Inspection Interval Extension
And Lifetime Extension Of
Mature Frame Gas Turbines
POWER-GEN International 2006 – Orlando, FL
November 28-30, 2006
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Copyright © 2006 Siemens Power Generation, Inc.
Copyright © Siemens AG 2006. All rights reserved.
INSPECTION INTERVAL EXTENSION AND LIFETIME EXTENSION
OF MATURE FRAME GAS TURBINES
Donald Fraser, Diego Caso
Siemens Power Generation Inc. - 4400 Alafaya Trail, Orlando, FL 32826-2399
ABSTRACT
Availability and Life Cycle Cost (LCC) are two key market drivers that directly impact the
profitability of mature frame gas turbines used to produce power for utility, industrial, and cogeneration facilities. Siemens Power Generation, Inc. has executed two programs, the Inspection
Interval Extension Product (IIEP) and Lifetime Extension (LTE) to address these service market
needs. These programs have targeted certain mature frame gas turbines and are aimed at
increasing availability and reducing LCC through continued reliable operation well into the twentyfirst century. Both of these programs build on the success of similar programs implemented on
the SGT6-1000F (formerly V64.3), SGT5-2000E (V94.2), SGT5-4000F (V94.3), SGT6-2000E
(V84.2), and SGT6-4000F (V84.3A) gas turbine frames. The design processes utilized in the
development of these packages are discussed.
The Inspection Interval Extension Product (IIEP) increases the current Combustor / Hot Gas Path
/ Major inspection intervals on the SGT6-3000E (W501D5 and W501D5A) gas turbines through
the use of enhanced durability component designs that can be implemented during scheduled
outages. The IIEP provides increased availability by extending the interval between inspections,
both in terms of hours and in terms of starts, and in some cases by eliminating the requirement
for some types of inspections... These user benefits can potentially result in significant cost
savings depending on operating mode, service history, and -parts inventory.
The specific LTE program discussed in this paper addresses the SGT6-3000E, formerly W501D5
and W501D5A, gas turbine components that are approaching or have surpassed engineered
design target lives. The LTE program evaluates unit-specific operating histories and develops a
set of customized service recommendations that, upon implementation, can potentially reduce the
risk of operation beyond design life. The process of validating these recommendations and the
resultant required inspections and services are discussed. The objective of the LTE program is to
reduce LCC and increase availability by extending the life of a mature frame gas turbine by two
additional major inspection intervals or approximately 100,000 Equivalent Operating Hours.
MARKET NEED
Gas turbine (GT) power plants and process support installations are typically large capital
ventures supporting potentially highly profitable operations. Considering that the GT is often the
highest operating cost item in a plant, successfully extending gas turbine life and decreasing
operating costs helps retain the operating margins of many facilities. The improved efficiencies of
new generation gas turbines often present an irresistible economic case for replacement.
However, it is also true that replacement does not always represent the best bottom line
opportunity. In some cases, processes have been built around the specifics of the GT. In this
case the different pressures and flows required for the new design GT to demonstrate higher
efficiencies may not practically fit into the process plant. In other cases, the capital cost of
replacement and the lower cost of ongoing maintenance of the existing GT outweigh the high
performance difference of the new machine. A few places may even rely upon the extreme
ruggedness of the earlier robust un-cooled blade designs. Also, while certainly the largest, the
USA is not the only market utilizing gas turbine technology for power generation. Worldwide,
there exists a very wide range of operating, maintenance, fuel efficiency, and life cycle cost
realities that can benefit from Original Equipment Manufacturer (OEM) supported Lifetime
Extension and Inspection Interval Extension programs.
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Copyright © 2006 Siemens Power Generation, Inc.
Siemens utilizes surveys to help define the future priorities of its customers’ needs. These
surveys justified the resource expenditure which supported the development of the LTE and IIE
programs. Survey results for several years have indicated the GT users’ strong desire for
extending the interval between inspections and extending the lifetime of the GT. It is gratifying to
see that after the significant time line of the product development cycle these products still rank
amongst the highest of the anticipated future needs according the latest survey results. It is also
interesting, if not somewhat predictable, how the ranking of these needs varies across the usage
spectrum. . Standby and Peaking units showed inspection interval extension and trip factor
reduction as high priority needs with less interest in lifetime extension, whereas Base loaded
plants ranked extended inspection intervals as a highest need with lifetime extension as a next-inrank need and dropped trip factor consideration off the scale.
