Multiple Choice Questions ( MCQ ) for the Design of Machine Element

 

Topic - Design of Cylinders and Pressure Vessels 

 

1. A cylinder is considered thin when the ratio of inner diameter to wall thickness is more than 5.
a) True
b) False
View Answer

Answer: b
Explanation: A cylinder is considered thin when the ratio of inner diameter to wall thickness is more than 15.

2. Tangential stress in a cylinder is given by [symbols have their usual meanings].
a) PD/2t
b) 2PD/t
c) PD/4t
d) 4PD/t
View Answer

Answer: a
Explanation: Considering equilibrium in half portion of cylinder of unit length, DP=2σt.

3. Longitudinal stress in a cylinder is given by [symbols have their usual meanings].
a) PD/2t
b) 2PD/t
c) PD/4t
d) 4PD/t
View Answer

Answer: c
Explanation: Considering equilibrium PxπD²/4=σxπDt.

4. A seamless cylinder of storage capacity of 0.03mᵌis subjected to an internal pressure of 21MPa. The ultimate strength of material of cylinder is 350N/mm².Determine the length of the cylinder if it is twice the diameter of the cylinder.
a) 540mm
b) 270mm
c) 400mm
d) 350mm
View Answer

Answer: a
Explanation: 0.03=πd²L/4 and L=2d.

5. A seamless cylinder of storage capacity of 0.03mᵌis subjected to an internal pressure of 21MPa. The ultimate strength of material of cylinder is 350N/mm².Determine the thickness of the cylinder if it is twice the diameter of the cylinder.
a) 12mm
b) 4mm
c) 8mm
d) 16mm
View Answer

Answer: c
Explanation: t=PD/2σ.

6. Cylinder having inner diameter to wall thickness ratio less than 15 are
a) Thin cylinders
b) Thick Cylinders
c) Moderate cylinders
d) None of the listed
View Answer

Answer: b
Explanation: Smaller dia to thickness ratio implies more thickness and hence these are classified under thick cylinder.

7. Lame’s equation used to find the thickness of the cylinder is based on maximum strain failure.
a) True
b) False
View Answer

Answer: b
Explanation: It is based on maximum principal stress theory.

8. Lame’s equation is generally used for ductile materials.
a) True
b) False
View Answer

Answer: b
Explanation: Lame’s equation is used to determine thickness of the brittle as it used principal stress theory.

9. The piston rod of a hydraulic cylinder exerts an operating force of 10kN. The allowable stress in the cylinder is 45N/mm². Calculate the thickness of the cylinder using Lame’s equation. Diameter of the cylinder is 40mm and pressure in cylinder is 10MPa.
a) 2.05mm
b) 4.2mm
c) 5.07mm
d) None of the listed
View Answer

Answer: c
Explanation: t=D/2[√[σ+ P /σ-P] -1 ].

10. The piston rod of a hydraulic cylinder exerts an operating force of 10kN. The allowable stress in the cylinder is 70N/mm². Calculate the thickness of the cylinder using Clavarinoe’s equation. Diameter of the cylinder is 240mm.μ=0.3 and pressure in cylinder is 15MPa.
a) 35mm
b) 30mm
c) 27mm
d) None of the listed
View Answer

Answer: c
Explanation: t=D/2[√[σ+(1-2μ) P /σ-(1+μ)P] -1 ].

11. Autofrettage is beneficial for the high pressure cylinder.
a) True
b) False
View Answer

Answer: a
Explanation: It increases pressure capacity of the cylinder and reduces compressive stresses.

12. Autogreggate is a process of ___ stressing the cylinder.
a) Pre
b) Post
c) Over
d) None of the listed
View Answer

Answer: a
Explanation: It is a pre stressing phenomenon to improve pressure capacity.

13. Can we pre-stress the cylinder by subjecting cylindrical portion near inner diameter in plastic range and outer diameter is still in the elastic range.
a) True
b) False
View Answer

Answer: a
Explanation: On releasing the pressure, outer portion contracts exerting pressure on the inner portion which has undergone permanent deformation. This induces residual compressive stresses at the inner surface.

