POWER April 2016 - 20

Covered Piping Systems
O&M Programs for CCGT
Plants
A great level of risk is present when operating
pressurized systems. Over the years,
industry safety concerns have increased
with the occurence of catastrophic events.
To help prevent further loss and damages,
expanded requirements for operations and
maintenance (O&M) were added to the
ASME Code for Pressure Piping, B31.
Power Piping-ASME B31.1- " Chapter
VII Operation and Maintenance " was created
in 2007 to prescribe guidelines that
promoted early failure detection and overall
safety. This was a fundamental change
to the scope of B31.1, which up until then
was strictly a design code; going forward,
it now serves a dual purpose.
Plant management teams have relied
on these standards for designing, as well
as updating, their maintenance programs.
Industry experience shows that combined
cycle gas turbine (CCGT) plants owned by
investment groups, municipal power companies,
and others without large in-house
engineering staffs find themselves needing
to take action. This is less of an issue
for regulated utilities that have established
high-energy piping programs, which
may address most of the requirements, although
some of the failures, including incidents
at W.A. Parish and Iatan, occurred
at plants operated by regulated utilities.
Incidents Lead to Changes
The latest version of the ASME Power Piping
code, published in 2014, has built a
foundation from tragic industrial experience.
It was the work of committees and
experts that drew conclusions from some
unfortunate events. Formal amendments
were enacted in previous editions of the
B31.1 as their work progressed. Two wellknown
incidents served as catalysts for
change.
One of them took place at the W.A. Parish
Station in 2003. A cold reheat steam
pipe failed and caused a great amount of
property damage. Extensive analysis, using
such tools as metallographic examinations,
computational fluid dynamics,
finite element analysis, and fracture mechanics,
concluded that fatigue cracking
caused the pipeline to explode. In 2007,
the Iatan power plant desuperheater attemperator
spray line suffered a failure
incident caused by flow-accelerated cor20
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POWER
| April 2016
rosion (FAC). Property damage as well as
personnel loss resulted.
O&M Scope and Requirements
The ASME covered piping systems (CPS)
O&M program places the responsibility for
safe operation and maintenance of power
piping on the operating company. Management
is charged with implementing a CPS
O&M program plan and conducting surveillances,
preventive maintenance, and inspection
activities that identify potential
problems before degradation progresses to
component failure or leakage.
A typical scope of a CPS program includes
pipe systems that have a 4-inch
nominal pipe diameter or greater and
additional systems the owners deem important.
The most common systems and
components are:
■ High-pressure (HP) steam/main steam,
including heat recovery steam generator
(HRSG) HP steam outlet manifold to
steam turbine admission and HP steam
bypass from HP steam piping to cold
reheat (modern combined cycle plant
configurations).
■ Hot reheat (HRH) steam, including
HRSG reheat steam outlet manifold to
steam turbine admission and HRH bypass
to condenser.
■ Cold reheat (CRH) steam, including HP
steam turbine nozzle to HRSG reheater
inlet manifold, intermediate pressure
(IP) steam from HRSG IP superheater
outlet to merge with CRH steam, the
portion of the HP bypass to CRH that is
downstream of the desuperheater spray
valve, extractions to gland steam systems,
extractions for combustion turbine
steam injection, and extractions
for condenser sparging.
■ Low-pressure (LP) steam, including
HRSG LP superheater steam outlet
manifold to steam turbine admission,
LP steam bypass to condenser, and LP
sparging steam to condenser.
■ Feedwater, including suction from LP
drum (or condensate pumps discharge)
to boiler feedwater pump nozzle, HP
discharge from feedwater pump nozzle
to HRSG HP economizer inlet, IP discharge
from feedwater pump nozzle to
HRSG IP economizer inlet, feedwater
supply to fuel gas heater (if installed),
feedwater supply to HP steam bypass
(to CRH) desuperheater sprays, feedwater
supply to CRH/seal steam desuperheater
sprays, and feedwater supply to
other auxiliary spraywater services.
Chapter VII covers the basic elements
that a program should include. From O&M
1. Hanger support anomaly. In this image, the variable spring pipe support is topped
out and needs to be adjusted. Courtesy: Tetra Engineering Group
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POWER April 2016

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