DEVELOPMENT PROGRAMS
Two separate programs were executed to respond to the different questions of what is needed to
extend the OEM recognized GT design life - and what is considered in extending the OEM
recommended inspection intervals. Siemens is a world wide company with very diverse
resources which is frequently quite advantageous to the customer. Lifetime Extension
development is one of those cases. The successful Lifetime Extension process for the Siemens
V-frames that was engineered in Muelheim and Berlin, Germany, was utilized heavily at the onset
of this product development program for the above-mentioned W-frames. The engineers had
already completed the evaluations necessary to define the recommended tests and inspections
for the Siemens design V frame GTs. While some parts of the Siemens and the Westinghouse
GT designs differ significantly, much of the designs share a similar design philosophy, and these
similarities helped considerably to reduce development time.
Life Assessment Development Approach
The approach used in life assessment development is outlined below:
•
Analyze critical component designs with potential life limiting issues such as rotor disks,
blading, cylinders, etc., using latest FEM tools, material property data, service
experience, etc. See Figures 1 and 2.
Figure 1. Component Evaluation Matrix
•
Figure 2. Processes Causing Aging
Define required inspections to thoroughly investigate and assess all areas of potential
concern. Figure 3 shows a blade sample cut up for inspection.
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Copyright © 2006 Siemens Power Generation, Inc.
Figure 3. Blade Sample
•
Identify any required special testing, material sampling, etc. (see Figure 4).
Figure 4. Surface Material Sampling Tool for Taking Casing Sample
•
Define service and maintenance history data required for review.
•
Establish acceptance criteria / allowable limits.
•
Develop standard recommendations to address issues, non-conformances, etc. For
example to repair a part or replace the component.
•
Document above requirements.
IIE Development Program
The development program for Inspection Interval Extension- (IIE)-for the W501D5, D5A and
STG6-3000E followed the stages shown in Figure -5. The customer feedback from the survey
process identified the ongoing need for the program. Marketing initiated a design specification
outlining the product requirements and program restrictions and obtained the funding to support
the program.
Program
Program
Initiation
Initiation
Empirical
Empirical
Data
Data
Analysis
Analysis
•• Requirements
Requirements
•• Data
Data
•• Program
Program Plans
Plans
•• Design
Design Spec
Spec
•• Data
Data Entry
Entry
•• Analysis
Analysis
•• Documentation
Documentation
Spec
Spec (PRS)
(PRS)
(PDS)
(PDS)
Collection
Collection
Life
Life Cycle
Cycle
Cost
Cost
Analysis
Analysis
•• Based
Based on
on
Empirical
Empirical
Data
Data
LCC
LCC Data
Data
LCC
LCC vs.
vs. PRS
PRS
••
••
•• Design
Design
Decision
Decision
Risk
Risk
Assessment
Assessment
••
••
••
••
••
••
FMEA
FMEA
Application
Application
Performance
Performance
Emissions
Emissions
ComponentComponent
Component-specific
specific
Mitigation
Mitigation
Actions
Actions
Technology
Technology
Analysis
Analysis
•• New
New
•• Advanced
Advanced
Frames
Frames
-Proven
•• FieldField
Field-Proven
•• Application
Application to
to
••
Engineering
Engineering
Analysis
Analysis
Mature
Mature Frames
Frames
Qualifications
Qualifications
••
••
Component
Component
Designs
Designs
Critical
Critical
Components
Components
Per
Per Latest
Latest
Design
Design Criteria
Criteria
Manufacturing
Manufacturing
Analysis
Analysis
Verification
Verification
Testing
Testing
•• Procurement
Procurement
•• Tooling
Tooling and
and
•• Component
Component
••
••
-times
•• LeadLead
Lead-times
••
Fixtures
Fixtures
Qualifications
Qualifications
Sourcing
Sourcing
and
and Design
Design
Dependent
Dependent
Acceptance
Acceptance
per
per Latest
Latest
Design
Design
Criteria
Criteria
Validation
Validation
Requirements
Requirements
•• Based
Based on
on Risk
Risk
Level
Level
•• Borescope
Borescope
Product
Product
Documentation
Documentation
•• PRS
PRS &
& PDS
PDS
•• Final
Final Design
Design
Inspections
Inspections
Review
Review
Package
Package
•• Occurs
Occurs Over
Over
•• Engineering
Engineering
Several
Several Years
Years
Specs
Specs
•• Drawings
Drawings &
&
BOM’
’s
BOM
BOM’s
•• Service
Service
Bulletins
Bulletins
•• PCM
PCM &
& PIB
PIB
Frame-specific Inspection Interval Extension R&D Process
Frame-specific Inspection Interval Extension R&D Process
Figure 5. Structured Development Process
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Copyright © 2006 Siemens Power Generation, Inc.
