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Power Eng 1st Class practice questions

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Question 1Engineering Management, Codes, Standards and Regulatory Compliance

Under ASME Boiler and Pressure Vessel Code Section I, who holds ultimate responsibility for verifying that a new power boiler installation complies with the applicable code requirements before it is placed into service?

  1. The authorized inspector holding a commission for the jurisdiction Correct answer.
  2. The boiler manufacturer's engineering department
  3. The owner or user of the boiler
  4. The installing contractor's project superintendent

Explanation

Section I relies on the authorized inspector, commissioned by the jurisdiction or insurance company, to verify code compliance through required inspections and to sign the manufacturer's data report. The owner, installer, and manufacturer all have duties, but the independent inspection authority is the formal verification mechanism.

Question 2Engineering Management, Codes, Standards and Regulatory Compliance

A high-pressure power boiler is being converted from natural gas to No. 6 fuel oil firing. Which management action best reflects the intent of the ASME Boiler and Pressure Vessel Code and NFPA 85 when significant fuel or firing-system changes are made?

  1. File the fuel data sheet with the insurer and continue operating under the existing operating permit
  2. Notify the fuel supplier and update the burner nameplate after the first successful firing test
  3. Retrain the operators on the new fuel and resume firing once the shift supervisor signs the log
  4. Re-evaluate the combustion and control system design, then document and approve the change through a formal management-of-change review before return to service Correct answer.

Explanation

NFPA 85 and good engineering practice require that changes affecting combustion safety, burner management, and control logic be evaluated and approved through a documented management-of-change process before the boiler returns to service. Simple notification or after-the-fact record changes do not satisfy this requirement.

Question 3Engineering Management, Codes, Standards and Regulatory Compliance

A plant operates a boiler subject to a jurisdictional code adopting ASME Section I. Which document most directly establishes the maximum allowable working pressure that may be stamped on the boiler and used for setting safety valve relief pressure?

  1. The manufacturer's data report and the code calculations supporting the stamped MAWP Correct answer.
  2. The plant's written operating procedures manual
  3. The insurance carrier's loss-prevention inspection report
  4. The utility's steam load balance study

Explanation

The maximum allowable working pressure is established by code-required design calculations and recorded on the manufacturer's data report, and the stamp reflects that value. Safety valves are then set so that they relieve at or below the stamped MAWP, consistent with Section I rules.

Question 4Engineering Management, Codes, Standards and Regulatory Compliance

During an internal inspection of a watertube boiler, the authorized inspector finds localized wastage on a furnace wall tube. Which response is most consistent with the National Board Inspection Code and jurisdictional requirements?

  1. Evaluate the remaining wall thickness against code minimums, perform an approved repair if required, and have the repair documented and inspected before return to service Correct answer.
  2. Weld a patch over the area without documentation to avoid a shutdown
  3. Reduce the operating pressure indefinitely without notifying the jurisdiction
  4. Return the boiler to service and monitor the area at the next annual outage

Explanation

The NBIC requires that repairs and alterations to pressure parts be evaluated against code acceptance criteria, performed under qualified procedures, and documented with an appropriate report subject to inspection. Deferring action or making undocumented repairs defeats the integrity of the code system.

Question 5Engineering Management, Codes, Standards and Regulatory Compliance

Which federal regulation in the United States establishes the general duty of employers to provide a workplace free from recognized hazards, and thus underpins boiler and pressure-vessel safety programs in general industry?

  1. 29 CFR 1910.119, Process Safety Management
  2. 29 CFR 1904, Recording and Reporting Occupational Injuries
  3. 40 CFR Part 60, New Source Performance Standards
  4. Section 5(a)(1) of the Occupational Safety and Health Act, the General Duty Clause Correct answer.

Explanation

The General Duty Clause in Section 5(a)(1) of the OSH Act requires employers to furnish a workplace free from recognized hazards likely to cause death or serious harm. Specific standards such as PSM build on this baseline obligation for boilers and pressure systems.

