Underground Infrastructure - November 2023 - 35

EDITION 88 | NOV 2023 | NASSCO.ORG
that area. A crack itself is not a system failure, but
rather an indicator that a design detail needs to be
adjusted to maximize the structure's service life.
Initiate Full Inspections
Even if a new coating looks good to the eye,
inspections need to be performed. That includes
traditional holiday inspections in which an
electrified brush is moved over the entire coated
surface to test the continuity of the coating. The
brush will spark and beep anywhere it completes a
circuit with the substrate under the coating
system, indicating that the coating in those areas
is not thick enough or may have a missed spot or
" holiday " in the coating system. Feedback is
based on the dielectric strength of the coating,
with the tester set to the voltage for the minimum
coating thickness required. Holiday detection is
especially important in high H2S environments,
including structures that have a turbulent flow
(Figure 1). High levels of H2S often occur
downstream of force main discharge structure,
near siphons, or in interceptors with slow moving
flow.
In addition, inspectors ought to do a simple
sounding test on every project, which involves
tapping on the system with a hammer or other
object and listening to the feedback. A hollow
sound may indicate the system is not properly
bonded to the structure, which means water could
get between the coating system and concrete
substrate and lead to premature deterioration.
Following the above advice - and selecting optimal
coatings for the environment (Figure 2) - will
provide the greatest potential for longer asset
service lives for underground concrete structures.
Figure 2. Applying a mortar resurfacer followed by
a resinous lining will best protect assets exposed to
high turbulence and elevated H2S levels.
Figures and Captions
All images courtesy of The Sherwin-Williams
Company unless otherwise noted.
Figure 1. High-flow, high-turbulence areas like this
flash mixer face increased corrosion potential due
to high levels of H2S gas that deposits on surfaces.
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Underground Infrastructure - November 2023

Table of Contents for the Digital Edition of Underground Infrastructure - November 2023

Underground Infrastructure - November 2023 - 1
Underground Infrastructure - November 2023 - 2
Underground Infrastructure - November 2023 - 3
Underground Infrastructure - November 2023 - 4
Underground Infrastructure - November 2023 - 5
Underground Infrastructure - November 2023 - 6
Underground Infrastructure - November 2023 - 7
Underground Infrastructure - November 2023 - 8
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Underground Infrastructure - November 2023 - 11
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