Extending the Lifespan and Performance of Gas Turbines: Paya Mavad’s Comprehensive Approach to Inner Casing Refurbishment
In the fast-paced world of energy production, gas turbines are the beating heart of power plants, playing a vital role in ensuring a stable electricity supply. These complex machines operate under extreme temperatures and pressures, exposing them to various mechanical and metallurgical degradations. Among the most critical internal components is the inner casing, which directs the flow of hot gases. Due to its exposure to a highly corrosive and high-pressure environment, this part requires specialized maintenance and refurbishment.
Completely replacing a gas turbine inner casing can be prohibitively expensive and time-consuming, significantly impacting the plant’s operational continuity and profitability. In this context, refurbishing and recovering worn turbine components offers a cost-effective and sustainable solution, helping to conserve resources and reduce environmental impact. Leveraging deep technical knowledge, advanced equipment, and extensive hands-on experience, Paya Mavad has emerged as a leader in this field, delivering comprehensive inner casing refurbishment services that meet the highest quality standards.
This article provides an overview of Paya Mavad’s multi-phase approach to gas turbine inner casing refurbishment — from initial component reception to final inspection and performance guarantee.
Phase 1: Reception and Initial Assessment – “As-Received” Condition Overview
The refurbishment process of the inner casing begins with the accurate reception and documentation of the worn component. After disassembly, the gas turbine inner casing is delivered to Paya Mavad’s specialized workshops, where it undergoes a comprehensive preliminary inspection. This phase includes several critical steps:
- Documentation Review and Material Identification:The first step involves verifying the received part against shipping documents and precisely identifying the alloy used — typically advanced nickel-chromium-cobalt superalloys such as Inconel 617.
- Non-Destructive Testing (NDT) and Dimensional Inspection:A meticulous visual inspection is conducted to detect any cracks, corrosion, erosion, deformation, or other visible damage. Dimensional measurements are taken to identify geometric deviations and non-conformities compared to original engineering drawings. In addition, Liquid Penetrant Testing (LPT) is used to detect surface-level cracks.
- Localized Wall Thickness Testing:Using ultrasonic testing techniques, the wall thickness is measured at critical points to assess material loss due to erosion or oxidation. These data are essential for determining the extent of required repair welding and for planning the next phases of the gas turbine refurbishment process.
At this stage, all findings are carefully recorded and documented This serves as a foundation for accurately planning the refurbishment and repair process of the gas turbine, as well as enabling a final comparison with the post-restoration condition of the part. The “as-received” condition often includes multiple cracks, severe corrosion, and significant deformations — all indicating a critical need for comprehensive refurbishment.
Phase 2: In-Depth Diagnostics and Degradation Mechanism Identification – Understanding the Root Causes
Following the initial assessment, the component enters a detailed metallurgical and mechanical diagnostic phase. The goal here is to gain a thorough understanding of the degradation mechanisms and the extent of damage at the microscopic level. This knowledge forms the basis for selecting the most appropriate restoration methods and estimating the remaining service life of the gas turbine components.
Due to the high-temperature and high-stress operating environment, the inner casing of the turbine is typically subjected to several major degradation mechanisms:
- Creep: Permanent plastic deformation that occurs at elevated temperatures under constant stress.
- Oxidation and Hot Corrosion: Chemical reactions between the material and hot gases result in oxide layer formation and gradual material loss.
- Thermal Fatigue: Repeated heating and cooling cycles create thermal stresses, which can initiate and propagate cracks.
- Loss of Ductility: Long-term structural changes in the material reduce its ductility, making it more susceptible to brittle fracture.
To identify and analyze these mechanisms, Paya Mavad utilizes advanced diagnostic tools and techniques:
- Metallography: Microscopic examination (using optical and scanning electron microscopes – SEM) to study the microstructure, grain size, carbide morphology, and signs of internal oxidation or corrosion.
- Mechanical Testing: Small samples are extracted from the component for tensile testing (at room and high temperatures) and creep testing. These tests determine the remaining mechanical properties and enable comparison with original material specifications and design standards.
This in-depth analysis provides a comprehensive picture of the material’s “health status” and identifies which areas require restoration, along with the most suitable techniques for recovering the mechanical and metallurgical properties of the material.
