A storage tank for 93 % phosphoric acid was built in Luka Koper from 7 mm thick ground hot-rolled plates of 316L stainless steel. The capacity of the storage tank is of the 750 m3, diameter of 11 m and the height of 8,2 m. The shell plates were welded manually using the shielded metal-arc and gas-metal-arc processes. Before the erection, welding procedure tests according to EN 288-3 were carried out. During the construction several non-destructive examination methods were used, such as radiographic testing and visual and liquid penetrant examination. After the entire tank and roof structure were completed, a hydrostatic leak test was carried out. The surfaces of all the welds on the internal surface of the vessel were ground and the roughness was checked on site. The surfaces of the base material and the ground welds were passivated and tested for resistance to corrosion with electrochemical measurements.