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Questions and answers for Marine Engineers Interview
The purpose of a list of 300 top questions and answers for the Marine Engineers Interview is to provide guidance and preparation for individuals looking to be hired as marine engineers. The list of questions and answers covers various topics related to marine engineering, such as technical knowledge, industry experience, problem-solving skills, and personal characteristics, among others. By preparing answers to these common questions, individuals can demonstrate their competency, confidence, and fit for the role of a marine engineer.
Read the related Topic–The Best Tutorial on|marine engineering
Q1-What is the purpose of O rings, wearing in a centrifugal pump?
Ans:-The purpose of O-rings in a centrifugal pump is to provide a static seal between two stationary parts (e.g. pump casing and cover) to prevent the leakage of fluid or gas. They are used in rotary equipment like pumps to prevent the escape of liquids or gases from high-pressure regions to low-pressure regions. Over time, O-rings can wear due to abrasion or other factors, leading to the need for replacement.
Q 2-Centrifugal Pump Priming proecedure
Ans-The centrifugal pump priming procedure involves filling the pump casing with liquid to ensure proper operation. The steps for priming a centrifugal pump are as follows:
- Fill the suction pipe with liquid and close the discharge valve.
- Open the vent valve on the pump casing to allow air to escape.
- Slowly pour liquid into the pump casing until it reaches the desired level.
- Close the vent valve and open the discharge valve.
- Start and observe the pump discharge pressure to ensure the pump is primed correctly and running smoothly.
- Continuously monitor the discharge pressure and adjust the flow rate to maintain optimal performance.
Note: Priming a centrifugal pump is essential as it helps to prevent cavitation, which can cause damage to the pump. It is also necessary to use the correct type of liquid for priming the pump, as specified by the manufacturer.
Q 3-What is the diffrence between Globe Valve and gate Valve?
Ans-A globe valve and a gate valve are both types of valves used to regulate the flow of fluid in a pipeline. The main difference between them is the way they regulate flow:
- Globe valves have a movable disk that is lifted or lowered by a stem to regulate flow. They are typically used for throttling or regulating flow in a pipeline.
- Gate valves have a gate that rises or lowers to open or close the flow of fluid. They are usually used for on/off control of flow, rather than regulating it.
Additionally, globe valves are typically more expensive and have a more complex design compared to gate valves, which are simpler in design and less expensive.
Q 4-How can you identify 2 stroke and four stroke Marine engines without opening?
Ans– You can identify 2-stroke and 4-stroke marine engines by the sound they produce. A 2-stroke engine has a distinctive high-pitched, uneven sound due to the power stroke occurring twice in each revolution of the crankshaft, while a 4-stroke engine has a more steady, low-pitched sound as the power stroke occurs only once in two revolutions of the crankshaft. Additionally- 2-stroke engines have exhaust valves at the top (cylinder head) and scavenging ports at the bottom, while 4-stroke engines have intake and exhaust valves at the cylinder head.
Q 5- What is the power transmission method from Marine generator to MSB?
Ans– In marine systems, power transmission from the generator to the main switchboard (MSB) is usually done through bus- bars/electrical cables associated with preferential trips and overload protections. The bus- bars /cables carry the electrical power generated by the generator to the MSB, where it is distributed to the various loads and systems on the vessel. This method of power transmission ensures that the electrical power generated by the generator is effectively utilized by the ship’s systems and equipment.
Q 6- Why wear down in main bearings is critical to the condition of the crankshaft and propeller shaft system on ships ?
Ans- Main bearing wear is critical to the condition of a ship’s crankshaft and propeller shaft system, as it can lead to shaft misalignment and looseness. Misalignment can cause excessive vibration and wear on the shafts and bearings, reducing their efficiency and lifespan. In extreme cases, it can also result in shaft failure, which can cause extensive damage to the ship’s propulsion system and pose a safety risk to the crew and passengers. To prevent these problems, it’s essential to regularly inspect and maintain the main bearings to ensure that they are functioning correctly and to minimize wear.
Q 7- Significance of large fillets in crankpins and journals ?
Ans- Oil holes in crankpins and journals are given large fillets for several reasons:
- To prevent stress concentration: Large fillets help distribute stress evenly across the surface, reducing the likelihood of stress concentration and cracking at the corners of the oil holes.
- To improve lubrication: The large fillets allow for better oil flow to the bearing surfaces, improving lubrication and reducing wear.
- To increase strength: The fillets increase the structural strength of the crankpins and journals, making them less susceptible to failure.
In summary, large fillets in oil holes in crankpins and journals help improve lubrication, increase strength, and prevent stress concentration.
Q 8- What are the causes and effects of torsional vibrations in crankshaft ?
