Evaluation of Economic Incentives and Weld Properties for Welding Steel Pipelines Using Friction Stir Welding

摘要

Pipelines have long been a key component in the transportation andrndistribution of petroleum resources. Reducing the cost of pipelines tornimprove the economics of transportation is critical to the cost effectiverndevelopment of resources in remote locations. This paper addresses therneconomics of using friction stir welding (FSW) for pipelinernconstruction and also documents a study concerning the welding of linernpipe steels.rnAn economic analysis of pipeline construction costs was conducted torncompare FSW to construction using conventional gas metal arc weldingrn(GMAW). Both offshore and onshore pipeline construction scenariosrnwere considered in the study. Several assumptions were made duringrnthe study with respect to factors such as FSW tool cost and weldingrnproductivity. It is estimated that FSW offers about 25% and 7%rnconstruction cost savings for offshore (J-lay) and onshore construction,rnrespectively.rnSeveral line pipe steels were welded using different process parameters.rnWeld properties were evaluated using microhardness tests, all-weldmetalrntensile tests and crack tip opening displacement (CTOD) tests.rnPrior austenite grain size in the stir zone was calculated from electronrnback-scattered diffraction (EBSD) patterns. Of the X65 linepipe steelsrntested, all showed good strength and toughness properties; CTODrnvalues were greater than 0.27 mm at -20°C. A computational fluidrndynamics model was developed and used to understand the effect ofrnprocess parameters on flow patterns in the weld stir zone. Effects ofrnwelding process parameters on weld defects are discussed in this paper.