Hoop strain:

ε_h =      σ _n / E  - v    σ _l / E

= ( pd /2tE) - v (pd /4t E)

=   (pd /4tE)  (2 - v)

 By using these expressions, we can proceed to attain the changes in length and diameter of the cylinder.

Change in length = Longitudinal strain × Original length = ε_l  × l

Though, it may be noted that since the circumference is a constant product of diameter, that means C = π d, the diametrical strain shall be the same as the circumferential strain.

Therefore, change in diameter = Hoop strain × Original diameter.