GE Frame 5 Service Manual

							GE Power & Water
Heavy-Duty Gas Turbine  
Operating and Maintenance 
ConsiderationsGER-3620M (02/15
)
Jamison Janawitz
James Masso
Christopher Childs
GE Power & Water
Atlanta, GA 
						

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Contents
Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . 1
Maintenance Planning   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . 1
Gas Turbine Design Maintenance Features   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Borescope Inspections  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Major Factors Influencing Maintenance and Equipment Life  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Starts and Hours Criteria  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Service Factors   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Fuel   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Firing Temperatures   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Steam/Water Injection   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Cyclic Effects and Fast Starts   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . 10
Hot Gas Path Parts  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Rotor Parts  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  13
Combustion Parts   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Casing Parts   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Exhaust Diffuser Parts   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Off-Frequency Operation   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Compressor Condition and Performance   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . 18
Lube Oil Cleanliness   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Moisture Intake   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Maintenance Inspections  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Standby Inspections  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Running Inspections   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Rapid Cool-Down   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Combustion Inspection   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Hot Gas Path Inspection  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Major Inspection   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Parts Planning  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . 28
Inspection Intervals   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . 30
Borescope Inspection Interval .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  30
Combustion Inspection Interval   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . 30
Hot Gas Path Inspection Interval   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . 32
Rotor Inspection Interval   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Personnel Planning  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . 34
Conclusion   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . 34
References   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . 35
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Appendix  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . .  .36
A .1) Example 1 – Hot Gas Path Maintenance Interval Calculation   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
A
 .2
 ) Example 2 – Hot Gas Path Factored Starts Calculation
 
  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
B) Examples – Combustion Maintenance Interval Calculations 
 .

   .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .  38
C) Definitions
 

 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
D) Estimated Repair and Replacement Intervals (Natural Gas Only)
 

 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
E) Borescope Inspection Ports
 

 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . . . . . . . . . . . . 44
F) Turning Gear/Ratchet Running Guidelines
 

 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . 45
G) B/E- and F-class Gas Turbine Naming 
 

 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . . . . . . . . . . 46
Revision History  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\
 . . . . . .  .48 
						

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Introduction
Maintenance costs and machine availability are two of the most 
important concerns to a heavy-duty gas turbine equipment 
owner. Therefore, a well thought out maintenance program that 
reduces the owner’s costs while increasing equipment availability 
should be instituted. For this maintenance program to be effective, 
owners should develop a general understanding of the relationship 
between the operating plans and priorities for the plant, the skill 
level of operating and maintenance personnel, and all equipment 
manufacturer’s recommendations regarding the number and 
types of inspections, spare parts planning, and other major factors 
affecting component life and proper operation of the equipment.
In this document, operating and maintenance practices for  
heavy-duty gas turbines will be reviewed, with emphasis placed 
on types of inspections plus operating factors that influence 
maintenance schedules. 
Note:
•	 The operation and maintenance practices outlined in this
document are based on full utilization of GE-approved parts,
repairs, and services.
•	 The operating and maintenance discussions presented
are generally applicable to all GE heavy-duty gas turbines;
i.e., Frames 3, 5, 6, 7, and 9. Appendix G  provides a list of common
B/E- and F-class heavy-duty gas turbines with current and
former naming conventions. For purposes of illustration, the
GE GT-7E.03 was chosen for most components except exhaust
systems, which are illustrated using different gas turbine models
as indicated. Also, the operating and maintenance discussions
presented for all B/E-class units are generally applicable to
Frame 3 and Frame 5 units unless otherwise indicated.
Consult the GE Operation and Maintenance (O&M) Manual
for specific questions on a given machine, or contact the
local GE service representative.
Maintenance Planning
Advanced planning for maintenance is necessary for utility, 
industrial, independent power, and cogeneration plant operators 
in order to maintain reliability and availability. The correct 
implementation of planned maintenance and inspection provides 
direct benefits in the avoidance of forced outages, unscheduled 
Heavy-Duty Gas Turbine 
Operating and Maintenance Considerations
repairs, and downtime. The primary factors that affect the 
maintenance planning process are shown in Figure 1 . The  
owners’ operating mode and practices will determine how each 
factor is weighted. Gas turbine parts requiring the most careful 
attention are those associated with the combustion process, 
together with those exposed to the hot gases discharged from the 
combustion system. These are called the combustion section and 
hot gas path parts, and they include combustion liners, end caps, 
fuel nozzle assemblies, crossfire tubes, transition pieces, turbine 
nozzles, turbine stationary shrouds, and turbine buckets.
Additional, longer-term areas for consideration and planning 
are the lives of the compressor rotor, turbine rotor, casings, and 
exhaust diffuser. The basic design and recommended maintenance 
of GE heavy-duty gas turbines are oriented toward:
•	 Maximum periods of operation between inspections
and overhauls
•	 In-place, on-site inspection and maintenance
•	 Use of local trade skills to disassemble, inspect, and re-assemble
gas turbine components
In addition to maintenance of the basic gas turbine, other station 
auxiliaries require periodic servicing including the control devices, 
fuel-metering equipment, gas turbine auxiliaries, and load package. 
The primary maintenance effort involves five basic systems: 
controls and accessories, combustion, turbine, generator, and 
balance-of-plant. Controls and accessories are typically serviced 
in outages of short duration, whereas the other four systems are 
maintained through less frequent outages of longer duration.   
This document is focused on maintenance planning for the basic 
gas turbine, which includes the combustion and turbine systems. 
The other systems, while outside the scope of this document, also 
need to be considered for successful plant maintenance.
The inspection and repair requirements, outlined in the O&M 
Manual provided to each owner, lend themselves to establishing 
a pattern of inspections. These inspection patterns will vary from 
site to site, because factors such as air and fuel quality are used 
to develop an inspection and maintenance program. In addition, 
supplementary information is provided through a system of 
Technical Information Letters (TILs) associated with specific gas 
turbines after shipment. This updated information, in addition 
to the O&M Manual, assures optimum installation, operation, 
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and maintenance of the turbine. (See Figure 2.) Many of the TILs 
contain advisory technical recommendations to help resolve 
issues and improve the operation, maintenance, safety, reliability, 
or availability of the turbine. The recommendations contained in 
TILs should be reviewed and factored into the overall maintenance 
planning program.
•	 O&M Manual
–
T