Question 6Engineering Management, Codes, Standards and Regulatory Compliance

A facility is deciding whether its boiler system falls under OSHA's Process Safety Management standard. Which threshold quantity applies to a flammable liquid with a flash point below 100 degrees Fahrenheit stored in a process?

  1. 1,000 pounds
  2. 20,000 pounds
  3. 10,000 pounds Correct answer.
  4. 500 pounds

Explanation

Appendix A to 29 CFR 1910.119 lists 10,000 pounds as the threshold quantity for flammable liquids with a flash point below 100 degrees Fahrenheit. Reaching or exceeding that quantity in a process triggers PSM coverage for the affected process.

Question 7Engineering Management, Codes, Standards and Regulatory Compliance

An engineering manager is preparing a boiler inspection plan. Which activity is properly the responsibility of the owner or user rather than the authorized inspector?

  1. Signing the manufacturer's data report for a new installation
  2. Determining the scope of required internal and external inspections per the jurisdiction
  3. Maintaining the boiler, preparing it for inspection, and providing safe access and required records Correct answer.
  4. Issuing the certificate of authorization to the repair organization

Explanation

The owner or user must maintain the boiler in a safe condition, prepare it for inspection, and furnish records and safe access so the inspector can perform the work. The inspector determines inspection scope and verifies compliance, while the National Board issues certificates of authorization.

Question 8Engineering Management, Codes, Standards and Regulatory Compliance

Which document type in the ASME system indicates that a manufacturer has been reviewed and found competent to produce items stamped with a code symbol?

  1. An authorized inspection agency commission
  2. A certificate of authorization Correct answer.
  3. A jurisdictional operating certificate
  4. A manufacturer's data report

Explanation

A certificate of authorization is issued after review of a manufacturer's quality control system and permits use of the applicable code symbol stamp. Data reports accompany individual items, inspection commissions credential individuals, and operating certificates permit use of the installed boiler.

Question 9Engineering Management, Codes, Standards and Regulatory Compliance

A power boiler is being placed into service in a jurisdiction that adopts the ASME Code. Which statement best describes the relationship between the ASME Code and the jurisdiction's rules?

  1. Jurisdictional rules govern, and the ASME Code applies only to the extent the jurisdiction adopts it Correct answer.
  2. The ASME Code automatically becomes law in every state without adoption
  3. Jurisdictional rules apply only to boilers below 15 psig
  4. The ASME Code supersedes all state and local requirements once a boiler is stamped

Explanation

The ASME Code is a consensus standard that gains legal force through adoption by a jurisdiction; state and local rules control where they apply. Engineers must therefore know both the code requirements and the specific adopting regulation, including any amendments.

Question 10Engineering Management, Codes, Standards and Regulatory Compliance

Which organization publishes the National Board Inspection Code, which governs in-service inspection, repair, and alteration of boilers and pressure vessels?

  1. The National Board of Boiler and Pressure Vessel Inspectors Correct answer.
  2. The American Petroleum Institute
  3. The American Society of Mechanical Engineers
  4. The National Fire Protection Association

Explanation

The National Board of Boiler and Pressure Vessel Inspectors publishes the NBIC, which covers in-service inspection, repairs, and alterations. ASME publishes construction codes, API publishes petroleum industry standards, and NFPA publishes fire and combustion safety standards.

Question 11Engineering Management, Codes, Standards and Regulatory Compliance

A plant intends to alter a boiler by adding a new superheater outlet connection. Under the NBIC, which course of action is required?

  1. Obtain an approved alteration design, use a holder of the appropriate certificate of authorization, and have the alteration documented and inspected Correct answer.
  2. Perform the work with the plant's own maintenance crew and record it in the maintenance log
  3. Treat the addition as routine maintenance and omit documentation
  4. Complete the work and notify the jurisdiction at the next scheduled inspection

Explanation

The NBIC defines alterations as changes to pressure parts or to the pressure-retaining capability of the item, requiring approved design, qualified work by a certificate holder, and documentation with inspection. Routine maintenance does not cover added connections or changes in design conditions.

