Evaluation of Economic Incentives And Weld Properties For Welding Steel Pipelines Using Friction Stir Welding

Abstract

Pipelines have long been a key component in the transportation and distribution of petroleum resources. Reducing the cost of pipelines to improve the economics of transportation is critical to the cost effective development of resources in remote locations. This paper addresses the economics of using friction stir welding (FSW) for pipeline construction and also documents a study concerning the welding of line pipe steels. An economic analysis of pipeline construction costs was conducted to compare FSW to construction using conventional gas metal arc welding (GMAW). Both offshore and onshore pipeline construction scenarios were considered in the study. Several assumptions were made during the study with respect to factors such as FSW tool cost and welding productivity. It is estimated that FSW offers about 25% and 7% construction cost savings for offshore (J-lay) and onshore construction, respectively. Several line pipe steels were welded using different process parameters. Weld properties were evaluated using microhardness tests, all-weldmetal tensile tests and crack tip opening displacement (CTOD) tests. Prior austenite grain size in the stir zone was calculated from electron back-scattered diffraction (EBSD) patterns. Of the X65 linepipe steels tested, all showed good strength and toughness properties; CTOD values were greater than 0.27 mm at -20°C. A computational fluid dynamics model was developed and used to understand the effect of process parameters on flow patterns in the weld stir zone. Effects of welding process parameters on weld defects are discussed in this paper.