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POWER ENGINEERING 2A2 PRACTICE PAPER
2026 COMPLETE SOLUTIONS
◉ Define 'Extractive' Metallurgy. Answer: - The study of extraction and purification of metals from their ores. This includes a stepped process which can utilize Pyrometallurgy, Hydrometallurgy or Electrometallurgy ◉ Define Pyrometallurgy: Answer: - Melting the ore in a furnace to release the metal ◉ Define Hydrometallurgy: Answer: - Dissolving the metal from the ore and recovering it as a powder ◉ Define Electrometallurgy: Answer: - Dissolving the metal from the ore with the use of electricity, plate the metal out of solution ◉ What is Mechanical Metallurgy? Answer: - The study of the techniques and mechanical forces that shape and make finished forms of metal
- The study of the effects of stress, time and temperature
◉ What is Physical Metallurgy? Answer: - The study of the structure of metals - property of metals are intimately related to their structures
- The physical metallurgy - or structure of a metal - can be changed by modifying chemical composition, alloys and heat treatments ◉ General characteristics of 'Metals'? Answer: - Good conductors of heat and electricity
- Generally malleable and ductile
- Occur naturally in ores in the form of chemical compounds such as sulphides or oxides ◉ What are Noble Metals? Answer: - A metal that resists chemical action and does not corrode or oxidize, and is not easily attacked by acids ◉ Metals can exist in 3 common physical states depending on what? Answer: Temperature and pressure ◉ Describe 'latent heat of fusion' in relation to metals. Answer: - Het energy is added until temperature no longer increases and the cohesive bonds holding the individual atoms together break. This causes the metal to melt.
◉ Define Malleability: Answer: - A materials ability to deform under compressive stress; often characterized by a materials ability to form a thin sheet by hammering or rolling - without fracture. ◉ Both ductility and malleability are aspects of a materials...? Answer: - Plasticity: the extent to which a solid material can be plastically deformed without fracture
- The plasticity is dependant on temperature and pressure ◉ Ductility and malleability are not always coextensive. True or False? Answer: True. Gold is both ductile and malleable while Lead has a very low ductility but high malleability. ◉ What is Shear Strength? Answer: - The strength of a material or component against the type of yield or structural failure when the component fails in shear. ◉ What is Shear Load? Answer: - A force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. ◉ Metals that have FCC unit cell structures in the solid state? Answer: - Gold, aluminum, silver, lead, nickel, gamma iron (iron between temperatures 910 - 1390 deg.C)
◉ # of atoms contained in a BCC structure? Answer: 9 atoms total ◉ Characteristics of metals with the Body-centered cubic structure? Answer: - High strength
- Low ductility
- Very resistant to shear deformities ◉ Examples of BCC metals? Answer: Chromium, tungsten, molybdenum, vanadium, alpha iron (solid state iron below 910 deg.C) and delta iron (iron above 1390 deg.C) ◉ How many atoms make up a Close-packed hexagonal structure? Answer: 17 atoms total ◉ Characteristics of CPH structured unit cells? Answer: Intermediate strength and Intermediate ductility ◉ Materials that possess CPH unit cell structures? Answer: Zinc, magnesium, cadmium, titanium ◉ When molten metal cools and solidifies, what action do unit cells take? Answer: - Unit cells become packed together to form 3 dimensional crystals that occupy a space lattice.
◉ What is Polymorphism and what does it have to do with metals? Answer: - The ability of a metal to change its unit cell structure through varying temperature ranges.
