A Study on the Economic Incentives of Welding Steel Pipelines Using Friction Stir Welding

摘要

Pipelines have long been a key component in the transportation and distribution of petroleum resources. Reducing pipeline cost to improve the economics of transportation is critical to the economic development of resources in remote locations. This paper addresses the economics of using friction stir welding (FSW) for pipeline construction. An economic analysis was conducted to compare pipeline construction costs based on the use of FSW versus conventional gas metal arc welding (GMAW). Both onshore and offshore pipeline construction scenarios were considered in the study. The onshore GMAW scenario was based on internal root welding followed by external (bug and band) mechanized GMAW. The offshore scenario was based on the J-lay technique where all welding is conducted from the outside of the pipe at a single welding station. The base case pipe diameters for onshore and offshore were assumed to be 42" and 12", respectively. For the purposes of the study, it was assumed that non-destructive evaluation (NDE) costs and repair rates would be equal between GMAW and FSW. Several assumptions were also made during the study with respect to such factors as FSW tool cost and tool life based on laboratory experience with FSW of pipeline steel. The analysis resulted in an estimate that FSW offers about 7% construction cost savings for onshore construction. It was also concluded that the use of an internal GMAW root weld to support an external FSW butt weld is significantly more efficient for large diameter, onshore construction than using an internal mandrel to support the FSW process. The estimated savings for J-lay offshore construction using the FSW process was found to be approximately 25%. For both the onshore and offshore scenarios, the sensitivity of the expected savings to key factors is presented. These key factors include: FSW equipment and tool costs, tool life, welding speed, and pipe wall thickness. It was found that savings increase with increase in wall thickness due to replacement of multiple arc welding passes with a single FSW pass.