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 $N/m{m}^2$ that can be allowed in the penstock will be _______
$[{\gamma }_{mw}=1.25,FOS=1.5]$

• A. 2.02

Answer 1

The correct option is A 2.02

Given that,
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,

$\text{d = diameter of the penstock = 1.4 m = 1400 mm}$

$\text{Resistance offered by the weld per unit length}$
$=2\times t_t\times \frac{f_u}{\sqrt{3}\times {\gamma }_{mw}}$

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

$=\frac{3.0299}{1.5}=2.02N/m{m}^2$