The invention relates to a method for investigating a structure and a structure for receiving and/or conducting a liquid or soft medium, the method comprising the steps of: a) exciting acoustic waves in the structure by means of at least one transmitter, b) converting at least a part of the energy associated with the acoustic waves (A) excited in the structure into volume sound waves of the medium, c) reconverting at least a part of the energy associated with the volume sound waves into acoustic wave energy of the structure thereby generating acoustic waves in the structure, d) receiving acoustic waves evoked by the transmitter by at least one receiver, and e) verifying whether a coating is present on a surface of the structure and/or if a coating is present determining properties of the coating by evaluating a signal generated by the receiver upon receipt of acoustic waves evoked by the transmitter and/or verifying whether a level of the medium (5) is below a predetermined value.