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Showing posts from 2022

How to prevent wear down of liner?

Use Low Sulphur oil. Maintaining high jacket water temperature. Running Main Engine at normal sea low , avoid running at low loads. Increase LO supply so that piston and liner seizure will not take place. By using proper TBN oil and correct grade of oil By avoiding ingress of moisture in charge air 

Unsafe condition, Unsafe act , Near miss and Accident

  Unsafe condition Unsafe condition mean any condition that could cause undue hazard to life , limb or health  of any person authorized or expected to be on or about the premises. Unsafe act An unsafe act is when an individual who has both knowledge and control of an existing unsafe condition or action , but choses to perform the action or ignore the condition . Generally perform unsafe acts in an effort to save time and /or effort Near Miss A near miss , near hit or close call is an unplanned event that has the potential to cause , but does not actually result in human injury , environmental or equipment damage or an interruption to normal operation. Accident An Accident is an unintended , normally unwanted event that was not directly caused by humans , the term accident implies that nobody  should be blamed , but the event may have been caused by unrecognized or unaddressed risks

CO2 extinguisher have no pressure gauge .Why

CO2 is a gas at room temperature until it is compressed to around 830psi at which point it begins to liquefy under that pressure .At that point the pressure will remain constant until the container is filled to its rated capacity(by weight) with liquid CO2. As long as there is some liquid CO2 in the container the pressure of the vapor above the liquid will remain at 830 psi.So a pressure gauge will show 830 psi without regard to the actual amount of liquid CO2 in the container

Induction hardening of crankshaft

It is a type of surface hardening in which a metal part is induction heated and then quenched . It increases the hardness and brittleness of the part . Induction hardening is used to selectively harden areas of a part or assembly without affecting properties of that part. Induction hardening is a non contact heating process which uses the principle of electromagnetic induction to produce heat inside the surface layer of workpiece . By placing a conducting material into strong magnetic field, electric current can be made to flow in the material by creating heat due to I2R losses in the material . In magnetic material , further heat is generated below curve point due to hysteris losses Advantages: Fast process No scaling  High wear and fatigue resistance Localized, constant and precise heating

Importance of Fuel pump

To time and meter the fuel accurately to the fuel injectors for combustion. Precise time of injection and constant same quantity delivered to each unit. Adaptability to change injection timing and quantity with load changes. Build up of fuel pressure from the very start to ensure atomization from the start and build of maximum power at the most desired point of the cycle for optimum peak pressure and cleaner emission.

Coupling Alignment

Coupling Alignment ( Temperature Adjustments ) :The operating temperature of a pump and a motor are often different. The motor will run at a specific temperature, which is usually indicated, on the motors data plate, and the pumps temperature will depend on the temperature of the fluid being pumped.  This change in temperature will cause the coupling to become misaligned at the units operating temperature. This situation has been compensated for. A few calculations will ensure that the coupling will be aligned when the pump is running.  The formula for this is Coefficient of expansion X temperature rise X centerline .  Coefficient of Expansion is the amount of expansion per unit length, per degree (F) rise or fall in temperature.  Temperature rise is the difference between ambient temperature and running temperature of the pump or motor. Ambient temperature is the surrounding temperature.  The center height is the center height of the pump and motor shafts.

NER and its location

NERs, sometimes called  Neutral Grounding Resistors , are used in an AC distribution networks to limit transient overvoltage that flow through the neutral point of a transformer or generator to a safe value during a fault event. In case of high voltage NER is used to reduce fault current. It is connected in between neutral to earth. If a generator is high voltage then it's neutral will be connected to earth via NER

Non reversing locking gear

  When two pumping units are fitted and only one is running, the idle pump might be driven in the reverse direction by fluid under pressure from the running pump, if non-reverse locking gear were not fitted. This gear is integral with the flexible coupling connecting motor and pump.  It consists of a number of steel pawls so mounted on the motor coupling that, when pumping units are running, they fly outward due to the centrifugal effect and remain clear of the stationary steel ratchet secured to the motor supporting structure.  The limit of this outward movement is reached when the pawls contact the surrounding casing, which revolves with the coupling. When the pumps stop, the pawls return to their normal, inward position and engage the ratchet teeth, so providing a positive lock against reverse rotation.  This action is automatic and permits instant selection and commissioning of either unit without needing to use the pump isolating valves, which are normally open - and are only clos

Difference Between Neutral, Ground and Earth?

