Question 1

Lead piping for potable water is unsafe because dissolved oxygen attacks Pb to form toxic Pb(OH)2. Which reagent readily corrodes lead pipes, accelerating contamination risk?

Accepted Answer

Introduction / Context: Material compatibility with drinking water systems is a public health issue. Lead can leach into water forming soluble or weakly adherent corrosion products; organic acids aggravate attack, raising toxicity risks. Given Data / Assumptions: Lead metal in contact with slightly acidic, oxygenated water. Common corrosives considered: mineral acids and organic acids. Concept / Approach: Lead exhibits complex corrosion behavior. It can form protective films (e.g., PbSO4 in concentrated sulfuric acid) or sparingly soluble salts (e.g., PbCl2) that slow attack in some environments. Acetic acid, however, forms soluble lead acetate species, increasing corrosion rate and lead dissolution into water. Step-by-Step Solution: 1) Evaluate HCl: PbCl2 is sparingly soluble; a passivating film may form, reducing sustained attack.2) Evaluate concentrated H2SO4: formation of PbSO4 film strongly inhibits further corrosion.3) Evaluate acetic acid: forms soluble acetate complexes; corrosion continues and lead can leach.4) Conclude acetic acid most readily corrodes lead piping in potable contexts. Verification / Alternative check: Plumbing corrosion studies and historical incidents emphasize organic acids (including acetate) increasing Pb solubility, consistent with the chemistry of lead acetate formation. Why Other Options Are Wrong: Dilute HCl: some attack occurs but often limited by PbCl2 film. Concentrated H2SO4: strong passivation; low continuous attack. None of these: incorrect because acetic acid is clearly aggressive. Dilute HNO3 (not chosen in options originally but noted): typically oxidizes lead, but the question targets common potable-water organics. Common Pitfalls: Assuming all strong acids are more corrosive without considering passivation or solubility of corrosion products. Final Answer: acetic acid (CH3COOH)

Question 2

Babbitt metal used for hydrodynamic bearings is traditionally a soft, conformable, anti-friction alloy. Which base type best describes classic Babbitt compositions?

Accepted Answer

Introduction / Context: Babbitt metals provide excellent embeddability and conformability in plain bearings, protecting shafts under boundary and mixed lubrication. Recognizing the base composition guides selection for speed, load, and temperature. Given Data / Assumptions: Classic Babbitt: soft matrix with hard intermetallics. Operating regime: hydrodynamic bearings in pumps, motors, turbines. Concept / Approach: Traditional Babbitt alloys are tin-base (Sn ~80–90%) with antimony and copper hard phases dispersed in a soft matrix, allowing seizure resistance and embeddability. Lead-base Babbitts also exist for lower-speed, lower-temperature service, but the archetypal “Babbitt metal” is tin-base. Step-by-Step Solution: 1) Identify key performance: conformability, embeddability, compatibility with shaft materials.2) Map to composition families: tin-base Babbitts deliver superior fatigue resistance at higher speeds vs. lead-base variants.3) Select tin-base as the classic answer. Verification / Alternative check: Standards (e.g., ASTM B23) list several tin-base Babbitts widely used in critical bearings, confirming the canonical base type. Why Other Options Are Wrong: Lead-base: valid for some applications but not the classic/primary Babbitt archetype. Aluminium- or copper-base: these are separate bearing bronze or Al–Si families with different tribological behavior. Magnesium-base: not used for Babbitt bearings. Common Pitfalls: Equating all bearing alloys with “Babbitt”; bronze and Al–Si alloys serve different regimes with less embeddability. Final Answer: tin-base alloy (Sn–Sb–Cu family)

Question 3

An alloy containing approximately 56% Ni and 17% Mo (balance Cr and others) is commercially known as which corrosion-resistant material?

