42
NuclearPlantJournal.com Nuclear Plant Journal, March-April 2016
Innovation
Improves...
Table 1 – Field Conditions, Potential Contributing Factors.
currents imparted unintentionally
from other cathodically protection
systems or structures.
Environment
(underground)
--
aggressive soil chemistry and
conditions, i.e. high chlorides,
low pH, dissolved salts, high
soil conductivity, retained water,
dissimilar
soils,
incompatible
backfill, differential aeration, etc.
Grounding -- improper grounding
of electrical systems, bonding of
equipment and circuit conductors
contribute to unwanted currents,
i.e. neutral return current, flow on
conductive materials, equipment,
grounding and bonding paths.
Localized Corrosion - pitting, crevice
corrosion or under-deposit corrosion
when the anodes and cathodes are
relatively stationary and corrosion
is localized, leading to aggressive
loss of wall thickness that may cause
leaks.
Microbiologically
Influenced
Corrosion (MIC) – an accelerated
corrosion mechanism due to the
presence of microbes causing
localized corrosion.
Pipe Construction or Repairs --
conditions where prior construction
or repairs leading to potential
corrosion, e.g. improper repairs,
backfill materials, etc.
Stray Currents -- externally induced
electrical currents, mainly from stray
direct currents (DC) but Alternate
currents (AC) can also affect
corrosion on metallic components,
i.e. proximity to high- and medium-
voltage conductors.
Where and when such factors or site
conditions were observed, we assessed
them and provided recommendations to
reduce the risk or remedy the condition
along with the results from the leakage
and analytical condition results. Some of
our overall recommendations included:
Further investigate or verify two
segments: excavated one possible
leak point, repair or replace the
affected length of pipe; and pressure
test another identified segment to
determine if there is a potential line
leak.
Increase monitoring and inspection
of a limited number of segments to
assure continued system function and
integrity, and initiate pre-planning
for possible piping in the future if
necessary for contingency purposes.
Conduct periodic system leakage
testing and conditional assessments
to monitor and verify overall system
and segment conditions and integrity.
Consider conducting tests and
analysis to evaluate sources of
stray currents/voltages in order to
determine exactly where the source
or sources of the problem may be,
and develop a plan to monitor and
control potential stray currents, stray
voltage conditions in a systematic
way.
Obtain soil samples to address
relevant factors that may contribute
to corrosion in the area of existing
buried pipe environment, e.g. pH,
Chlorides, Sulfates, MIC; and
conduct Soil Resistivity Tests to
determine soil resistivity values
and possible variations, due to soil
makeup, chemical content, moisture,
temperature, etc.
Share the results of this effort with
affected departments involved in
asset management, underground
piping and tanks integrity initiatives,
facilities
maintenance,
fire
protection, etc.
In summary, using innovative
approaches and technologies helped
to pin-point possible leakage areas
and segments of pipe with degraded
conditions, as well as a number of site
factors, that warranted additional attention
without disruption to system availability
or operations personnel. The results
yielded some 14 recommendations on
the path forward ranging from continued
systems focus and monitoring to some
additional confirmatory investigations
to the possible repair/replacement of a
very limited amount of piping. While
this effort developed important data and
information, the overall results helped
to localized issues of import and aided
in decision making going forward. The
level of effort that this project cost was
a small fraction of the potential cost of a
multi-million dollar replacement options
earlier considered; Thus, reducing the
CapEx exposure and allow the availability
of plant funds to be allocated in the
future to other more pressing operations
or maintenance needs. Estimated cost
savings or avoided costs were on the
order of $3-5 million.
Contact: Joe Grillo, telephone:
(603) 531-0297, email: Joe.Grillo@
IBEXesi.com or Rob Sweeney, telephone:
