Ultrasonic method of residual thickness measurement is the main one in determining the value of corrosion wear of gate elements and valve of navigable locks in operation. The accuracy of residual thickness measurements required in regulatory documents cannot always be achieved during operational inspection of said metal structures. There are cases where the results of residual thickness measurements do not correspond to its actual average value. Analysis of components of measurement error of residual thickness of gate elements and gates of shipping locks is performed taking into account various operational factors. It has been established that starting from a certain stage of the corrosion process, its effect on the value of measurement error is prevailing. Conditions are defined limiting the possibility of using ultrasonic methods of measuring residual thickness of metal articles, including through protective dielectric coatings, when monitoring the technical condition of gates and gates of shipping locks. Keywords: ultrasonic wall thickness testing, navigation lock, gate, valve, operation, corrosion, residual thickness, precision of measurements, technical condition.