rock the bed plate and thus the engine. To counter attack this problem, the tie rods were kept as close to the centerline of the engine as possible and due to space restrictions, the jack bolts were used to keep the bearing top covers tight(reaction force through the entablature). Note that there was only one cover for the main bearing having two jack bolts. Now recent development has waisted studs on the main bearing cap but the are OFFSET FROM the transverse centerline of the engine. Waisted studs give more comression as they have more elasticity and resilience. As a matter of fact, from the foundation bolts to the con rod bolts, the x-head bolts etc are all waisted studs. So care has to be taken while working as the necked region should not be marked, scored or cracked as due to reversal os stresses, fatigue will cause a crack initiation and finally fracture. The use of studs as opposed to bolts provides a more accurate and uniform clamping load pattern..Waisted studs give more comression as they have more elasticity and resilience...Studs also offer component installation advantages over bolts. Studs act as guide pins during alignment.Studs are available with "bullet" noses, where a slightly diminished-diameter bare tip is featured. This greatly eases nut installation, allowing the nut to be dropped into position before thread engagement begins. Q. COMPRESSION RATIO, SIGNIFICANCE, DO THE LIFE BOAT ENGINE AND E/M GEN. ENGINE AND MAIN ENGINE HAS GOT THE SAME RATIO?

Q. The Total Base Number (TBN) is an indication of the quantity of alkali, i.e. base, Total base number (TBN) is a measure of a lubricant's reserve alkalinity. It is measured in milligrams of potassium hydroxide per gram (mg KOH/g).TBN determines how effective the control of acids formed will be during the combustion process. The higher the TBN, the more effective it is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time. Q.WHAT IS BACK PRESSURE VALVE? Back pressure regulation valves is used in the suction line of reefer plant, and their function is to prevent the evaporator pressure falling

below a predetermined or controlled value, although the compressor suction pressure may be lower.The application of a back pressure regulating valve is to: 1. Prevent damage to a liquid chilling evaporator which might result from freezing of the liquid. 2. Prevent frost forming on an air cooling evaporator, where this is close to freezing point, or where a temporary malfunction cannot be permitted to interrupt operation. 3. Permit two or more evaporators, working at different load temperatures, to work with the same compressor. 4. Modulate the evaporator pressure according to a varying load, controlled by the load temperature. 5. Act as a solenoid valve, controlled by a pilot solenoid valve. Q.Sac Volume of fuel injectors The “Sac” is a small volume within the fuel flow path of an electronic fuel injector. In this study, it is defined as the volume between the valve seat (fuel shut off point) and the entrance to the final metering orifice of the injector. This sac causes fuel injectors to deliver uncalibrated excess fuel when the engine is operated under closed throttle, high manifold vacuum conditions such as vehicle decelerations or idle. Q. Required Properties of Ideal Refrigerant: 1) The refrigerant should have low boiling point and low freezing point. 2) It must have low specific heat and high latent heat. Because high specific heat decreases the refrigerating effect per kg of refrigerant and high latent heat at low temperature increases the refrigerating effect per kg of refrigerant. 3) The pressures required to be maintained in the evaporator and condenser should be low enough to reduce the material cost and must be positive to avoid leakage of air into the system. 4) It must have high critical pressure and temperature to avoid large power requirements. 5) It should have low specific volume to reduce the size of the compressor. 6) It must have high thermal conductivity to reduce the area of heat transfer in evaporator and condenser. 7) It should be non-flammable, non-explosive, non-toxic and non-corrosive. 8) It should not have any bad effects on the stored material or food, when any leak develops in the system. 9) It must have high miscibility with lubricating oil and it should not have reacting properly with lubricating oil in the temperature range of the system. 10) It should give high COP in the working temperature range. This is necessary to reduce the running cost of the system. 11) It must be readily available and it must be cheap also.

