This European Standard describes acoustic emission testing (AT) on metallic surroundings filled with liquids for the detection of corrosion processes that are active at the time of the test. It is applicable to metallic storage tanks, such as those used in the chemical and petrochemical industry. The results provide a qualitative statement regarding the condition of the test object and a recommendation regarding the maximum allowable duration of the followon service period, based on the AT indications and additional information in order to characterize the AT indications. In the case of flat bottomed storage tanks (FBST) the procedure described within this standard provides testing of the complete bottom, the tank shell up to the filling height and in case of a floating roof tank also the roof sheets in contact with the stored liquid. As for every application of acoustic emission testing, the measured data contain information regarding active sources. An ongoing corrosion process, such as general corrosion and localized corrosion defined in EN ISO 8044, leading to progressive loss of wall thickness will be detected. A corrosion process which has stopped does not produce acoustic emission and will therefore not be detected at the time of test.