Accepted Answer

Introduction / Context: Material selection in corrosive chemical environments often involves nickel-based alloys. Recognizing signature compositions helps quickly identify candidates for acids, chlorides, and reducing media. Given Data / Assumptions: Typical composition near: Ni ~56%, Mo ~16–17%, Cr ~15–16% (Hastelloy C family). Service: strong corrosion resistance, especially in chlorides and mixed acids. Concept / Approach: Hastelloy C-type alloys (e.g., C-276) are Ni–Mo–Cr systems optimized for broad corrosion resistance. Monel is Ni–Cu; Inconel is Ni–Cr–Fe (high-temperature oxidation resistance); bronzes are Cu-based; Nichrome is Ni–Cr heating alloy. The given Ni–Mo signature points to Hastelloy C. Step-by-Step Solution: 1) Match high nickel and molybdenum content to alloy families.2) Exclude Ni–Cu (Monel) and Ni–Cr–Fe (Inconel) based on Mo content.3) Select Hastelloy C as the correct commercial name. Verification / Alternative check: Supplier datasheets list Hastelloy C-276: Ni ~57%, Mo ~16%, Cr ~16%, confirming the characteristic composition and application domain. Why Other Options Are Wrong: Monel: lacks significant Mo; mainly Ni–Cu. Inconel: designed for high-temperature oxidation with Ni–Cr–Fe; Mo lower or absent depending on grade. Bronze: Cu-based, unrelated composition. Nichrome: Ni–Cr heating element alloy; no high Mo content. Common Pitfalls: Confusing trade names among Ni-based families; always check key alloying elements to distinguish corrosion vs. high-temperature roles. Final Answer: Hastelloy C

Question 4

The classic “18-4-1” high-speed steel designation indicates approximate mass percentages of which alloying elements, in order?

Accepted Answer

Introduction / Context: High-speed steels (HSS) retain hardness at elevated cutting temperatures. The numeric shorthand (e.g., 18-4-1) encodes the principal alloying elements that deliver hot hardness, wear resistance, and secondary hardening. Given Data / Assumptions: Designation: 18-4-1 (T1-type HSS). Interpretation: percentages correspond to W, Cr, and V respectively. Concept / Approach: In 18-4-1 HSS, the three numbers refer to ~18% tungsten, ~4% chromium, and ~1% vanadium. Tungsten provides hot hardness via carbides; chromium contributes hardenability and corrosion resistance; vanadium improves wear resistance and grain refinement. Step-by-Step Solution: 1) Map 18 → W; 4 → Cr; 1 → V.2) Evaluate options to find the sequence W–Cr–V.3) Select “tungsten, chromium and vanadium.” Verification / Alternative check: Standard references for T1 HSS confirm the W–Cr–V interpretation for 18-4-1, with minor additions of carbon and others as specified. Why Other Options Are Wrong: Reordered sequences misrepresent the standard convention; substituting molybdenum or changing positions does not fit the canonical designation. Common Pitfalls: Confusing Mo-based HSS (like M2) with W-based HSS (T1). Always verify the numeric shorthand mapping. Final Answer: tungsten, chromium and vanadium

Question 5

German silver, also called nickel silver, is an alloy composed primarily of which three elements?

Accepted Answer

Introduction / Context: Trade names can be misleading. “German silver” looks like silver but is a base-metal alloy widely used for its appearance and corrosion resistance in decorative and instrument components. Given Data / Assumptions: No precious metal (Ag) in standard German silver compositions. Typical composition ranges: Cu-rich with Ni and Zn. Concept / Approach: Nickel silver alloys combine copper, nickel, and zinc. Nickel imparts a silvery color and increases strength; zinc improves castability and reduces cost; copper provides the base matrix and ductility. Step-by-Step Solution: 1) Exclude options containing silver as a major component; the name is historical and cosmetic.2) Identify the classic Cu–Ni–Zn triad.3) Choose “copper, nickel and zinc.” Verification / Alternative check: Materials handbooks list numerous nickel silver grades (e.g., CuNi25Zn18) conforming to this tri-element system. Why Other Options Are Wrong: Options including silver are incorrect for standard German silver. Copper, tin and zinc corresponds to brass/bronze families, not nickel silver. Common Pitfalls: Assuming nomenclature implies elemental content; always confirm with compositional standards. Final Answer: copper, nickel and zinc

Question 6

Among the main stainless steel families, which is generally non-magnetic in the annealed condition due to its face-centered cubic (FCC) structure?

Accepted Answer

Introduction / Context: Stainless steels are categorized by microstructure: ferritic (BCC), martensitic (BCT), austenitic (FCC), and duplex (mixed). Magnetic behavior correlates strongly with structure and processing condition. Given Data / Assumptions: Condition: annealed (solution-treated) state. Family chemistries: austenitic (e.g., 304, 316) high Ni stabilizing FCC. Concept / Approach: Austenitic stainless steels have an FCC lattice stabilized by nickel (and sometimes manganese/nitrogen). FCC austenite is generally non-magnetic. Cold work can induce partial martensite, causing slight magnetism, but the annealed baseline is essentially non-magnetic. Step-by-Step Solution: 1) Map families to structures: ferritic = BCC (magnetic), martensitic = BCT (magnetic), austenitic = FCC (non-magnetic in annealed state).2) Identify typical grades: 304/316 are non-magnetic when properly annealed.3) Conclude: austenitic is the non-magnetic family. Verification / Alternative check: Quick shop-floor test: annealed 304 shows negligible attraction to magnets, while 430 (ferritic) and 410 (martensitic) are magnetic. Why Other Options Are Wrong: Ferritic and martensitic are magnetic due to BCC/BCT structures. “None of these” is incorrect because austenitic is well known to be non-magnetic in annealed condition. Duplex (not in original list but included as a distractor) is ferrite+austenite and shows partial magnetism. Common Pitfalls: Observing magnetism in cold-worked austenitic stock and assuming the family is magnetic; cold work can induce strain martensite. Final Answer: Austenitic

