J K Sahu

The influence of high-temperature oxidation resistant titanium aluminide coating on low-cycle fatigue behaviour of titanium alloy IMI 834 at 600 °C

The low-cycle fatigue behaviour of titanium alloy IMI 834 was comparatively studied in bare condition and with titanium aluminide (Al2Ti) coating at 600 °C in air. Results revealed that at higher values of total strain amplitudes (Δεt/2), Al2Ti-coated IMI 834 alloy has longer fatigue life (Nf) compared to the bare IMI 834 alloy, which appears to be due to load shifting to the coat. At lower values of Δεt/2, Al2Ti coating on IMI 834 alloy seems to have no effect on Nf. Higher values of cyclic strength coefficient (K′) and cyclic hardening exponent (n′) for coated IMI 834 alloy indicate that coating offers resistance to cyclic plastic deformation at 600 °C in air, and hence it is beneficial. The coating adheres well to the substrate and is also fairly resistant to high-temperature corrosion in sea water atmosphere at 600 °C.

Phase transformations and numerical modelling in simulated HAZ of nanostructured P91B steel for high temperature applications

This paper critically assesses phase transformations occurring after welding and subsequent post weld heat treatments in simulated sub-heat affected zones (HAZ) of P91B steel. Samples for weld-HAZ simulation were produced corresponding to grain-coarsened HAZ, grain-refined HAZ and inter-critical HAZ. Analyses revealed diverse phase transformation mechanisms (for GCHAZ = pipe-diffusion and for GR/ICHAZ = GB-diffusion) owing to manipulation in grain size and boron-enriched nanosized particles as regards virgin steel after welding. However, after PWHT, same phase transformation mechanism (interface diffusion) in all simulated sub-HAZs is observed. Hardness evaluations and prior austenite grain boundaries dissolution confirm GB embrittlement after welding. Boron segregation, the presence of borides and boron-enriched particles heads to ~ 50% drop in hardness deviations enhancing GB hardening after PWHT. Particle refinement is observed after PWHT which is further validated by numerical modelling. In addition, particle evolution during cooling from peak temperature of weld thermal cycle and isothermal holding of PWHT is analysed. Apparent activation energy of nucleation/growth follows descending order, i.e. GC/GR/ICHAZ for nanosized particles during welding.

Stress Analysis and Creep Behavior of Service Exposed Primary Superheater Tube in a Thermal Power Plant

The elastic, inelastic deformation and stress distribution pattern of a seventeen years service exposed primary superheater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element computer code ANSYS was used for stress analysis. The methodology is a valuable design tool for development of new boiler tubes as well as for considering the effects of numerous operating variables on creep life. The health of the tube was also assessed based on microstructure, hardness and a few conventional creep tests carried out at 500 degrees C at various stress levels (40-177 MPa). Results revealed that there was not much variation in the microstructure and hardness of the service exposed tubes compared to the virgin material. Creep deformation behavior of the service exposed and virgin tubes of the same material at 40 MPa reveal that deterioration of the creep properties fall within the 20% scatter band, which is well within the specified limits of ASTM standard. The service exposed primary superheater tube is thus in a good state of health.

Creep Behaviour and Stress Analysis of a Seventeen-Year Service-Exposed Primary Super Heater Tube in a Thermal Power Plant

Abstract The elastic, inelastic deformation and stress distribution pattern of a seventeen year service-exposed primary super heater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element computer code ANSYS® was used for stress analysis. The methodology is a valuable design tool for development of new boiler tubes as well as for considering the effects of numerous operating variables on creep life. The health of the tube was also assessed based on microstructure, hardness and a few conventional creep tests carried out at 500 °C at various stress levels (40 to 177 MPa). Results revealed that there was not much variation in the microstructure and hardness of the service-exposed tubes compared to the virgin material. Creep deformation behaviour of the service-exposed and virgin tubes of the same material at 40 MPa revealed that deterioration of the creep properties fell within the 20% scatter band, which is well within the specified limits of ASTM standard. The service-exposed primary super heater tube is thus in a good state of health.