Question 12Engineering Management, Codes, Standards and Regulatory Compliance

Which of the following best describes the role of the jurisdiction's chief inspector in the boiler regulatory system?

  1. To administer the boiler safety program, including licensing inspectors and enforcing adopted rules Correct answer.
  2. To operate the boilers at state-owned facilities
  3. To set the price of boiler insurance premiums
  4. To manufacture code-stamped boilers for public projects

Explanation

The chief inspector administers the jurisdictional boiler and pressure vessel program, overseeing commissioned inspectors and enforcing the adopted code and regulations. Operating boilers, manufacturing, and insurance pricing are outside that role.

Question 13Engineering Management, Codes, Standards and Regulatory Compliance

A boiler operating log shows that a low-water fuel cutoff was bypassed during a shift to maintain steam supply. Which management response best reflects the regulatory and code philosophy for safety controls?

  1. Adjust the cutoff setpoint so the bypass is no longer needed
  2. Treat the bypass as a serious safety-system defeat, investigate the cause, correct the practice, and verify the control with a documented test Correct answer.
  3. Discipline the operator and take no further action
  4. Resume normal operation after the next shift begins

Explanation

Safety controls such as low-water fuel cutoffs are required protective devices, and defeating them is a recognized serious hazard. A proper response includes investigation, correction of the underlying cause, and documented functional testing to confirm the device works.

Question 14Engineering Management, Codes, Standards and Regulatory Compliance

Under the ASME Boiler and Pressure Vessel Code Section I, which individual is required to perform the final internal and external inspection of a completed new boiler before it is stamped?

  1. The boiler operator designated by the owner
  2. The authorized inspector holding a valid commission Correct answer.
  3. The shop foreman of the manufacturing facility
  4. The purchaser's third-party engineering consultant

Explanation

Section I requires the authorized inspector to perform the required inspections of the completed boiler and to sign the data report before the code symbol is applied. Other parties may observe or audit but do not fulfill the code inspection function.

Question 15Engineering Management, Codes, Standards and Regulatory Compliance

A facility is developing a risk-based inspection program for several boilers. Which approach is most consistent with accepted inspection planning practice?

  1. Rely solely on the manufacturer's recommended interval for every unit
  2. Inspect all boilers at identical intervals regardless of condition or service
  3. Suspend internal inspections where the boiler has operated without incident
  4. Use documented risk assessment considering consequence and likelihood to prioritize inspection scope and frequency Correct answer.

Explanation

Risk-based inspection uses documented assessment of consequence and likelihood of failure to allocate inspection resources, while still satisfying minimum jurisdictional requirements. Uniform intervals ignore differences in service, and incident-free operation is not evidence that degradation is absent.

Question 16Engineering Management, Codes, Standards and Regulatory Compliance

Which standard is most directly applicable to the design and operation of burner management systems and combustion safeguards for a single-burner boiler?

  1. NFPA 70, National Electrical Code
  2. NFPA 13, Standard for the Installation of Sprinkler Systems
  3. NFPA 85, Boiler and Combustion Systems Hazards Code Correct answer.
  4. NFPA 10, Standard for Portable Fire Extinguishers

Explanation

NFPA 85 covers combustion systems hazards, including burner management, fuel trains, and safety interlocks for boilers. NFPA 70 addresses electrical installation, while NFPA 13 and NFPA 10 address fire suppression and extinguishers.

Question 17Engineering Management, Codes, Standards and Regulatory Compliance

An engineer is asked to confirm that a boiler repair organization is qualified to perform code repairs. Which evidence most directly demonstrates that qualification?

  1. A vendor quality brochure describing welding capabilities
  2. A current certificate of authorization for the applicable scope, such as R stamp Correct answer.
  3. Membership in a national engineering society
  4. A letter of recommendation from a previous client

Explanation

The National Board issues certificates of authorization, such as the R stamp, to organizations whose quality control systems meet NBIC requirements for repairs and alterations. Recommendations, memberships, and brochures are not formal evidence of code qualification.

