GE Frame 5 Service Manual

7
Service Factors
While GE does not subscribe to the equivalency of starts to hours, 
there are equivalencies within a wear mechanism that must be 
considered. As shown in Figure 8, influences such as fuel type and 
quality, firing temperature setting, and the amount of steam or 
water injection are considered with regard to the hours-based 
criteria. Startup rate and the number of trips are considered with 
regard to the starts-based criteria. In both cases, these influences 
may reduce the maintenance...

8
severity factor typically requires a comprehensive understanding 
of fuel constituents and how they affect system maintenance.  
The selected fuel severity factor should also be adjusted based   
on inspection results and operating experience. 
Heavier hydrocarbon fuels have a maintenance factor ranging 
from three to four for residual fuels and two to three for crude   
oil fuels. This maintenance factor is adjusted based on the   
water-to-fuel ratio in cases when water injection for NO
x 
abatement...

9
degradation equal to that seen with fuel-related contaminants. 
GE specifications define limits for maximum concentrations of 
contaminants for fuel, air, and steam/water.
In addition to fuel quality, fuel system operation is also a factor in 
equipment maintenance. Liquid fuel should not remain unpurged  
or in contact with hot combustion components after shutdown   
and should not be allowed to stagnate in the fuel system when 
strictly gas fuel is run for an extended time. To minimize varnish 
and...

10
heat transfer to the buckets and nozzles and can lead to higher 
metal temperature and reduced part life.
Part life reduction from steam or water injection is directly  
affected by the way the turbine is controlled. The control system   
on most base load applications reduces firing temperature as 
water or steam is injected. This is known as dry control curve 
operation, which counters the effect of the higher heat transfer 
on the gas side and results in no net effect on bucket life. This 
is the...

11
Starts-Based Combustion InspectionAs = 4.0 for B/E-class
As = 2.0 for F-class
Starts-Based Hot Gas Path Inspection P
s = 3.5 for B/E-class
P
s = 1.2 for F-class
Starts-Based Rotor Inspection F
s = 2.0 for F-class*
* See Figure 22 for details
Figure 14  . Peaking-fast start factors
7F .03 Starts-Based Combustion Inspection
As = 1.0 for 7F nominal fast start
As = 1.0 for 7F peaking-fast start
7F  .03 Starts-Based Hot Gas Path Inspection
P
s = Not applicable for 7F nominal fast start 
(counted as normal...

12
Figure 19 compares a normal operating cycle with one that 
includes a trip from full load. The significant increase in the   
strain range for a trip cycle results in a life effect that equates 
to eight normal start/stop cycles, as shown. Trips from part 
load will have a reduced effect because of the lower metal  temperatures at the initiation of the trip event. Figure 20 
 
illustrates that while a trip from between 80% and 100% load   
has an 8:1 trip severity factor, a trip from full speed no...

13
metal temperatures. As a result, a trip from peak load has 
a trip severity factor of 10:1. 
Trips are to be assessed in addition to the regular startup/shutdown 
cycles as starts adders. As such, in the factored starts equation  
of  Figure 43 , one is subtracted from the severity factor so that the 
net result of the formula ( Figure 43) is the same as that dictated   
by the increased strain range. For example, a startup and trip   
from base load would count as eight total cycles (one cycle for...

14
The rotor maintenance factor for a startup is a function of the 
downtime following a previous period of operation. As downtime 
increases, the rotor metal temperature approaches ambient 
conditions, and thermal fatigue during a subsequent startup 
increases. As such, cold starts are assigned a rotor maintenance 
factor of two and hot starts a rotor maintenance factor of less  
than one due to the lower thermal stress under hot conditions.   
This effect varies from one location in the rotor structure...

15
Figure F-1 describes turning gear/ratchet scenarios and operation 
guidelines (See Appendix ). Relevant operating instructions and 
TILs should be adhered to where applicable. As a best practice, 
units should remain on turning gear or ratchet following a planned 
shutdown until wheelspace temperatures have stabilized at or   
near ambient temperature. If the unit is to see no further activity 
for 48 hours after cool-down is completed, then it may be taken   
off of turning gear.
Figure F-1 also...

16
•	Continuous mode operation is defined as operation in a
combustion mode for longer than what is required during normal
startup/shutdown.
•	 Extended mode operation is defined as operation in a
combustion mode at a firing temperature greater than the
transfer temperature to the next combustion mode.
The DLN combustion mode recommended for continuous mode 
operation is the premixed combustion mode (PM), as it achieves 
lowest possible emissions and maximum possible part life. 
Continuous and extended...