14. A compound cylinder consists of
a) 2 cylinders
b) Cylinder and a jacket
c) 2 jackets
d) At least two cylinders
View Answer

Answer: b
Explanation: Inner diameter of jacket increase and outer diameter of cylinder decreases when the jacket is heated.

15. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². Calculate the shrinkage pressure.
a) 5.88N/mm²
b) 2.28N/mm²
c) 4.56N/mm²
d) 3.66N/mm²
View Answer

Answer: b
Explanation: σ=P[D₃²+D₂²]/[D₃²-D₂²] where D₂=40mm and D₃=60mm.

16. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². Calculate the interference [E=210kN/mm²].
a) 2.8mm
b) 4.6mm
c) 5.4mm
d) 4.8mm
View Answer

Answer: a
Explanation: Δ=PD₂[2D₂²(D₃²-D₁²)] / Ex[(D₃²-D₂²)(D₂²-D₁²)].

17. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². Calculate the radial stresses due to shrink shift in jacket.
a) +2.56[(45/r) ² – 1]
b) 1.824[(45/r) ² – 1]
c) -1.824[(45/r) ² – 1]
d) None of the listed
View Answer

Answer: c
Explanation: σ(r)=-PD₂²[D₃²/4r² – 1]/ [D₃²-D₂²].

18. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². Calculate the tangential stresses due to shrink shift in jacket.
a) +2.56[(45/r) ² – 1]
b) 1.824[(45/r) ² – 1]
c) -1.824[(45/r) ² – 1]
d) None of the listed
View Answer

Answer: b
Explanation: σ(t)=+PD₂²[D₃²/4r² – 1]/ [D₃²-D₂²].

19. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². Calculate the radial stress due to shrink shift in inner tube.
a) +3.04[1-(15/r) ²]
b) -3.04[1-(15/r) ²]
c) -3.04[1-(10/r) ²]
d) +3.04[1-(10/r) ²]
View Answer

Answer: b
Explanation: σ(r)= σ(r)=-PD₂²[1-D₁²/4r² ]/ [D₂²-D₁²].

20. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². Calculate the tangential stress due to shrink shift in inner tube.
a) +3.04[1+ (15/r) ²]
b) -3.04[1+ (15/r) ²]
c) -3.04[1-(10/r) ²]
d) +3.04[1-(10/r) ²]
View Answer

Answer: b
Explanation: σ(r)= σ(r)=-PD₂²[1+D₁²/4r² ]/ [D₂²-D₁²].

21. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². In service the cylinder is further subjected to an internal pressure of 25MPa. Calculate the radial stress in compound cylinder.
a) -3.75[(45/r) ² – 1]
b) +3.75[(45/r) ² – 1]
c) -3.75[(45/r) ² -+1]
d) +3.75[(45/r) ² +1]
View Answer

Answer: a
Explanation: σ(r)=-PD₁²[D₃²/4r² – 1]/ [D₃²-D₁²]. Here P=30.

22. A high pressure cylinder consists of a steel tube with inner and outer diameters 30 and 60mm respectively. It is jacketed by an outer steel tube, having an outer diameter of 90mm. Maximum principal stress induced is 80N/mm². In service the cylinder is further subjected to an internal pressure of 25MPa. Calculate the tangential stress in compound cylinder.
a) -6.75[(45/r) ² + 1]
b) +3.75[(45/r) ² +1]
c) -3.75[(45/r) ² +1]
d) -3.75[(45/r) ² -1]
View Answer

Answer: b
Explanation: σ(t)=+PD₁²[1+ D₃²/4r² ]/ [D₃²-D₁²]. Here P=30.

23. A gasket is a device to allow easy diffusion of fluids across mating surfaces of a mechanical assembly.
a) True
b) False
View Answer

Answer: b
Explanation: A gasket acts as a barrier between two mating surfaces to prevent fluid flow.

24. Asbestos gaskets like other non-metallic gaskets can be used only up to a temperature of 70⁰C.
a) True
b) False
View Answer

Answer: b
Explanation: Asbestos can be used upto a temperature of 250⁰C while all other non-metallic gaskets can be used only upto a temperature of 70⁰C.

