Mechanical Engineering Interview Questions for freshers Part 2
Questions 21 to 40
21. How pipe flanges are electrically insulated?
Pipe flanges are protected from corrosion by means of electrolysis, with dielectric flanges. The piping system is electrically insulated by what is called a sacrificial anode. A bag of readily corrodible metal is buried in the ground with a wire running from the pipe to the bag so that the sacrificial anode will corrode first. If any electrical current charges the pipe, it also serves as a ground.
22. What is a Process Flow Diagram?
A Process Flow Diagram (or System Flow Diagram) shows the relationships between the major components in the system. It also has basic information concerning the material balance for the process.
23. Where pneumatic system is used?
Any system needs redundancy in work needs pneumatics, because the compressor of the pneumatic system has periodical operations (intermittent work, not as hydraulic pump). The compressed air could be accumulated in tanks with high pressures and used even if the compressor failed.
24. Why gas containers are mostly cylindrical in shape?
The most efficient shape for withstanding high pressure is a sphere but that would be costly to manufacture. A cylinder with a domed top and a domed bottom (look underneath, the flat base is actually welded around the outside, the bottom of the gas container is actually domed) is a much cheaper shape to manufacture whilst still having good strength to resist the internal gas pressure.
25. How is martensite structure formed in steel?
Martensite transformation begins when austenite is cooled below a certain critical temperature, called the matrensite start temperature. As we go below the martensite start temperature, more and more martensite forms and complete transformation occurs only at a temperature called martensire finish temperature. Formation of martensite requires that the austenite phase must be cooled rapidly.
26. What is an orthographic drawing?
Orthographic projections are views of a 3D object, showing 3 faces of it. The 3 drawings are aligned so that if the page were folded, it would create part of the shape. It is also called Multiview projections. The 3 faces of an object consist of its plan view, front view and side view. There are 2 types of orthographic projection, which are 1st angle projection and 3rd angle projection.
27. What is representative elementary volume?
Smallest volume over which measurements can be made that will yield a representative of the whole.
28. Why are LNG pipes curved?
LNG pipes are curved because LNG is condensed gas (-164 deg cel) so it can expand the pipes that is what engineers designed the LNG pipes are curve type.
29. What does angular momentum mean?
Angular momentum is an expression of an objects mass and rotational speed. Momentum is the velocity of an object times it is mass, or how fast something is moving how much it weigh. Therefore, angular momentum is the objects mass times the angular velocity where angular velocity is how fast something is rotating expressed in terms like revolutions per minute or radians per second or degrees per second.
30. Can you use motor oil in a hydraulic system?
Hydraulic fluid has to pass a different set of standards than motor oil. Motor oil has tackifiers, lower sulfur content, and other ingredients that could prove harmful to the seals and other components in a hydraulic system. If it is an emergency only should you do it.
31. What causes white smoke in two stroke locomotive engines?
That is the engine running too lean (lack of fuel). This condition will lead to overheating and failure of the engine.
32. What is the role of nitrogen in welding?
Nitrogen is used to prevent porosity in the welding member by preventing oxygen and air from entering the molten metal during the welding process. Other gases are also used for this purpose such as Argon, Helium, Carbon Dioxide, and the gases given off when the flux burns away during SMAW (stick) welding.
33. What does Green field project mean?
Green field projects are those projects, which do not create any environmental nuisance (pollution), follows environmental management system and EIA (environment impact assessment). These projects are usually of big magnitude.
34. Is it the stress that, produces strain or strain produces stress?
A Force applied to an object will cause a displacement. Strain is effectively a measure of this displacement (change in length divided by original length). Stress is the Force applied divided by the area it is applied. (E.g. pounds per square inch) Therefore, to answer the question, the applied force produces both Stress and Strain. Stress and Strain are linked together by various material properties such as Poisson’s ratio and Young’s Modulus.
35. How does iron ore turn into steel?
To make Steel, Iron Ore is refined into iron and all the carbon is burned away using very high heat (Bessemer). A percentage of Carbon (and other trace elements) are added back to make steel.
36. What is knurling?
Knurling is a machining process normally carried our on a centre lathe. The act of Knurling creates a raised criss-cross pattern on a smooth round bar that could be used as a handle or something that requires extra grip.
37. What is the mechanical advantage of a double pulley?
It only takes half the effort to move an object but twice the distance.
38. What is extrude aluminum?
Extrusion is the process where a metal or a metal bar is pulled through a mandrel to elongate it and/or give it a final shape. Extruded Aluminum is a common form of making small aluminum wire, bars or beams and many varieties of small non-structural, decorative pieces.
39. What is a Newtonian fluid?
A Newtonian fluid possesses a linear stress strain relationship curve and it passes through the origin. The fluid properties of a Newtonian fluid do not change when any force acts upon it.
40. What are the points in the stress strain curve for steel?
Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.