A case study investigation into the effects of spatially dependent convection coefficients on the fatigue response of a power plant header component

Abstract

Societal and environmental pressures are forcing thermal power plant operators to deviate greatly from the generation strategies of the past. The application of high frequency start up/shut down/partial load cycles to components that may well be outside their design life makes research into the long-term integrity of at risk assets paramount. Decoupled thermal/mechanical analyses have been used in the literature to estimate anisothermal fatigue in header components, with convective boundary conditions typically assumed for internal surfaces in order to determine heat fluxes and hence a temperature field. In reality, convective coefficients are heavily dependent upon local velocity profiles. In the present work, computational fluid dynamics is used in order to better approximate the steam flow in a real power plant header, leading to a convection coefficient field that is used to solve the thermal problem. Anisothermal fatigue analysis is finally conducted using a Chaboche type model. The results of computational fluid dynamics have illustrated that heat transfer coefficient values can vary (spatially) by a factor of 5.49 over the internal header wall, with noticeable hot spots in the wake of the stub penetrations. Peak differences of 6.47% in accumulated plastic strain levels have been observed between simulations conducted with constant (simplified) and variable (computational fluid dynamics derived) thermal boundary conditions.

On the use of small ring testing for the characterisation of elastic and yield material property variation in additively manufactured materials

“…Initial conditions derived from this "conventional" data will subsequently be modified in the optimisation procedure so that FEA elastic-plastic model results match a given set of experimental data. For the sake of brevity the material parameter fitting procedure is omitted here, however it should be noted that it is based on Cottrell's stress partitioning method [44], uses a linear regression approach to determine the onset of plasticity, and may be found in the author's previous work [45,46,47]. The well known Ramberg-Osgood equation (see equation (28), where E RO , K RO , and n RO are fitting parameters) is used as a smoothing function in this procedure to limit the effect of noise in the experimental data.…”

Fatigue Life Assessment of the Shell Structure of Purified Terephthalic Acid Filter Press

“…Usually, the researchers mainly focus on the single weld joints in the laboratory [ 5 ], which is independent of the complex structure. However, the weld joints are exposed to more complicated conditions, e.g., the combination of weld residual stress [ 6 , 7 ], the thermal stress [ 8 ], the external loads [ 7 , 9 ], post-weld heat treatment [ 7 ], etc. Those studies are bound to show different fatigue failure mechanisms.…”