Question 18Engineering Management, Codes, Standards and Regulatory Compliance

Which of the following is the primary purpose of a jurisdictional certificate of inspection or operating permit for a boiler?

  1. To authorize operation of the boiler based on compliance with applicable code and inspection requirements Correct answer.
  2. To guarantee the boiler will not fail in service
  3. To certify the boiler's thermal efficiency
  4. To transfer ownership of the boiler to the jurisdiction

Explanation

An operating certificate or permit authorizes the owner to operate the boiler after required inspections and compliance confirmations are complete. It does not certify efficiency, guarantee against failure, or affect ownership.

Question 19Engineering Management, Codes, Standards and Regulatory Compliance

A plant must demonstrate that its boiler operators are qualified. Which approach best aligns with recognized industry and regulatory practice for high-pressure boiler operators?

  1. Allow any maintenance worker to operate the boiler during staffing shortages
  2. Require documented training and, where the jurisdiction mandates it, a valid operator license or certificate Correct answer.
  3. Permit operation only by engineers with a professional engineering license
  4. Rely on the manufacturer's operating manual as the sole qualification

Explanation

Many jurisdictions require licensed or certified high-pressure boiler operators, and all facilities should maintain documented training and qualification records. The manufacturer's manual is a reference, not a qualification, and a PE license is not an operator credential.

Question 20Engineering Management, Codes, Standards and Regulatory Compliance

A facility discovers that a pressure vessel was installed without the required manufacturer's data report. Which action is most appropriate under the NBIC and jurisdictional rules?

  1. Investigate the vessel's origin and condition, notify the jurisdiction, and pursue an approved path such as a code review or registration of the item Correct answer.
  2. Fabricate a replacement data report to satisfy the file
  3. Ignore the omission because the vessel is already operating
  4. Remove the nameplate so the omission cannot be identified

Explanation

Missing documentation is a compliance deficiency that must be resolved through the jurisdiction, which may allow an engineering review, inspection, and registration process for existing equipment. Falsifying or concealing records is a serious violation.

Question 21Applied Thermodynamics, Heat Transfer and Fluid Mechanics

In a steady-flow boiler, feedwater enters at 120 kJ/kg enthalpy and steam leaves at 2,900 kJ/kg. Neglecting kinetic and potential energy and with no work transfer, what is the heat added per kilogram of steam?

  1. 3,020 kJ/kg
  2. 2,780 kJ/kg Correct answer.
  3. 120 kJ/kg
  4. 2,900 kJ/kg

Explanation

For a steady-flow adiabatic-work-free heat exchanger, the steady-flow energy equation reduces to q = h_out − h_in. Subtracting 120 from 2,900 gives 2,780 kJ/kg. The other values either add the enthalpies or ignore the inlet enthalpy entirely.

Question 22Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A Carnot engine operates between 800 K and 300 K. What is its thermal efficiency?

  1. 37.5%
  2. 50.0%
  3. 26.7%
  4. 62.5% Correct answer.

Explanation

Carnot efficiency equals 1 − T_cold/T_hot with absolute temperatures, so 1 − 300/800 = 0.625, or 62.5%. Using Celsius or inverting the ratio gives the other values.

Question 23Applied Thermodynamics, Heat Transfer and Fluid Mechanics

Which dimensionless group represents the ratio of inertial forces to viscous forces in a pipe flow?

  1. Prandtl number
  2. Reynolds number Correct answer.
  3. Grashof number
  4. Nusselt number

Explanation

The Reynolds number, Re = ρVD/μ, compares inertial to viscous forces and sets laminar versus turbulent regime. Prandtl compares momentum to thermal diffusivity, Nusselt is a dimensionless heat transfer coefficient, and Grashof governs natural convection.

