Abstract: An apparatus for the treatment of an exterior pipe surface includes one or more nozzles or other treating means which are carried by a frame. The frame can be mounted around the pipe to be treated and is capable of moving along the pipe surface in longitudinal direction thereof, due to the provision of travelling wheels. Disclosed are provisions for allowing the apparatus to keep itself in balance on the pipe during operation. Such provisions include detection means (e.g. a pendulum with sensors) for detecting undesired displacements of the frame in circumferential direction of the pipe, and control means (such as e.g. hydraulic cylinders with a common system of hydraulic lines and valves) for adjusting the wheel axes of one or more travelling wheels in angular position, in response to a signal delivered by the detection means.