INDEX 1.BDN 2.BOILER BLOWDOWN 3.CATALYTIC FINES 4.CRANKCASE INSPECTION 5.BABITTING 6.PROPELLER SHAFT AND RUDDER STOCK STRAIGHTENING 7.CLEANING OF FUEL OIL TANK 8.TURBOCHARGER 8.TURBOCHARGE R SURGING 9.SAE 10.BOILER STARTING FAILURE 11.ALUMINIUM WELDING 12.Dry dock inspection of anchor 13.Diff between MC/MC-C AND ME/ME-C 14. Final Inspection Before UNDOCKING
Bunker delivery note It is a requirement of Regulation 18 that any fuel oil for combustion purposes delivered to and used onboard shall be recorded by means of a Bunker Delivery Note (BDN). This implies that a bunker delivery note shall be presented for every barge delivery and every grade. Bunker Delivery Notes are required to contain all specific information as follows: -Name and IMO number of receiving ship -Bunkering Port -Date of commencement of bunkering -Name, address, and telephone number of marine fuel oil supplier -Product name -Quantity (metric tons) -Density at 15 oC (kg/m3) -Sulphur content (% m/m) -A declaration signed and certified by the fuel oil supplier's representative representative that the fuel oil supplied is in conformity with regulation 14 and 18 (I.e. that the fuel supplied has a sulphur level below 4.5% and that the fuel is free from inorganic acid, does not include any added substance or chemical waste which either jeopardises the safety of ships, adversely affects the performance of the machinery, is harmful to personnel, or contributes overall to additional air pollution). Further, Resolution MEPC.96(47) recommends that the seal number of the associated associa ted MARPOL Annex VI fuel sample is included in the BDN’s for crossreference purposes. The BDN’s are to be kept on board and readily available for inspection at all times. It shall be retained for a period of three years after the fuel oil has been delivered on board.
BOILER BLOWDOWN Even with the best pretreatment programs, boiler feedwater often contains some degree of impurities, such as suspended and dissolved solids. The impurities can remain and accumulate inside the boiler as the boiler operation continues. The increasing concentration of dissolved solids may lead to carryover of boiler water into the steam, causing damage to piping, steam traps and even process equipment. The increasing concentration of suspended solids can form sludge, which impairs boiler efficiency and heat transfer capability. To avoid boiler problems, water must be periodically discharged or “blown down” from the boiler to control the concentrations of suspended and total dissolved solids in the boiler. Surface water blowdown is often done continuously to reduce the level of dissolved solids, and bottom blowdown is performed periodically to remove sludge from the bottom of the boiler. The importance of boiler blowdow blowdown n is often overlooked. Improper blowdown can cause increased fuel consumptio consumption, n, additional chemical treatment requirements, and heat loss. In addition, the blowdown water has the same temperature and pressure as the boiler water. This blowdown heat can be recovered and reused in the boiler operations. Boiler Blowdown Benefits • Less water, fuel and treatment chemicals needed; • Less maintenance and repair cost (minimized carryover and deposits); • Saves manual supervision for other tasks (with automatic control); • Cleaner and more efficient steam; • Reduced operating cost (reduction in consumption, disposal, treatment and heating of water); • Minimized energy loss from boiler blowdown can save about 2 percent of a facility’s total energy use with an average simple payback of less than one year. Flash Tank System The flash tank system shown in the figure below can be used when expense and complexity must be reduced to a minimum. In this system, the blowdowns blowdowns from the boilers are sent through a flash tank, where they are converted into low-pressure steam. This low-pressure steam is most typically used in deaerators or makeup water heaters. see