Answer: a [Reason:] Welding is basically classified into fusion and plastic types. The plastic type of welding is further classified as autogenous, homogeneous, and heterogeneous. In the autogenous process, no filler metal is used, whereas the other two processes involve usage of filler metal.

Answer: a [Reason:] The oxy-acetylene system is employed depending on the manner in which acetylene is supplied for welding. In the high-pressure system, the pressure of acetylene at the welding torch is 0.66-1.0 bar and it is 0.1-3.5 bar for oxygen. The low-pressure system pressure for oxygen should be 0.5-3.0 bar.

Answer: c [Reason:] For gas welding, a head of oxygen and acetylene are used for the process. Both the gases are stored in separate cylinders. The standard color for oxygen cylinder is black, where the oxygen is stored at a pressure of 125-140 kg/cm². The acetylene cylinder has a standard color of maroon and is fitted with a fusible light to avoid the explosion.

Answer: c [Reason:] In arc welding process, the heat for joining the metals is developed using an electric arc. The workpiece is melted by the arc and the electrode also melts, making the two join together. The temperature of the arc is about 5000-6000^oC.

Answer: b [Reason:] Depth of fusion is defined as the depth to which the metal is melted and deposited. The molten metal is forced out of the pool by an electric arc, which forms a small depression in the parent metal where the molten metal is piled up. This is known as arc carter. The distance between the tip of the electrode and the bottom of the arc crater is called arc length.

Answer: d [Reason:] An AC machine (transformer) is preferred for welding as it has a higher efficiency of 80-85%. Moreover, it has a lower power consumption and low cost of equipment. The efficiency for a DC machine (generator) is a low 30-60%.

Answer: b [Reason:] The metal of the electrode depends on the kind of parent metal used. For wrought iron, low carbon steel rods are used. Cast iron rods, mild steel copper coated rods, and low alloy steel rod containing 0.25% carbon are used for cast iron, mild steel, and alloy steel workpieces respectively.

Answer: b [Reason:] The metal of the electrode depends on the kind of parent metal used. For carbon steel, soft steel wires containing 0.1-0.18% carbon and 0.0025-0.04% phosphorus and sulfur are used. Cast aluminum alloy rods, copper rods, drawn brass rods containing are used for aluminum, copper casting, and brass workpieces respectively.

Answer: a [Reason:] Gas metal arc welding or MIG welding is a common welding process where an electric arc is produced between a consumable metal electrode and the workpiece. The arc and welding zone are surrounded by an inert gas. For MIG welding, argon or helium are used as the inert gas.

Answer: a [Reason:] Tungsten inert gas welding or TIG welding is a common welding process where an electric arc is produced between a non-consumable tungsten electrode and the workpiece. The electrode used in this process is tungsten. As it has a high melting point of 330oC, it will not melt during welding.

Answer: c [Reason:] Plasma is a high temperature ionized gas which is passed through the torch. The arc is initiated in the beginning by supplying electrical energy between the nozzle and tungsten electrode. This will release a high amount of heat, usually between 10000 and 30000^oC.

Answer: b [Reason:] When cracks are present, the ability of a material to resist fracture is an important characteristic. The fracture resistance of a material in the presence of cracks and discontinuities is defined as its fracture toughness.

Answer: b [Reason:] Fracture toughness is regarded as the rate of strain energy released per unit area of the crack. Its SI unit is joule per meter square (J m^-2) and is denoted as Gc.

Answer: b [Reason:] Although aluminum has a range of 20-100 J m^-2, the true surface energy lays at less than 2 J m-2. This value for polystyrene is about 2 J m^-2 even though it is relatively brittle.

Answer: b [Reason:] It is known that polymeric materials become brittle below the glass transition temperature T_g. Molecular activity is stationary below this temperature.

Answer: b [Reason:] Ductile fractures occur with large plastic deformation. This failure is caused due to the effect of shear stress. Brittle fracture, on the other hand, is caused due to direct stress.

Answer: c [Reason:] Brittle fracture occurs at a point where microcracks are more in number. Here, the rate of crack propagation is rapid. On the other hand, the rate of crack propagation in ductile materials is slow.

Answer: a [Reason:] To prevent ductile fracture, the material must have fine grains, a high hardness value, and must not show any defects or dislocations. Additionally, it is preferred that the material has high Young’s modulus and cohesive energy.

Answer: b [Reason:] To prevent fatigue fracture, a good design must be used to avoid stresses, and must have no residual stresses or dislocations. It must have a fine grain structure and a control over the surface finish. Special care must be taken to effect of corrosion by polishing and coating the material.

Answer: d [Reason:] Pyroceram is otherwise known as crystallized glass. It has excellent thermal and mechanical shock resistance due to its fine grain size. The grain size found in pyroceram is about 0.1 μm.

Answer: b [Reason:] Intergranular failure occurs due to the continuous brittle phase at the boundary. In steels, the presence of sulfur creates a brittle iron sulfide film. This can be prevented by the addition of manganese in steel.