Neutral Neutral is return path for an AC circuit which is supposed to carry current in normal condition. This current may be because of many reasons, primarily because of phase current imbalance and some time because 3rd and 5th harmonics also.  There may be others reasons too but the magnitude of this current is in fraction of phase current and in few case it can be even double of phase current. So Neutral wire is always assumed to be charged (in active circuit). This neutral wire is given to ground (by grounding) to make the second terminal of neutral wire at zero potential. Earth or Ground Earth or Ground is for safety concerns against leakage or residual currents on the system via least resistance path. While phase and neutral is connected to main power wiring, earth may be connected to body of equipment or to any system which in normal condition doesn’t carry current but in case of some insulation failure, is supposed to carry some minor current. This current is not directly comin

Air-conditions and Refrigeration are always rated in Tons.Why?

Air conditioners are designed on the basis of quantity of heat removal from room, hall or specific area.  Quantity of heat is termed in Tons means if an air conditioner is able to remove 1000 kilocalories of heat or 4120 kilojoules or 12000 BTU of heat in an hour that AC rated as 1 Ton of AC because 1000 Kilocalories or 4120 kilojoules or 12000 BTU ( BTU = British thermal unit. A measurement of heat, specifically, the amount of heat needed to raise the temperature of a pound of water by 1°F ) equal to one Ton of heat.  Also, this is the same case for freezer and refrigerator i.e. refrigeration system.    Ton of Refrigeration : A Ton of refrigeration  is a unit of power used to describe the heat extraction capacity of air conditioning and refrigeration equipments.  It is defined as the heat of fusion absorbed by melting 1 short ton of pure ice at 0 °C (32 °F) in 24 hours.

Why rudder is situated aft of the ship?

To make use of propeller outflow for thrust. The increased velocity of the propeller outflow results in a greater lift force. If a rudder is placed just forward of the propeller, it will have the same turning effect with respect to direction, but the magnitude won’t be the same. The pivoting point of ship is 1/6 to 1/3 rd of length of ship from bow, the greater the perpendicular distance between point of action of force and pivoting point, the better rudder movement. Better protected at astern from damage. Drag is reduced if rudder is situated aft

Use of Concentric Spring in Auxiliary Engine Valve Arrangement.

  If one would look carefully, it is noticed that the two springs have their coil in opposite direction.One is right handed and other left handed. This is important since when the springs compress and decompress at high speed , there is a side thrust acting on the spring retainer due to coils of spring. To cancel this side thrust, another spring with opposite coil direction is introduced. Since the side thrust from second spring is opposite to that of first spring, the net side thrust is zero.  There is the effect of resonance at high engine speed. To prevent the matching of natural frequency of the running engine to the natural frequency of the spring, additional spring is added. This addition increases the natural frequency of the spring combination much higher than the engine's natural frequency, thus preventing any damage to the engine by excessive amplitude of vibration.  Tw o spring do provides an additional safety in case of failure of one. But remember th

Boiler steam drum is curved. Why

Circular hoops can withstand internal pressure by pure tension in the tankmaterial instead of bending. Materials can take more force in tension than inbending.  If the shape were not circular, then there would be bending stresses in the tank wall and it would not be able to withstand as much pressure without breaking.  Spheres are more efficient than cylinders if you just care about minimizing the mass of the tank to hold a certain amount of pressurized gas. But cylinders are easier to pack together. So it’s a trade-off between efficiency and practicality.

RAKE and SKEW of propeller

  RAKE: When the propeller is viewed from sideways, we see that the blades of the propeller are not perpendicular to the surface of the hub. It is ‘tilted’ at an angle either towards the fore-end or the aft end of the ship. This is termed as Rake.  One of the biggest reasons for the rake is allowing higher clearance between the blades and the vicinal hull surface. If the blade tip happens to be very close to the hull plating (which is very prone in case of no or little raked ones), there is a chance of induced vibration due to ship propeller action.  When the blade is raked forward, that is in the direction of the shaft axis towards fore-end, it is called Negative Rake. Conversely, when it is raked aft, it is called Positive Rake  SKEW:  When we look at the ship propeller surface from behind). The blade appears to be ‘Skewed’, that is, bent or twisted sideways.  After years of experimentation, analysis and sea trials, it was observed that aptly skewing a ship propeller nullifies or con

Floodable length and Permissible length

  Floodable Length:  It is also the maximum length of the ship that can be flooded without submerging the margin line. Margin line is a line just below the top of the bulkhead deck.The floodable length of a vessel varies from point to point throughout her length and is usually the greatest amidships and the smallest near the quarter length.  Permissible Length:  The floodable length of each point along the ship’s length is multiplied by the permeability to obtain the Permissible Length. The permissible length curves for 85 percent and 60 percent permeability are now incorporated into the floodable subdivision diagram. Here, for machinery compartments (e.g. engine room compartment BC) the vertices for the triangle needs to be checked against the 85% curve, instead of the floodable length (100%) curve The general values of permeability used for different types of compartments are listed below, followed by a logical understanding of the variation in the values: Watertight Compartment – 95