diagrams on post dated 3-02-2011 3-02 -2011 by me(felix pinto) Flash Tank Heat Exchanger System The system shown below below consists of of a flash tank and a heat exchanger. The temperature of the blowdown leaving the flash tank is usually still above 220°F. The heat of this flash blowdown can be used to heat makeup water by sending it through the heat exchanger, while cooling the blowdown at the same time. Heating boiler makeup water saves on fuel costs. An additional advantage of cooling blowdown is in helping to comply with local codes regulating the discharge of high temperature liquids into the sewer system. –
Catalytic Fines Catalytic Fines Origin: By-product from the catalytic cracking process in the refinery. Catalyst consists of complex crystalline particles containing aluminium silicate. Catalytic fines result from catalyst particles breaking into smaller particles Catalyst is expensive, i.e. refiners minimise loss but not 100% Effects * Severe wear of Liners * Severe wear of Rings * Wear out of Cyl-grooves * Scuffing of liner * Abrasive Wear of Spindle-Guide & cut-off shaft & nozzles * Scuffing of Fuel Pump spindle guide Specification Variable in size size ranging from sub microic to to about 30 microns microns – – even seen larger Frequently considered spherical spherical but this is not necessarily the case. Hard particles Hardness not directly related to relative hardness of Al or Si Can cause abrasive wear ISO 8217 specifies the catalyst fines by Al and Si ISO 8217 limit is 80 mg/kg Al+Si for marine residual fuels (Note: ISO 8217 limit is for bunker not at engine inlet) Reduction Gravitational settling. Centrifuge (Note: Homogenisers will not reduce the amount of catalyst fines but might instead break them into even smaller particles) Overhaul and maintenance intervals must be kept according to manufacturers Recommendation. Temperature control very important. The higher the temperature the better the separation efficiency. Both density and viscosity of the oil decrease when the temperat temperature ure rises, thereby increasing the settling velocity (Stokes’s law) (If the separation temperature is lowered from 98ºC to90ºC the separator throughput has to be reduced by25-30% to maintain the same separation efficiency!!)
CRANK CASE INSPECTION (20 points) 1. Firstly check the oil condition for any smell, discolouration or degradation.
2. Turn the Engine to BDC & start checking from under stuffing box area for any signs of black oil, if so indication of stuffing box leaking. 3. Check piston rod surface for scoring marks & roughness. 4. Check Piston palm bolts & locking device for slackness & fretting. 5. Check guide & guide shoe bearing general condition & area around frame where guide is attached for any visible cracks. 6. Check guide shoe end cover bolts in place & not slack. 7. Check cross head general bearing condition. 8. Top & Bottom end of the con rod bolt, nut & locking devices for slackness, sign of fretting etc. 9. Check sliding of bottom end bearing (floating of con rod). 10. Check for slip of web & journal by checking the reference mark. 11. Check the web in the area of stress concentration & check tie bolts (bottomside). (bottomside). 12. Check cross girder , area around main bearing & bearing keep for signs of cracks & check the main bearing. 13. All bearings to be checked for silvery colour, (indicates bearing bearing wiping) 14. Check all the surrounding oil pan area of all units for any sludge deposits, bearing metal pieces etc. 15. Check crankcase relief door (wire mesh should be wet, spring tension sealing condition etc.) 16. Check the teeth of transmission gears for signs of wear. 17. Check chain drive for tightness. 18. Oil mist detector sampling pipe to be checked for clear passage. 19. Clear all foreign materials from the C.C. & tools accounted for. 20. Start L.O.p/p & X-Hd p/p & check oil flow & distribution. 21Check C.C.door sealing condition & close the door.
