for Circumferenctial Stress S = pD/2t
for Longitudinal Stress S = pD/4t

where p - internal pressure, D - diameter, t - thickness.

So substitute the given to the equations gving; (be consistent in units)

Sc = (25 x 2000) / (2 x 20) = 1250 kN/mm2 (circumferential)
Sl = (25 x 2000) / (4 x 20) = 625 kN/mm2 (longitudinal)

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