<p>In the testing of an underwater pipeline contg. oil under press. esp. at 14-352 atmos (gauge) a directional receiver for ultra sonic energy is moved at a distance of up to 1500 m (measured in the horizontal plane) from the pipeline a receiver is used sensitive only in the range 20-70 k Hz and with a directional characteristics corresponding to an arc of angle of 10 degrees in the horizontal plane. Linear velocity of the receiver and the distance from the pipeline are corrected so as to detect solely the ultra-sonic energy on the range 20-70 kHz resulting from an escape of oil from a leak and to locate this leak. The use of ultra-sonic energy receivers sensitive to a restricted frequency range and of a narrow-sector of emitted energy enables background noise to be excluded and more accurate location to be achieved.</p>