Types of Rudders

  Spade or balanced rudder: A rudder has 20-40% of the area forward of the stock, similarly there is no torque on the rudder stock at certain angles and it is called balanced. The axis of the rudder is placed near to the center of gravity, so torque required to move the rudder will be very less. Semi-balanced rudder: A rudder with 20% of its area forward of its stock is called semi-balanced rudder. It is often found in twin screw ships. In this at no angle, rudder is balanced. Unbalanced rudder: A rudder with whole of its area aft of its stock is called unbalanced. In this at no angle, rudder is balanced

How to order welding machine

Single phase or 3 phase transformer. System current requirement to be mentioned. (10 A – 200 A) Cable size and insulation requirements. Holder size (3.5 mm to 18 mm) Physical size of transformer Only for welding transformer rating in KW, (5 to 40 KW)

Working of welding transformer

More number of turns on primary and less number of turns on secondary, which produces high current and low voltage.  One end connected to the secondary electrode and other to work piece and other to work piece to be welded.  Due to high contact resistance, very high current flows. Therefore more I2R heat produces and electrode melts and fills the gap between the pieces.

Leakage Detection in Shell and Tube Type Cooler

The working pressures in case of jacket water system or lubricating oil system are usually of higher pressure than sea water system. If the leakage takes place in the jacket cooling water side or lubricating oil side, the flow from any point of leakage is in to the sea water side of the cooler. If the leakage is heavy then, usual indication is loss of jacket cooling water or lubricating oil. Procedure: Ensure the end covers are removed from the sea water box side and secure the tube stack by dog clamp arrangement-tube stack should not be disturbed when shell is under pressure. • Clean the sea water side of the cooler. • Start the fresh water cooling pump or lubricating oil pump. • Let the fluid circulate through the cooler spaces on the outside of the tubes. • Leakage within the tubes or at the junction of the tube plate will show up as liquid trickling. • Identify the tube which is leaking. It is a time consuming procedure so be patient. Fluorescent Halo Test Small leaks are extremely

Testing of Refer compressor Suction and Discharge valves

 Testing Compressor Discharge Valves Close the liquid valve in the receiver outlet and collect the refrigerant. The compressor will stop on LP trip. Shut the suction and discharge valves quickly. Observe the suction and discharge pressure gauges. If the discharge pressure falls roughly by 1 bar and above in five minutes and simultaneously if suction pressure rises, then the discharge valve is leaking. Testing of Compressor Suction Valve Run the compressor under manual control. Close the suction valve slowly to prevent foaming of lubricating oil in the crankcase. With the suction valves shut, the compressor should develop a vacuum of 0.4 bar or more. This indicates the suction valves are ‘holding’ and functioning correctly.

Purging of air from 4 ram type steering gear system

 The procedure refers to purging of air from 4 ram type steering gear system: Carry out the system isolation as mentioned before. In case of hydraulic ram type steering gear, the casing and the sump should be maintained with 75% of its capacity. Turning bar inserted in the holes of flexible coupling between motor and pump. The air release purge screws on the cylinders are then opened partially. Use correct allen key. The pump put on stroke by pressing the end button of the bi-directional valve. The gear is slowly moved from one direction to another. Ram movement should be on both sides. The level in the tank should start to fall. Air free or bubble free liquid should escape through air release valves. Stop pressing the end button of the bi-directional valve and stop turning the pump. Switch on the breaker and Start the electric motor. Put the switch on local. Under local control, use bi directional valve to move the gear should be moved from one side to another. The air release on the

Advantage of Roof top burner in boiler

Increased efficiency due to the longer length allowed for the flame giving more time for complete combustion. This also allows more heat to be released as radiant rather than convective cutting down the required number of screen wall generating tubes. The longer period allowed for complete combustion means that less excess air is required, this has the knock on effect of lowering the Dew Point of the flue gasses. Better gas flow.  Better flame propagation  Maximum utilization of heat  Easy maintenance Lower furnace exit gas temperature

Elcometer test

The Elcometer range of digital coating thickness gauges has been specifically designed to provide highly accurate, reliable and repeatable coating thickness measurements on almost any substrate, whether ferrous or non-ferrous.  Dry Film Thickness can be measured on either magnetic steel surfaces or non-magnetic metal surfaces such as stainless steel or aluminium using a digital coating thickness gauge.  The principle of electromagnetic induction is used for non-magnetic coatings on magnetic substrates such as steel.  The eddy current principle is used for non-conductive coatings on non-ferrous metals substrates.