Answer: a [Reason:] Polishing of the surface removes surface irregularities, while shot peening introduces compressive stress, both of which increases the fatigue strength. Carburizing and nitriding increase shock resistance of creation of cracks. On the other hand, decarburizing lowers the fatigue resistance by producing a soft surface layer.

Answer: b [Reason:] In combined aeration, both diffused air aeration and mechanical aeration take place using both diffuser plate and paddles.

Answer: a [Reason:] The detention period of a Sheffield mechanical aeration tank is 15 hours. Its return sludge is 15-20% of sewage flow.

Answer: c [Reason:] The detention period of combined aerator lies between 3 to 4 hours and the minimum detention period is 3 hours.

Answer: c [Reason:] The cones, with spiral vanes rotates at a high speed of 60rpm that results in the formation of bubbles in a simplex aerator resulting in the aeration of sewage.

Answer: a [Reason:] Dorroco aerator is a type of combined aerator which is efficient in comparison to diffused air and mechanical aerator.

Answer: b [Reason:] Simplex aerator is a type of mechanical aerator where a square or rectangular tank with a hopper bottom is used.

Answer: b [Reason:] Carbon dioxide gas is produced in the aerobic digestion of sludge by the oxidation of organic matter by bacteria into CO₂.

Answer: c [Reason:] The process involved in the treatment of sludge are thickening, stabilization, dewatering and dying.

Answer: c [Reason:] Drying of the sludge is the final stage in the sludge treatment process where the most stable form of sludge is obtained.

Answer: c [Reason:] In the sludge digestion process, the organic solids are converted into more stable form. It makes the dewatering and drying process of sludge simpler.

Answer: b [Reason:] In sludge thickening, the solid content of sewage is increased by gravity flotation and clarifier.

Answer: a [Reason:] Dewatering is the process of removal of water from the sludge. It can be done by drying or subjected the sludge with pressure.

Answer: c [Reason:] In sludge conditioning, the sludge is treated with chemicals in order to separate the water from the sludge and improving the dewatering characteristics of sludge.

Answer: a [Reason:] ‘A’ represents the coagulant pipe which is used for discharging the coagulant into the flash mixer.

Answer: c [Reason:] ‘D’ represents the drain valve which is used for the removal of sludge from the mixer.

Answer: d [Reason:] Temporal mean velocity is the average of velocities at a point over a definite period of time. It is represented by G.

Answer: b [Reason:] ‘B’ represents the outlet of the mixer which goes to the flocculation tank.

Answer: a [Reason:] Temporal mean velocity G = (P/μV) ^1/2, where P is the power, μ is the dynamic viscosity and V is the volume of the tank. It is measured in per second.

Answer: d [Reason:] E represents the Impeller which is driven by the electric motor to revolve in the tank.

Answer: c [Reason:] The speed of impeller in a flash mixer is between 100 to 120 rpm and the propeller type impeller is used.

Answer: c [Reason:] ‘C’ represents the deflecting wall, whereas the boundary below the inlet and outlet of the tank is the flash mixer wall.

Answer: a [Reason:] The detention period of flash mixer lies between 30 seconds to 2 minutes.

Answer: a [Reason:] Impeller is connected to impeller shaft which is further connected to electric motor so as to drive the impeller and mixing of coagulant in water takes place.

Answer: a [Reason:] The breaking of the biomass from the slime layer in conventional filter is called sloughing. It makes the effluent turbid.

Answer: a [Reason:] The minimum hydraulic loading of percolating filter is 1m³/m²/day whereas, the maximum hydraulic loading of percolating filter is 4m³/m²/day.

Answer: d [Reason:] Low rate trickling filter is called as a conventional trickling filter. It is also called as standard rate and percolating filter.

Answer: b [Reason:] The BOD of the effluent obtained after the filtration of sewage from the low rate trickling filter is between 80 to 90% and the effluent obtained is highly nitrified and stabilized.

Answer: d [Reason:] The efficiency of a percolating filter is given by η = 100/(1+0.0044 (μ)^1/2) where, μ is the organic loading in kg per hectare meter per day.

Answer: b [Reason:] When the loading conditions are less, the efficiency of the filter will be more and the removal of BOD from the effluent will be more.

Answer: b [Reason:] Efficiency of low rate trickling filter = 100/(1+0.0044 (μ)^1/2) = 100/(1+0.0044 (900)^1/2) = 100/1.132 = 88.3.

Answer: c [Reason:] The organic loading in a trickling filter is measured in kg / hectare-meter/day where, 1 hectare = 10⁴m³.

Answer: b [Reason:] The hydrogen sulfide gas is formed when the fixed nozzles are used during the filtration process, so sewage is chlorinated to prevent the formation of H₂S gas.

Answer: b [Reason:] The recirculation factor F = (1+ R/I) / (1+0.1 (R/I)) ² = (1+0) /(1+0)² = 1.