A method for non-destructive testing of walls of components, at least one ultrasonic transducer (1) which is fixed to a surface of the wall is used to emit horizontally polarized transverse waves (3) in a lateral propagation direction and compression waves or vertically polarized transverse waves (6) in a radial propagation direction. The at least one ultrasonic transducer (1) and/or at least one further ultrasonic transducer arranged at a known distance from the at least one ultrasonic transducer (1) on the respective wall of the component (2) is/are used to detect horizontally polarized transverse waves (4) reflected by defects and compression waves or vertically polarized transverse waves (7) after or while running the non-destructive testing of the wall in order to determine the respective wall thickness.