Application of Magnetic Stir Welding to Dissimilar Metal Structural Weld Overlay

Abstract

Alloy 600 and associated welds, Alloy 82/182 of the Pressurized Water Reactor (PWR) plants have been known as being susceptible to the Primary Water Stress Corrosion Cracking (PWSCC). Dissimilar metal (DM) piping butt welds were welded with Alloy 82/182. As one of the mitigation techniques of the PWSCC, Structural Weld Overlay (SWOL) has been applied to the DM welds, but it has tendency to occur weld cracks on the first layer. One of the reasons of the weld cracks is the sulfur which is highly contained in stainless steel base metals, because old stainless steels would contain higher sulfur (e.g. 0.02%) than later ones. In response to this situation, Magnetic Stir Welding (MSW) was proposed to apply for the first layer of SWOL, and tested to evaluate its weldabilities. MSW has been developed for several years, and it is generally known that MSW has characteristics to improve a heat transfer in the molten pool, so that it could reduce a dilution. The purpose of this study is to evaluate weldabilities of MSW for welding Alloy 52 and/or Alloy 52M as filler metal on high sulfur contained stainless steel pipe. Single bead tests and all position welding tests were conducted. As a result of this study, MSW can prevent from occurring weld cracks and lack of fusion due to stirring effects of the molten pool. Therefore, SWOL can be welded without weld cracks on the first layer by applying MSW, even though the stainless steel base metal contains relatively high sulfur. In addition, MSW can weld at high wire supply rate because of prevention of lack of fusion. So it could improve weld efficiency.