Flange Bolt Hole Coating for Permanent Corrosion Repair
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Solution Overview
Problem
Current repair methods for corroded flange bolt holes in gas turbine engines, particularly those made of martensitic stainless steel, are inadequate as they do not provide a permanent solution to pitting corrosion and can lead to repeated repairs due to the sacrificial nature of aluminum slurry coatings and potential hydrogen embrittlement.
Innovation Solution
A coating system comprising a corrosion-resistant layer, such as nickel super alloy or ceramic materials like titania and alumina, applied over a sacrificial aluminum layer, which is applied via thermal or cold spray processes, providing a permanent barrier against corrosion and improving mechanical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum slurry based coating is applied to protect against corrosion, then corrosion resistance is improved, but the coating is sacrificial and loses efficacy over time leading to repeated repairs
Solution Approach 1:
The patent applies a composite coating system consisting of multiple layers: a corrosion-resistant topcoat layer (such as ceramic or metallic) over a sacrificial aluminum slurry layer. This composite structure combines the long-term protection of the corrosion-resistant topcoat with the galvanic protection of the aluminum layer, eliminating the need for repeated repairs while maintaining effective corrosion resistance throughout the service life of the component.
2Reliability
If sacrificial aluminum coating is used for corrosion protection, then corrosion resistance is improved, but reduction reactions generate hydrogen leading to hydrogen embrittlement
Solution Approach 1:
The patent extracts or removes the harmful byproduct (hydrogen) from the corrosion protection process by using a corrosion-resistant topcoat layer that prevents the sacrificial aluminum from undergoing reduction reactions. This isolates the beneficial galvanic protection function from the harmful hydrogen generation, allowing the aluminum layer to provide cathodic protection without generating embrittling hydrogen in the martensitic stainless steel substrate.
3Reliability
If reaming process is used to flush pits, then corrosion damage is removed, but the hole dimensions approach the allowable limit requiring welding and re-drilling
Solution Approach 1:
The patent applies the coating system as a preliminary protective measure before the component reaches critical wear limits. By coating the flange bolt holes with a corrosion-resistant topcoat over a sacrificial aluminum layer, the system prevents pit formation and progression, eliminating the need for subsequent reaming, welding, and re-drilling operations. The coating maintains hole dimensions within allowable limits throughout the component's service life.
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
The coating system effectively reduces the occurrence of corrosion, eliminates the need for repeated repairs, and enhances the mechanical integrity of the components, reducing the risk of hydrogen embrittlement and maintaining effectiveness even at elevated temperatures and in humid environments.
Implementation Method 1
applied via thermal or cold spray processes
Implementation Method 2
applied via thermal or cold spray processes
Implementation Method 3
the aluminum slurry based coating is sacrificial and may lose its efficacy over a period of time. In addition, the reduction reactions that take place during the sacrificial corrosion process
Data Source
Figure 1~2
Figure 3A~3C
Figure 4
AI summary
Methods for repairing flange bolt holes and the resulting flange bolt holes are provided. The methods and products include the incorporation of a coating system comprising a corrosion resistant layer, which can be formed by resistance plug welding, slurry or sol-gel processing, or thermal/cold spray processing. The corrosion resistant layer can be a super alloy or ceramic material and is different than the base material of the flange bolt hole. Corrosion of the flange bolt hole can be reduced or prevented from occurring with the use of the coating system.