urbine-specific manual provided to customer
–
I

ncludes outline of recommended Inspection and
Repair requirements
–
H

elps customers to establish a pattern of systematic
inspections for their site
•	 Technical Information Letters (TILs)*
–
I

ssued after shipment of turbine
–
P

rovides O&M updates related to turbine installation,
maintenance, and operation
–
P

rovides advisory technical recommendations to help
resolve potential issues
* Specific smaller frame turbines are issued service letters known as  Customer Information Notices (NICs) instead of TILs
Figure 2
 . K

ey technical reference documents to include in maintenance 
planning
Gas Turbine Design Maintenance 
Features
The GE heavy-duty gas turbine is designed to withstand severe 
duty and to be maintained on-site, with off-site repair required 
only on certain combustion components, hot gas path parts, and 
rotor assemblies needing specialized shop service. The following 
features are designed into GE heavy-duty gas turbines to facilitate 
on-site maintenance:
•	 All casings, shells and frames are split on machine horizontal
centerline. Upper halves may be lifted individually for access to
internal parts.
•	 With upper-half compressor casings removed, all stationary
vanes can be slid circumferentially out of the casings for
inspection or replacement without rotor removal.
•	 With the upper-half of the turbine shell lifted, each half of the
first stage nozzle assembly can be removed for inspection,
repair, or replacement without rotor removal. On some units,
upper-half, later-stage nozzle assemblies are lifted with the
turbine shell, also allowing inspection and/or removal of
the turbine buckets.
Figure 1 .  Key factors affecting maintenance planning
Manufacturer’s
Recommended
Maintenance Program
Diagnostics &
Expert Systems
Reliability Need On-Site
Maintenance Capability Design Features
Duty CycleCost of
Downtime
Type of Fuel
Replacement Parts
Availability/ Investment
Reserve
Requirements
Environment
Utilization Need
Maintenance
Planning 
						

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•	All turbine buckets are moment-weighed and computer charted
in sets for rotor spool assembly so that they may be replaced
without the need to remove or rebalance the rotor assembly.
•	 All bearing housings and liners are split on the horizontal
centerline so that they may be inspected and replaced when
necessary. The lower half of the bearing liner can be removed
without removing the rotor.
•	 All seals and shaft packings are separate from the main
bearing housings and casing structures and may be readily
removed and replaced.
•	 On most designs, fuel nozzles, combustion liners and flow
sleeves can be removed for inspection, maintenance, or
replacement without lifting any casings. All major accessories,
including filters and coolers, are separate assemblies that are
readily accessible for inspection or maintenance. They may
also be individually replaced as necessary.
•	 Casings can be inspected during any outage or any shutdown
when the unit enclosure is cool enough for safe entry. The
exterior of the inlet, compressor case, compressor discharge
case, turbine case, and exhaust frame can be inspected during
any outage or period when the enclosure is accessible. The
interior surfaces of these cases can be inspected to various
degrees depending on the type of outage performed. All interior
surfaces can be inspected during a major outage when the rotor
has been removed.
•	 Exhaust diffusers can be inspected during any outage by
entering the diffuser through the stack or Heat Recovery
Steam Generator (HRSG) access doors. The flow path surfaces,
flex seals, and other flow path hardware can be visually
inspected with or without the use of a borescope. Diffusers
can be weld-repaired without the need to remove the exhaust
frame upper half.
•	 Inlets can be inspected during any outage or shutdown.
As an alternative to on-site maintenance, in some cases plant 
availability can be improved by applying gas turbine modular 
replacements. This is accomplished by exchanging engine modules 
or even the complete gas turbine with new or refurbished units. 
The removed modules/engines can then be sent to an alternate 
location for maintenance.  Provisions have been built into GE heavy-duty gas turbines to 
facilitate several special inspection procedures. These special 
procedures provide for the visual inspection and clearance 
measurement of some of the critical internal components 
 
