Damage behaviour of nickel-based transition welds under cyclic thermomechanical loading

Abstract

The present study was performed on dissimilar nickel-based transition girth welds on superheater tubes. The results of a testing programme including tube tests under cyclic pressure, axial load and thermal loading with dwell times at 625°C will be presented. The pressure and the axial load were varied between 290 and 480 bars, 0 and 42 kN respectively. For testing times below 8,000 hours, failure occurred in the X10CrMoNbV9-1 tube, however, not at the fusion line to the NiCr20Nb weld metal. However, for the longest testing time of 20,000 hours, high-resolution scanning electron microscope investigations showed significant microstructural changes at the fusion line. Single creep cavities were observed in the interfacial region of the martensitic steel when a crack had propagated there from an oxide notch at the tube surface.