Q. Pinching screw is fitted to keep tie rod in centre and it is fitted at antinodal points so it reduces the span of tie rod and hence reducing the vibration in tie rod.. reduces the maximum amplitude of vibrations Q.What is galling? Galling usually refers to the adhesive wear and transfer of material between metallic surfaces in relative converging contact during sheet metal forming and other industrial operations. Q.Variable injection pressure (VIP)?? Its a nox control measure...used in modern electronic control engines...injector inject 2 times at different pr(300 bar and 1200 bar).. also known as rate shaping Q.Lip clearance in boiler....how to measure? By means of a lead ball and approx it is around 3 mm Q.LONG STROKE AND SUPER LONG STROKE ENGINES CONSTRUCTION DIFF?? Long stroke can have exh ports but super long stroke have to have exh v/v otherwise size of piston skirt will be too large to keep at least exh ports closed even when piston at TDC (which is not possible) to avoid by-passing of scavange air directly to exhaust side. WEBS ARE BIGGER AND THICKER IN SIZE IN SUPER LONG THAN IN LONG. MOREOVER DISTANCE B/W CRANK PIN AND JOURNAL PIN IS MORE IN SUPER LONG STROKE. Q.FUEL OIL INDEX NUMBERS? The fuel index is an indication of the active stroke of the fuel pump. This is controlled by push rods on the individual fuel pumps connected to the fuel rack, which in turn is controlled by the engine governor. When the engine is given a speed command the governor increases the fuel index, subject to certain limitations, until the requested engine speed is reached.

Q.Difference btw a/e and m/e flywheels ?? For the same engine size ...a/e flywheel will be bigger than m/e flywheel. angular momentum conservation: 4/s engine main power stroke is every 2nd cycle..so to conserve the angular momentum,a flywheel with a larger moment of inertia is required. the weight/power ratio will be higher for A/E fly wheel , moreover the inertia for A/E flywheel will be lesser due to the size limitations which again demands for added weight in order to achieve the required Inertia Q.How to check m/e air distributer timing is correct (means following the firing order of engine) after overhauling of the same? In b&w, there is a marking on distributor cam which u can match with flywheel marking.....just bring the no1 unit on TDC n then check with pin gauge.....check that TDC marking scratch on the starting cam is positioned vertically at the valve slide of cylinder no1...if not then adjust the position of starting cam by loosening the center screw and turning the starting cam until the scratch mark comes vertically at valve slide of cyl no1 n then tighten the screw.... Q.Why spring in governor is conical In governor measured parameter is speed and measured by the flyweights. Flyweights sense the speed by centrifugal force, so C.F is mw2r (where w is angular velocity), so since the speed is measured in power of square, the correcting action should also be in power of square. In conical spring the stiffness also behaves in power of square pattern (stiffness= force/deflection, so when u apply a unit force, the deflection is in power of square). So the springs are conical. Its observed that variation of spring force has a non linear relationship with the variation of speed.spring force is directly proportional to w^2 .the desired linear relationship is obtained by designing the spring as a conical one or a combination of springs of varying diameter and stiffness. Q.6S60MC-C? M: Engine Program (a software which MAN B&W has tht generates the required specs for a particular ship) C: Camshaft controlled................earlier it used to be for Container vessels. -C: Compact (space saving done on MC type) Q.What is VIT and super VIT?

Before the Super VIT was introduced , variable injection timing was obtained by means of a special profile on the fuel pump plunger. Hence there was a fixed relationship between the injection timing and the fuel index. Thus it was not possible to adjust the fuel index of the individual pumps without also altering the injection timing. For this reason the Super VIT was introduced, where it is possible to adjust the fuel index and the injection timing independently. In VIT beginning of injection could be controlled, but end of injection was fixed, due to profile of plunger n thus amount of fuel injected could not be changed with varying angle of injection at beginning. Thus MAN came up with super VIT where beginning n end both could be controlled by raising or lowering barrel in relation to plunger. Sulzer system when introduced vit way back in 80's it could control both beginning n end. Thus super VIT is for MAN B&W engines only. in VIT the plunger is having two helix, one at top, one at bottom............the top helix controls the beginning of injection n bottom helix controls the ending......so if u rotate the plunger fuel index n vit index both will change.......................but in case of Super VIT only the bottom helix is there which controls the fuel index.............vit index is independently controlled by motion of barrel............so in Super VIT, u can control fuel index n vit index separately.... The breakpoint is the point where the maximum cylinder pressure has been reached and the injection timing is advanced the most. Above the breakpoint the injection timing is gradually retarded back until it reaches its original setting at 100% MCR load. The position of the breakpoint is determined by the layout of the engine. Formerly it was generally considered to be at approximately 85% MCR load, but it also has to be ensured that the maximum pressure rise from compression to maximum cylinder pressure is 35 bar or less (recommended by MAN B&W Diesel A/S). For this reason the breakpoint has tended to be somewhat higher on the latest engines (approximately 90% MCR load).

