POWER September 2016 - 55

COMBINED CYCLE O&M
■ Examine compliance with general HRSG
maintenance and operational guidelines
■ Recommend action items
Information collected and reviewed in this
process is compiled and evaluated with respect
to issues most important to improve or maintain
HRSG reliability. Plant-specific reports are prepared
to provide management with recommendations
for the next five to 10 years.
Factors Affecting Reliable HRSG
Life
Most combined cycle plants in the North
American fleet were designed and constructed
during the initial bubble of rapid expansion
of natural gas-fired power plants. Over the
years, many potential issues have emerged for
HRSGs, including the following.
Operating factors:
■ HRSG cycling service
■ Water chemistry control and layup practice
■ High-temperature drain capacity and
controls
Effects on HRSG pressure parts:
■ HP superheater and reheater (RH) panel
tube failures
■ HP evaporator tube and lower header failures
■
FAC, erosive wear (EW), and liquid droplet
impingement (LDI) thinning of lowpressure
(LP) evaporator system tubes,
headers, and riser piping
■ Attemperator piping thermal impingement
and quench damage
■ LP economizers tube failures
■ Cold end corrosion, tube fouling, and
backpressure issues
■ Corrosion under insulation
Each plant's final report includes an evaluation
of each of these potential issues plus
recommended, prioritized actions grouped
by HRSG panel section and component.
HRSG Failure History
A complete review of the failure history at
each plant is conducted, including reviews of
relevant root cause failure analyses, metallurgical
laboratory reports, and related field inspection
and testing records. These documents
are important to identify currently active damage
mechanisms, issues that have been resolved
by prior repairs and alterations as well
as the result of other actions to reduce the rate
of damage progression (such as changes in
water chemistry control and operating procedures).
The data include failures that-while
plant-specific-are grouped into the following
common systems:
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September 2016 | POWER
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55
■ High-temperature pressure parts (HP superheater
and reheater)
■ HP steam system
■ Intermediate pressure (IP) steam system
■ LP steam system, including external deaerator,
if present
■ Interstage attemperator piping (HP/RH)
■ Other interconnecting piping
■ Small-bore piping (drains and vents)
■ Baffles, casing, penetrations, structures,
and other non-pressure parts
These reviews include the review of NBIC
R1 reports from prior pressure part repairs.
HRSG Inspection Report
Summaries
The level of detail in available HRSG inspection
reports varies substantially from plant to
plant and across the fleet because different
contractors provide these services (and for
different purposes). The types of inspection
reports reviewed in the course of an assessment
include the following:
http://www.powermag.com
POWER September 2016

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