# Machine Design Questions and Answers – Longitudinal Butt & Circumferential Lap Joints for Boiler Shell

This set of Machine Design online test focuses on “Longitudinal Butt & Circumferential Lap Joints for Boiler Shell”.

1. Corrosion allowance is the metal removed to reduce the thickness required to withstand internal pressure.
a) True
b) False

Explanation: corrosion allowance is the extra metal added to increase the thickness.

2. Unwin’s formula is used to find _____ of rivets.
a) Diameter
b) Thickness
c) Strength
d) None of the listed

Explanation: d=6√t is unwin’s formula.

3. The rivets in outer row of longitudinal boiler shell butt joint are subjected to double shear.
a) True
b) False

Explanation: Rivets in middle and inner row are subjected to double shear and in outer row are subjected to single shear.

4. A cylindrical pressure vessel with a 2m wide inside diameter is subjected to internal steam pressure of 1.5Mpa. Calculate the thickness of the plate required if corrosion allowance is considered as 2mm. The permissible value of tensile stress is 80N/mm².
a) 15mm
b) 19mm
c) 21mm
d) 17mm

Explanation: t=PD/2σ + CA or t=1.5×2000/2×80 + 2.

5. If number of rivets subjected to single shear per pitch length is 2 and those subjected to double shear per pitch length are 3, then find the shear resistance of rivets is diameter of rivets is 20mm and permissible shear 60N/mm².
a) None of the listed
b) 146.1kN
c) 150.7kN
d) 140.2kN

Explanation: P=Axτxn₁+2xAxn₂xτ.
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6. Calculate the thickness of the strap required in longitudinal butt joint if pitch of the rivets is 150mm and diameter of rivets 30mm. Also thickness of plate is 20mm.
a) None of the listed
b) 16.7mm
c) 13.4mm
d) 10.2mm

Explanation: t=0.625t[p-d/p-2d].

7. Longitudinal and circumferential both types of joints try to make a ring from the steel plate.
a) True
b) False

Explanation: Longitudinal joint makes a ring from the steel plate while circumferential connects one ring to the other.

8. Number of rivets in the circumferential joint can be found by which formula? Symbols have their usual meanings.
a) (D/d)²x2(P/τ)
b) (D/d)²x(P/τ)
c) (d/D)x(P/τ)
d) (D/d)x(P/τ)

Explanation: nx[πd²τ/4]=[πD²/4]xP.

9. The efficiency of circumferential joint is 62%. Calculate the pitch of circumferential joint if diameter of rivets is 25mm.
a) None of the listed
b) 66mm
c) 60mm
d) 54mm

Explanation: 0.62=p-25/p.

10. Calculate the efficiency of the circumferential joint if pitch of rivets is 60mm and diameter of rivets is 22mm.
a) 89%
b) 63.33%
c) 62%
d) 50%

Explanation: Effeciency=p-d/p.

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