Question 7

Materials engineering—Invar alloy used in thermocouples and instrumentation Invar used with certain thermocouple and precision instruments is an alloy of nickel and which metal?

Accepted Answer

Introduction / Context: Invar is a famous low thermal expansion alloy widely used in precision engineering. In temperature measurement systems and certain thermocouple assemblies, support and lead components must maintain dimensional stability across temperature swings to minimize error. Knowing the base metals in Invar helps engineers select compatible materials for instrumentation and thermal systems. Given Data / Assumptions: The question asks about the metallic constituents of Invar. Focus is on composition, not on exact percentage tolerances. Application context includes thermocouples and precision devices where low expansion is beneficial. Concept / Approach: Invar is a nickel–iron alloy specifically formulated to exhibit an extremely low coefficient of thermal expansion near room temperature. This property is a result of a delicate balance in the ferromagnetic structure that compensates normal thermal expansion. Because of this, Invar has been adopted for precision rods, pendulum components, measuring tapes, and structural elements in temperature-sensitive instruments and thermocouple housings or lead frames where dimensional stability matters. Step-by-Step Solution: Recall standard composition of Invar: primarily iron and nickel.Recognize typical nominal composition: around 36% Ni with balance Fe, engineered for minimal thermal expansion.Match the alloy partners in the options with this known composition.Conclude that Invar is the nickel–iron system, therefore the second metal is iron. Verification / Alternative check: Handbooks of materials and instrumentation consistently list Invar as Fe–Ni with low expansion coefficient. Laboratory data and dimensional metrology standards corroborate its use where thermal stability is essential. Why Other Options Are Wrong: Copper: Ni–Cu alloys form cupronickel and Monel type systems with different properties and higher expansion than Invar. Chromium: Ni–Cr combinations are common for resistance heating alloys but do not yield the hallmark low expansion of Invar. Lead: Ni–Pb combinations are not used for precision low-expansion alloys and are mechanically unsuitable for such roles. Common Pitfalls: Confusing Invar with other nickel alloys such as Nichrome or Monel. Also, assuming the presence of chromium due to its popularity in high temperature alloys; Invar targets dimensional stability, not high temperature oxidation resistance. Final Answer: iron

Question 8

Cast irons—identifying properties of white cast iron White cast iron is not which of the following?

Accepted Answer

Introduction / Context: Cast irons are classified by microstructure and resulting properties. White cast iron is characterized by a hard, brittle phase due to carbon existing mainly as iron carbide rather than as graphite. Understanding which mechanical attributes do or do not apply is essential for material selection in wear and abrasion environments versus ductility applications. Given Data / Assumptions: White cast iron microstructure: cementite and pearlite with minimal free graphite. Mechanical requirements: consider hardness, brittleness, and ductility. Color descriptor refers to the fractured surface appearance. Concept / Approach: In white cast iron, rapid cooling or specific chemistry promotes carbide formation. Cementite confers high hardness and excellent abrasion resistance but at the cost of ductility. The fracture surface appears bright or whitish because of the carbide network, in contrast to the dull grey appearance of graphite in grey cast iron. Malleability refers to the ability to deform plastically without fracture, a property white iron does not possess until it is heat treated to become malleable iron (through prolonged annealing that transforms carbides). Step-by-Step Solution: Identify key traits: white cast iron is very hard and brittle.Color: fracture surface looks white due to cementite, so the whitish description is appropriate.Strength and hardness: both are relatively high, especially hardness and wear resistance.Malleability: inherently poor; white iron is not malleable without extensive heat treatment. Verification / Alternative check: Materials handbooks list white cast iron with high hardness, low impact resistance, and brittle fracture. Applications include wear plates and grinding balls, consistent with non-malleable behavior. Why Other Options Are Wrong: Whitish in color: correct descriptor of fracture surface, so not the answer. Brittle: accurately describes white cast iron. Strong and hard: hardness is indeed high; compressive strength can be high though tensile ductility is poor. Common Pitfalls: Confusing malleable iron (a heat-treated product made from white iron) with as-cast white iron. The as-cast state is brittle; malleability is developed only after controlled annealing that decomposes carbides. Final Answer: malleable

Question 9

Bearing materials—selection for heavy duty applications Heavy duty bearings are usually manufactured from which material class?

