POWER September 2016 - 59

COMBINED CYCLE O&M
7. Too young for this problem.
Creep fatigue failure of reheater 1 at the upper
header was not expected after 100,000
hours if operating stresses were consistent
with design assumptions. Courtesy: Tetra Engineering
Table
2. Prioritized risks from low-load and load-following operation
(500-MW CCGT). Source: Tetra Engineering
Key risk
priority Description
1
2
3
4
5
6
7
8. Breach. One plant experienced a pipe
failure in the reheater attemperator ( " candycane "
crossover link between the two RH
sections). Courtesy: Tetra Engineering
8
Foreign object retrieval from steam
turbine generator (STG)
Wet surface air cooler (WSAC)
concrete degradation
Recommended action
Open STG, retrieve foreign object as soon
as practicable
Major repair to WSAC concrete structure
115 kV transmission line failures Periodic repair using cable stored onsite
CTG trips and forced outages
Implement controls upgrades, others
Heat recovery steam generator
(HRSG) low-pressure (LP) evaporator
performance
HRSG tube leaks
Distributed control system obsolescence
Combustion
turbine
generator
(CTG)
controls obsolescence
Table 3. HRSG life consumption and tube panel replacement priorities
(500-MW CCGT). The final column is the total life expended considering all operating
modes; the other columns allocate the portion of the consumed life by operating mode. Components
where we do not expect to achieve full design life have a " total life expenditure " that
exceeds 100%. It's another way of saying that remaining life is being consumed at a rate that
will prevent the component from making it to intended design life. Source: Tetra Engineering
Component
High-pressure
secondary
superheater 1
9. Reconfigured. This shot shows the attemperator
alteration implemented at a plant
that provided a long expansion loop. Note the
drainpot connection at the lower left to remove
condensate and excess spraywater. No
further leaks have occurred after the alteration.
Courtesy: Tetra Engineering
Secondary
reheater 1
Secondary
reheater 2
Primary
reheater 1
Feedwater
heater (inlet)
Cold start
to unfired
Warm
start to
unfired
Hot
start to
unfired
0.49% 4.31% 14.65%
0.75% 3.99% 5.10%
1.12% 5.79% 6.96%
0.66% 5.13% 15.39%
0.05% 1.20% 17.27%
Recommended CAPEX and
Maintenance Actions
Based on all the information gathered, plantspecific,
prioritized
recommended action
items are presented in each plant's condition
assessment report to summarize prior actions
or to prioritize future recommended actions
(Tables 2 and 3) to improve HRSG reliability
for the remainder of service life.
plants unless recent upgrades have mitigated
their occurrence.
Attemperator Piping Cracking,
Thinning, and Drainage
Many plants in the fleet have had a long and
beleaguered experience with leaks in the interstage
RH attemperator piping. A few plants
have completed major alterations after a series
of pipe leak incidents (Figures 8 and 9).
September 2016 | POWER
Healthcare for Combined Cycle
Plants
HRSG condition assessments and health checks
are essentially comprehensive reviews of the
condition of the HRSG that go beyond more
traditional evaluations of calculated damage
rates, accumulated corrosion wear, and expected
remaining creep life. They also examine the
actual plant history and programs for preventive
www.powermag.com
Cold
start to
full fired
1.72%
3.93%
5.91%
2.62%
0.13%
Warm
start to
full fired
13.29%
19.77%
29.00%
18.00%
2.65%
Hot start to
full fired
43.38%
106.11%
153.99%
109.38%
146.36%
Total life
expenditure
fatigue
77.84%
139.65%
202.78%
151.19%
167.66%
maintenance and repair. In some cases, they also
include calculation of additional VOM charges
to account for the " extra " damage incurred by
cycling and/or low-load operation.
As such, these assessments are a new way
to implement a comprehensive evaluation of
key issues for maintaining HRSG reliability,
consistent with current and expected future
plant dispatch. They have provided important
and useful information for capital planning,
maintenance planning, and the implementation
of new and improved operator procedures
and practices for many combined cycle
gas turbine plants. ■
-Peter S. Jackson, PE (peter.jackson@
tetra-eng.com) is director of field services
and David S. Moelling, PE (david.moelling@tetra-eng.com)
is chief engineer at
Tetra Engineering Group.
59
Modify LP drum internals, upgrade leading
row tube bends
High-pressure economizer header modifications
Upgrade
Upgrade
to Mark VI
Cost estimate ($
thousand)
200
250
120
In other costs
175
300
1,750
1,000-2,000
http://www.powermag.com

POWER September 2016

Table of Contents for the Digital Edition of POWER September 2016

Contents
POWER September 2016 - Cover1
POWER September 2016 - Cover2
POWER September 2016 - Contents
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