An enormous volume of data is collected on the operating fleet. Access to this data and the
cooperation of select users permitted verification of analytical models and additional real time
data collection, which made the successful execution of the development program possible.
In the end, certain factors showed themselves to be dominant in the overall life expectancy
prediction of new and repaired components. These factors were then balanced against the
desired life cycle cost target for the gas turbines as a whole on a component by component basis.
The resulting recommendations for each part and for operational requirements were integrated to
derive the end products, in this case the Inspection Interval Extension package and the Lifetime
Extension program.
THE PRODUCTS
Inspection Interval Extension Package, IIEP
The IIEP as developed offers benefits for gas turbines covering the full range of operating modes
from continuous base load operation to peaking / standby. Hours based inspection intervals are
utilized by plants that average many hours of operation per each start. These plants, in the
W501D5 and W501D5A / SGT6-3000E gas turbine frames, are typically associated with
refineries or other industrial operations and are co-generators, combined cycle, or both. They
operate on natural gas primarily and some utilize refinery off-gases such as Hydrogen. They have
a high ratio of equivalent base operating hours (EBH) to equivalent starts (ES). This ratio,
EBH/ES is typically greater than 100.
Benefit
The IIEP benefit for hours based operations is seen in Figure 6.
Lifetime Extension
Standard
Intervals 0
Extended 0
Intervals
C
C HGP C
C Major C
C HGP C
C Major
8K 16K 24K 32K 40K 48K 56K 64K 72K 80K 88K 96K
C
16K
HGP
32K
C
48K
Major
64K
C
80K
HGP
96K
C
112K
Major
128K
Figure 6. Hours-Based Inspection Interval Extension
With the Inspection Interval Extension upgrade, the hours based GT user is able to extend
inspection intervals as follows:
• Combustor inspection interval increased from 8,000 EBH to 16,000 EBH
• Hot gas path inspection interval increased from 24,000 EBH to 32,000 EBH
• Major inspection interval increased from 48,000 EBH to 64,000 EBH
The net effect is that two combustor inspections have been eliminated from the full major
inspection cycle, and the cycle interval has been extended by 33%. This represents a significant
increase in unit availability. Additionally, Lifetime Extension, which would normally be
recommended for the second standard major inspection interval at 96,000 EBH, has been
approved for the second extended inspection interval at 128,000 EBH on units equipped with the
Lifetime Extension upgrade.
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Copyright © 2006 Siemens Power Generation, Inc.
Many gas turbines are no longer operating in high EBH/ES mode. Often these turbines require
inspections based on equivalent starts. The benefit of applying the IIE products to these units is
also significant (see Figure 7).
Figure 7. Starts-Based Inspection Interval Extension
Starts-based gas turbines equipped with the IIEP upgrade package are able to completely
eliminate combustor inspections. As an added benefit, the equivalent start factor for full load trip
events has been greatly reduced from 20ES to 8 ES for each full load trip event, with proportional
trip factor reductions for trip events at part load. Based on the average fleet operating profile over
the past 10 years, this trip factor reduction would be expected, on average, to increase the users
overall operation between inspections by approximately 50%. This benefit is not included in
Figure 7, shown above. If it were, it would show that for the average (10 year reporting plant
history) peaking plant the effective ES to a major would be about 2500. The economic benefits of
delaying hot gas path and major inspections and eliminating combustor inspections will be quite
significant to many operators.
Requirements
The parts requirements are summarized below. Depending on the frame and upon the
combustion system, parts either can be upgraded to the new configuration or would require
replacement with a new part design. An overall parts configuration pedigree review is required to
assure the applicable part styles are in place. Where differences are found, recommendations
will be made. For example, non OEM parts or repairs that have not been researched and
recommend for extended inspection interval would require replacement. There are also
potentially some very old part styles in less critical areas that may not be acceptable for extended
operations. One very positive feature of implementing the program is that the parts and
modifications can be phased in at appropriate outages thereby minimizing the loss of useable life
on some existing parts. Figure 8, below, summarizes the affected parts and required actions.
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Copyright © 2006 Siemens Power Generation, Inc.
