Marine solutions

Single phasing is said to be occur when one of the phase is broken in a three phase line. This will cause no current passing through one of the line and 2.4 times more current in other two lines for normal load. Cause       One of the fuse may blown off.      Line wore broken.      Relay contacts damaged. Effects       High current passing through other two lines which will gradually damage them.        Due to single phasing uneven torque will be produced which will result in vibration of motor.         It is impossible to start a motor wiit single phasing.         Motor speed may get reduced.         Motor winding will melt due to overheat.   Protection           Overload relay        Thermostats which will indicate an alarm by temperature change due to single phasing.  

The stress on the liner is proportional to the gas pressure inside the cylinder liner, as the piston moves downwards the gas pressure reduces . Thus the liner is thicker at top to withstand high stress due to high gas pressure and thickness is gradually reduced at bottom where the gas pressure is relatively low.

Bilge keel is a longitudinal structure that runs along much length of the ship down to lower side of ships hull which reduces rolling of the ship to a greater extent. The major use of bilge keel is to          Reduce rolling motion of the ship.          Increase structural strength of the ship.          Prevent bilges while grounding.

SULZER MAN Crosshead bearing surface area is smaller Large crosshead bearing surface area Bearing shell is smooth surface Grooves with machined channel to retain lubricating oil The lube oil is supplied by separate crosshead pump The lube oil is supplied by same main lube oil system pump The lube oil pressure is maintained at 12-16 bar The oil pressure is maintained at 2-4 bar i.e. system pressure Lube oil is injected once in one cycle @ 20 deg. Before TDC Injected twice every engine cycle Lube oil is supplied to crosshead by means of swinging or articulated pipe at crosshead Lube oil is supplied to crosshead by means of telescopic pipe connected to the guide

Crosshead is attached on the upper part of the connecting rod, which connects the con-rod to the piston rod. The guide and the guide shoe runs on the guide rail to support the crosshead pin and to transfer the side thrust of the crosshead to the engine frame. In some old MAN B&W engines and SULZER RND engines, the piston rod passes through a bore in the crosshead and is bolted from the bottom by means of fine threaded nut. In the new design engines such as MAN SMC/ ME and SULZER RTA/ RT flex, the pison rod palm rests on the crosshead flat surface and four hydraulic bolts are used to tie them together. Guide and guide shoe, along with the connecting rod and crosshead, is an important arrangement as the guide directs the guide shoe in reciprocating direction while absorbing the side thrust produced during the motion of the connecting rod. The guide comprises of guide rail (normally integrated/ bolted with the frame) and guide plates, in which, the guide shoe moves up and do

The  tie rods on a 2 stroke marine diesel engine hold the components of the engine together in compression and transmit the firing loads to the bedplate. Breakage, usually due to a fatigue fracture, can be caused by incorrect tightening, misalignment between the mating surfaces, overloading of the engine etc. Sods law dictates that often the bolt will fail at mid length. The top half can be removed by lifting it out, however the removing the bottom half will present a challenge, due to the restriction in headroom in the crankpit. Broken tie bolt (above) and right, detail of fatigue fracture. The most obvious method of removal may seem to be to cut the tierod out in small pieces using a grinding wheel/ burning gear. This is not recommended. Two alternatives are available: The first involves passing a wire loop down the tierod tube to the bottom of the tiebolt and lifting the bolt out. The second method outlined below involves jacking the bolt out from below. I

Land-based Installations On land based electrical systems, such as those found in homes and factories, the neutral wire (or phase) is connected to the ‘Earth’. The Earth wire is a safety feature that allows the safe direction of ‘fault currents’ into the ground, and away from people and livestock. As electricity will travel along the easiest ‘path’, the earth connection provides this. If a piece of equipment with a metal case did not have an adequate earth, and a fault caused the casing to become ‘live’, then the electricity would travel through a person touching the case. This is because the human body will conduct electricity (it is very moist). The electricity therefore will use the persons body as a low resistance path between the ‘live wire /or casing’ , and the earth (ground). Just to be clear about this, what is happening is that the electricity is in effect using the body as a conductor, similar to a wire. The above scenario is not good for the human body, and a

*Circuit breakers. *Fuses *Over current relay *Dead front panel *Rubber insulation mat *Insulation resistance *Reverse power trip *Ebonite Handel *Earth fault lamp *Under voltage trip *Over voltage trip *Preferential trip

Hot corrosion             It is basically vandium corrosion. Vanadium is present in fuel oil,when vandium and sodium is present in a ratio of 1:3 vanadium pentoxide a hard component is formed whose melting point is 630°. Due to high temperature in combustion chamber these melts into metal surface and leaving the surface exposed to corrosion is called as hot corrosion. Cold corrosion           Cold corrosion occur due to presence of sulphuric acid inside liner surface. This abnormal corrosion can cause wear and tear inside liner. This occurs due to new regulations that engine should be operated at high pressure and low temperature. This temperature below due point will result in deposit of water droplets inside liner surfaces and this water combine with sulphur in fuel to form sulphuric acid.

Main bearing           It is measured between journal pin and top shell when the piston is at any convenient position. Crosshead bearing           It is measured between top shell and crosshead pin, piston should be at 45° aftrr TDC. GUIDESHOE CLEARANCE             Measured between GUIDESHOE and guide bar. Bottom end bearing             Measured between bottom shell and con rod. Piston should be at BDC.     NOTE ALL CLEARANCE SHOULD BE BETWEEN 0.25-0.4MM

In B&W engine,there is a measured set of channels in the lower shell of crosshead bearing, through which lub oil can supply. The geometry is such that loaded area of pin are flushed with cooling oil twice during every engine cycle.           In sulzer a separate pump is provided to supply crosshead lub oil at a pressure of 12 bar.