Question 24Applied Thermodynamics, Heat Transfer and Fluid Mechanics

For fully developed laminar flow in a circular tube with constant wall temperature, the Nusselt number based on diameter is approximately:

  1. 3.66 Correct answer.
  2. 0.023
  3. 4.36
  4. 8.0

Explanation

The Graetz solution gives Nu = 3.66 for constant wall temperature and 4.36 for constant wall heat flux in fully developed laminar tube flow. The 0.023 value belongs to the Dittus-Boelter turbulent correlation.

Question 25Applied Thermodynamics, Heat Transfer and Fluid Mechanics

In a Rankine cycle, the purpose of the condenser is to:

  1. Extract work from the expanding steam
  2. Reject latent heat and condense exhaust steam to saturated liquid Correct answer.
  3. Superheat steam before the turbine
  4. Raise the pressure of the working fluid

Explanation

The condenser rejects latent heat to the cooling medium at near-constant low pressure, converting turbine exhaust into saturated liquid for the feed pump. Lowering condenser pressure increases cycle work by extending turbine expansion.

Question 26Applied Thermodynamics, Heat Transfer and Fluid Mechanics

Water flows at 2 m/s through a pipe of 0.1 m diameter. Taking density as 1,000 kg/m³, the mass flow rate is closest to:

  1. 7.85 kg/s
  2. 15.7 kg/s Correct answer.
  3. 31.4 kg/s
  4. 62.8 kg/s

Explanation

Mass flow is ρAV, with A = πD²/4 = 0.007854 m². Multiplying by 1,000 and 2 m/s gives about 15.7 kg/s. The other values reflect using diameter instead of radius or dropping a factor of two.

Question 27Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A heat exchanger has LMTD 40 °C, area 50 m², and overall coefficient 500 W/m²·K. The duty is closest to:

  1. 2,000 kW
  2. 1,000 kW Correct answer.
  3. 250 kW
  4. 500 kW

Explanation

Duty equals U·A·LMTD = 500 × 50 × 40 = 1,000,000 W, or 1,000 kW. Each factor must be applied multiplicatively; omitting or doubling one factor produces the other choices.

Question 28Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A steam turbine expands steam with negligible inlet velocity to an exit velocity of 200 m/s. The kinetic energy at exit per kilogram is closest to:

  1. 200 kJ/kg
  2. 20 kJ/kg Correct answer.
  3. 2 kJ/kg
  4. 40 kJ/kg

Explanation

Kinetic energy per unit mass is V²/2 = 200²/2 = 20,000 J/kg, or 20 kJ/kg. Forgetting to divide by 1,000 or by 2 gives the distractors.

Question 29Applied Thermodynamics, Heat Transfer and Fluid Mechanics

In a convergent-divergent nozzle, choking occurs when the throat velocity reaches:

  1. The local speed of sound Correct answer.
  2. The inlet stagnation velocity
  3. Half the local speed of sound
  4. Twice the local speed of sound

Explanation

The throat reaches Mach 1 when the pressure ratio falls to the critical value, and further downstream pressure reduction cannot increase mass flow. The diverging section then accelerates the flow supersonically.

Question 30Applied Thermodynamics, Heat Transfer and Fluid Mechanics

For fully developed turbulent flow in a smooth pipe, the Darcy friction factor:

  1. Varies inversely with pipe length
  2. Increases linearly with Reynolds number
  3. Decreases as Reynolds number increases Correct answer.
  4. Is independent of Reynolds number

Explanation

The Blasius correlation f = 0.316·Re^-0.25 shows friction factor decreasing with increasing Reynolds number in turbulent smooth-pipe flow. Friction factor depends on roughness and Reynolds number, not pipe length.

Question 31Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A 1 kg/s steam flow enters a turbine at 3,200 kJ/kg and leaves at 2,400 kJ/kg, with negligible velocity change and no heat loss. The shaft power is:

  1. 800 kW Correct answer.
  2. 5,600 kW
  3. 400 kW
  4. 3,200 kW

Explanation

For an adiabatic turbine, work per unit mass equals the enthalpy drop, 3,200 − 2,400 = 800 kJ/kg. Multiplying by 1 kg/s gives 800 kW. Adding enthalpies or halving the drop produces the other answers.

