Development of thermal stress concentration factors for life assessment of turbine casings

The major components of thermal power plants are made of low-alloy steel and operated under high temperature and pressure conditions. Even though such facilities have design lives of 100,000 h, unexpected failure can occur due to thermal fatigue or creep damages during operation. In particular, high-pressure and intermediate-pressure casing components are susceptible to frequent cracking due to thermo-mechanical low-cycle fatigue at the nozzle fit corner radius and other stress concentration shapes. Thus, for effective maintenance, it is necessary to have accurate knowledge of transient thermal stresses at critical positions that are susceptible to failure. In this paper, thermal stress concentration factors for the inner surface of the casing and valve are defined to account for variations in the geometry using three-dimensional finite element analysis. In addition, the total strain range is obtained to assess the low-cycle fatigue life according to the life assessment procedures in Korea.

► Analytical model of thermal stress concentration factors of casing was developed.
► TSCFs take into account variations in geometry through three-dimensional FEA.
► TSCFs from approximated equation correspondence with TSCFs from FEA.
► TSCFs from approximated equation is independent of disk length L.