Ans- Torsional vibrations in crankshafts are caused by imbalances in the rotating mass, variations in the elasticity of the shaft and its components, and combustion forces within the engine. The effects of torsional vibrations can range from annoying noises to severe damage to the crankshaft and engine components, including bearings, connecting rods, and even the cylinder block. Over time, these vibrations can cause fatigue and the crankshaft’s failure, leading to engine failure and costly repairs. It is essential to design crankshafts and engines to minimize torsional vibrations and to regularly maintain and inspect engine components to prevent and detect problems early.
Q 9- What is critical speed and it’s adverse effects on ships ?
Ans- The critical speed of a ship refers to the speed at which the natural frequency of the ship’s hull and superstructure matches the excitation frequency of the waves in the sea. The vessel is susceptible to excessive vibrations and structural damage at this speed, leading to reduced stability, structural fatigue, and increased risk of capsizing. Adverse effects of critical speed can include discomfort for passengers and crew, damage to equipment, and reduced overall efficiency of the ship.
Q 10- What are fatigue cracks and crankshaft operating factors affect the likelihood of fatigue cracks?
Ans- Fatigue cracks occur in materials due to repeated loading and unloading, which can cause failure over time. The likelihood of fatigue cracks in a crankshaft can be affected by several operating factors, including:
- Load Magnitude: The magnitude of the load applied to the crankshaft can increase the likelihood of fatigue cracks.
- Load Frequency: The load applied to the crankshaft can also affect the likelihood of fatigue cracks.
- Stress Concentration: The presence of stress concentrations, such as sharp corners or notches, can increase the likelihood of fatigue cracks.
- Material Properties: The material properties of the crankshaft, such as its strength and hardness, can affect its resistance to fatigue cracks.
- Operating Temperature: High operating temperatures can weaken the crankshaft and increase the likelihood of fatigue cracks.
- Corrosion: Corrosion can weaken the crankshaft and increase the likelihood of fatigue cracks.
It is essential to monitor these factors and maintain the crankshaft properly to minimize the likelihood of fatigue cracks and ensure safe operation.
Q 11- How a detuner or torsional vibration damper can reduce the effects of torsional vibration ?
Ans- A torsional vibration damper, also known as a detuner, works by introducing a mechanical impedance to the torsional vibration system, reducing the amplitude of the vibrations. Vibration reduction is achieved by adding mass or damping elements, such as rubber or fluid, to the rotating system, which absorb the energy from the vibration and dissipate it as heat. The damper effectively changes the natural frequency of the torsional vibration system, moving it away from the excitation frequency and reducing the resonant amplification of the vibrations. By doing so, torsional vibration dampers can help prolong the lifespan of rotating machinery and improve its overall performance.
Q 12- How to identify a fatigue failure ?
Ans- Fatigue failure is a type of failure that occurs due to repeated loading and unloading of material. The following characteristics can identify it:
- Crack initiation: small cracks may appear on the material’s surface due to repeated stress.
- Crack propagation: with continued loading, the cracks will grow larger, eventually leading to complete fracture.
- Fracture surface: a fatigue fracture typically has a characteristic saw-tooth appearance caused by the crack’s progression over time.
- Location: fatigue failure often occurs at stress concentrations, such as notches, sharp corners, or holes.
- Loading history: a material that has undergone many loading cycles is more likely to fail due to fatigue than one that has undergone fewer cycles.
In conclusion, to identify a fatigue failure, one should look for a combination of surface cracks, fracture surface characteristics, location of the failure, and loading history.
Q 13- How a fatigue crack is initiated ?
Ans- Fatigue crack initiation occurs due to repeated cyclic loading on a material, causing microscopic cracks to form and grow over time. These cracks start at the material’s surface and propagate into the interior as the loading continues, eventually leading to failure. Factors influencing fatigue crack initiation include material properties (such as grain structure and composition), loading conditions (such as stress amplitude and frequency), and the presence of defects or inclusions in the material.
Q 14- The event leading to the main engine crankcase explosion?
Ans- The atmosphere inside the crankcase is stable; there are no sources of ignition or fuel, so there is no combustion or explosion.
Therefore, the first event is the creation of an explosive mixture. This phenomenon happens when a “hot spot heats the lubricant in the crankcase,” and the lubricant in contact with it vaporizes. The vaporized oil rises in the crankcase and condenses in the cooler parts of the crankcase. The resulting white mist is within the explosion range and flammable. The second event ignites this white fog by the same or different hot spots in the crankcase. When the oil mist ignites, a crankcase explosion occurs, and the pressure rises.
Q 15- What is mist detector in Marine engine?
A mist detector constantly monitors the oil mist concentration in the crankcase. If the concentration exceeds the set value due to overheating the bearings, the mist level is displayed, and an alarm is sounded.