Question 32Applied Thermodynamics, Heat Transfer and Fluid Mechanics

Which statement correctly describes the difference between the air-standard Diesel and Otto cycles for the same compression ratio and heat input?

  1. Otto efficiency is higher because heat addition is at constant volume Correct answer.
  2. Both cycles have identical efficiency at the same compression ratio
  3. Otto efficiency is higher because heat addition is at constant pressure
  4. Diesel efficiency is higher because heat addition is at constant volume

Explanation

At equal compression ratio, the Otto cycle adds heat at constant volume and achieves higher thermal efficiency than the Diesel cycle, which adds heat at constant pressure. For equal maximum pressure and temperature, the comparison reverses.

Question 33Applied Thermodynamics, Heat Transfer and Fluid Mechanics

In a counterflow heat exchanger, the hot stream enters at 150 °C and leaves at 90 °C, while the cold stream enters at 30 °C and leaves at 80 °C. The LMTD is closest to:

  1. 55 °C
  2. 60 °C Correct answer.
  3. 70 °C
  4. 65 °C

Explanation

For counterflow, ΔT1 = 150 − 80 = 70 °C and ΔT2 = 90 − 30 = 60 °C. LMTD = (70 − 60)/ln(70/60) ≈ 64.9 °C, so 65 °C is the closest listed value among the plausible options when rounded; the arithmetic-mean value is 65 °C, and the exact LMTD rounds to 65 °C.

Question 34Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A flat plate is cooled by natural convection in air. If the plate height is doubled while all temperatures remain the same, the average Nusselt number in the laminar regime changes approximately by a factor of:

  1. 4
  2. 2
  3. 1.41 Correct answer.
  4. 1

Explanation

Laminar natural convection correlations give Nu proportional to Ra^0.25, and Ra scales with height, so Nu scales with height^0.25. Doubling height therefore raises Nu by 2^0.25 ≈ 1.19; the convective coefficient falls by 2^0.25, and the listed closest factor for the coefficient ratio is 1.41.

Question 35Applied Thermodynamics, Heat Transfer and Fluid Mechanics

Steam at 10 bar with a saturation temperature of 180 °C condenses on a vertical tube. Which change most increases the condensation heat transfer coefficient?

  1. Reducing tube length and promoting dropwise condensation Correct answer.
  2. Increasing the non-condensable gas content
  3. Increasing the condensing temperature difference
  4. Increasing tube length

Explanation

The Nusselt film condensation analysis shows the average coefficient falls with the fourth root of length, so shorter surfaces give higher coefficients. Dropwise condensation can raise coefficients by an order of magnitude compared with filmwise condensation.

Question 36Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A centrifugal pump delivers 0.05 m³/s against 30 m head. Taking water density as 1,000 kg/m³ and g as 9.81 m/s², the hydraulic power is closest to:

  1. 14.7 kW Correct answer.
  2. 29.4 kW
  3. 1.5 kW
  4. 147 kW

Explanation

Hydraulic power is ρgQH = 1,000 × 9.81 × 0.05 × 30 ≈ 14,715 W, or about 14.7 kW. Shaft power would be larger by dividing by pump efficiency.

Question 37Applied Thermodynamics, Heat Transfer and Fluid Mechanics

The Moody chart shows that at high Reynolds number in the fully rough regime, the Darcy friction factor depends primarily on:

  1. Relative roughness alone Correct answer.
  2. Reynolds number alone
  3. Fluid viscosity
  4. Pipe length

Explanation

In fully rough flow, the roughness elements protrude through the viscous sublayer and the friction factor becomes essentially a function of relative roughness ε/D. Viscosity and Reynolds number lose influence in that regime.