Accepted Answer

Introduction / Context: Choosing bearing materials requires balancing load capacity, fatigue strength, embeddability, compatibility with shafts, and resistance to wear and seizure. Different operating severities call for different alloys. For heavy duty service, the material must carry high specific pressures and resist scoring while still offering reasonable machinability and dimensional stability. Given Data / Assumptions: Service is classified as heavy duty with high loads. Lubrication is present but may be imperfect at times. Operating temperatures are moderate to elevated depending on duty. Concept / Approach: Phosphor bronze (a copper–tin alloy with small phosphorus additions) offers high fatigue strength, good load carrying ability, and decent wear resistance. It is a traditional choice for heavy duty plain bearings and bushings, especially in slow to medium speed, high-load applications. Babbitt or white metal (tin- or lead-based) excels in conformability and embeddability but is softer and therefore generally better for light to medium duty. Monel and zinc do not meet the typical tribological requirements for heavy duty bearing linings in standard practice. Step-by-Step Solution: Identify the operating severity: heavy load and potential edge conditions.Map properties: phosphor bronze provides strength and wear resistance under such loads.Contrast with white metal: softer, used where embeddability is prioritized over high load capacity.Eliminate unsuitable materials like monel and zinc for typical bearing liners. Verification / Alternative check: Machine design texts specify phosphor bronze and certain aluminum bronzes for heavy duty bushings. White metal is recommended where compatibility and seizure resistance are critical under moderate loads. Why Other Options Are Wrong: White metal: excellent embeddability and conformability but insufficient strength for heavy loads. Monel: corrosion resistant nickel–copper alloy, not a standard bearing liner for heavy duty. Zinc: lacks the mechanical and tribological profile for high-load bearings. Common Pitfalls: Assuming the softest material is always best due to conformability; for heavy duty, strength and wear resistance are decisive. Final Answer: phosphorous bronze

Question 10

High-temperature heat recovery—materials for ceramic recuperators Ceramic recuperators used for furnace heat recovery are generally made of which refractory material?

Accepted Answer

Introduction / Context: Recuperators reclaim heat from hot flue gases to preheat combustion air. Ceramic designs are employed at very high temperatures where metallic heat exchangers would oxidize or creep. Material selection must account for thermal shock, corrosion from combustion products, mechanical strength at temperature, and thermal conductivity. Given Data / Assumptions: Service in hot flue gas streams and preheated air streams. Exposure to thermal cycling and potential corrosive species. Need for durability and heat transfer performance. Concept / Approach: Silicon carbide components offer a compelling combination: excellent thermal shock resistance, high thermal conductivity for efficient heat transfer, good strength retention at elevated temperatures, and oxidation resistance under many furnace atmospheres. These attributes make silicon carbide a common choice for ceramic recuperator elements such as tubes, honeycombs, or plates. Fireclay and high alumina refractories provide refractoriness but have lower thermal conductivity and often poorer thermal shock resistance for thin-section heat exchange elements. Calcium carbide is not used as a structural refractory for recuperators and decomposes under humid or oxidizing conditions. Step-by-Step Solution: List required properties: thermal shock, conductivity, high-temperature strength, corrosion resistance.Match materials: silicon carbide satisfies these simultaneously for thin-wall heat exchange duty.Eliminate options with inadequate property combinations for recuperator cores. Verification / Alternative check: Industrial furnace catalogs and refractory datasheets consistently present silicon carbide as the preferred material for ceramic recuperator tubes and cores due to high conductivity and robustness. Why Other Options Are Wrong: Calcium carbide: chemically unsuitable in hot, potentially moist, oxidizing environments. Fireclay bricks: lower conductivity and thermal shock resistance for thin sections. High alumina bricks: good refractoriness but less ideal conductivity and shock behavior for recuperator elements. Common Pitfalls: Equating refractoriness alone with suitability. Heat exchangers need both refractoriness and thermal conductivity, where silicon carbide excels. Final Answer: silicon carbide.