25. An unfired pressure vessel is used to carry stem, gases or fluids at pressure
a) Less than atmospheric pressure
b) Greater than atmospheric pressure
c) Equal to atmospheric pressure
d) None of the mentioned
View Answer

Answer: b
Explanation: Terminology.

26. Class 1 pressure vessels are used to contain
a) Lethal substances
b) Light duties applications
c) None of the listed
d) LPG
View Answer

Answer: a
Explanation: Class 1 pressure vessels are used exclusively for lethal substances. LPG doesn’t fall in the category of lethal substances.

27. An oil seal is a mechanical device made of elastic material which is used to prevent leakage of fluid between two machine components.
a) True
b) False
View Answer

Answer: b
Explanation: It is made of elastomer material.

28. Does oil seal consist of any spring in its structure?
a) Yes
b) No
View Answer

Answer: a
Explanation: It consist of garter spring which exerts a radial pressure on the rotating shaft and prevents leakage.

29. Which of the following isn’t true about oil seals?
a) Cheap
b) Can be used over a wide range of lubricating oils
c) Can’t tolerate misalignment
d) All of the mentioned
View Answer

Answer: c
Explanation: Oil seals can tolerate the misalignment to some extent.

30.   Internal pressure of 2.5 Mpa acts on a pressure vessel of thickness 15 mm and internal diameter of 1500 mm. What is the stress induced in longitudinal direction?

a. 36.63 N/mm²
b. 59.13 N/mm²
c. 65.62 N/mm²
d. 131.25 N/mm²

ANSWER: C. 65.62 N/mm²

31.   Which type of formed threads are used for vertical pressure vessels in the pressure range of 0.1 N/mm² to 1.5 N/mm²?

a. Plain formed head
b. Torispherical dished head
c. Semi-elliptical dished head
d. All of the above

ANSWER: b. Torispherical dished head

32. Design pressure for unfired pressure vessels is 1.05 times of _______

a. minimum working pressure
b. maximum working pressure
c. hydrostatic test pressure
d. none of the above

ANSWER: b. maximum working pressure

33. Class 3 pressure vessels having welded joints are __________

a. fully radio-graphed
b. partially radio-graphed
c. spot radio-graphed
d. not radio-graphed

Answer: d. not radio-graphed

34. Which type of welded joints are not included in class 3 pressure vessels?

a. Double welded butt joint with full penetration
b. Single welded but joint with back strip
c. Single full fillet lap joints
d. None of the above

ANSWER: b. Single full fillet lap joints

35.  In unfired pressure vessels, category A consists of _________

a. joints connecting flanges and flat heads
b. welded joints connecting nozzles with main shell
c. circumferential welded joints joints
d. longitudinal welded joints

ANSWER: d. longitudinal welded joints

36. Which of the following is not an unfired pressure vessel?

a. Heat exchanger
b. Storage vessels
c. Steam boilers
d. None of the above

ANSWER: c. Steam boilers

37. What is the weld joint efficiency if pressure vessel is fabricated with single full fillet lap joint?

a. 1.0
b. 0.55
c. 0.65
d. 0.85

ANSWER: b. 0.55

38.  A cylindrical pressure vessel is subjected to an internal pressure of 3 Mpa on internal diameter of 1000 mm. The vessel is fabricated with single weld butt joint with back strip and is not radio-graphed. What is the thickness of flat head, if head made of alloy steel has an ultimate tensile strength of 400 N/mm² ? (corrosion allowance = 2)

a. 110 mm
b. 120 mm
c. 150.23 mm
d. 152.13 mm

ANSWER: a. 110 mm

39.  A cylindrical pressure vessel is subjected to operating pressure of 0.55 Mpa and corrosion allowance of 2. What is the thickness of pressure vessel shell if its internal diameter is 2000 mm? (σ_all = 120 N/mm² & η_l = 0.75)

a. 6.5 mm
b. 7 mm
c. 9 mm
d. 9.5 mm

ANSWER: c. 9 mm