BABBITTING is a process by which relatively soft metals are bonded chemically or mechanically to a stronger shell or stiffener, which supports the weight and torsion of a rotating, oscillating, or sliding shaft. The babbitt, being softer than the shaft and having h aving excellent antifrictional qualities, prevents galling and/or scoring of the shaft over long periods of use. Compositions and selected properties properties of babbitts are summarized in Tables and Fig.. Babbitting is named for Isaac Babbitt, who patented the process in the United States in 1863. Babbitt metals, which are more widely known as white metals, are comprised principally of tin alloys (hardened with copper and antimony) or lead alloys (hardened with tin and antimony and, in some cases, arsenic). arsenic) . In the babbitting process, the relatively soft bearing material (babbitt) is bonded to a stronger supporting base metal, typically mild steel, cast iron, or bronze. The base metal may be in the form of mild steel strip unwound from a coil, a half-round mild steel pressing or bushing, or a bronze or iron casting. The bonded bimetal material is shaped and machined to make plain, fluid film lubricated bearings for a wide variety of automotive, industrial, and marine applications. Babbitt is used in small bearings for high-volume
applications, such as electric motors and internal combustion engines, and for large rotating and reciprocating machinery with low to modest volume requirements, such as high-speed turbines and low-speed marine diesel engines. In addition, babbitt has been used for jewellery, shot, filler metals, and various other applications. Leadbase alloys enjoy a cost advantage, while tin alloys offer modest technical advantages, particularly in high-speed centrifugal equipment . It should be noted that government regulations now discourage the use of lead-base alloys for health and hazardous waste disposal reasons. Babbitting of bearing shells can be accomplished by three methods: Static babbitting (hand casting), Centrifugal casting, Metal spray babbitting . Centrifugal casting and static (gravity) casting are the two babbitting methods used in the manufacture and repair of large, low-volume journal (radial) (radial) and thrust bearings. bearings. Centrifugal casting of journal bearings offers both technical and economic advantages if special spinning equipment is available. Flat shapes (thrust bearings) are usually statically cast. Repairing of industrial and marine babbitted bearings is routinely accomplished by melting off the old metal and rebabbitting rebabbittin g the shells with new metal, following the same basic casting methods described below for producing new products. Emergency repair methods using proprietary tinning compounds, babbitt babbitt spray, or welding techniques can be employed. Suppliers of such repair equipment should be consulted for operating instructions. Thin-wall babbitted babbitted half bearings, rolled bushings, and flat thrust washers are mass produced from bimetal strip stock. The strip stock is produced by continuously feeding coils of low-carbon steel in ribbon form first through appropriate cleaning and tinning baths and then through a stream of molten babbitt, which is gravity cast on the moving strip. The strip is immediately water-chilled from below. After excess babbitt is removed, the stock is recoiled and is ready for press blanking, forming, and finish machining operations.
PROPELLER SHAFT & RUDDER STOCK STRAIGHTENING Large diameter shafts, such as, for example, propellor shafts, rudder stocks etc. are subject to bending which can occur during manufacturing, processing or in subsequent use. Such bending can occur in the rough forging of the shaft and when machining to final dimensions. In lively forgings the final cut for a keyway or the like can create bends. Under some circumstances, such shafts will become bent after period of use or if a propellor, for example, strikes an obstruction. Acceptable limits of bend or eccentricity have been established and as a norm, a permissible eccentricity has been established at 7.4 thousandths of an inch for some operational uses. Above such a figure, mechanical and technical difficulties arise. Heretofore, methods for the straightening of shafts have been devised including a "hot spot" method and a "peening" method. The hot-spot method involves quickly heating heating a local spot (on the outside of a bend) to an elevated temperature. As a result of the local heat, the heated region tends to
expand, but also due to the elevated heat, the yield strength of the material is reduced. Due to these combined effects, the metal yields such that the shaft bulges slightly in the heated region. When the heat is removed, the metal then hardens and remains in the bulged position and the residual tensile stresses introduced into the outside of the bend of a shaft tend to straighten the shaft. The hot-spot method is characterized by the following intrinsic disadvantages: 1. The heating process is not accurately controllable. There is no precise method of determining the amount of heat applied to the shaft. 2. The metallurgy of the shaft can be adversely affected. 3. The process is extremely slow; after each heating the entire shaft must be allowed to cool to a uniform temperature before the results can be assessed. With the peening method, method, a hammer or equivalent technique is used to hammer or peen the shafting surface on the inside of a shaft bend. The residual compressive stresses thereby introduced into the shaft tend to straighten the shaft. The peening method entails the following intrinsic disadvantages: 1. The magnitude of the peening effort required to straighten shafts of large diameter, especially those of high tensile strength, exceeds that which can be accomplished with the usual peening techniques. 