Question 11

Corrosion science—electromotive series and corrosion tendency Metals occurring at the lowest (noblest) position in the electromotive series typically:

Accepted Answer

Introduction / Context: The electromotive series ranks metals and alloys by their standard electrode potentials. Position in this series correlates with thermodynamic tendency to undergo oxidation. Engineers use this ranking to predict galvanic couples, select materials for corrosive environments, and design cathodic protection systems. Given Data / Assumptions: Lower position means more noble (more positive potential). Environment considered is a typical aqueous electrolyte unless otherwise specified. Metals compared on a thermodynamic basis, not considering protective films or kinetics in detail. Concept / Approach: Noble metals such as gold, platinum, and palladium lie toward the noble end of the series. Their positive electrode potentials indicate a low tendency to oxidize, hence strong corrosion resistance in many environments. By contrast, active metals like magnesium, zinc, and aluminum lie toward the anodic end, readily oxidize, and are often used sacrificially. Mechanical traits like brittleness or thermal conductivity are unrelated to electromotive ranking per se. Step-by-Step Solution: Interpret series position: lowest in the galvanic table implies noble behavior.Translate to corrosion tendency: low oxidation tendency means better corrosion resistance.Select the statement aligning with noble metal behavior. Verification / Alternative check: Standard electrode potential tables confirm noble metals resist spontaneous oxidation. Galvanic series in seawater shows noble metals acting cathodically and suffering minimal corrosion when coupled properly. Why Other Options Are Wrong: Do not resist corrosion: opposite of noble behavior. Very brittle: brittleness is a mechanical property, not dictated by electrochemical potential ranking. Heat insulators: many noble metals are excellent electrical and thermal conductors. Common Pitfalls: Ignoring kinetic effects and protective passive films. Some metals (e.g., stainless steels, titanium) owe corrosion resistance to passivation even if their base potential is not as noble; however, nobility still correlates with resistance. Final Answer: resist corrosion very strongly.

Question 12

Instrumentation alloys—composition of Constantan used in sensors Constantan is an alloy composed of which pair and approximate proportions?

Accepted Answer

Introduction / Context: Constantan is well known for its relatively constant electrical resistivity over a wide temperature range, making it ideal for precision electrical measurements, strain gauges, and as a leg in certain thermocouples (e.g., copper–constantan). Correctly identifying its composition helps avoid mix-ups with other copper alloys used in electrical and thermal instrumentation. Given Data / Assumptions: Focus on principal alloying elements and typical nominal composition. Function relates to resistivity stability and thermoelectric behavior. Concept / Approach: Constantan belongs to the copper–nickel family. Around 55% copper and 45% nickel optimize the temperature coefficient of resistance, yielding a near-constant resistance versus temperature. This property is crucial in bridge circuits, strain gauges, and thermocouple reference legs, where predictable electrical behavior ensures measurement accuracy and compensation schemes. Step-by-Step Solution: Recall primary use: stable resistivity for sensors.Match composition: copper–nickel with roughly 55/45 split.Eliminate other copper alloys that do not exhibit the same resistivity stability. Verification / Alternative check: Manufacturer datasheets list constantan or Advance alloy as about 55% Cu and 45% Ni, confirming the nominal pairing and purpose. Why Other Options Are Wrong: Cu–Sn (bronze): mechanical bearings and springs, different resistivity profile. Pt–Rh: thermocouple type S or R combinations, precious metals, not constantan. Fe–Ni (Invar-type): low expansion alloys, not constant resistivity alloys. Common Pitfalls: Confusing constantan with Invar or Nichrome. Nichrome is Ni–Cr for heaters; Invar is Fe–Ni for low expansion; constantan is Cu–Ni for stable resistivity. Final Answer: Cu (55%) & Ni (45%).

Question 13

Surface protection—purpose of galvanising iron sheets What is the principal purpose of galvanising iron sheets?