without removal of the casings. These procedures include gas   
path borescope inspection (BI), radial clearance measurements, 
and turbine nozzle axial clearance measurements.
A GE gas turbine is a fully integrated design consisting of stationary 
and rotating mechanical, fluid, thermal, and electrical systems. 
The turbine’s performance, as well as the performance of each 
component within the turbine, is dependent upon the operating 
interrelationship between internal components and the total 
operating systems. GE’s engineering process evaluates how new 
designs, design changes, and repairs affect components and 
systems. This design, evaluation, testing, and approval assures 
the proper balance and interaction between all components and 
systems for safe, reliable, and economical operation.
The introduction of new, repaired, or modified parts must be 
evaluated in order to avoid negative effects on the operation   
and reliability of the entire system. The use of non-GE approved 
parts, repairs, and maintenance practices may represent a 
significant risk. Pursuant to the governing terms and conditions, 
warranties and performance guarantees are predicated upon 
proper storage, installation, operation, and maintenance, 
conforming to GE approved operating instruction manuals   
and repair/modification procedures.
Borescope Inspections
An effective borescope inspection program monitors the condition 
of internal components without casing removal. Borescope 
inspections should be scheduled with consideration given to the 
operation and environment of the gas turbine and information 
from the O&M Manual and TILs.
GE heavy-duty gas turbine designs incorporate provisions in   
both compressor and turbine casings for borescope inspection   
of intermediate compressor rotor stages, first, second and third-
stage turbine buckets, and turbine nozzle partitions. These 
provisions are radially aligned holes through the compressor 
casings, turbine shell, and internal stationary turbine shrouds   
that allow the penetration of an optical borescope into the 
compressor or turbine flow path area, as shown in Figure 3 . 
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Borescope inspection access locations for F-class gas turbines 
can be found in Appendix E.
Figure 4  provides a recommended interval for a planned   
borescope inspection program following initial baseline 
inspections. It should be recognized that these borescope 
inspection intervals are based on average unit operating modes. 
Adjustment of these borescope intervals may be made based 
on operating experience, mode of operation, fuels used, and the 
results of previous borescope inspections.
In general, an annual or semiannual borescope inspection uses 
all the available access points to verify the condition of the 
internal hardware. This should include, but is not limited to, signs 
of excessive gas path fouling, symptoms of surface degradation 
(such as erosion, corrosion, or spalling), displaced components, 
deformation or object damage, material loss, nicks, dents, cracking, 
indications of contact or rubbing, or other anomalous conditions.
Borescope Gas and 
Distillate 
Fuel Oil
At combustion inspection or annually, 
whichever occurs first
Heavy 
Fuel Oil At combustion inspection or 
semiannually, whichever occurs first
Figure 4 .
 Borescope inspection planning
During BIs and similar inspections, the condition of the upstream 
components should be verified, including all systems from the filter 
house to the compressor inlet.
The application of a borescope monitoring program will assist with 
the scheduling of outages and preplanning of parts requirements, 
resulting in outage preparedness, lower maintenance costs, and 
higher availability and reliability of the gas turbine.
Primary Inspection Access 
(Normal Inspection)
Secondary Inspection Access 
(Additional Stators & Nozzles)
Access for Eddy-current 
& Nozzle Deflection Inspection
Legend
LE = Leading Edge
TE = Trailling Edge18º
18º
18º
Compressor
-4th Stage
Compressor
-12th Stage
Compressor
-17th Stage
1st Nozzle TE
1st Bucket LE
32º
1st Bucket TE
2nd Nozzle LE
34º
2nd Nozzle TE
2nd Bucket LE
42º
2nd Bucket TE
3rd Nozzle LE
34º
3rd Nozzle TE
3rd Bucket LE
42º
Figure 3 . 7E.03 gas turbine borescope inspection access locations 
						