2. The residual stresses introduced into the shaft are distributed non-uniformly. 3. Peening subjects the shafting surface to possible damage. 4. Due to the superficial nature of the compressive residual stresses introduced, introduced, efforts to improve the surface finish of the shafting after peening by cutting a small amount of metal from the shaft will tend to destroy the effect achieved because the residual stresses in the metal removed from the shaft will not be uniform around the circumference of the shaft. The selective cold rolling method involves the use of cold rolling equipment such as is commonly used in connection connection with propeller propeller shafts & rudder stocks on ships, ships, however, instead of using a constant roller load and introducing residual compressive stresses uniformly around the circumference of a shaft, the roller load is varied selectively so as to use a higher roller load, with consequent higher residual compressive stresses, on the inside of a bend thereby tending to straighten the shaft. The selective cold rolling of a shaft is accomplished by pressing a small roller against the shaft with alternating loads as the shaft is slowly rotated. A specified length of the shaft is rolled r olled by slowly advancing the roller along the shaft as it rotates. The roller has a crowned face and is sized with radii of curvature which are much smaller than those of the shaft such that a very small elliptical contact area exists between the roller and the shaft. The combination of a heavy roller load on the shaft and the small contact area results in very large contact stresses between the shaft and roller. These stresses cause a yielding of the shaft material near the surface which then leaves a residual compressive stress in the material adjacent to the surface. By controlling the roller load, the magnitude and depth of the residual stress can also be controlled. The residual stress over the yielded depth actually produces a residual force in the area adjacent to the shaft surface and it is this residual force which is utilized to straighten a shaft.
Advantages associated associated with with the selective cold cold rolling method include include the following: following: 1. The variables required to straighten a shaft can actually be calculated. 2. The method is easily controlled such that predictable results can be achieved. 3. The residual stresses introduced in the shaft are not distributed erratically. 4. The results achieved can be assessed immediately after a rolling operation. 5. The straightening can be accomplished by introducing residual compressive stresses completely around the shaft circumference but more deeply on one side of the shaft than the other; this permits a small amount of metal to be removed from the shaft without affecting the straightening results achieved. 6. The metallurgy of the shaft material is not adversely affected. Procedure for Cleaning Fuel Oil Tanks on a Ship: Preparations Done before Cleaning The following steps are to be followed before starting the cleaning process: 1) Empty the tank as much as possible; strip the tank by trimming the ship forward or aft depending on the suction valve location. 2) When the ship is going for dry-dock the keel plan is to be sent to the shore facility so that they should not put any keel block in the way of the plug present in the bottom shell plating. 3) The tank has to be properly ventilated as it is an enclosed space and might contain flammable gases. 4) It is to be made sure that the steam connections are closed and proper signs and placards are displayed so that during cleaning nobody opens the valve and gets burnt or hurt. 5) The tank has to be checked for flammable gases. gases. 6) The tank has to be checked for oxygen content content with the help of oxygen analyser. 7) The tank is drained off left over oil with the help of plugs. 8 ) The location l ocation of plug can be found out in shell plating diagrams. 9) Generally this plug is covered with cement and made streamlined with the shell plating. 10) Enclosed space entry checklist is filled out so that no safety issues are compromised or left. During cleaning 1) Entry is only to be made inside the tank if the oxygen level is 21% by volume and
flammable gases are vented out. 2) One person should always standby outside the manhole door and should be in communication communication with the person inside. 3) The person outside should continuously communicate with person inside and with the duty officer. 4) In case of hot work to be carried out, a fire line is to be carried inside. Also, a small fire extinguisher for small fire should be there. Inform Port state authority before commencing hot work. 5) The tank is cleaned manually with the help of brushes, rags etc. 6) The oxygen content is continuously monitored and in case the alarm indicates low level, the space has to be evacuated immediately without any delay. After cleaning 1) Make sure no tool are left inside which may get stuck in the valve or damage the transfer pump 2) The place where crack repair is done should be checked for leaks. 3) If it was a steam leak repair, the coils needs to be checked for steam leak inside. 4) In case of crack or plate renewal the tank has to be pressure tested and checked for leak. If the repair is major it has to be inspected by class surveyor before putting it in operation. 5) Close the manhole after inspection, repairs and cleaning. 6) Close and remove the sign – sign – permit to work.
