Section I of the ASME Boiler and Pressure Vessel Code currently has a Code Case that provides rules for the construction of unstayed flat heads with integral flanges (butt welded hubs) from forged material. This Code Case is currently being considered for adoption into the Section I rules; therefore, the existing requirements of the Code Case are under review. In particular, feedback on the Code Case indicated that the required minimum hub length presents manufacturing challenges in certain situations, so the necessity of this hub is being reviewed. As this type of flat head is commonly used in high temperature operation, evaluation of the expected creep behavior is critical, especially in the proposed weld area at the head junction to the attached shell (typically a header). Example geometries were developed using the current Code Case requirements and their suitability for high temperature operation was initially evaluated using elastic analysis. Detailed inelastic analysis was then performed to further quantify the expected time-dependent high temperature behavior. Additionally, a series of failures of end plates designed to the TRD code was reported to have occurred in Europe in the 1990s. In order to assess the potential relevance of these failures to heads designed per the proposed Section I rules, additional examples were developed using the design rules of the TRD code rules. The predicted creep behavior and damage for these examples were then compared to the Code Case designed examples.

A case study for life prediction of Grade 91 heat recovery steam generator (HRSG) superheater outlet header of typical combined cycle power plants (CCPP) is presented in this paper. The effect of high cycling and fast startup along with elevated design temperature and pressure on the creep life is studied. A consistent material model based on MPC Omega is used to evaluate the creep damage of HRSG header components. In addition, a robust unified constitutive model (UCM) based on continuum damage mechanics (CDM) (see [1]) is used for creep-fatigue damage evaluation of the header components. The performance of the UCM is compared against creep and damage focused models in predicting the life of HRSG header components subjected to steady operation condition with low cycle fatigue scenario.