High cycle fatigue is a factor that influence gas turbine buckets lifetime and it’s due to high frequency vibrations during service. Rotation and fluid flow around the blades cause static and dynamic stresses on the buckets row. For this reason the natural frequencies and HCF resistance evaluation are fundamental in the design phase of gas turbine engines in order to avoid resonance problems during service. Single crystal and directionally solidified superalloys shows anisotropic material properties, in particular single crystal can be modeled as orthotropic material in lattice directions for FEM simulations purposes. In this paper the influence of the lattice growth orientation, identified by two angles, on the natural frequencies of first stage bucket has been investigated. Six-sigma analysis has been performed in order to obtain a transfer function between lattice orientation and bucket vibration. The Design of Experiment (DoE) has been performed using FEA modal results on ten different vibration modes. The results obtained by FEA are verified by an experimental test on the real Heavy Duty MS5002 buckets.

Fatigue impacts the life of all components subject to alternating loads, including lube oil injection quills. These occurrences are more frequent if a defect (initial flaw) nucleates in the component due to corrosion, high stress, machining imperfections, etc. The design of components undergoing high fluctuating pressures needs advanced technologies, like autofrettage, and design methods, like FEM or fracture mechanics. This component can be identified as a cylinder with different outside diameters and notches deriving from the geometry variation and threaded connection. The inner diameter is the most stressed area and will require an adequate stress analysis. A sensitivity analysis of the autofrettage pressure can be performed to identify the most appropriate residual stresses on the inner diameter and to obtain a threshold defect larger than the minimum detectable. Fracture mechanics allows the analysis the propagation of an initial defect with materials having different properties and considering different autofrettage pressures. Finite Element Analysis is used to validate the residual stresses predicted by calculation for each autofrettage pressure. An optimized solution of the hypercompressor injection quill can be designed.

The successful growth of an EHS culture, focus on equipment availability and reliability, as well as continuous pressure on increased production is causing a higher demand for improvements in Root Cause Analysis (RCA) quality and speed of completion. Root causes investigations need to be driven to a strong level of understanding and resolution to guarantee safe operation, to optimize production and to reduce costs. RCA processes are many times based on different disciplines to investigate the most challenging failures having the following characteristics: - Top Critical: potential impact on safety and production; - First occurrence: no similar cases investigated before; - Lack of information: no operation data and only fragmented information available. In these cases only a multi disciplinary approach allows studying various aspects of the failure and validating the results as an overall system solution. In this paper the authors present a recent study where finite element stress model calculations, metallurgical laboratory analysis (fractography examination, mechanical testing, fracture mechanics), dynamic analysis, fatigue tests and field measurements were used to investigate causes of coupling failure and determinate corrective actions. Results of each study are presented with special focus on comparative analysis and data matching.