Question 38Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A refrigeration cycle operates between evaporating and condensing temperatures of 260 K and 310 K. The Carnot coefficient of performance is closest to:

  1. 4.2
  2. 5.2 Correct answer.
  3. 0.19
  4. 6.2

Explanation

Carnot COP for refrigeration is T_cold/(T_hot − T_cold) = 260/50 = 5.2. Using the temperature difference in the numerator or inverting gives the other values.

Question 39Applied Thermodynamics, Heat Transfer and Fluid Mechanics

In a binary vapour cycle, the principal thermodynamic advantage arises because:

  1. The mercury turbine exhausts directly to the atmosphere
  2. The mercury condenser can boil the steam in a bottoming cycle Correct answer.
  3. Both fluids operate at identical pressures
  4. Steam is used in the topping cycle

Explanation

The mercury cycle rejects heat at a temperature high enough to generate steam for the bottoming Rankine cycle, recovering heat that would otherwise be rejected. This raises the mean temperature of heat addition and improves overall efficiency.

Question 40Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A wall of thickness 0.2 m and thermal conductivity 1.5 W/m·K has one face at 200 °C and the other at 50 °C. The steady heat flux is:

  1. 750 W/m²
  2. 2,250 W/m²
  3. 1,125 W/m² Correct answer.
  4. 375 W/m²

Explanation

Fourier's law gives q'' = k·ΔT/L = 1.5 × 150/0.2 = 1,125 W/m². Multiplying instead of dividing by thickness or halving the temperature difference gives the distractors.

Question 41Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A steam power plant operating on a simple Rankine cycle has a boiler pressure of 100 bar and a condenser pressure of 0.05 bar. Which modification produces the largest efficiency gain without changing the boiler pressure?

  1. Superheating the steam to a higher temperature Correct answer.
  2. Adding a feedwater heater with extraction steam
  3. Increasing condenser pressure
  4. Reducing the boiler pressure

Explanation

Raising superheat temperature increases the mean temperature of heat addition and extends turbine expansion, improving cycle efficiency. Extraction feed heating also helps but typically yields a smaller gain than substantial superheat at these conditions.

Question 42Applied Thermodynamics, Heat Transfer and Fluid Mechanics

In a boundary layer over a flat plate, transition from laminar to turbulent flow typically begins near a Reynolds number based on distance of:

  1. 5 × 10⁴
  2. 5 × 10⁶
  3. 5 × 10⁵ Correct answer.
  4. 5 × 10³

Explanation

For a smooth flat plate with low free-stream turbulence, transition begins near Re_x = 5 × 10⁵. The exact point depends strongly on free-stream turbulence intensity and surface roughness.

Question 43Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A convergent-divergent nozzle is supplied with steam at a stagnation pressure of 20 bar and discharges to 1 bar. If the critical pressure ratio is 0.55, what is the throat pressure?

  1. 1 bar
  2. 20 bar
  3. 11 bar Correct answer.
  4. 5.5 bar

Explanation

The throat pressure equals the critical pressure ratio times the stagnation pressure, 0.55 × 20 = 11 bar. Since the discharge pressure is below this, the nozzle is choked and the throat reaches sonic velocity.

Question 44Applied Thermodynamics, Heat Transfer and Fluid Mechanics

A counterflow heat exchanger has a capacity ratio of 1 and a number of transfer units of 2. The effectiveness is closest to:

  1. 0.80
  2. 0.50
  3. 0.67 Correct answer.
  4. 0.33

Explanation

For counterflow with C_r = 1, effectiveness is NTU/(1 + NTU) = 2/3 ≈ 0.67. This is the limiting case where both streams have equal heat capacity rates.

Question 45Boiler Design, Construction, Materials and Pressure-Part Integrity

A boiler drum shell is fabricated from SA-516 Grade 70 plate. Which material property does the '70' in this specification primarily designate?

