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Development of a fully automatic both-side welding method for pipeline construction was achieved in terms of combining an internal clamp and welding device with a two external head welding device. A double-V butt joint of 40 degree geometry was applied with simultaneous three head operation (one internal and two external heads), reducing the deposited area to a half and increasing the welding rate by about five times in comparison with the former 60 degree joint geometry and an external single head GMA penetration welding method. The new process also provides the method of inprocess on-line tracking of the weld line as the welding proceeds, because the optical sensor is capable of detecting the variation in parameters such as joint and deposit geometries. In addition, as the welding conditions can be properly controlled under a real time, it was achieved to stabilize the weld quality and save labor.

To increase safety and reduce costs in maintaining buried pipelines, we have been studying various types of robots capable of inspecting and repairing such pipelines from inside, and we have recently succeeded in developing automatic welding robots to reinforce welds from the inside of a steel pipe with a diameter of 600 mm. It is now within our scope to put it into practical use. This paper presents a general description of three such robots models which we have developed. These robots, designed to travel over more than 100 m in a complex of piping with bends, can do welding to reinforce existing welds. This paper chiefly discusses techniques used in our development to solve the most difficult problems, namely the determination of the most appropriate travelling and welding methods. Through our activities, we have obtained useful findings to further the study of robotic systems for pipeline inspection and repair.