Power Turbine Disk Machining for LTHC Corrosion Life Recovery
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Solution Overview
Problem
Power turbine disks in marine environments suffer from corrosion damage due to Low Temperature Hot Corrosion (LTHC), leading to degradation of mechanical properties and reduced operational life, necessitating a method to extend service life without compromising safety and reliability.
Innovation Solution
A repair method involving thermal analysis, machining to remove corrosion, and quality assurance through predicted safe cyclic life calculations and metallographic evaluations to ensure the machined disk meets new disk standards, including machining trials and residual stress evaluations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If corrosion damage is removed by machining the disk, then the mechanical properties and safety are improved, but the disk material is reduced and operational life is shortened
Solution Approach 1:
The patent performs comprehensive thermal analysis, stress analysis, and predicted safe cyclic life (PSCL) calculations before finalizing the machining depth. This preliminary assessment ensures that the maximum amount of material is removed only when necessary, preserving disk life while maintaining safety. The methodology includes conducting thermal analyses of both baseline and machined configurations, and calculating PSCL for critical features to determine the optimal repair strategy.
Solution Approach 2:
The patent systematically varies and optimizes multiple parameters including machining depth, thermal analysis parameters, and stress analysis parameters to find the optimal balance between removing corrosion and preserving disk life. By changing these parameters and analyzing their effects on PSCL and mechanical properties, the methodology determines the minimum necessary material removal while ensuring safety and reliability standards are met.
2Reliability
If extensive machining is performed to remove all corrosion, then the quality and mechanical properties are improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent applies partial machining action by determining the minimum necessary machining depth based on corrosion severity and PSCL calculations. Instead of uniformly machining the entire disk surface, the methodology targets only the affected regions with calculated precision, reducing manufacturing complexity while ensuring quality. The approach uses statistical methods to establish appropriate machining depths without excessive material removal.
Solution Approach 2:
The patent replaces extensive mechanical machining with a combination of thermal analysis and computational modeling to determine the optimal repair strategy. By using finite element analysis for thermal and stress calculations, and computational methods for PSCL prediction, the methodology reduces the need for trial-and-error machining operations, thereby simplifying the manufacturing process while maintaining quality standards.
3Reliability
If the disk is machined to a greater depth, then the corrosion is more effectively removed, but the residual stress and distortion increase
Solution Approach 1:
The patent incorporates feedback loops where thermal analysis and stress analysis results are used to adjust and optimize the machining depth. The process iteratively refines the machining parameters based on calculated thermal stresses and residual stress distributions, ensuring that corrosion is effectively removed while keeping residual stress within acceptable limits. The PSCL calculations provide feedback on whether the machining depth is appropriate or needs adjustment.
Solution Approach 2:
The patent performs preliminary thermal and stress analyses before machining to predict the residual stress distribution that will result from different machining depths. This allows the methodology to select a machining depth that effectively removes corrosion while minimizing the generation of harmful residual stresses and distortion, rather than dealing with stress management after machining is complete.
Data Source
AI summary
A repair method (72) for extending a service life of a power turbine disk (12) having corrosion damage, wherein the power turbine (14) includes stages (16, 18, 20, 22) and interstage gaps (26, 28, 30, 32). The method (72) includes conducting a first thermal analysis (74) of a baseline configuration of a baseline disk that does not have corrosion to determine a first steady state temperature distribution (44). A corrosion damaged disk (12) is then machined (76) to a depth suitable for repairing the corrosion to form a machined disk. A second thermal analysis (78) of the machined disk is conducted to determine a second steady state temperature distribution of the machined disk. A first predicted safe cyclic life (PSCL) (80) is then calculated for disk axisymmetric features (1-10) of the machined disk. A second PSCL (82) is also calculated for disk firtree features (70) of the machined disk. Further, the method (72) is qualified (84) to ensure that the quality of the machined disk is consistent with a new disk.