State of Technology Report for Force Main Rehabilitation, Final ...

7.0 GAPS BETWEEN NEEDS AND AVAILABLE TECHNOLOGIES
All of the tools for force main system rehabilitation programs are not yet in place. This section addresses
the gaps that need to be closed in order to provide utilities with the decision-making processes and the
rehabilitation technologies necessary to develop such programs. The first section will address data gaps
in terms of knowledge of the host pipe condition and the second section will address capability gaps in
terms of available renewal technologies.
7.1 Data Gaps
The data gaps between needs and available technologies are significant.
The available inspection technologies can obtain the required data concerning the condition of force
mains, which is necessary for assessment and renewal design purposes. But these technologies cannot be
used cost-effectively or without shutdown of the main, which is generally not possible or entails major
cost. Data may be obtained either externally or internally. External data require excavation for inspection
on the pipe surface. For reasons of cost and practicality, this can only be done at a small number of
discrete locations along a pipeline. As a result, the sample size is extremely small and the confidence
level of the findings in terms of being representative of the pipeline as a whole is very low. Internal data
require the main to be shut down and dewatered for inspection. This is extremely costly due to the
service interruption, which may require by-pass pumping or honey wagons to be used to transport the
wastewater in the absence of upstream storage capacity.
As a result, little data are obtained on force main condition upon which assessment and subsequent
rehabilitation decisions can be based. Rehabilitation decision-making can only be made on the basis of
operational indicators such as power consumption, air release valve operation, or main breaks. The
alternative is to consider consequence of failure and to renew high risk lines irrespective of any
knowledge of their condition. This is inefficient and results in higher cost than either preventative
maintenance or rehabilitation intervention based on condition assessment within a risk-based framework.
The WERF report titled Inspection Guidelines for Force Mains addresses this issue (WERF, 2009). It
sets out guidelines for inspection based on material. It also covers prioritization of inspections and the
key considerations in the development of an inspection plan.
A key finding based on international experience reviewed is that utilities consider that there is benefit in
being able to make a proactive decision on whether to renew based on risk. Part of this is to know where
problems do not exist so expenditure can be deferred. The renewal decision is based on three elements:
the rate of deterioration of assets; the condition of critical locations; and whether spending can be
deferred. Risk analysis can also help indicate where the “wait and see” approach is most cost-effective.
It is also important to take into account that inspection can create liabilities. Knowledge of a defect
creates a need to do more than “wait and see.”
A first step is to establish risk-based assessment methods to identify force mains with serious
consequences of failure, either in operational or environmental and public impact terms, or both. This
will drive the need to understand the likelihood of failure and will identify the characteristics of force
mains for which this information is needed. A second step is to consider prioritization for external data
collection. A method for identifying high risk locations in terms of likelihood of failure based on
environment and operating characteristics could pinpoint high risk locations, which would be selected for
direct inspection. This would increase the chance that the small sample obtained would identify more
critical conditions than otherwise.
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