GE Vernova GER-3620 Operating and Maintenance

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Doc Name : GER-3620 Rev P Released Date : 2021/03/15 Page 10 of 60
These various EOH methods are illustrated in Figure 6.
Inspection Intervals
EOH
(Equivalent
Operating
Hours)
FFS or WCE
Evolution of Hot
Gas Path Design
Linear All Fleet
Elliptical F-Fleet
Extended Linear F-Fleet
Extended Linear B/E-Fleet
Box (F-Fleet)
FFH or WOH
Figure 6. Hot gas path maintenance interval comparisons.
GE Vernova method vs. EOH method. FFS = Factored Fired Starts, FFH
= Factored Fired Hours, WCE = Weighted Cyclic Events,
WOH = Weighted Operating Hours.
Service Factors
The effect of fired starts and fired hours on component
lifetime are not the only wear mechanisms which must be
considered. As shown in Figure 7, 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 intervals.
Typical baseline inspection intervals (6B.03/7E.03):
Hot gas path inspection 24,000 hrs or 1200 starts
Major inspection 48,000 hrs or 2400 starts
Criterion is hours or starts (whichever occurs first)
Factors affecting maintenance:
Hours-Based Factors
•
Fuel type
•
Peak load
•
Diluent (water or steam injection)
Starts-Based Factors
•
Start type (conventional or peaking-fast)
•
Start load (max. load achieved during start cycle, e.g.
part, base, or peak load)
•
Shutdown type (normal cooldown, rapid cooldown, or trip)
Figure 7. Maintenance factors
6
When these service or maintenance factors are involved
in a unit’s operating profile, the hot gas path maintenance
“rectangle” that describes the specific maintenance
criteria for this operation is reduced from the ideal case,
as illustrated in Figure 8. The following discussion will
take a closer look at the key operating factors and how
they can affect maintenance intervals as well as parts
refurbishment/replacement intervals.
Maintenance Factors Reduce Maintenance Interval
1,400
1,200
1,000
Starts
800
600
400
200
0
Starts-Based
Factors
• Start type
• Start load
• Shutdown type
Hours-Based
Factors
• Fuel type
• Peak load
• Diluent
0 20 24 28
4 8 12 16
Thousands of Fired Hours
Figure 8. GE Vernova maintenance intervals
Fuel
Fuels burned in gas turbines range from clean natural
gas to residual oils and affect maintenance, as illustrated
in Figure 9. Although Figure 9 provides the basic
relationship between fuel severity factor and hydrogen
content of the fuel, there are other fuel constituents that
should be considered. Selection of fuel 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 NOx abatement is used. These fuels
generally release a higher amount of radiant thermal
energy, which results in a subsequent reduction in
combustion hardware life, and frequently contain corrosive
elements such as sodium, potassium, vanadium, and lead
that can cause accelerated hot corrosion of turbine nozzles
and buckets. In addition, some elements in these fuels
can cause deposits either directly or through compounds
formed with inhibitors that are used to prevent corrosion.
These deposits affect performance and can require more
frequent maintenance.
Non-Public- Class II (Non Critical) - NLR