Friction stir seal welding (FSSW) tube-tubesheet joints made of steel

This paper demonstrates the feasibility of successful seal welding process of tube-tubesheet joints using the relatively new friction stir welding (FSW) process. The purpose of the reported study is to develop the process parameters and to test the feasibility of friction stir welding ASTM 179 seamless colddrawn carbon steel tube into an ASTM A516 Grade 70 tubesheet. All welds were performed in position control on a fully instrumented experimental friction stir welder using a watercooled tool holder and a shroud for argon shielding gas. A proprietary tungsten-rhenium pin tool with a 1.54 mm pin length and shoulder diameter of 4.9 mm was used to perform the seal weld between the roller expanded tube and tubesheet. A steel plug was employed during each weld in order to maintain support for the weld throughout the circumference of the weld. Sound welds were achieved in the FSW of ASTM 179 seamless cold-drawn carbon steel tube into an ASTM A516 Grade 70 tubesheet. Welding was improved by avoiding tool contact with the tube plug or the flash of the previous weld. Though a root void has been observed, which is typical of partial penetration butt welds, it is believed that the weld would still achieve a hermetic seal. Tool wear features of the W-Re pin has also been documented.