A pipeline is being designed to withstand a total maximum pressure of 2.13 x 106 Pa. The 20 cm diameter pipeline is ductile iron and conveys water at 40 L/s. Determine the required thickness of the pipe wall if the operational pressure head (pressure head in the pipe under regular flow conditions) is 40 m and if the flow control valve on the downstream end closes suddenly, developing a water hammer in the pipeline. Assume that the longitudinal stresses will be negligible, and Poisson's ratio is 0.25.