Axial Compressor Rotor Repair With Solid-Hub Disc Replacement
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Solution Overview
Problem
The existing methods for repairing a gas turbine's multi-stage axial compressor rotor are burdensome, requiring the complete removal and replacement of the shaft to replace damaged bladed discs, which is time-consuming and costly, and necessitates the use of expensive, high-temperature-resistant materials like stainless steel.
Innovation Solution
The method involves cutting the rotor shaft to separate sections, using new discs with solid hubs and a new shaft end portion with solid cross-sections, and securing them with anchor bolts, allowing for easier replacement and reducing the need for heat-shrinkage and expensive materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heat-shrinkage method is used to secure bladed discs on shaft, then secure coupling is achieved, but repair becomes extremely burdensome requiring complete shaft replacement
Solution Approach 1:
The shaft is divided into two separate parts: a reusable portion with intact discs and a sacrificial portion that is removed and replaced. This segmentation allows the reusable portion to be preserved while only replacing the damaged section, dramatically reducing repair burden.
Solution Approach 2:
The sacrificial shaft portion is designed as a temporary, disposable component that is removed during repair. Instead of preserving the entire shaft, only the necessary sacrificial portion is replaced, reducing overall repair costs and complexity.
2Strength
If high interference fit is used for bladed discs on shaft, then secure coupling at high temperatures is achieved, but disc removal becomes impossible without damaging shaft
Solution Approach 1:
By segmenting the shaft into reusable and sacrificial portions, the design allows strong interference fits on the reusable portion while the sacrificial portion can be cleanly removed with discs attached, enabling easy disc replacement without compromising shaft integrity.
Solution Approach 2:
The sacrificial shaft portion containing the damaged discs is extracted and removed entirely. This extraction allows discs to be replaced without attempting to remove them from the reusable shaft portion, avoiding shaft damage.
3Ease of repair
If complete shaft replacement is performed to replace damaged discs, then all discs can be replaced, but repair time and costs increase significantly
Solution Approach 1:
The shaft is segmented into reusable and sacrificial portions, allowing only the necessary sacrificial portion to be replaced rather than the entire shaft. This dramatically reduces repair time while still enabling complete disc replacement.
Solution Approach 2:
The reusable shaft portion is recovered and preserved for future use, while only the sacrificial portion is discarded and replaced. This recovery approach reduces both time and material costs compared to complete shaft replacement.
4Temperature
If stainless steel is used for bladed discs, then high temperature resistance is achieved, but cost increases and hydrogen embrittlement occurs
Solution Approach 1:
Different materials are used for different portions: stainless steel discs maintain high temperature resistance where needed, while the sacrificial shaft portion uses less expensive material since it will be removed and discarded after serving its purpose.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces repair time and costs, enables the use of less expensive micro-alloyed steel, and simplifies future disc replacements by eliminating the need for complete shaft replacement and heat-shrinkage, while avoiding hydrogen embrittlement issues.
Implementation Method 1
heating the discs so as to increase the internal diameter thereof and thus reduce to zero the interference with the shaft
Data Source
Figure 1
Figure 2~3
AI summary
A method is described for repairing a rotor (10) of a multi-stage axial compressor of a gas turbine, by replacing a given number of last bladed discs (14N-2, 14N-1, 14N) with new bladed discs (14N-2", 14N-1", 14N"), wherein each of the last bladed discs (14N-2, 14N-1, 14N) to be replaced comprises a hub (16) having a central bore (20) and is mounted by interference fit on a shaft (12) of the rotor (10) rotatable about an axis of rotation (x). The method comprises the steps of: a) cutting the shaft (12) at a section plane (P) perpendicular to the axis of rotation (x) of the shaft (12) so as to separate the portion of the shaft (12) on which the bladed discs (14N-2, 14N-1, 14N) to be replaced are mounted from the remaining portion (12') of the shaft (12); b) providing, for each bladed disc (14N-2, 14N-1, 14N) to be replaced, a corresponding new bladed disc (14N-2", 14N-1", 14N") with a respective hub (16") having a solid cross-section; c) providing a new end portion (12") of the shaft with a solid cross-section; and d) clamping the new bladed discs (14N-2", 14N-1", 14N") between the remaining portion (12') of the shaft and the new end portion (12') of the shaft, securing them to the remaining portion (12') of the shaft by anchor bolts (28, 30).