Turbocharger Surging: Surging of turbocharger occurs when the air pressure after the compressor is higher than the pressure compressor can internally maintain. This means, when the pressure of the air delivered by the compressor is higher than the pressure inside the compressor a reverse flow of air is created towards the impeller and inlet of the compressor, which reduces the speed of the turbine shaft and creates noise and vibration. Surging can better be understood by drawing a graph of pressure ratio against mass airflow of the system. From the graph it can be seen that surging is an unavoidable phenomena. The efficiency of compressor is highest near the surge line. This means that if high turbocharger efficiency is desired, a compromise between high efficiency or surging needs to be made. Surging leads to a sharp fall in the flow and acceleration of air mainly because of the reversal pressure. This imbalance in the demand and supply also leads to heavy damage of the turbocharger
Turbo charger surging may be defined as a high pitch vibration of audible level coming from the blower end or compress compressor or end of the turbocharger. Whenever the breakdown of gas flow takes place, a reversal of scavenge air takes place through diffuser and impeller blades into the blower side which causes surging. Surging is to be avoided as it interferes with the combustion in the main engine and may cause damage to the thrust bearings. There are mainly three things on which the functioning of turbocharger turbocharger depends. They are : Pressure ratio Air volume flow Speed When the air enters the compressor it follows the direction of diffuser vanes. The radial velocity attained by the rotational motion of the impeller is converted into pressure by the diffuser. This increases pressure at the compressors outlet. When surging occurs, due to the reverse air flow the velocity angles are disturbed which causes breakdown of the boundary layers. Turbulence is created near the t he boundary which reduces the air flow area, causing resistance. When the turbulence increases beyond a certain limit, the diffusion of air ai r drastically reduces leading to reduced pressure. Thus the pressure downstream of the diffuser goes higher than the diffuser pressure, leading to increase in reversal of air flow. Causes of Turbocharger Surging: 1) Improper power distribution between distribution between the main engine cylinders may cause turbocharger surging as one unit is producing more power and other is producing less. Due to this the air consumption required by both the turbochargers differs, which leads to surging. 2) Fouled compressor on turbine side – – In this case if the inlet filters are dirty then enough air can not be supplied for combustion, which leads to surging. Similarly if the turbine side is also dirty i.e. nozzle, blades etc enough air can not be produced for combustion. 3) Highly fouled exhaust i.e. exhaust i.e. economizer, if fitted may cause back pressure in the turbocharger and thus finally lead to surging. 4) Bad weather – – This is one more reason for surging. Due to bad weather the engine suddenly starts racing and sudden load change takes place. This happens because during bad weather or pitching the propeller moves in and out of the water, causing the change in load on the engine.
