Abstract: Ultrasonic probes are automatically moved and oriented on the edges of a weld in off-shore structures. An open U squirrel cage is fixed on a secondary member of an off-shore structure; an open U squirrel cage rotor rotates in the squirrel cage and bears a retractable sleeve within which an inspection arm moves. The end .OMEGA. of the arm has an orientable telescopic elbow of length .OMEGA..GAMMA.. From a wrist .GAMMA. of the arm extend two hands bearing ultrasonic feelers. The position of .GAMMA., the angle of the hands between them, and their orientation, are programmed by numerical control from theoretical geometries. The compensation of the manufacturing tolerances is integrated into the design of the hands. The device is useful for checking the welds of nodes in off-shore platforms.