W501D5A
W501D5
Component
DLN
DF-42
DLN
DF-42
Combustor Basket
New Design**
New Design**
New Design**
New Design**
Transition
New Design**
New Design**
Upgrade*
Upgrade*
Transition Cylinder
New Design**
New Design**
New Design**
New Design**
Fuel Nozzle
Existing
Existing
New Design***
Existing
Turbine R1V
Upgrade*
Upgrade*
Upgrade*
Upgrade*
Turbine R1B
Upgrade*
Upgrade*
Upgrade*
Upgrade*
Turbine R2V
Upgrade*
Upgrade*
Upgrade*
Upgrade*
Turbine R2B
Upgrade*
Upgrade*
Upgrade*
Upgrade*
Turbine R1RS
New Design**
New Design**
New Design**
New Design**
Turbine R2RS
New Design**
New Design**
New Design**
New Design**
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A pedigree review of all remaining major consumable components is required to verify applicability to the
interval extension product.
This product can be installed in phases. Example: Combustor components during a planned CI, then
turbine components during a planned HGP.
* Current inventory and/or in-service components may be upgraded depending on style and remaining design life.
** Requires a new component purchase (cannot be upgraded from current field hardware).
*** Requires a support housing alteration in conjunction with the new design DLN pilot nozzle.
Figure 8. Replacement Parts and Required Actions
LIFETIME EXTENSION
Lifetime Extension is a program that provides OEM recommendations for the non-consumable
portions of the engine, based upon a pre-determined set of inspections and tests. These
investigations are based on the fact that the original equipment design was performed assuming
a specific design life. In the case of the former Westinghouse W501D5 and W501D5A / SGT63000E gas turbines the design life was based on 100,000 EBH and or 3,200 equivalent starts.
This represents the original evaluation criteria of material properties retention due to time at
temperature and alternating stress and strain. These processes affect metallic materials in
different ways and, of course, the engineering task is to design equipment that operates safely
under the conditions and for the periods specified.
Since the original design efforts of the W501D5/D5A frames in the late 1970’s, new tools,
materials, and processes have changed the engineering analyses capabilities. Chief among
these is the advent of the digital electronic computer. The computational power of the computer
has enabled a vast increase in the efficiency of analytical techniques based on numerical
methods. Most eminent and useful of these include Finite Element Method, Boundary Element
Method, and Flow Computational Analysis. These tasks were quite onerous in the early days of
gas turbine design. Many components were “over designed” with safety factors to accommodate
less strenuous analysis methods. Another area of increased capability has occurred in material
design. Overall increase in technology has permitted material scientists and engineers to
develop alloys with tremendously improved strength, wear, and creep properties. The combined
effect of computational methods and materials improvements has greatly increased not only the
potential life of products but also the prediction of how and when they fail. The following
examples illustrate some of those potential failure mechanisms (see Figures 9-13).
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Copyright © 2006 Siemens Power Generation, Inc.
Figure 9. Compressor Blade Pitting from Wet Corrosion
Failure probability curve over part life, how knowledge and experience can support a “Life Extension”
Figure 10. Expansion Bolt failure Probability Curve
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Copyright © 2006 Siemens Power Generation, Inc.
Figure 11. Expansion Bolt Failure
Coatings can extend part life, but eventually creep strain dominates at a given heat and stress
Figure 12. Parts’ Life Expectancy and Creep Strain
Metallic surface investigations reveal property changing effects
Figure 13. Metallic Surface Investigations
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Copyright © 2006 Siemens Power Generation, Inc.
Figure 14 shows which W501D5/D5A non-consumable components were considered to be
critical.
Blade Rings
Compressor Disks
Inlet
Turbine Disks
IGVs
Rotor Shaft
Exhaust Manifold
Expansion Joint
Engine Supports
Cylinders
Figure 14. W501D5/D5A Critical Components
The Lifetime Extension program targets normal modes of service degradation. These include
time dependent aging mechanisms including creep, alloy instability and loss of material
properties, oxidation, corrosion, component distortion, mechanical damage such a erosion, wear,
vibratory wear, and turning wear. The LTE also searches for signs of damage due to low and
high cycle fatigue and for crack propagation. LTE focuses primarily on non-consumable
components that are typically not replaced or regularly repaired during normal inspections such
as combustor inspections or hot gas path inspections. The first major inspection, where both the
compressor and turbine covers are removed typically is the first inspection that provides the
opportunity to view all of these areas shown in Fig. 14. While some signs of normal minor wear
and tear are expected to be seen here and there such as in the exhaust manifold, there little
concern is at the time for the integrity of the material composing the items unless very unusual
findings are discovered. The LTE, in contrast, searches specifically to find the evidence, or lack
of evidence, that these usually robust components are “wearing out” and losing their mechanical
properties.
