A Cylindrical Tank Is Assembled by Welding Steel Sections in a Helical

A cylindrical tank is assembled by welding steel sections in a helical pattern with angle $\alpha = 50 ^ { \circ }$ . Tank diameter is 1. diameter is $1.6 \mathrm {~m}$ , thickness is $20 \mathrm {~mm}$ , and internal pressure is $2.75 \mathrm { MPa }$ . Modulus $E = 210 \mathrm { GPa }$ and Poisson's ratio $v = 0.28$ . The circumferential strain in the wall of the tank is approximately:

A) $1.9 \times 10 ^ { - 4 }$
B) $3.2 \times 10 ^ { - 4 }$
C) $3.9 \times 10 ^ { - 4 }$
D) $4.5 \times 10 ^ { - 4 }$