NEWSROOM

By Tom Reid, Vice President of Power Generation Services, ENTRUST Solutions Group

Gas turbine hot-section hardware requires regular refurbishment after a specified number of operating hours, stop-start cycles or a combination of the two. These repairs are critical to maintaining optimal performance and extending the life of the equipment. However, the repair processes present significant challenges due to the variability in part conditions, process complexities and the human element. 

To ensure success, careful attention and expertise must be applied to every stage of refurbishment.

Key Gas Turbine Repair Processes

1. Inspection
2. Coating Removal
3. Joining
4. Machining
5. Coating Application

Common Failure Mechanisms

Key failure mechanisms for hot-section hardware include oxidation, creep, cracking and dimensional distortion. It is vital to conduct robust incoming inspections to accurately define the repair scope and identify unrepairable hardware from the outset.

Coating Removal

After a service interval, coatings are typically depleted or spalled. Ceramic coatings are removed through abrasive grit blasting, while metallic bond coats are removed via acid stripping. 

Common issues include excessive base metal removal, inter-granular acid attack and incomplete coating removal. These challenges require precision to mitigate potential damage.

Repairing Cracking

Cracking from thermal-mechanical fatigue is often present and can be particularly challenging to repair, especially with the increased use of nickel-based superalloys. Welding and brazing are the most common processes for addressing cracks. 

Factors such as material selection, surface preparation and pre- and post-process heat treatment significantly impact the quality of repair.

Machining and Dimensional Restoration

Material build-up and machining are often necessary during refurbishment. Processes such as tip repair or hard face restoration must address part creep and distortion, which complicate achieving desired dimensional results. 

Reliable fixturing and adaptable machining techniques are critical to maintaining precision despite the variability in part condition.

Coating Reapplication

Thermal spray processes are frequently used to apply new coating systems to hardware. Recoating existing components, especially those with features like cooling holes and seal slots, is more complex than coating newly manufactured parts. 

Factors affecting coating quality include part geometry, pre-heat temperature, surface preparation, gas and powder properties and coating gun condition.

Recommended Guidelines to Enhance Repair Quality

1. Get Engaged Early in the Process

• Develop a comprehensive repair specification that leverages lessons learned from previous repairs and industry best practices.
• Define review points at key stages of the repair process to ensure accurate execution.
• Proactively discuss non-conformances or deviations to address issues promptly.
• Whenever possible, visit the repair facility and audit the process firsthand to ensure alignment with specifications.

2. Integrate Thorough Quality Checks

Inspection is crucial to achieving satisfactory results. Incorporate the following quality checks at key process stages:

• Non-Destructive Testing (NDT): Ensures no hidden defects are present.
• Destructive Testing (Material Samples): Validates processes like coating removal and reapplication without sacrificing critical components.
• Flow and Pressure Checks: Verifies air and fuel systems remain uncompromised.
• Coating Thickness Checks and Cooling Hole Blockage Analysis: Confirms proper coating application and functionality of cooling systems.

These checks contribute to verifying that the refurbishment meets stringent quality requirements.

3. Review Post-Repair Documentation and Perform Visual Inspections

After repairs are completed, carefully evaluate the results and documentation.

• Review the scope of work and ensure tasks were completed as specified.
• Conduct dimensional inspections, verifying that key metrics such as blade movement weights, flow areas and harmonics conform to acceptable tolerances.
• Look for outliers in measurement data to identify potential inconsistencies.
• Perform a final visual inspection to ensure no issues were overlooked.

Investing the time to conduct these additional steps ensures the equipment is ready for reliable operation.

Moving Forward with Confidence

Active involvement in the refurbishment process is essential to achieving successful results. This begins with a well-defined repair specification, extends through ongoing collaboration during the repair process and concludes with a rigorous review of post-repair documentation.

Finally, don’t skip the step of examining parts upon receipt. Carefully removing and inspecting refurbished hardware before use ensures minor issues are caught early, avoiding significant operational consequences.

At ENTRUST Solutions Group, we specialize in providing expert guidance and comprehensive support for gas turbine part refurbishment. By investing in a thorough refurbishment process, turbine operators and maintenance teams can confidently achieve the desired maintenance intervals and extend the life of their critical assets.

For more information or further assistance on your gas turbine part refurbishment needs, reach out to ENTRUST Solutions Group and speak with one of our experts today!

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Tom has spent the entirety of his 15-year career in the power generation industry. 

In his current role as Vice President of Power Generation for ENTRUST, Tom oversees a team of approximately 100 engineers, whose expertise covers power plant equipment, modeling, and testing. 

Prior to ENTRUST, Tom held turbine design and repair roles at General Electric. Tom is a graduate of GE’s Edison Engineering Development Program and holds 7 U.S. patents. He holds an BSME degree from Virginia Tech, an MSME degree from Georgia Tech, and is a registered professional engineer in the state of Delaware.