Q. Wear rings can be defined as a device used to seal the pressure leakage of the liquid between the inlet of the impeller and the pump casing. Wear rings are typically found on pumps with closed impellers. A similar device that serves the same function called a wear plate can be found on some pumps with a semi-open impeller.The typical reason for using a wear ring is to decrease the amount of leakage loss around the impeller. Due to more work available to push the pumped liquid out the discharge there is a slight improvement in pump efficiency. Q.What is delamination? Delamination is the peeling off of layers of the bearing. It is not a slow, steady process like wear - instead whole layers of the bearing break off, causing uneven and excessive clearance. Q.How does delamination occur? Laminated bearings are manufactured in layers, with a fibre or cloth reinforcement. As wear at the bearing surface occurs, water penetrates the exposed micro-channels that are formed by the cloth. Swelling occurs along these surfaces, causing weakness between the layers of the laminate. The result is that the surface layers of the bearing material start peeling off. Q. How much is Needle vv lift? Generally 1mm maximum for 320 bar lifting pressure.

Q. Boiler corrosion how it happens and how to prevent? The most common causes of corrosion are dissolved gases (primarily oxygen and carbon dioxide), under-deposit attack, low pH, and attack of areas weakened by mechanical stress, leading to stress and fatigue cracking and pitting corrosion: scales such as calcium and magnesium salts.Many corrosion problems occur in the hottest areas of the boiler-the water wall, screen, and superheater tubes. Other common problem areas include deaerators, feedwater heaters, and economizers. Prevention: • maintenance of proper pH and alkalinity levels between 8.5 and 9.5 • control of oxygen and boiler feedwater contamination (less than 7 ppb oxygen for a 900 psig boiler) • reduction of mechanical stresses • operation within design specifications, especially for temperature and pressure • proper precautions during start-up and shutdown • effective monitoring and control

Q.What is a Diesel Switch? Changeover from preheated HFO to cold MDO/ MGO and vice versa represents a risk of fuel pump sticking or seizure due to the very small clearances in the fuel pump. The Diesel Switch is able to do the changeover in a controlled way so that rapid temperature deviations are avoided. This tendency is likely to spread and will, for instance, be introduced in European harbours from 1 January, 2010. This means more frequent changeovers. As we find that the changeover between HFO and distillate fuels can give problems for the fuel equipment, the process will need a high degree of automation to avoid incidents. MAN Diesel now offers the Diesel Switch, which ensures the necessary flexibility and safety when changing between HFO and

MDO/MGO. The principle of the Diesel Switch - Today MAN Diesel recommends to reduce the load to 25-40% to control the changeover. The Diesel Switch ensures a controlled and safe changeover independent of the engine load. The Diesel Switch operates on a combination of the temperature at the engine and the time. If the fuel temperature at the engine inlet exceeds 2 degrees/minute the Diesel Switch will give an alarm and put the process on hold. The process will be logged in the Diesel Switch so that it can be used as documentation to port authorities after the changeover. Q. AE inlet vv big or exhaust vv big and y? (Inlet valves are bigger so that there is no back pressure in t/c , free flow, better scavenging , exhaust gas expelled easily, and exhaust v/v is smaller so as to reduce power required to open the valve)

Q. Accumulation of pressure test in boiler? Classification Societies require that that when initially fitted to boilers , safety valves must be subjected to an accumulation of pressure test to ensure the valves are of the correct discharge capacity for the boiler. To conduct such a test, all feed inlets and steam outlets to and from the boiler must be closed and maximum firing load achieved. Accumulation of pressure must then not exceed 10% of working pressure. Duration of test is not to exceed 15 minutes for cylindrical boilers and 7 minutes for water tube boilers.

Q. How to reduce maintenance in exhaust valve? Good quality fuel usage, VIT adjustment, avoid running engine on low load, check fuel injection system, good scavenging, maintaining cooling water temp, check rotation of exhaust v/v.

