This article presents the results of the assessment of corrosion damage occurred in a storage tank made of stainless steel, in order to determine its probable origin. Before the tank was put in service (storage of sulfonic acid solution), corrosion damage of stainless steel sheets and welded joints were observed after an hydrostatic test. The water used for the hydrostatic test was kept inside the tank for about 7 weeks after the test was performed. In the meantime, a corrosion process took place, which was accelerated by water aggressiveness and by a bad internal finishing of sheets and welded joints. On site evaluation was followed by laboratory tests. © 2012 Universidad Simón Bolívar.