i want to know how to calculate the suitable thickness for an open tank ...the tank is stainless steel 304.. and it's 1000 liter hot water storage tank ...this tank is two layers with inlet and outlet diameters and between them a layer of polyurethan insulation (5 cm) ...the length of the tank is 160 cm (horizontal tank)

please assume any diameters ...i need that help ASAP.