Note on Shear Load-Testing Feedwater Heater Tube Joints

Abstract

This paper describes some results of shear load testing of welded and hybrid expanded tube–to–tube-sheet joints. The construction consisted of strength welding SA-688-TP 304N tubes to SA350LF-2 tube sheets clad with stainless-steel type 308∕309 weld wire followed by hybrid expanding the tubes into the full thickness of thick double-grooved tube sheets. The author theorizes that the mechanism that led to all failures reported to have occurred in the welds∕heat-affected zones instead of the anticipated tube yielding resulted from loss of interfacial pressure between the expanded tubes and surrounding ligaments. The author further speculates that elastic and plastic tube deformation during application of axial loads during shear load testing caused loss of interfacial pressure, which eliminated the holding capacity of the expanded-in length of tubes and that there was sufficient flattening of the tube metal deformed into the annular grooves to permit the applied loads to be carried to the welds.