Figure P13.23 shows a closed-ended cylindrical steel tank of a radius r = 4 m and a heig...

Figure P13.23 shows a closed-ended cylindrical steel tank of a radius r = 4 m and a height h = 18 m. The vessel is completely filled with a liquid of density = 15 kN/m³ and is subjected to an additional internal gas pressure of p = 500 kPa. Based on an allowable stress of 180 MPa, calculate the wall thickness needed (a) at the top of the tank; (b) at quarter-height of the tank; (c) at the bottom of the tank.