It can also happen due to sudden change in the engine load or speed. Imbalance in cylinder power or faulty injectors
Un-cleaned turbine nozzle ring. Damaged blades Dirty or choked filter The capacity of turbocharger is larger than required. Increased back-pressure back-pressure at the turbine side. Sometimes a dirty hull that makes the ship run at full torque t orque has also been shown as the reason for surging. Malfunction of engine's fuel system may also lead to surging. How to Prevent Turbocharger Surging? The following are the ways to prevent turbocharger surging. However, it is to note that some points may vary with design and construction of the turbocharger. Keep the turbocharger intake filter clean. Water-wash the turbine and the compressor side of the turbocharger. Proper maintenance and checks should be done on turbocharger t urbocharger periodically. periodically. Soot blow should be done from time to time in case of economizer or exhaust boiler. Indicator cards to be taken to assess cylinder and power distribution of individual units. How to evalute t/c performance? In order to evaluate the turbocharger performance it is necessary to carry out performance measurements,, including the temperatures and pressures before and after the turbocharger. measurements t urbocharger. The performance measurements are then compared to earlier measuremen measurements, ts, e.g. the sea trial results, in order to ascertain whether the turbocharger performance performance has deteriorated. However, as marine engineer, You should look at the following can affect the turbocharger performance AA) Exhaust side side - Exhaust gas economizer condition( Fouling, Excess back pressure, Many tubes plugged etc.,) - Fouled uptake pipes - Fouled sealing air passages - Choked drains and air blow lines in drains choked BB) Blower side- Dirty air from Ventilation fans(Sucking the engine exhaust, dirty cargo dust, sand storms micro dust and similar circumstances) - Air cooler fouling is very common- always track the Differential pressure near to sea trail value. - Blower side duct passages- fouled oily adhesions to blower ducts, Though the direct influence in not there for turbocharge turbochargerr performance, but the dirty scavenge and under piston spaces influence turbocharger indirectly. - Another Issue is Hot well steaming and locations of steam leaks l eaks near turbocharger is
another concern can deteriorate the performance - Pressure charge in Engine rooms is another serious issue- if you left open the engine room doors, there is no sufficient air charge for turbocharger suction. - Exhaust leakages around turbocharger is another serious concern for turbo t urbo charger performance deterioration.
Boiler Starting Failure Troubleshooting: 1) Fuel inlet valve to the burner is in close position: –
The fuel line for boiler’s burner consists of several valves located at fuel tank, pumps suction, discharge valve, or valve before the boiler burner. Any of these can be in closed position resulting in starvation of fuel. 2) Line filter at the inlet of the fuel line for burner is choked: If the system runs in heavy oil then there are chances of filters in the line getting choke. To avoid this, boiler system are normally built for changeover from diesel to heavy oil during starting and heavy to diesel during stopping. This keeps the filter and the fuel line clean. 3) Boiler fuel supply pump is not running: There are two main reasons for fuel pump not running. Normally when the pumps are in pairs, the change over auto system is kept in manual position, and if the operating pump trips, the stand by pump will not start automatically. Another reason is tripping of pump due to short circuit in the system etc. 4) Solenoid valve in the fuel supply line is malfunctioning Nowadays most of the system adopts advance automation, but there can be a possibility wherein the solenoid in the fuel supply line is malfunctioning and not opening. 5) Flame eye is malfunctioning: A Flame eye is a photocell photocell operated flame flame sensor fitted directly directly on the refractory refractory to detect wether the burner is firing or not. If the flame eye unit is malfunctioning, then it will give a trip signal even before the burner starts firing. 6) Air or Steam ratio setting is not proper
For proper and efficient combustion, air fuel ratio is very important, if the supply of air is less then there will be excess of smoke, and if it exceeds the normal level the combustion will burn off causing flame failure. 7) Forced draft fan flaps malfunctioning malfunctioning For removing excess gases trapped inside the combustion chamber forced draft fan (FDF) are used for pre purging and post purging operation and are connected with a timer to shut the fan flaps. If the flaps are malfunctioning malfunctioning then continuous forced air will go inside the chamber, preventing the burner from producing a flame causing flame failure of the boiler. 8) Any contactor switch inside Control panel is malfunctioning malfunctioning Boiler control panel consist of several contactors and PLC cards. Even one contactor malfunctioning may result in trouble for boiler starting. 9) Trip not reset If any previous trips like low water level, flame failure, emergency stop etc. has not been reset than boiler will not start. 10) Main Burner atomiser is clogged Main burners consist of atomizer for efficient burning of fuel. If the atomizer is clogged by sludge and fuel deposits then burner may not produce flame and trip the boiler.. 11) Pilot Burner nozzle is choked : A Pilot burner nozzle is very small and can be be blocked by carbon carbon deposits and sludge resulting in flame failure. Some pilot burner consists of small filter which can be clogged after continuous operation resulting in flame failure because of carbon accumulation. 12) Electrodes are not generating spark Initial spark for generating a flame is produced by electrode which may be due to carbon
The Welding of Aluminium
The most common commercial co mmercial aluminium and aluminium alloy welding methods use an electric arc with either a continuously fed wire electrode [with
DC current, with and without pulsed current] or a permanent tungsten electrode plus filler wire [with AC current].
