POWER November 2015 - 45

FUNDAMENTALS
magnification, a nondestructive examination
technique called replication metallography
can be used. It provides a mirrored image of
a material's structure.
In order to provide this level of detail, the
material to be tested needs to be cleared of
any contaminants and polished to a smooth
mirror-like finish. This can be a time-consuming
and laborious process, as manual
techniques are typically required to clear
scale and rust from the installed material
(Figure 4).
After the material has been cleaned and
polished, a chemical etchant is applied to the
surface that allows the grain structure to be
revealed. The chemical used, and duration
of application (to reveal the material's grain
structure), will be chosen based on the material
being tested.
A replicating material will then be applied
to the material surface to embed the
grain structure into the replicating material.
Once the material dries, it can be removed
and sent for microscopic observation. The
replicating material will now reveal the
grain structure of the material without compromising
the integrity of the material itself.
The process will give insight into only the
grain structure at the surface of the material
and is used on base metals and critical
welds alike.
High-Energy Pipe Surveillance
In addition to employing nondestructive examination
techniques, conducting surveys of
a plant's high-energy piping systems should
be a routine occurrence. High-energy piping
systems typically include main steam, hot
reheat, cold reheat, boiler feedwater, and
turbine extraction piping systems. Highenergy
piping surveys analyze stress and
strain on the piping and support system.
This is critical for extended plant operation,
because the survey can detail areas of concern
that can be corrected prior to a material
or pipe support failure.
As these high-energy systems operate
over time, hanger adjustments are sometimes
made that change the dynamics of the system.
Additionally, poor initial designs, changes
in modes of operation, or plant preferences
can result in the addition or removal of key
pipe support elements. Because high-energy
piping expands and contracts considerably
during startup and shutdown cycles, if such
changes are not properly implemented, the
system will grow, bend, or cycle in an undesirable
way.
In order to effectively evaluate these highenergy
systems, they need to be observed in
the two extreme states of operation. Documenting
the hanger positions in both hot
(full-load operation) and cold (zero-load
November 2015 | POWER
www.powermag.com
ABSOLUTE
MATERIAL FLOW
CONTROL
* Optimum material flow
* Up to 80% decrease in mate
* Reduced dust and noise leve
* Virtually maintenance free
* Greatly reduced spillage
* Significant reduction in belt d
cold plant) conditions allows engineers to
model the stress and strain of the system.
This modeling can then be compared against
the original design and evaluated for proper
support and growth allowance. The results
will dictate if adjustments to hangers are required
or if new support hardware is necessary
to bring the system back into allowable
stress ranges.
Although it may be challenging to continually
inspect and document the material condition
of steam-generating equipment and
high-energy piping, the payback will come
in the form of increased equipment reliability
and availability. Shutdowns as a result of
forced outages are costly, due to the likelihood
of expedited material purchases and
uncertain availability of skilled craft labor.
Establishing programs to track and plan for
repairs will lead to fewer forced outages and
longer plant life. ■
-Brandon Bell, PE (bbell@valdeseng.
com) is lead project manager for power
projects at Valdes Engineering Co.
ABSOLUTE MATERIAL FLOW CONTROL
Phone: 800-425-2356
Email: caryhenken@powertechniques.net
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Coralynne & Associates +27 (011) 849 3142
http://www.powermag.com
POWER November 2015

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