A development of high-speed GMA girth welding system for pipelines

Pipelines are typical ways to transport natural gas or oil economically and effectively in middle or long distance. Particularly, in Southeast Asia, the demand for the offshore pipeline construction has been increasing. The construction of offshore pipelines has been performed by a special work-barge and many workers such as welders, mechanics, engineers and sailors are necessary on the barge. This means that large expenses are incurred though the daily operation of the work-barge. It is no exaggeration to say that the cost for the pipeline construction is dominated by the daily installed pipeline distance which depends on the number of welded joints per day. Therefore, the most important subject to reduce the cost is to increase the productivity of welds. To do this, it is considered that the development of the high-speed girth welding process is the most effective because the welding time is the longest in all works, including coating, beveling and non-destructive inspection.

Generally, when a pipeline is welded under high welding speed, some welding flaws, such as hot cracking and incomplete fusion, would likely occur. To solve those problems, two methods are considered. Firstly, a preventing method from the initiation of hot cracking is studied. In addition, a control method which keeps controlling welding torches at the center in the groove is developed to prevent the occurrence of incomplete fusion. Using results of the above, the full automatic dual torch GMA girth welding system is developed and it has been applied for some offshore pipeline constructions. In this paper, some technology used in the system is mentioned.