- Most metals exhibit this property; most important for the study of iron. ◉ What is the allotropy of Iron? Answer: - The change in atomic cell structure dependant on temperature
- Various physical forms of metals can affect their: melting point, hardness, metal solubility, and alloying chemistry. ◉ Properties of pure Iron? Answer: - Relatively soft
- Ductile
- Low strength
- Possesses few of the noble properties commonly associated with steel ◉ Percentage carbon content in Carbon Steels and Cast Iron? Answer: Carbon Steels: Alloys containing 2% or less carbon Cast Iron: 2% - 6% carbon ◉ Three grades of Carbon Steel? Answer: Low carbon steel: .04% to .30% carbon (mild steel) Medium carbon steel: .31% to .60% carbon steel
High carbon steel: .61% to 1-1.50% carbon steel (tool steel) ◉ Steel properties as carbon content increases? Decreases? Answer:
- Hardness and brittleness increase as carbon content increases
- Ductility, softness and weldability increase as carbon content decreases ◉ Weldability is more difficult for higher content carbon steels and even more difficult for cast-iron metals. True or False? Answer: True. The higher carbon content, the harder to weld. ◉ 4 varying factors that determine Iron-Carbon Equilibrium? Answer: - The initial concentration of carbon in the ferrite mixture
- Temperature
- Cooling rate
- Presence of other alloy metals ◉ Describe Austenite. Answer: - Structural name of Iron in the FCC form; also referred to as 'Gamma Iron'
- Contains dissolved carbon up to 2% concentration
- All quenching heat treatment procedures must begin from the gamma iron phase
- Non-magnetic allotrope of Iron that exists of the critical Eutectoid temperature of 727 deg.C
◉ Purpose of the Lower Critical Change Line on the Iron-Carbide Equilibrium diagram? Answer: - The temperature at which an iron alloy of ANY carbon composition returns to a BCC unit cell structure. The diagram indicates this temperature at 723 deg.C ◉ What is Pearlite in relation the Iron-Carbide Equilibrium diagram? Answer: - Layered Structure (microscopically) of Ferrite and Cementite
- Appears dark grained in colour and forms in iron-carbon alloys BELOW the lower critical change line (723 deg.C)
- Occurs in steels and cast irons
- Forms from slow cooling from 723 deg.C and occurs as a Eutectoid reaction ◉ Describe the Peritectic reaction in relation to the upper left of the Iron-Carbide Equilibrium diagram. Answer: - The point where liquid delta iron, in the BCC form, changes directly into solid austenite without going through a pasty state phase
- Occurs at 1492 deg.C ◉ Describe Hypoeutectoid Steels. Answer: - At room temperature, low and medium carbon steels (below 0.8% C) always have a Ferrite component that make them tough and ductile and an FE-C influence from the Pearlite that lets them remain moderately Hard.
◉ Describe Eutectoid Steel. Answer: - 0.8% Carbon exactly
- Made of 100% Pearlite (layered Ferrite and Cementite)
- Used for railway rails ◉ Hypereutectoid Steels? Answer: - Carbon content exceeds 0.8%
- Exhibits high tensile strength and used in tools such as axes and chisels
- at 723 deg.C thee steels become a mixture of cementite and pearlite ◉ Purpose of heat treating a metal? Answer: - To force a physical and/or chemical transformation in the alloy and then cool it at a rate that the material retains the desired properties
- Heat treatment for the purpose of stress relieving is the main concern for power engineers ◉ Referring to the Eutectoid Reaction Region, Define the following points:
- A
- Ar
- Ac1 Answer: A1: Critical temp. between pearlite phase field and austenite phase field (eutectic transformation line @ 723 deg.C) Ar1: Critical temp. between Pearlite and Austenite during cooling Ac1: Critical temp. between Pearlite and Austenite during heating
- Annealing produces pearlite microstructures (ferrite, pearlite, cementite) ◉ Describe the Full Annealing Process. Answer: 1) Heat the steel to just above the transition temperature required to produce Austenite (temperature depends on %Carbon)
- Temperature required for steels 0.8% C and greater is 723 deg.C
- Hold temperature to allow for uniform crystal restructuring
- Cool very slowly to room temperature; maximum rate of 38 deg.C/hour. Typical procedure is to leave in the annealing furnace or pack in sand or some other type of insulator ◉ Annealing in High Carbon Steels? Answer: - Annealing in high carbon steels can induce brittleness by allowing larger grain formation ; reducing toughness and ductilityTrue ◉ Heat Soaking for too long a period encourages grain enlargement in any annealing procedure (no matter what %C content) and increases brittleness in the metal. True or False? Answer: True ◉ Sub-critical Annealing (Process annealing)? Answer: - The steel is heated to just below its austenite transformation temperature and cooled slowly to reduce internal stresses
