Question

A circular penstock of mild steel, 1.4 m in diameter, is fabricated in workshop with 12 mm thick plates. The plates are severed by 8 mm size fillet welds, provided on the inside and outside of the lapped ends as shown in figure. The safe internal pressure that can be allowed in the penstock will be $N/m{m}^2$.
${\gamma }_{mw}=1.25,FOS=1.5]$

• A. 2.02

Answer 1

The correct option is A 2.02
Given size of weld, S = 8 mm
Effective throat thickness,
$t_t=ks=0.7\times 8=5.6mm$
Internal force causing bursting of the penstock = $\frac{P_{u}d}{2}where,(P_u$ = ultimate internal pressure, d = diameter of the penstock = 1.4 m = 1400 mm
Resistance offered by the weld per unit length $=2\times t_t\times \frac{f_u}{\sqrt{3}\times {\gamma }_{mw}}$
Hence, $\frac{P_{u}d}{2}=2t_t.\frac{f_u}{\sqrt{3}.{\gamma }_{mw}d}$
$\Rightarrow P_u=\frac{4t_t{f}_u}{\sqrt{3}.{\gamma }_{mw}d}=\frac{4\times 5.6\times 410}{\sqrt{3}\times 1.25\times 1400}=3.0299N/m{m}^2$
Hence, safe internal pressure $=\frac{3.0299}{1.5}=2.02N/m{m}^2$