Fatigue strength of electron beam welded stainless steel pipe

For the cooling pipes for multi-purpose high temperature gas reactors, multiple wall pipe structure is adopted, and because the maintenance of high degree of straightness is required, electron beam welding is employed. As for the form of welding joints, the joints with underlips are adopted in most cases for maintaining the straightness and preventing contamination due to burn through and sputtering. Most of the underlips are removed, but it is impossible to remove in some places. It is necessary to examine thoroughly the fatigue strength of the joints with underlips having notches and Uranami joints. In this study, the plate and cylindrical test pieces were used to test the electron beam-welded joints of SUS 316 steel pipes, and the fatigue strength at room temperature and 500 deg. C was examined. The joints from which underlips had been removed showed good fatigue strength same as the parent material. The fatigue strength reduction coefficient for the cylindrical test pieces of the joints with underlips was 2.4 at room temperature and 2.7 at 500 deg. C. When the difference in the wall thickness to be welded is small, the coefficient becomes smaller. In case of Uranami joints, the coefficient determined with plate test pieces was 1.3 at room temperature and 1.05 at 500 deg. C, accordingly practically it does not matter. (Kako, I