◉ What % carbon content is the threshold for when Normalizing is used in steels? Answer: - Carbon steels with LESS than 0.8% Carbon ◉ 3 purposes of Normalizing? Answer: - Relieve internal stresses from welding, forging or machining
- Refine grain size and promote uniform composition to increase ductility and toughness
- Improve machinability ◉ Describe the Normalizing Process. Answer: - Raise steel temperature approx. 55 deg.C above the recrystallization temperature into the austenite region
- Hold at that temperature to ensure even Normalizing throughout
- Cool in still air at a rate not exceeding 100 deg.C/hour
- Furnace should have an oxygen free atmosphere to prevent oxide scale formation ◉ All high alloy steels have less than 0.8% carbon in their alloy. True or False? Answer: True. No transformation products other than Pearlite and Ferrite are produced during Normalizing ◉ Normalizing produces the toughest possible steels. True or False? Answer: True. The ASME codes require normalized and tempered materials in any of their specifications for steel forgings and
◉ What is the Critical Cooling Rate in regards to Hardening? Answer: The slowest that a material can be cooled before undesirable Pearlite is formed instead of Martensite ◉ Cooling mediums for Hardening Processes? Answer: Water, brine, oil, air and is usually promoted by agitation ◉ What is Case Hardening? Answer: - Heat treatment process that produces martensite in the outer layer only, leaving the interior alloy to retain a tough ferrite-pearlite composition ◉ Examples of real world products that are typically Case Hardened? Answer: Bearings, machine tools, crankshafts, cams, valves, gears, rollers, hand tools ◉ What are 2 common Thermochemical case hardening processes for low alloy steels? Answer: Carburizing and Nitriding ◉ Describe Carburizing as a Heat Treatment hardening process. Answer: - The part is heated to the transformation temperature in an atmosphere of carbon monoxide (CO). Carbon diffuses into the surface of the metal increasing martensite formation in this area. The part is then later quench hardened
- Example would be Carburizing with an acetylene rich torch and then quenching in oil
◉ Describe Nitriding as a Heat Treatment hardening process. Answer: - Completed at temperature BELOW the transformation (recrystallization) range of iron (500-600 deg.C) in a ammonia environment
- Ammonia dissociates into nitrogen and hydrogen at these temperatures
- Atomic nitrogen diffuses into the surface layer of the steel forming IRON NITRIDES which are extremely hard
- Nitriding does not require subsequent quench hardening ◉ Nitriding produces the hardest surface out of all Hardening processes possible. True or False? Answer: True. ◉ Describe the Carbonitriding process. Answer: - A source of carbon and nitrogen is introduced into the furnace at a temperature above the transformation temperature for the given steel
- A less severe quenching process follows the hardening process ◉ Describe the Quenching process. Answer: - Steel with a carbon content over 0.8% is heated above the upper transformation temperature and held there to allow the formation of austenite
- Part is then quickly immersed in a liquid such as brine, water or oil
◉ All piping, tubing, fittings and structural materials used in Plants can be categorized into 6 groups of metals: Answer: 1) Low carbon steel (mild): < .30% carbon
- Medium carbon steel: >.30% - <.60%
- High carbon steel: >.60% - <1.5%
- Cast Irons: Carbon content = 2% and 6%
- Alloy steels: Low carbon steels with alloys including manganese, chromium, vanadium, nick, moly, tungsten, and other elements
- Non Ferrous metals: Copper, aluminum, brass, nickel, tungsten, zirconium ◉ Most common steels in a Power Plant? Answer: Low carbon steels and Alloy steels ◉ 2 factors that are considered when choosing the type of steel for a particular job? Answer: - The basis of safety
- The metal survivability A factor of safety must always be retained. ◉ American Society for Testing and Materials (ASTM) piping specifications "A" and "B" are defined as what 2 categories? Answer:
- "A": represents all carbon steels and alloys
- "B": represents all non-ferrous materials ◉ 1? B31.1 lists codes for what?
- B31.3 lists codes for what?
- B16.5 lists codes for what? Answer: 1) Power piping
- Hydrocarbon process piping
- Pipe flanges and fittings ◉ Points typically listed in a Metal Specification Chart? Answer: - Type of metal according to ASTM #
- Title including composition and how its welded
- Commonly used type/grade within specification
- Description of material
- Its end use ◉ What is a Material Test Report? Answer: - Also known as a certificate of testing, these reports are made available by the vendor and give a comprehensive chemical and physical analysis of the metal before the part was manufactured. It is essentially a copy of the recipe for the metal produced.
- Identifies heat number, chemical composition, ASME spec number, grade of steel, schedule #, tensile strength, yield point, and any results of any specialized testing
