Investigations on creep life of Alloy 617 material for the final stage superheater coils for ultra super critical thermal power plants

Abstract

Thermal power plant will continue to cater to the power demand of India at least for two more decades. Research is going on continuously to increase the temperature of operation of the materials used in power plant to increase the operating efficiency, conserve the fuel and reduce the environmental impact of power generation. Superheater coils made of nickel based alloys have an advantage over conventionally used materials like AISI 316, P91, P92 in powerplants. In the present work, an attempt is made to understand the creep related life of nickel based superalloy, Alloy 617 material in India powerplants. Alloy 617 can be a potential material for an ultra-super critical powerplant as it is known to withstand temperatures of around 700 °C and supercritical pressure upto 300 bar. These parameters significantly higher than the present operating values of 600 °C and 250 bar pressure in a typical Indian scenario. Extensive literature survey was carried out to understand the existing creep models, the thermophysical properties and parameters for evaluating Larson-Miller Parameter (LMP). Heat transfer simulation was carried out using ANSYS to predict the temperature field and the hoop stresses induced in the final stage of super heater coil exposed to the severest operating conditions in the power boiler, was predicted based on the boiler operating pressure in the ultra-super critical region. Formation and growth of oxide scale was not considered in the present model as literature suggests that the rate of oxide formation is negligible for the present material at 700 °C. Hoop stress and temperature distribution were used to predict the total life by applying Larson Miller Parameter approach. Robinson’s damage summation rule was attempted to determine the creep life of the material for the above conditions. Based on the analysis, it is observed that Alloy 617 can be the most suitable material for final stage superheater coil operating at around 700 °C.