Q. How signal is carried to ECR from rpm indicator? Magnetic pick up sends signal to transducer. An output coming from a transducer is filtered, signal conditioned and chopped. Finally it is converted into square waves. The square wave is passed through Phase Lock Loop multipliers. This output is gated by a precise time base generated through piezo crystals and then counted. This counts are displayed on bright LED's. It's nothing but R.P.M. with accuracy of ± 1 RPM. (Can also read – R.Sen page 364) Q. What happens when all the flywheel markings are somehow erased and how will u check the timings, tappets etc? The cam shaft will give a brief idea regarding position of the engine. There will be two units which will be in TDC so just rotate the push rod to see which one is there in the power stroke because the unit which will be in TDC, the push rods will be rotating freely and thus we can check the tappet of that engine. For timing also we have to see the cam position and marking on the pump plunger but it is very difficult to know the value exactly when fuel injection is starting and stopping as there is no marking in the flywheel. Q. Cylinder lubrication, TBN how much it should be (HFO-70, LSFO-30-40) Q. What causes ovality of liner? (Crosshead guideshoe and guide clearance) Q. What are liner ribs and why they are in segments and use ?(Provided at upper parts of liner to withstand combustion pressure and strengthening, in segments for freedom of coolant to flow) Q. What is the special construction of pedestal bearing on free end of rotor in auxiliary engine (Margin for expansion) Q. A waste gate arrangement is a valve in turbocharger that regulates amount of exhaust gases in the turbine side of t/c diverting some of the exhaust gases directly in exhaust piping , this will regulate the speed of t/c and thus the compression ratio on the compressor side of t/c. This is sometimes required in winter season as the air is cold thereby dense and less compression is needed as t/c are designed on normal temp so this arrangement is sometimes there for winter season.Also nowadays the t/c are super efficient and thus supply a greater amount of air than needed. Q. An Inducer is an axial flow impeller with blades that wrap in a helix around a central hub. An Inducer serves as a small booster pump for the main impeller. Usually inducers have between 2 and 4 vanes, although there may be more. The inducer imparts sufficient head to the liquid so that the NPSH requirement of the adjacent main impeller is satisfied. Although the inducer usually has a lower NPSH requirement than the main impeller, it can, and often does, cavitate during normal operation. The key is that there is so little horsepower involved with an inducer that there is virtually no noise, vibration, or resulting mechanical problems. Meanwhile, the higher horsepower main impeller sees sufficient head to operate without cavitation. Inducer: its purpose is to ensure tat supply of fluid to impeller is at sufficient press. To avoid cavitation,thus alow pump to operate with low NPSH

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What is a thermal boiler? Water and steam are typically used as heat carriers in process heating systems. But at high temperatures, water and steam requires a corresponding high operating pressure.In industrial heating systems this high temperature level is often a great advantage in order to get a high output of the process. Thus establishing this with water and steam, you must deal with