Accepted Answer

Introduction / Context: Galvanising applies a protective zinc coating to steel or iron to combat corrosion. This is ubiquitous in roofing, automotive panels, and outdoor structures. Understanding the primary protection mechanism informs maintenance practices and suitability for various environments. Given Data / Assumptions: Zinc coating is continuous and intact at installation. Service exposure includes atmospheric moisture and oxygen. Role of sacrificial action and barrier protection are both relevant. Concept / Approach: Corrosion of iron requires oxygen and moisture. A zinc layer first acts as a physical barrier that separates steel from oxygen in air. Second, zinc is anodic relative to iron; when the coating is breached, zinc preferentially oxidizes, protecting steel cathodically. While water facilitates corrosion, the fundamental chemical reaction is oxidation; oxygen access to iron is critical. Thus the essential purpose is preventing oxygen attack on the steel surface, with water presence accelerating the process but not being the oxidizing agent itself. Step-by-Step Solution: Identify corrosive requirements: oxygen plus moisture.Determine barrier function: zinc coating blocks oxygen diffusion to steel.Consider galvanic protection: zinc sacrifices itself when coating defects occur.Conclude the primary intent: prevent oxygen attack on the iron surface. Verification / Alternative check: Galvanic series shows zinc more active than iron, explaining sacrificial protection. Field performance of galvanized steel in atmospheric exposure supports oxygen-blocking and sacrificial behavior. Why Other Options Are Wrong: Harden the surface: galvanising does not primarily harden the base metal. Increase glossiness: appearance is secondary and varies with spangle; not the engineering purpose. Prevent the action of water: water assists corrosion, but oxygen is the reactant reduced at the cathode; the core target is oxidation prevention. Common Pitfalls: Attributing corrosion control solely to water exclusion. Even in humid or marine environments, oxygen reduction drives rust formation; zinc addresses the oxidation pathway. Final Answer: prevent the action of oxygen.

Question 14

Chemical plant construction—sulphur melting pit materials in sulphuric acid manufacture Sulphur melting pits in sulphuric acid plants are commonly constructed from which material(s)?

Accepted Answer

Introduction / Context: Prior to burning sulphur for sulphuric acid production, elemental sulphur is melted and filtered. The melting pit must tolerate molten sulphur temperatures, mechanical loading, and occasional impurities, while being economical and maintainable in a corrosive plant environment. Material selection balances temperature capability, corrosion behavior, and cost. Given Data / Assumptions: Molten sulphur typically handled near 120 to 150 degrees Celsius. Environment is largely non-oxidizing for sulphur itself; heavy acids are not present in the pit. Structural robustness and practicality are required. Concept / Approach: Steel constructions or concrete pits lined with acid-resistant bricks or cement-brick linings are common. Sulphur at its melting temperature is not strongly corrosive to carbon steel or to suitable masonry linings, which explains the pervasive use of these economical materials. Lead lining is unnecessary and impractical here, and hardwood lacks temperature resistance and durability. Cast iron can be brittle and less favorable structurally for large pits compared to reinforced concrete or fabricated steel structures with appropriate linings. Step-by-Step Solution: Identify thermal conditions: moderate temperatures for metals and refractory linings.Evaluate chemical compatibility: molten sulphur is manageable with steel and cement-brick linings.Eliminate exotic or unsuitable options lacking economic or mechanical justification. Verification / Alternative check: Industry practice and plant design literature show steel tanks with refractory or brick linings, or concrete pits lined with acid-resistant bricks, as standard for sulphur melting service. Why Other Options Are Wrong: Lead lined stainless steel: excessive cost and unnecessary corrosion allowance for this duty. Cast iron: brittle and less favorable for large structural pits. Hard wood: inadequate temperature and chemical durability. Common Pitfalls: Confusing sulphur melting service with sulphuric acid storage; acid requires specific corrosion resistant alloys or linings, whereas molten sulphur service is less aggressive. Final Answer: steel or cement-brick lined.

Question 15

Alloying effects—role of nickel additions in steels Adding nickel to steel primarily improves which property?

Accepted Answer

Introduction / Context: Alloying elements profoundly influence the microstructure and properties of steels. Nickel is widely used in structural, stainless, and low-temperature steels. Understanding its dominant effects guides grade selection for corrosive service, cryogenic applications, and general engineering requirements. Given Data / Assumptions: Nickel additions are at typical alloying levels observed in structural and stainless steels. Comparison is among corrosion resistance, cutting ability, and wear resistance. Concept / Approach: Nickel increases toughness, refines grain structure, and improves resistance to corrosion, particularly in combination with chromium in stainless steels. It stabilizes the austenitic phase, enabling good ductility and impact strength at low temperatures. Cutting ability is associated more with high-speed tool steels containing tungsten, molybdenum, vanadium, and cobalt. Wear resistance often correlates with carbides from chromium, vanadium, or high carbon content, not primarily nickel. Therefore, the most direct and characteristic improvement due to nickel is corrosion resistance (and toughness), especially in austenitic stainless steels like 304 and 316. Step-by-Step Solution: List typical effects of Ni: corrosion resistance and toughness enhancement.Contrast with cutting ability: dominated by tool steel carbides and cobalt additions.Contrast with wear resistance: improved more by hard carbides and surface treatments.Choose the property most strongly and directly tied to Ni. Verification / Alternative check: Materials standards show austenitic stainless steels with significant Ni content offering excellent corrosion resistance. Low alloy Ni steels are chosen for cryogenic and marine environments because of improved corrosion behavior and toughness. Why Other Options Are Wrong: Cutting ability: not a hallmark of nickel; tool steels rely on other elements. Wear resistance: nickel contributes indirectly via toughness, but primary wear resistance comes from hard phases. All of the above: overstates nickel effects across unrelated properties. Common Pitfalls: Assuming an alloying element improves all properties uniformly. Each element has targeted benefits and trade-offs. Final Answer: corrosion resistance.

