3002002659 Collaborative Effort Enables NYPA to Repair Gas Turbine Compressor Blades in Place

Success Story
Collaborative Effort Enables NYPA
to Repair Gas Turbine Compressor
Blades in Place
The New York Power Authority (NYPA) worked with EPRI to determine the extent of
blending repairs that could be safely performed in place on a pair of gas turbine com-
pressor blades (airfoils) to avoid removing the rotor to replace the blades. The analysis
results not only allowed NYPA to proceed with the repair but also added to the base
of knowledge that EPRI and the industry have compiled on compressor field repairs.
Blade Damage and Repair
Rotating compressor blades are subject to foreign object damage, corrosion, erosion, rubbing,
and occasionally clashing, causing localized bent edges, dents, grooves, pits, cracks, and
thinning. It is general practice to address these commonly occurring issues by trimming or blend-
ing out the damaged area. Blending repairs involve graduated polishing beyond the damaged
area to conform with the remaining portion of the blade. Removal and replacement of dam-
aged blades can require extensive unit and rotor disassembly, and associated outage time.
In some cases, when the damage is relatively confined, a localized repair may be feasible
without removing the damaged blade. However, any modification of an original blade design
should carefully consider structural impacts, particularly possible reduction of the margin of reso-
nant vibration. A foundation of engineering is needed to evaluate the potential risk that might
result from any modification to the original design.
Providing the Engineering Basis for Repair
For several years, EPRI has performed research to provide the engineering basis for material
trimming and blending repairs to compressor rotating blades. This information is designed to
help operators to perform safe repairs and avoid possible risk of airfoil failure due to high-cycle
fatigue.
EPRI has compiled the information in regularly updated repair guidelines, such as the recent
Gas Turbine Compressor Field Repair Guideline: GE 7FA (3002002389).
Modeling and Stress Analysis of NYPA Compressor Blade
During inspection of a gas turbine compressor rotor at one of its plants, NYPA discovered con-
cerning damage on a ninth- and twelfth-stage blade. Since the location of the damage was
close to the root, questions arose as to whether the blades could be safely repaired in place.
NYPA staff worked with EPRI to analyze the blades and determine whether the blades could be
repaired without removal. A complex effort was required to coordinate the data from the OEM
and the plant site, perform finite element modeling of the proposed repairs, and conduct the
stress analysis of the results.
“This project provided
NYPA with greater insight
into the underlying factors
which impact compressor
airfoil stability and the
repair tolerance limits by
which they are bound.
With the increased knowl-
edge gained through EPRI’s
assistance, we were confi-
dently able to perform the
repair and return to service
expeditiously, and achieve
a significant cost savings.”
~ Paul Tartaglia
Senior Vice President, Energy
Resource Management,
New York Power Authority
NYPA’s Astoria 500-MW plant in
Queens, NY.
14097712

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800.313.3774 • 650.855.2121 • [email protected] • www.epri.com
© 2014 Electric Power Research Institute (EPRI), Inc. All rights reserved. Electric Power Research Institute, EPRI, and TOGETHER . . . SHAPING THE FUTURE OF ELECTRICITY are
registered service marks of the Electric Power Research Institute, Inc.
Related EPRI Work
Gas Turbine Compressor Field Repair Guideline: GE 7FA. EPRI. Palo
Alto, CA: December 2013. 3002002389.
3002002659 February 2014
For more information, contact the EPRI Customer
Assistance Center at 800.313.3774 ([email protected])
CONTACTS
John Scheibel, Technical Executive
Combined Cycle Turbomachinery Program
650.855.2446, [email protected].
Based on this work, NYPA was able to validate the OEM opinion that
the work could be safely performed. To date, no further issues have
been reported with the repaired blades.
Cost Avoidance and New Lessons Learned
By repairing the blades in place, instead of removing the rotor and
disassembling and replacing the blades, NYPA was able to save a
significant amount of time and money.
In addition, the analysis in this case went beyond the typical repair
limits specified by the OEM in published literature and those already
defined in the EPRI repair guidelines. As a result, the work involved in
developing the component models and conducting the stress analysis
of the NYPA blade repair identified an area where the EPRI repair
guidelines needed to be further developed, and the experience gained
during this repair process was included in the guidelines update.
“This project provided NYPA with greater insight into the underlying
factors which impact compressor airfoil stability and the repair toler-
ance limits by which they are bound,” said Paul Tartaglia, NYPA’s SVP
of Energy Resource Management. “With the increased knowledge
gained through EPRI’s assistance, we were confidently able to perform
the repair and return to service expeditiously, and achieve a significant
cost savings.”
14097712