Investigation into thermal stresses in gas turbine transition-piece: Influence of material properties on stress levels

Transition-piece accommodates hot gas emanating from the gas generator and received by the power turbine. The thermal stress developed in the outer wall casing of the transition-piece reaches high levels due to attainment of high temperature. In the present study, flow through a transition-piece resembling the actual gas turbine operation is considered and thermal stress levels in the outer casing of the transition-piece are computed. In order to demonstrate the material response to the high temperature, the substrate material (AISI 660 stainless steel or A286 iron-base superalloy) of the transition-piece is heat treated at elevated temperature for 2 h. Tensile and three-point bending tests are accommodated to determine the elastic modulus of the heat treated and as-received materials. In the numerical simulation of the flow and temperature field, the control volume approach is introduced while stress field is computed using the finite element model. It is found that the elastic modulus of the heat treated specimen is considerably lower than that of as-received material. This is because of the formation of η-phase (hcp-Ni3Ti) and dissolution of γ′ at the grain boundaries. Consequently, von-Mises stress level is significantly lower for the transition-piece subjected to the heat treatment than that of the as-received transition-piece material.