Evaluation of a Fractured Gas Turbine Alloy 718 Rotor Bolt

A metallurgical evaluation was performed on a marine and industrial gas turbine LPT rotor bolt after it fractured/liberated in-service. The bolt was discovered after a borescope inspection and revealed extensive downstream damage resulting in customer disruption and high replacement costs. The evaluation found that the bolt fractured with features consistent with sustained-peak low-cycle fatigue (SPLCF) that initiated at the base of a pre-crack with features consistent with assembly damage.