Thrust blocks : The main thrust block transfers forward or astern propeller thrust to the hull and limits axial movement of the shaft. Some axial clearance is essential to allow formation of an oil film in the wedge shape between the collar and the thrust pads (Figure 8.6). This clearance is also needed to allow for expansion as parts warm up to operating temperature. The actual clearance required, depends on dimensions of pads, speed, thrust load and the type of oil employed. High bearing temperature, power loss and failure can result if axial clearance is too small. A larger than necessary clearance will not cause harm to the thrust bearing pads, but axial movement of the shaft must be limited for the protection of main machinery. The accepted method of checking thrust clearance, involves jacking the shaft axially to the end of its travel in one direction and then back to the limit of travel in the other. Total movement of the thrust shaft (about 1 mm being typical) is registere

NPSH NPSH is the difference between pressure at the suction of the pump and vapour pressure of the liquid. It is very important to avoid cavitation in centrifugal pumps. NPSH=PRESSURE AT SUCTION INLET-                         VAPOUR PRESSURE OF LIQUID Available NPSH - NPSH a  or NPSHA The Net Positive Suction Head available from the application to the suction side of a pump is often named NPSH a . The NPSH a   can be estimated during the design and the construction of the system, or determined experimentally by testing the actual physical system. Required NPSH - NPSH r  or NPSHR The NPSH r , called as the Net Suction Head as required by the pump in order to prevent cavitation for safe and reliable operation of the pump. The required NPSH r  for a particular pump is in general determined experimentally by the  pump manufacturer  and a part of the documentation of the pump.                      The available NPSH a  of the system should always exceeded the required N

Causes of Crankcase Explosion As we all know, for a fire or explosion to take place, there are three basic elements that are required to complete the fire triangle. These three components are – heat/energy, oxygen and fuel. In the presence of all these three elements, in proportional ratio and within the flammable limits, the reaction which causes fire or explosion becomes cyclic. In the crankcase of the main engine, the oil particles are churned into small particles of up to 200 micro meters in diameter. These small particles cannot ignite readily even with some naked flame. If a hot spot comes in contact with these small particles, it reduces the size of these particles, resulting in the formation of mist, which can be readily ignited with a hot spot. In the crankcase of the main engine all the three elements required for fire are available. Lubricating oil as the fuel source is sufficiently present, the air as one of the three things necessary is also present and the heat or

 scavenge fire  Carbonized lube oil, unburnt fuel oil and carbon from the residual products of the combustion spaces are accumulated in the scavenge spaces with the running of the engine. Under certain faulty running condition of the engine, these may ignite causing a fire in the enclosed scavenge space, known as scavenge fire. Causes  Blow past of combustion products caused by leaky, sticky or broken piston rings, worn out liner, faulty cylinder lubrication, or insufficient axial clearance of the piston rings. Overheated piston dissipates heat to the under piston area caused by faulty atomization and injection pressure, faulty fuel pump timing, loss of compression, engine overload, failure of coolant circulation or insufficient cooling due to formation of scale. Blow back of exhaust gases caused by exhaust back pressure or deposits on exhaust ports, fouling of grid before turbine inlet, fouling of turbine blades, choking of EGB or economiser gas outlet. Presence of fuel oi

PV VALVE                           Moderate pressures of 0.24 bar acting on large surfaces in liquid cargo tanks are sufficient to cause damage and rupture. The pressure on each unit of area multiplied by the total area gives a large loading on the underside of the top of a tank or other surface, which may then buckle or the metal plate may be torn. Similarly, pressure drop within a tank can cause damage due to greater atmospheric pressure on the outside. Pressure vacuum valve or PV valve in the ventilation system will prevent either over or under pressure. They are set usually so that tank pressure of about 0.14 bar will lift the main valve (The smaller valve will lift along with it) and release excess pressure. The vapour passes to atmosphere through a gauze flame trap. Drop in tank pressure compared with that of the outside atmosphere will make the s mall valve open downwards to equalize internal pressure with that outside.  Pressure vacuum valve or pv valve can relieve modera

A transformer can be defined as a static device which helps in the transformation of electric power in one circuit to electric power of the same frequency in another circuit. The voltage can be raised or lowered in a circuit, but with a proportional increase or decrease in the current ratings. In this article we will be learning about Transformer basics and working principle The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance. The working principle of the transformer can be understood from the  Definition: Transformer is a static device which convert electrical power from one circuit to another without changing its frequency. it Step up (or Step down) the level of AC Voltage and Current. Working principle:  it works on the pr

During starting of the motor the slip of the motor is very less i.e Slip=Synchronous speed(Ns)-speed of the                 rotor(Nr) As the rotor is stable during starting ,the no of magnetic flux (which is created by the stator) cut by the rotor is very high, hence high starting current. Once the rotor start rotating the slip of the motor decrease i.e no of flux cut by stator decreases and hence the current.

SAFETY VALVES At least two safety valves have to be fitted to the boiler. They may be both mounted on a common manifold with a single connection to the boiler. The safety valve size must not be less than 38mm in diameter and the area of the valve can be calculated from the following formula C x A x P = 9.81 x H x E where H= Total heating surface in m3 E = Evaporative rate in Kg steam per m2 of heating surface per hour P = Working pressure of safety valves in MN/m2 absolute A = Aggregate area through the seating of the valves in mm2 C = the discharge coefficient whose value depends upon the type of valve. C=4.8 for ordinary spring loaded valves C=7.2 for high lift spring loaded valves C= 9.6 for improved high lift spring loaded valves C= 19.2 for full lift safety valves C= 30 for full bore relay operated safety valves LIFT PRESSURE The safety v/v must be set at a pressure not exceeding 3% of the approved boiler working pressure. It is normal to set the suphtr saf