Installation of new pipelines is predicted to grow at a rapid rate over the next twenty years, due in part to the increase use worldwide of combined cycle power generation plant using natural gas a fuel. The need to construct large diameter pipelines over long distances has led to an increased demand to improve the productivity of pipeline girth welding. Many novel techniques have been tried in the past to achieve productivity gains, including laser welding, flash butt welding, homopolar welding, and radial friction welding. In spite of the failure to gain wide acceptance, there is still current development aimed at achieving their eventual implementation. Single wire mechanised gas metal arc welding (GMAW) remains the dominant pipe girth welding technique, and has been optimised in the past to produce the maximum productivity possible with this process. Continued development of GMAW with dual torch, tandem GMAW welding and novel techniques for GMAW roots is leading to further significant gains in arc welding productivity. This paper describes a new development, the CAPS project, (Cranfield Automated Pipe-welding System), where tandem GMAW in a narrow groove has been applied to pipeline girth welding with two tandem torches in a single welding head. The CAPS system offers welding productivity three to four times higher than that possible with the conventional single wire GMAW technique, while still producing a weld which is very similar to that generated by single wire welding. The development of the system is described, as well as recent successful trials under field conditions. The development of high power lasers has spurred a current high level of interest in the possibility of application to pipeline welding, and current research is described in which the feasibility of pipeline laser welding has been established.
Welding; GMAW; pipeline; productivity