The arc is protected by argon gas (or argon-helium gas mix) to shield the weld pool and the electrode from the surrounding atmosphere. Arc welding is easy to use, attains a high temperature, provides high heat input and is easy to regulate. To ensure an acceptable weld quality, there are two basic factors to consider breaking loose and removing the oxide film, and preventing the formation of new oxide during the weld process. It is essential that proper preparations and precautions always be taken before welding commences. commences. The surfaces to be jo joined ined and the area around the weld zone [~50 mm] must be degreased using a solvent [acetone or toluene] and a clean cloth. The area must be clean and completely co mpletely dry as grease and moisture can form gases and cause pores in the welded joint. The metal surface must be lightly mechanically mechanically brushed in and around the weld, after degreasing, to remove surface oxides and to avoid oxide inclusion in the weld. Use a brush reserved for aluminium use only and kept free of oil contamination. contamination. The high melting- temperature [~2000ºC] surface oxides must be removed just prior to welding (at least within three hours or less). Welding must not be done in draughty areas as draughts can easily reduce the inert gas protection and interrupt the arc, resulting in a sub-standard weld. The weld must be properly shielded with the inert gas at the corr ect flow rate, and of the required purity, and nozzle distances must not vary from the weld point.
Welding Processes for Aluminium
A variety of welding processes can be used to join aluminium including including the fusion methods GMAW (standard MIG, plasma and pulse) and GTAW (standard
TIG and plasma) giving high quality, all-position welding, manual, mechanised or fully automatic. Also resistance, MMA (metal arc, stick) and advanced processes such as solid state and friction stir welding. Choice of process is based on technical and/or economic reasons. For most structural economical and quality welds, TIG and MIG are recommended for aluminium. TIG welding is generally preferred for light gauge work up to 6 mm and for pipe work and intricate assemblies where
excellent control over weld appearance and penetration is possible. possible. Thicker material can be welded using TIG, but the very high currents needed, together with the very slow welding speeds required, render the process uneconomic for thick materials (> 12,5 mm). Butt, fillet, lap and edge welds can be carried out using TIG welding. MIG welding is preferred for thicker sections [to over 75 mm] and where high
productivity is needed for economic reasons. MIG welding can deposit up to about 4,5 kg per hour with weld travel speeds of 500 to 1000 mm per minute. Drawbacks of the MIG welding process are that control of penetration is difficult and edge welds are not possible. Pipe welding using MIG welding is not common because of the poor penetration control. Butt, fillet and lap joints are the most common configurations for MIG welding. Joint preparation is needed for thickness above typically 6 mm. MIG advantages over TIG are greater penetration depths, narrower HAZs and one-handed semi-automatic semi-automatic welding. MIG weld joint quality compared to TIG welding gives better strength, penetration (especially into the r oot of fillet welds), corrosion resistance, durability and finish appearance and less distortion. MIG welding welding is easier to learn than TIG. TIG welding is preferred for repair welding of castings, but MIG is preferred when welding castings to sheet and plate and extrusions [fabrication]. MIG welding speeds are about twice that of TIG, and higher for thick section welding. High speeds result in fast cooling of the weld area, which minimises distortion. High speeds and fast cooling of the weld area prevent mechanical properties of the joint from being reduced as much as they are by slower welding. Speed means corrosion resistance of the base metal in the HAZ is not reduced as much by MIG as by TIG. When TIG welding, the operator is limited to the length of weld that can be made by the length of filler wire – usually not more than 25 cm - without
breaking the arc. With MIG and the filler wire being added automatically, welds of 60 cm are possible without breaking the arc. This results in fewer weld craters and more cm of weld per hour. TIG manual filler addition means the welder has complete control of the weld puddle at all times - a definite advantage, and especially in butt welding of small and medium angles and other shapes. This control is an advantage in welding of castings where variable material thickness is often encountered. Good seam welds are essentially a result of optimally set welding parameters. Good TIG seams have a regular ripple finish and on both sides of the seam there is a narrow, white de-oxidised zone. The seam surface has a bright finish and is smooth and free of scaling deposits. Good MIG seams have a uniform fine ripple finish on the seam with an excellent transition to the basic material.