The program for LTE requires a combined customer and OEM effort. The cooperation begins
with mutual planning that must occur as far in advance of the LTE outage as possible. This
allows both the customer and the OEM to collect the required operating and service history data.
A checklist is provided and used to organize the data and execute frame-specific inspection and
maintenance requirements. The OEM then has the time to evaluate the data against the newly
developed standards and to evaluate “outliers”, data points that are not normally seen and which
require special consideration. Within Siemens PG the Total Maintenance Services (TMS)
program is the ideal setting for this organization of activities. The close customer communication
facilitated by the Technical Service Managers helps to enable the resolution of those odd data.
For example, a second or third material sample in slightly different areas may provide engineering
the knowledge to explain the “outlier”. These new samples can then be taken during the next
planned outage and there is still time to formulate the recommendations and manufacture the
new parts, if that is what is necessary. Figure 15 describes graphically the LTE Actions Flow
Chart.
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Copyright © 2006 Siemens Power Generation, Inc.
Customer
Hot Gas Path
Last Combustor
Inspection before LTE
Combustor
inspection
Unit Specific
Investigation
C
LTE
LTE
C
Component
Samples
Customer
Benefit
Site-specific PreInvestigation
Checklist for
LTE
LTE
Recommendations
Frame Specific Component Review
Investigation
Component Analysis
Modernization & Upgrades Development
s
Figure 15. Flow Chart of LTE Actions
Once all of the data has been evaluated and the samples which are identified by engineering are
obtained and analyzed, the final recommendations are assembled along with the expected
customer benefits. Some of these recommendations may include utilizing upgraded components
that can improve the plant profitability by improving efficiency, power output, or, as in the
Inspection Interval Extension package described above, improve availability by reducing the
number of required outages.
The word “recommendations” has been used frequently. LTE is a set of suggested inspections
and investigations. It has been determined that many components can operate safely long
beyond their original design life. However, realities of operation ranging from out of spec. fuels to
operating out of OEM identified parameters and materials that are perhaps slightly different than
the expected alloy specification can all cause accelerated wear and tear. The challenging
engineering issues when designing for life center on the fact that the point of component failure
can be reached suddenly due to accelerated degradation of properties when approaching end of
life. The LTE program is experiential and statistical in nature. Evaluation of operational history
through records and thorough sampling and testing of the critical areas that typically receive no
periodic maintenance minimizes the risk of sudden unexpected and potentially catastrophic
failure. In the end, it is the customer, the plant owner and operator that must decide whether to
accept and enact the LTE recommendations or not.
Ultimately, the LTE outage is an extended major inspection where the final samples can be taken
and inspections and investigations performed. It is a perfect time to install new and improved
parts, if applicable. The owner can then plan for the ensuing operation knowing that areas that
are typically ignored and yet potentially important to the unit’s safe and reliable operation have
been investigated and considered. The unit degradation will be lessened where the
recommendations have been followed and it will operate at higher performance levels and at the
highest possible availability levels if the improvements and upgrades such as the IIE have been
implemented.
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Copyright © 2006 Siemens Power Generation, Inc.
SUMMARY
In summary, the Inspection Interval Extension and the Lifetime Extension programs are available
for the work horse W501D5 and W501D5A / SGT6-3000E engines. The world market has
demanded the benefits of longer operational life and inspection intervals. Siemens engineering
has thoroughly investigated the issues related and have provided these excellent programs in
response. These critical machines can now be relied upon to operate satisfactorily well into the
next decade provided Siemens’ recommendations are implemented. Siemens continually
upgrades and enhances its products to improve their competitiveness and add value to their
operators.
ACKNOWLEDGEMENTS
Recognition and thanks should be given to Siemens Service Engineering groups located in
Orlando, Florida and Mulheim, Germany for the development efforts themselves as well as the
photographs and illustrations used here and specifically to Barton Pepperman, Andreas Dibbert
for their contribution.
PERMISSION FOR USE
The content of this paper is copyrighted by Siemens Power Generation, Inc. and is licensed only
to PennWell for publication and distribution. Any inquiries regarding permission to use the content
of this paper, in whole or in part, for any purpose must be addressed to Siemens Power
Generation, Inc. directly.
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Copyright © 2006 Siemens Power Generation, Inc.