Failure analysis of gas turbine torque tube bolts

Abstract The cracking of torque tube bolts of a 130 MW gas turbine is investigated in the current work. Visual inspections along with microstructural and finite element analyses were performed for determining the cracking mechanisms. It was observed that the fracture surface was intergranular in appearance indicating crack growth along the grain boundaries. Furthermore, finite element results indicated that crack growth direction was relatively in accordance to the simulated stress distribution in the bolt. Microstructural analysis was performed and a continuous M23C6 carbide layer was observed along the grain boundaries. Although it was not clear what mechanism was responsible for the cracking, one potential mechanism of the cracking could be stress corrosion cracking (SCC). Remedial actions are proposed to minimize future occurrences of cracking.