Mechanical Dynamics & Analysis (MD&A) can extend the service life of gas turbine components whose OEM service limit has passed or whose configuration is no longer suitable to operate. Significant savings can be realized by opting for lower-cost repaired spares instead of new parts.
Elevated temperatures take a big toll on gas turbine components. Repair enhancements can extend a part’s life by slowing its degradation and extending its usable service life.
Formerly PW Powers Systems’ IGT division, the MD&A San Antonio Texas Service Center team have years of experience evaluating the life-limiting factors for gas turbine vanes and blades. Such factors include cracks, corrosion, wall thickness, and material condition. Most crack limiting locations are found at the platform or shroud transition. Smaller percentages occur at the blade tip, the blade airfoil, or the root. Vane limiting factors are usually related to the wall thickness and material condition.
Platform degradation can be reduced in many ways: by operating in base load only ( although dispatch conditions may prevent that from being a practical solution), by pursuing a robust platform weld repair program, by improving the integrity of the platform coating, and by making platform improvements.
Thermal mechanical fatigue cracks will eventually lead to platform failure. Design modifications often are required, incorporating a robust repair procedure. The life cycle enhancement process used by our experts exceeds OEM platform properties.
Our experts at the San Antonio Service Center combine years of experience with state-of-the-art equipment to deliver exactly the right solutions to your specific set of parts!
7EA 2nd Stage Blade Case Study
Our San Antonio facility evaluated two sets of 7EA 2nd Stage Blades to determine if they are capable to operate for a third service interval. The blades had previously operated through two service intervals and underwent one repair.
An x-ray inspection was performed on the components in their as-received condition. No areas of concern were detected, and no clogging was observed on the cooling holes.
An FPI inspection was performed to look for the presence of cracks. The area around the shroud radius was also evaluated for cracks. No major areas of concern were found during the preliminary FPI inspection.
The condition of the internal coating was deemed acceptable and in good condition to operate for one more service interval. The external coating protected the external surfaces and was recommended for removal to allow a good FPI inspection of the hot gas-path surfaces.
Microhardness readings taken at several blade locations showed a significant drop in the base material hardness where parts had been exposed to higher temperatures. These areas also showed significant degradation to the gamma prime structure under inspection by a Scanning Electron Microscope.
Hardness values after heat treatment demonstrated that the GTD 111 responded well to the process and the overall blade hardness values were improved.
For heat treatment, our experts utilize a vacuum heat treat furnace, where we control the heating and cooling of metals to alter their physical and mechanical properties. The specific heat treatments selected for a set of parts depend on a number of factors. Several separate heat treatment cycles are conducted throughout the course of repair including 1) pre-weld solution heat treatment, 2) post-weld stress relief heat treatment, 3) coating diffusion, and 4) precipitation hardening (or aging) heat treatment.
Samples were removed from the blades for stress rupture testing and in the as-received condition did not meet the minimum expected strength requirements for GTD 111. The samples tested after heat treatment exceeded the minimum requirements.
After the repair heat treatment, the stress rupture test results improved by roughly 100 test-hours (tested @ 1600F / 50KSI). This demonstrates that the repair heat treatment was able to rejuvenate the parts sufficiently to operate for one more service interval.
In conclusion, our experts evaluated each component in the as-received condition and in the post-repair heat-treated condition. Improvements in the alloy mechanical properties were evaluated to determine if the two sets are candidates for a Life Time Extension (LTE) repair. Once established as candidates for Life Time Extension, our Experts employed repair practices to further extend the useable life of the components.
MD&A’s available Gas Turbine services range from full turnkey major inspections to rotor unstacking, gas turbine alignment, and control services. MD&A is a global full-service OEM alternative for services, parts, and repairs.
Call our MD&A San Antonio Service Center, or our Gas Turbine Parts Service Facility today at +1 (210) 256-5000.
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