Dry Dock Chain Inspection Anchor & Anchor Chain Chain Cable Anchors and anchor anchor chain cable if ranged should should normally first be examined as follows:Anchor heads, flukes and shanks should be surface examined for cracks. If any such defects are found they may be weldable, otherwise renewal will probably be necessary. In such cases welding may be attempted as a temporary measure pending availability of the new equipment, which may take 3 to 6 months.Anchor months.Anchor head crown pins and anchor shackle pins should be hammer-tested, hammer-tested, hardened-up if slack, or renewed if excessively worn or bent.Swivels if fitted, should be closely examined so far as possible in way of the threaded connection, as many have been lost in service due to concealed wastage in this area. If in doubt the swivel should be recommended to be removed. Consideration should be given gi ven to simply eliminating any questionable swivels, they are normally not essential.Patented essential.Patented type detachable connecting links should be opened out and slack or corroded taper locking pins renewed their holes rereamed and new lead keeper plugs peened in."U" i n."U" type connecting shackles should be examined for excessive neck wear, slackness in the
pins and for shearing of keeper pins. The pin must be a snug fit all around in these shackles, otherwise the keeper pin may shear when a strain is put on the chain.Anchor chain cable should be surface examined, hammer-tested and loose or missing studs replaced by welding at one end of the stud only, at the end of the stud opposite the link butt weld. The rest of the chain cable should be further examined for excessive wear and gauged if necessary to ensure continued compliance with the Rules.Verify that the number of shots of anchor chain as fitted port and starboard, equal the total length leng th required by the Classification Rule Equipment Numeral.
Differences between MC/MC-C and ME/ME-C engines The electro hydraulic control mechanisms of the ME engine replace the following components of the conventional MC engine: • Chain drive for camshaft • Camshaft with fuel cams, exhaust cams and indicator cams • Fuel pump actuating gear, including roller guides and reversing mechanism • Conventional fuel pressure booster and VIT system • Exhaust valve actuating gear and roller guides • Engine driven driven starting air distributor • Electronic governor with actuator • Regulating shaft • Engine side control console • Mechanical cylinder lubricators. The Engine Control System of the ME engine comprises: • Control units • Hydraulic power supply unit • Hydraulic Hydraulic cylinder units, including: • Electronically controlled fuel injection, and • Electronically controlled exhaust valve activation • Electronically controlled starting air valves • Electronically controlled auxiliary blowers
• Integrated electronic governor functions • Tacho system • Electronically controlled Alpha lubricators
Final Inspection Before UNDOCKING Final Inspection B4 Undocking :Check paintwork is completed. Hull repair is completed. All Tank plugs are in place. All Anodes are fitted, grease/paper grease/paper used to cover them during painting is removed. Echo Sounder Transducer is cleaned of paper & grease. Propeller rope guard is fitted properly in place. Oil is not leaking from stern tube. Propeller is free from paint & free from any other object. Check freedom of movement of rudder with steering gear, smooth movement. Jumping & Pintle clearances taken. Rudder plugs are in place. Sea Grids are in place & secured properly. Ensure all sea v/v's are shut. Ensure all tanks are at same level as when entry ~ to maintain same trim when re-floating.
