Recent, brittle fracture in Grade 23 power plant components at relatively low temperatures has increased the need to assess the cracking behavior of this material. Time-dependent cracking in the heat-affected zone of Grade 23 weldments was assessed using crack growth testing of subsize compact tension specimens at a temperature (482°C, 900°F) characteristic of the upper portion of a furnace wall in supercritical boilers. Results of additional testing at a higher, typical design temperature (566°C, 1050°F) for superheater and reheater tubing and headers will be reported later. Post-test metallurgical evaluation of the cracking morphology was conducted using traditional light microscopy and laser microscopy. Although large-scale creep deformation is absent under these lower test temperature conditions, significant weldment heat-affected zone intergranular cracking was documented. An example of application of the data to the inservice integrity and life assessment of a furnace tube is also described, providing preliminary perspective on the factors controlling lifetime and manageability of integrity.
Paper published with permission.