Q 16- How can overheating be indicated in an engine other than by mist detectors?
Ans-
Overheating in an engine can be indicated through the following ways apart from mist detectors:
- Temperature gauges: Engine temperature gauges measure the temperature of the coolant and provide an indication of overheating.
- Warning lights: Many modern vehicles have a warning light that illuminates the dashboard to indicate overheating.
- Engine performance: Overheating can also be indicated by a decrease in engine performance, such as a lack of power or acceleration.
- Engine sounds: Abnormal engine sounds, such as knocking or ticking, can indicate overheating.
- Smoke: Excessive smoke from the engine, mainly white smoke, can indicate overheating.
It’s essential to address overheating issues promptly, as they can lead to engine damage if left unchecked.
Q 17- How to limit the severity of a crankcase explosion ?
Ans- A rapid build-up of pressure in the crankcase can cause the engine structure to explode, causing physical damage and resulting in flames spreading throughout the engine compartment, resulting in personal injury. This pressure rise is limited by the forced use of a relief valve mounted in the crankcase. These doors open when the pressure exceeds 0.02-0.1 bar to prevent over-pressurization of the engine structure. The door also serves the additional function of quickly closing the relief door to prevent fresh air from entering the crankcase where hot combustion gases are present.
Q 18- Procedure in the event of Crankcase overheating being indicated ?
Ans- An explosion is an uncontrolled event, so great care must be taken to ensure the safety of the engine room engineers.
- Leave the crankcase door immediately
- Slow down to slow down and ask the bridge to stop
- When the engine stops, stop the fuel supply
- Stop auxiliary fan
- Open skylights and storage hatches
- exit the engine room
- Lock the engine room entrance door and keep people out
- Prepare firefighting equipment.
- Do not open the crankcase for more than 20 minutes after stopping the engine, and make sure the oil mist detector (or bearing temperature monitor) alarm has been reset.
- Stop the LO circulation pump. Close the starting air and turn on the rotary gearbox.
- Identify “hot spots” (causes of overheating oil)
- Perform a permanent fix for the error
Q 19- What are the issues associated with effectively lubricating liner and piston assemblies in large slow speed engines?
Ans- Lubricating liner and piston assemblies in large slow-speed engines can present several challenges, including:
- Contamination: Dirt and other contaminants can interfere with the lubricant and cause wear and damage to the engine components.
- Temperature: High operating temperatures can cause the lubricant to degrade, reducing its effectiveness and leading to increased wear and tear.
- Pressure: The high pressure within the engine can cause the lubricant to be expelled, leading to insufficient lubrication and increased wear and tear.
- Cavitation: The rapid movement of the pistons and liners can create cavitation, which is the formation and collapse of vapor pockets in the lubricant. Cavitation can cause damage to the components and reduce the lubricant’s effectiveness.
- Compatibility: The lubricant must be compatible with the engine components, the fuel, and the environment to provide adequate lubrication and prevent damage to the engine.
- Lubricant consumption: Large slow-speed engines typically consume large quantities of lubricant, which can be a cost issue for ship owners.
- Oil is injected at defined points, which can lead to oversupply at delivery points and undersupply away from these points.
- Residual fuels that are normally used contain acids and abrasives that reduce the lubricating properties of the oil.
- In normal piston motion, the piston stops at the top dead center, and the hydraulic pressure built up between the ring and liner collapses.
- The high temperature at the top dead center reduces the lubricant’s effectiveness.
- The lubricating oil supply rate is usually regulated by engine speed. The result is a mismatch with the actual lubricant requirements over the wide operating range of the engine. Usually, when injecting too little oil at low loads or when the engine load changes.
These issues must be carefully considered and managed to ensure adequate lubrication and prolong the life of the liner and piston assemblies in large slow-speed engines.
Q 20- What investigations and corrective actions are required if the engine will not turn on air?
Ans- If the engine does not start in the air, investigate the following points and take corrective action.
- No air pressure in the starting air vessel. The air tank valve is checked and opened if found to be closed.
- Low air pressure in engine manifold. Low air pressure could indicate that the air compressor is not working or is consuming excess air. All air compressors start, and air consumption is limited to engine operation only.
- Carry out the visual inspection of The turning gear position and the interlock switch. Disengage the turning gear if found in the engaged position.
Blog Conclusion
In conclusion, this blog provides an overview of some of the most common questions and answers for a marine engineer interview. As a marine engineer, it’s essential to be knowledgeable about the ship’s machinery, have hands-on experience, and be able to articulate your skills and experiences effectively. Preparing for the interview by practicing your responses to these questions can help increase your chances of landing the job. Remember to focus on your strengths, highlight your relevant experience, and emphasize your passion for the maritime industry. Good luck!
