pwr_february-2025 - 22

TURBINE MRO
corrosion, wall thickness, and material
condition. Repair enhancements can extend
a part's life by slowing its degradation
and pushing out its usable service
life. Operators can see significant savings
by opting for lower-cost repaired
spares rather than purchasing new parts.
For example, MD&A's Gas Turbine Parts
Service Facility in San Antonio, Texas,
evaluated two sets of 7FA second-stage
blades to determine if they were capable
to operate for a third service interval. The
blades had operated through two service
intervals and undergone one repair.
The team performed an X-ray inspection
on the components in their as-received
condition, which did not reveal
any areas of concern, nor clogging on the
cooling holes. A fluorescent penetrant inspection
(FPI, Figure 3) was performed
to look for significant cracking, paying
close attention to the platform side face
due to the substantial number of starts
reported. The area around the shroud radius
was also evaluated for cracks. The
team found no major areas of concern
during the preliminary FPI inspection
but still performed a more thorough inspection
once the metallic coating was
chemically stripped.
The MD&A San Antonio facility
deemed the condition of the internal
coating as 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, a GEdeveloped
nickel-based superalloy used
in gas turbine blades due to its excellent
high-temperature
strength
and
corrosion
resistance, responded well to the
process and the overall blade hardness
values were improved.
For heat treatment, MD&A experts
use a vacuum heat treat furnace in
which the heating and cooling of metals
is controlled to alter their physical
and mechanical properties. There is a
pre-weld heat treatment, post-weld heat
treatment, and a diffusion or aging heat
treatment solution.
Samples were removed from the
22
3. A fluorescent penetrant inspection (FPI)
uses black light technology to pinpoint any
cracks. Courtesy: MD&A
blades for stress rupture testing. The asreceived
condition did not meet the minimum
expected strength requirements
for GTD 111. However, the samples tested
after heat treatment exceeded the
minimum requirements.
After the repair heat treatment, the rupture
strength was improved. This demonstrates
that the repair heat treatment was
able to rejuvenate the parts sufficiently to
operate for one more service interval.
In the end, MD&A 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 were candidates
for a lifetime extension repair.
Once deemed that they were, the team
employed repair practices to further extend
the useable life of the components.
Overcoming Maintenance
Challenges
MD&A told POWER that one of the most
challenging types of turbine repairs it encounters
involves addressing potentially
catastrophic failures, such as cracked rotors
or extensive blade damage caused
by operational stresses or foreign object
impacts. These types of repairs require
not only technical expertise, but also precision
and innovation to restore the turbine's
integrity and efficiency. Eldridge
said MD&A approaches these challenges
with a structured and collaborative
methodology that includes:
■ Thorough Assessment. MD&A's process
begins with detailed inspections
using advanced non-destructive testing
(NDT) techniques and 3D scanning
technology. This allows the company's
experts to understand the full scope of
the damage and identify root causes.
■ Reverse Engineering Expertise. For
components where OEM parts are
unavailable or outdated, MD&A leverages
its in-house reverse engineering
www.powermag.com
capabilities to manufacture high-quality
replacements that meet or exceed
industry standards.
■ Custom Solutions. MD&A said it recognizes
that every repair is unique.
Whether it involves intricate welding,
specialized heat treatments, or alternatives
to OEM design, the company
tailors its solutions to address the specific
challenges of each case.
■ Testing and Validation. Once repairs
are complete, MD&A rigorously tests
the components to verify performance,
including full-speed testing in
its High-Speed Balance Facility, to ensure
reliability and long-term success.
" Our goal is to not only restore functionality,
but also to enhance reliability and efficiency,
helping our customers minimize
downtime and achieve peak performance, "
Eldridge said. " It's this commitment to
innovation and precision that has earned
MD&A its reputation as a trusted OEMalternative
in the power industry. "
Secrets to Success
In the end, turbine owners and operators
must balance the need for thorough
inspection and maintenance with operational
schedules. Success often requires
a strategic approach that prioritizes efficiency,
flexibility, and collaboration.
Among the most important aspects that
lead to a positive outcome are:
■ Planning
and Scheduling. Owners
and operators must work closely with
contractors to develop a customized
maintenance plan that aligns with a
unit's operational goals.
■ Communication. Clear and constant
communication among owners, operators,
contractors, and suppliers is
essential.
■ Project Execution. Project managers
must diligently manage all aspects
of turbine MRO work in order to hit
schedule and budget targets, and
complete a successful outage.
" Ultimately, the key to reducing downtime
lies in balancing proactive maintenance
with experienced execution, "
said Eldridge. " By blending cutting-edge
technology, engineering expertise, and a
deep understanding of aging equipment,
MD&A helps customers maximize the
value of their turbine assets, keeping
them reliable and efficient well beyond
their original design lifespans. " ■
-Aaron Larson is POWER's
executive editor.
POWER | February 2025
http://www.powermag.com
pwr_february-2025

Table of Contents for the Digital Edition of pwr_february-2025