Question 16

Mechanical design—properties required for shock resisting steels Shock resisting steels should predominantly exhibit high which property?

Accepted Answer

Introduction / Context: Components subjected to impact, sudden loads, or dynamic conditions require steels capable of absorbing energy without fracturing. The material choice for chisels, hammers, pneumatic tools, and impact-loaded parts emphasizes resistance to crack initiation and propagation under shock loading. Given Data / Assumptions: Service involves sudden or repeated impact rather than steady static loads. Failure modes include brittle fracture and fatigue crack growth under dynamic stress. Concept / Approach: Toughness is the ability to absorb energy up to fracture and is the key property for shock resistance. While hardness contributes to wear resistance and tensile strength describes load-bearing capacity under static conditions, neither alone ensures survival under impact. A balanced microstructure with adequate ductility prevents brittle cracks from advancing. Alloy design and heat treatment aim to produce tempered martensite or bainitic structures with high Charpy impact energy, ensuring reliable performance under shock. Step-by-Step Solution: Define requirement: resist sudden impacts → maximize energy absorption capacity.Identify property: toughness measured by impact testing (e.g., Charpy V-notch).Differentiate from hardness and tensile strength, which do not guarantee impact resistance.Conclude that toughness is the primary design criterion for shock resisting steels. Verification / Alternative check: Standards for shock resisting tool steels (e.g., S-series) specify high impact toughness values and tempered microstructures, confirming design emphasis on toughness. Why Other Options Are Wrong: Hardness: improves wear resistance but can increase brittleness if excessive. Tensile strength: valuable for static loads; high strength without toughness can be catastrophic under shock. Wear resistance: useful for abrasion, not chiefly for impact survival. Common Pitfalls: Over-hardening a steel for wear without ensuring sufficient toughness, leading to spalling or brittle fracture under impact. Final Answer: toughness

Question 17

Materials selection for gas holders: Which construction material is commonly used for acetylene gas holders/cylinders to ensure safety and compatibility?

Accepted Answer

Introduction / Context: Acetylene (C2H2) is an industrial fuel gas that forms explosive compounds with certain metals. Choosing the correct material for gas holders and cylinders is critical for safety, durability, and regulatory compliance in chemical and welding operations. Given Data / Assumptions: Stored gas is acetylene at cylinder conditions with porous mass and solvent (e.g., acetone or DMF). Question concerns standard industrial practice for vessel material. Compatibility with acetylene and mechanical strength under pressure are required. Concept / Approach: Materials in contact with acetylene must not form metal acetylides, which are impact-sensitive and explosive. The vessel must also provide high strength and toughness, meet codes, and be weldable and inspectable. Steel satisfies these criteria for pressure cylinders and gas holders. Step-by-Step Solution: Identify unsafe metals: copper, silver, and their alloys can form explosive acetylides with acetylene.Assess mechanical and code requirements: cast iron is brittle and unsuitable for pressure cylinders.Select standard practice: seamless or welded steel cylinders and steel gas holders are industry norm. Verification / Alternative check: Look at national cylinder standards and safety data: acetylene cylinders are specified in steel with porous filler and solvent to keep free acetylene partial pressure low. Why Other Options Are Wrong: Copper: forms hazardous copper acetylide; unsafe. Cast iron: too brittle for pressure service. Monel: excellent corrosion resistance but not the standard, cost-effective choice for acetylene storage vessels. Common Pitfalls: Assuming corrosion resistance alone dictates the choice; for fuel gases, reactivity and mechanical integrity dominate. Final Answer: Steel

Question 18

Bimetallic thermometers — low-expansion alloy: Name the iron–nickel alloy (~36% Ni) universally used for the low-expansion strip in bimetallic thermometers.