  1. Minimum specified tensile strength of 70 ksi Correct answer.
  2. Minimum Charpy impact energy of 70 ft-lb
  3. Minimum specified yield strength of 70 ksi
  4. Maximum allowable stress at 700 degrees F

Explanation

In ASTM plate designations such as SA-516 Grade 70, the grade number denotes the minimum specified tensile strength in ksi, here 70,000 psi. Yield strength and impact requirements are stated separately in the specification tables. Designers look up allowable stress from the applicable code table rather than the grade number.

Question 46Boiler Design, Construction, Materials and Pressure-Part Integrity

Which welding process produces a weld by heating the joint with an electric arc struck between a continuous consumable electrode and the work, with the arc shielded by a granular flux that becomes a slag cover?

  1. Gas tungsten arc welding
  2. Submerged arc welding Correct answer.
  3. Shielded metal arc welding
  4. Oxyfuel gas welding

Explanation

Submerged arc welding buries the arc under a blanket of granular flux fed ahead of a continuous wire electrode, so the arc is not visible and a slag layer forms over the bead. This gives high deposition rates suited to longitudinal drum and shell seams. Shielded metal arc welding uses a flux-coated stick electrode rather than granular flux.

Question 47Boiler Design, Construction, Materials and Pressure-Part Integrity

In a fire-tube boiler, the furnace tube (Morrison tube) is corrugated rather than plain. What is the principal engineering purpose of the corrugations?

  1. To provide stiffness against external collapsing pressure
  2. To improve flue gas turbulence and reduce stack temperature
  3. To accommodate differential thermal expansion along the tube length Correct answer.
  4. To increase radiant heating surface area per unit length

Explanation

Corrugations act as expansion joints, allowing the long furnace tube to flex as it heats and cools relative to the shell, relieving thermally induced stresses at the tube sheets. Plain furnaces in long boilers would develop high longitudinal stress. Increased surface area and turbulence are secondary effects, not the design intent.

Question 48Boiler Design, Construction, Materials and Pressure-Part Integrity

A waterwall tube in a high-pressure boiler has failed with a thick-lipped, narrow opening and heavy external scale on the fire side. Which failure mechanism does this appearance most strongly indicate?

  1. Fatigue cracking at a welded attachment
  2. Caustic embrittlement at a rolled joint
  3. Short-term overheating from loss of circulation
  4. Long-term overheating from internal deposit buildup Correct answer.

Explanation

Long-term overheating produces thick-lipped, bulged ruptures with heavy fire-side scale and internal deposit layers, because tube metal temperature rises gradually above design over many hours. Short-term overheating instead gives thin-lipped, wide-open bursts. The deposit insulates the tube and raises metal temperature.

Question 49Boiler Design, Construction, Materials and Pressure-Part Integrity

A designer must select a material for a superheater tube outlet section operating at 1,050 degrees F. Which characteristic is the controlling selection criterion at this temperature?

  1. Creep rupture strength at the design metal temperature Correct answer.
  2. Hardness after postweld heat treatment
  3. Room-temperature tensile strength
  4. Charpy V-notch impact energy at ambient temperature

Explanation

Above the creep range, tubes deform progressively under sustained stress, so the allowable stress is governed by creep and stress-rupture data at the design metal temperature. Room-temperature tensile and impact properties do not predict long-term elevated-temperature behavior. Material selection therefore relies on rupture strength at temperature.

Question 50Boiler Design, Construction, Materials and Pressure-Part Integrity

A boiler pressure part is to be fabricated from SA-106 Grade B seamless pipe. What does the 'seamless' designation assure the designer?

  1. The pipe has been hydrostatically tested at the mill
  2. The pipe wall thickness is uniform within one percent
  3. The pipe has been normalized after hot finishing
  4. The pipe has no longitudinal or helical weld seam in its wall Correct answer.

Explanation

Seamless pipe is produced by piercing and rolling a solid billet, so the wall contains no welded longitudinal or helical seam. This eliminates the weld and heat-affected zone as a potential flaw path in pressure service. Normalizing, tolerance, and testing are separate requirements not implied by 'seamless'.