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systems and components of high pressure. This means large dimensions, weights, more safety issues and thus extra costs.In thermal oil boilers (thermal oil heaters), a special oil-based thermal fluid is used as the heat carrier, instead of water or steam. This oil operates at atmospheric pressure up to 300°C. Comparing to water and steam, it would require a corresponding pressure of 85 bar to obtain this temperature. This system is used in ships which carry cargo like bitumin n coaltar). Draw the diagram(side-view) of an axial vibration damper for a MAN B & W engine (Sanyal 157-158, leaf springs and oil chambers) What is a torsion meter? (it is a device to determine the torque or torsion in a shaft usually by measuring the twist in a calibrated length of shaft. ) What are persistent oils? What are its effects on marine environment? (Persistent oils generally contain a large proportion of heavy fractions or boiling materials. Don’t dissipate rapidly) What is differential switch in crane? What are the safety features in crane other than limit switches? (braking, override controls, hydraulic oil high temp. alarm and trip, hydraulic oil tank low level alarm) The m/e t/c lub is supplied by m/e lo p/p, during sudden lub p/p failure , how t/c is it protected? (POST LUBRICATION TANK and lubrication system. During normal engine operation the post lubrication system is continuously filled by lub oil via a small bypass line from the m/e l.o. system that also supplies the t/c. Excessive l.o. is unpressurised supplied back to the m/e l.o. circuit by means of a free o'flow.In case of a shutdown or blackout of the m/e where the l.o. supply from the m/e to the t/c is interrupted, the l.o. flows down from the post lubrication tk by gravity, ensuring the lubrication and cooling of the two plain bearings during running out of the rotor for up to 20 mins. The m/e should be stopped within this time!! This system features 2 separate oil inlet pipes and 2 running down pipes with different levels from the post lubrication tk to the brgs. This ensures that in case of standstill of m/e and shut off l.o. supply that the turbine side brg is lubricated for a longer period than the blower side brg. This tk is at atmospheric pressure.) WHAT IS CCAI NUMBER? (Calculated carbon aromaticity index, 800-860 (Refer Saif tole motor pg-13) Index of the ignition quality of residual fuel oil. VALENCE BAND? (Is the highest range of electron energies in which electrons are normally present at absolute zero temp.) SPCV IN SULZER (Spcv is stagnation pressure control valve used to suppress the after injection on RTA engines. If the SPCV is removed, the fuel pump is directly connected to the high pressure pipe allowing stagnation pressure to drop to a level where cavitations can occur.) SCR system, ammonia slip, catalyst? (Selective catalyst reduction - exhaust is mixed with ammonia and passed through a catalytic reactor, hence reduction in NOx. And soot in exhaust. Temp.- 290-450 C. Final products are water and Nitrogen(PG 78-80 POUNDERS)) Economiser if the area of heat transfer is 1000 sq m ,, what all will come under it and draw the construction of fins (surface area of fins and tubes) Why 3 injectors are used in modern 2 stroke engines (There will be better turbulence since three fuel injectors at an angle and the scavenge air enters at an angle so there will be better turbulence, there will be better heat dissipation in piston and cylinder head) DESUPERHEATED STEAM. WHY AFTER SUPERHEATING WE ARE USING DESUPERHEATER ? Desuperheating, sometimes called attemperation or steam conditioning, is the reduction of gas temperature. Its most common application is the reduction of temperature in a steam line through the direct contact and evaporation of water. Most Desuperheaters incorporate the venturi design which uses the velocity of the steam to atomize the cooling water. In addition, Ejector Atomizing Desuperheaters, Attemperator Desuperheaters, Surface Absorption Desuperheaters and Mechanical Atomizing Desuperheater designs are available. In most types, water pressure requirements are the same as the steam line pressure COP OF REFERIGERATION. (A refrigerator is a device for removing heat at a cold temp so heat absorbed in the evaporator fi(in),the cop is also called advantage and is defined as C.O.P. In a refrigeration cycle, the ratio of the heat energy extracted by the heat engine at the low temperature to the work supplied to operate the cycle; When used as a heating device, it is the ratio of the heat delivered in the high-temperature coils to the work supplied) Where do you find underslung bearing in Man B&W main engine (Camshaft bearing) What is lean mixture in dual fuel combustion engine? (Lean burn means the mixture of air and gas in the cylinder has more air than needed for complete combustion, reducing peak temp- less NOx, efficiency increases bcoz of higher compression ratio and optimised injection timing. What and why material of sounding bob. (brass - non sparking, softer than steel) How does MGPS works? (2 purposes: Cu kills sea growth and Al stops corrosion, the system is based on electrolytic reaction and dc supplied to anodes)(Subir Roy Page – 125) What is dealuminification , where is it observed and why? (Form of corrosion in which amount of aluminium decreases in an alloy…pumps, valves because Al is comparatively more reactive) It has been learned through experience that there are two methods for preventing dealuminification, which occurs primarily in seawater applications. The first, used primarily in North America, is to give the casting a special heat treatment known as a temper anneal. The purpose of the heat treatment is to break up and eliminate the deleterious gamma2 phase.. The second method, preferred in Europe for preventing dealuminification, is based on the observation that increasing nickel content suppresses the formation of the gamma2 phase. An empirical formula has been developed which, if followed, will guarantee that a continuous gamma2 phase is not formed in the alloy. The formula is: Al < 8.5 + Ni/2.

20) How to prevent Dezincification? (Put soft iron anodes) 21) What’s the time period to discard a chain and renew with new one in B&W? Tell the percentage elongation max allowed in 1 inch chain link? (max allowable limit of elongation is 1.2% , chains should be renewed once in 8 yrs or 50,000 hours)

22) Exhaust gas of all units’ high cause? (Bad quality fuel, faulty fuel system, poor scavenging) 23) Under which condition would u change the stuffing box spring? (stuffing box spring should/can be changed 1) when from tell tale hole of individual unit of stuffing box lot of oil is coming and lube oil loss is there, u don’t have sealing ring, scrapper ring, or lamellas....so for time being u can change the spring. 2)when u completely overhaul stuffing box 3) when spring elongation is exceeded as per manual.....usually checked by hanging it from a fixed point and applying fixed amount of force at the other end . new length -original length gives the elongation, check with manual for limits.....discard, replace with new one ) 24) Why water drained from air bottle is milky white in color? (Due to emulsion of water and oily) 25) Describe the items of a RO plant that require frequent overhaul and maintenance. How is sterilization carried out in it? (Semi permeable membrane, acid addition, chlorination, u.v.sterlizers) 26) What is the similarity and difference between a m/e governor and flywheel? ( Gov maintains speed of engine, flywheel controls cyclic fluctuation of engine rpm, flywheel works on virtue of inertia alone, governor uses inertia to actuate fuel linkage to counter change in rpm)