Accepted Answer

Introduction / Context: Bimetallic thermometers rely on differential thermal expansion of two bonded metals to convert temperature into pointer motion. One alloy is typically chosen for exceptionally low thermal expansion to maximize sensitivity and linearity of the composite strip. Given Data / Assumptions: Target alloy contains roughly 36% nickel in iron. Application is the low-expansion leg in a bimetal. Need: dimensional stability with temperature changes. Concept / Approach: Invar (Fe–Ni ~36% Ni) has a very low coefficient of thermal expansion, about one twentieth that of common structural metals. In a bimetallic pair, Invar is bonded to a higher-expansion alloy so that temperature changes cause curvature and pointer movement. Step-by-Step Solution: Identify alloy with 36% Ni: Invar fits the composition.Match property: lowest practical expansion among the listed choices.Conclude: Invar is the correct low-expansion alloy used. Verification / Alternative check: Instrumentation catalogs and materials handbooks list Invar as the standard for precision bimetal strips, pendulums, and metrological components. Why Other Options Are Wrong: Constantan: Cu–Ni alloy used for resistance measurement (strain gauges, thermocouple negatives), not ultra-low expansion. Chromel/Alumel: nickel-based thermocouple materials for type K, selected for emf generation, not for low expansion. Common Pitfalls: Confusing electrical-thermocouple alloys with mechanical low-expansion alloys. Final Answer: Invar

Question 19

Engineering properties of aluminium: Which of the following is a key disadvantage of aluminium as a construction material in process equipment?

Accepted Answer

Introduction / Context: Aluminium is widely used due to its light weight, good corrosion resistance, and formability. However, when selecting materials for process vessels and structures, trade-offs between properties must be considered. Given Data / Assumptions: Comparison is to common carbon and stainless steels. Focus on mechanical limitations versus advantages. General-purpose applications, not specialized heat-treated grades. Concept / Approach: Aluminium’s density is one-third of steel, giving excellent strength-to-weight ratio when alloys are optimized. Nonetheless, absolute tensile strength (especially in annealed or non-heat-treated tempers) is lower than typical steels, limiting use in high-stress, high-temperature pressure applications without significant design allowances. Step-by-Step Solution: Identify incorrect distractors: availability is not scarce; cost is not extremely high relative to specialty alloys.Strength-to-weight: aluminium actually has a favorable ratio in many alloys.Conclude the primary disadvantage: comparatively lower absolute tensile strength. Verification / Alternative check: Compare typical yield strengths: mild steel ~250 MPa; 304 stainless ~200–215 MPa; common Al alloys vary widely but many service grades are lower unless heat-treated, and temperature capability is also lower. Why Other Options Are Wrong: Very high cost: untrue versus stainless or nickel alloys. Very low strength-to-weight ratio: opposite of reality. Scarce availability: aluminium is abundant and widely produced. Common Pitfalls: Ignoring temper/heat-treatment effects when comparing properties; overlooking reduced high-temperature strength of aluminium. Final Answer: Rather low tensile strength (compared to steels)

Question 20

Tin-based bearing alloys (Babbitts): What property improvement is primarily obtained by adding antimony (Sb) to tin-based alloys?

Accepted Answer

Introduction / Context: Tin-based Babbitt alloys are classic bearing materials. Alloying elements such as antimony and copper adjust hardness, load capacity, and high-temperature behavior to match bearing duty and lubrication regimes. Given Data / Assumptions: Tin is the primary matrix metal. Antimony content is a few percent to stiffen the matrix. Service involves boundary or mixed lubrication where surface integrity is critical. Concept / Approach: Antimony in tin-based alloys forms hard intermetallics and strengthens the matrix, raising hardness and hot strength. This improves load-carrying capability and resistance to creep at elevated temperatures, often described as improved rupture strength and hot hardness for bearing operation. Step-by-Step Solution: Recognize the role of Sb: solid-solution plus intermetallic strengthening in Sn matrix.Connect property changes to bearing duty: higher hot hardness supports oil film and reduces wiping at temperature.Select the option listing rupture strength and hot hardness as the core improvements. Verification / Alternative check: Materials handbooks list Sn–Sb–Cu Babbitts where Sb increases hardness/strength, while Cu refines structure and further strengthens; combined they raise fatigue resistance. Why Other Options Are Wrong: Impact/bonding strength only: not the principal documented effect of Sb in Babbitts. Deformation resistance only and wear resistance only are incomplete; improvements arise primarily via increased hot hardness/load capacity. Common Pitfalls: Attributing all bearing performance gains to one element; in practice, Sb and Cu act together, and microstructure and casting practice are crucial. Final Answer: Rupture strength and hot hardness are improved

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