Underground Infrastructure - July 2023 - 35

EDITION 84 | JULY 2023 | NASSCO.ORG
Pipe sections resulting in high structural grades
typically require engineering assessment. O&M
defects trigger routine maintenance and
operational activities such as pipe cleaning, root
removal and infiltration control. Pipes displaying
high O&M ratings and low structural ratings may
trigger short term intervention strategies from
Operations. A pipe section displaying both
structural and operational failures would result in
an engineering assessment as structural failures
take precedence over conveyance issues and
O&M defects are removed during repair or
replacement activities.
The Quick Rating reports the worst-case scenario
in the pipe. It is often overlooked because it is an
alphanumeric 4-digit rating system. PACP Quick
Rating reports the peak severity grade observed in
the pipe in addition to the number of occurrences
of that grade. The PACP Quick Rating, therefore,
suggests a condition-based priority to the pipe
section as well as a high-level determination of the
extent of the repair required; four or more
occurrences of structural defects may suggest
full-length pipe attention while one or two
occurrences may suggest a localized replacement
or repair. Similarly, 45 occurrences of 10%
deposits may require heavier cleaning or several
passes of a jetter. When displaying condition data
within a GIS, it is often best to thematically map
condition using the first number of the Quick
Rating. This reports the worst-case scenario to
asset owners.
The pipe rating is an infinite number, and one
might incorrectly assume that the higher the
number, the worse the condition of the pipe. For
example, 9 occurrences of a grade 5 defect
would result in a Pipe Rating 45. Similarly, 45
occurrences of a grade 1 defect would also result
in a Pipe Rating 45.
Finally, the Pipe Rating Index reports the average
severity grade observed in the pipe to one or two
decimal places. Since it is reported on a scale of
1-5, asset owners prefer the Pipe Rating Index for
reporting and mapping. Asset owners should
beware of prioritizing works based on averages;
consider a Pipe Rating Index 3, it takes only 6
grade 1 defects to " hide " the fact that there are 6
grade 5 defects within the pipe section.
All stakeholders should have a solid
understanding of PACP data, how it is collected
and how condition ratings are reported.
Remember, condition ratings are assigned to
each survey; should a survey be abandoned, and
a reversal is performed, two surveys' combined
condition ratings should make up the overall
condition of the pipe section.
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Underground Infrastructure - July 2023

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