Phase 3: Refurbishment and Repair Strategies – Restoring Functionality
With a comprehensive understanding of the component’s condition, Paya Mavad develops a precise and customized plan for refurbishing the inner casing. This plan includes the following key processes:
Heat Treatment One of the most critical steps in restoring the properties of Inconel 617 is the annealing heat treatment. This process is carried out at controlled temperatures. The primary objective of annealing is to dissolve the large and continuous carbide precipitates present along the grain boundaries, which are responsible for material embrittlement. By redistributing alloying elements and forming finer precipitates, this operation enhances the material’s ductility and makes it more resistant to crack initiation and propagation.
Welding Repair To restore cracks, wear, and deformations, advanced welding processes are applied. Paya Mavad utilizes certified welding specialists and appropriate filler metals, such as Inconel 617, to precisely repair damaged areas. All welding is performed according to the Welding Procedure Specification (WPS).
Dimensional and Surface Restoration Any deformation, wear, or dimensional loss is corrected using precise dimensional restoration methods, including welding and machining, to return the component to allowable tolerances. This stage is particularly critical for parts such as “castles” or “disks,” which are frequently subjected to wear and distortion.
Phase Four: Quality Control and Performance Verification – Ensuring Final Quality
- After the completion of the refurbishment processes, the gas turbine inner casing undergoes a series of precise quality control (QC) tests to ensure that the component has been restored to the required standards and is ready to return to service:
- Final Visual and Liquid Penetrant Testing (LPT):The component is thoroughly inspected once again, both visually and using LPT, to ensure that no new surface cracks have developed and that all previously identified cracks have been fully repaired.
- Final Dimensional Inspections:Key dimensions of the inner casing are re-measured and compared against standard tolerances and original engineering drawings to confirm geometric accuracy and ensure compatibility with final assembly.
- Final Wall Thickness Testing:The wall thickness in critical areas is re-measured to confirm that the repair processes have restored sufficient and safe thickness levels.
- Post-Rebuild Mechanical Testing:New samples are extracted from the refurbished component for tensile and creep testing. The results are compared with the “as-received” condition and the properties of the original material. This comparison validates the success of the refurbishment process in restoring the material’s mechanical integrity.
Phase Five: Remaining Life Assessment and Warranty – Ensuring the Future
One of the key advantages of gas turbine component refurbishment by Paya Materials is the precise evaluation of the component’s remaining life (Remaining Life Assessment – RLA). Using advanced engineering methods such as the damage fraction rule and fracture mechanics- and creep-based approaches (e.g., the Larson-Miller method), Paya Materials’ experts predict the remaining useful life of the inner casing. This estimation is based on the component’s operational history, metallurgical and mechanical test results, and consideration of all degradation factors.
For the gas turbine inner casing, after restoration and rejuvenation processes and under optimal operating conditions, Paya Materials provides an estimated additional useful life of about 35,000 hours, equivalent to 4 years. This predictive capability helps power plant operators optimize their maintenance schedules and avoid sudden and costly shutdowns.
As a symbol of confidence in the quality and performance of Paya Materials’ refurbishment processes, the company guarantees the performance of the refurbished inner casing for 8,000 operating hours or 12 months after delivery (provided proper operation). This warranty assures operators that their investment in refurbishment will yield sustainable results.
Conclusion: Sustainable Value Creation with Paya Materials
The refurbishment of gas turbine inner casings by Paya Materials is more than just a simple repair; it is a comprehensive, engineering-based process that, using up-to-date metallurgical knowledge, advanced inspection and repair techniques, and rigorous quality control, leads to the full restoration of performance and a significant increase in the service life of these critical turbine components.
This approach not only substantially reduces the operational costs of power plants and optimizes the utilization of existing assets, but also helps protect the environment and promote a circular economy by reducing the need for new part production. With a commitment to delivering the highest quality and ensuring reliable performance, Paya Materials is a trusted partner for power plants on the path toward efficiency and sustainability in energy production. Choosing Paya Materials is a smart decision for longer lifespan and flawless operation of your gas turbines.