							5
Major Factors Influencing 
Maintenance and Equipment Life
There are many factors that can influence equipment life, 
and these must be understood and accounted for in the 
owner’s maintenance planning. Starting cycle (hours per start), 
power setting, fuel, level of steam or water injection, and 
site environmental conditions are some of the key factors in 
determining maintenance interval requirements, as these factors 
directly influence the life of replaceable gas turbine parts.
Non-consumable components and systems, such as the 
compressor airfoils, may be affected by site environmental 
conditions as well as plant and accessory system effects. Other 
factors affecting maintenance planning are shown in Figure 1. 
Operators should consider these external factors to prevent the 
degradation and shortened life of non-consumable components. 
GE provides supplementary documentation to assist in this regard.
In the GE approach to maintenance planning, a natural gas fuel 
unit that operates at base load with no water or steam injection 
is established as the baseline condition, which sets the maximum 
recommended maintenance intervals. For operation that differs 
from the baseline, maintenance factors (MF) are established to 
quantify the effect on component lives and provide the increased 
frequency of maintenance required. For example, a maintenance 
factor of two would indicate a maintenance interval that is half of 
the baseline interval.
Starts and Hours Criteria
Gas turbines wear differently in continuous duty application and 
cyclic duty application, as shown in Figure 5 . Thermal mechanical 
fatigue is the dominant life limiter for peaking machines, while 
creep, oxidation, and corrosion are the dominant life limiters for 
continuous duty machines. Interactions of these mechanisms 
are considered in the GE design criteria but to a great extent 
are second-order effects. For that reason, GE bases gas turbine 
maintenance requirements on independent counts of starts and 
hours. Whichever criteria limit is first reached determines the 
maintenance interval. A graphical display of the GE approach 
is shown in Figure 6 . In this figure, the inspection interval 
recommendation is defined by the rectangle established   
by the starts and hours criteria. These recommendations   
for inspection fall within the design life expectations and are  selected such that components acceptable for continued use 
at the inspection point will have low risk of failure during the 
subsequent operating interval.
•	
Continuous Duty Application
–
R

upture
–
C

reep Deflection
–
C

orrosion
–
Ox

idation
–
E

rosion
–
H

igh-Cycle Fatigue
–
R

ubs/Wear
–
F

oreign Object Damage •	
Cyclic Duty Application
–
T

hermal Mechanical
Fatigue
–
H

igh-Cycle Fatigue
–
R

ubs/Wear
–
F

oreign Object Damage
Figure 5 . Causes of wear – hot gas path components
An alternative to the GE approach, which is sometimes employed 
by other manufacturers, converts each start cycle to an equivalent 
number of operating hours (EOH) with inspection intervals based 
on the equivalent hours count. For the reasons previously stated, 
GE does not use this approach. While this logic can create the 
impression of longer intervals, it actually may result in more 
frequent maintenance inspections, since separate effects are 
considered additive. Referring again to Figure 6 , the starts and 
hours inspection “rectangle” is reduced by half as defined by the 
diagonal line from the starts limit at the upper left hand corner 
to the hours limit at the lower right hand corner. Midrange duty 
applications, with hours-per-start ratios of 30-50, are particularly 
penalized by this approach.
This is further illustrated in Figure 7  for the example of a 7E.03 
gas turbine operating on natural gas fuel, at base load conditions 
with no steam or water injection or trips from load. The unit 
operates 4000 hours and 300 starts per year. Following GE’s 
recommendations, the operator would perform the hot gas path 
inspection after four years of operation, with starts being the 
limiting condition. Performing maintenance on this same unit 
based on an equivalent hours criteria would require a hot gas 
path inspection after 2.4 years. Similarly, for a continuous duty 
application operating 8000 hours and 160 starts per year, the   
GE recommendation would be to perform the hot gas path 
inspection after three years of operation with the operating   
hours being the limiting condition for this case. The equivalent 
hours criteria would set the hot gas path inspection after   
2.1 years of operation for this application.
GE Power & Water | GER-3620M (00015001200140018
)  
						

							6
Figure 7 . Hot gas path maintenance interval comparisons. GE method vs. EOH method
GE vs. Equivalent Operating Hours (EOH) Approach
1400
1200
1000 800
600
400
200
0 0  4  8 12  16 20  24  28
Thousands of Fir ed Hours
StartsCase 2
8,000 Hrs/Y r
160 Star ts/Yr
GE Every 3 Yr
EOH Every 2.1 Yr
Case 1
4,000 Hrs/Y r
GE Method 300 Star
ts/Yr
GE Every 4 Yr
EOH Every 2.4 Yr
Continuous
Unit
Figure 6 . GE bases gas turbine maintenance requirements on independent counts of starts and hours