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

8.5 Sound, Risk-Based, Decision-Making Process Development
This also falls into the area of asset management. Overall system risk may be defined as the risk of
failing to achieve the service level desired. Each element in the system contributes to this risk. The
likelihood of force main failure and the consequence for the system both need to be known to assess
risk and to prioritize assessment and intervention in a cost-effective manner. If consequence of failure
is low, there is little value in knowing likelihood because it has no impact on decisions made or
actions taken. Therefore, the first step is to identify critical assets for which consequence of failure is
high. When this is done, it becomes necessary to identify the likelihood of failure for assets where the
consequence of failure is above a certain threshold. Inspection and condition assessment of the assets
support this effort. The level of likelihood of failure identified from inspection and assessment then
drives management of the asset, comprising maintenance, operation (possibly actions such as
reducing operating pressure), and rehabilitation or replacement. This management approach is
designed to maintain risk at an acceptable level as defined in an asset management plan.
8.6 Cost-Effectiveness of Decision-Making Processes
The decision-making process relies on data from inspection to assess risk levels and to decide on
necessary actions. Determining the level of data or information required to support effective
decisions is a key aspect of the process. Too little data and the wrong decisions may be made; too
much data and the cost of obtaining the data may exceed its value in the process. Neither scenario is
cost-effective.
In general, more information leads to better decisions. But this leads to a quest for perfect
information to eliminate risk from the decisions to be made. This is not cost-effective. Decisionmaking
processes that can be effective with limited information are necessary. Bayesian belief
networks provide one platform for such processes. In addition, these processes need to be combined
with expertise, experience, knowledge, and engineering judgment if they are to be robust and reliable,
while also mitigating risk. For this reason, “black box” processes that can be blindly followed by
non-specialists are high risk processes with the potential for overlooking unusual conditions or
contributing factors to risk.
A key element in the decision-making process as to the method of rehabilitation chosen is the degree
of deterioration present in the force main. The differences in the design of a liner designed for a
partially deteriorated main versus a fully deteriorated main can be substantial. When insufficient data
are available to make that distinction, owners tend to err on the conservative side and chose a solution
appropriate for a fully deteriorated asset. More cost-effective solutions are eliminated from the
decision-making process as a result of such actions.
8.7 Timing for Rehabilitation Action
One element not addressed in this report is the determination of when is the most appropriate time for
a rehabilitation action to be implemented on an asset class. This report alludes to the “end of life” of
an asset as the point where rehabilitation is required. The “end of life” can be defined in several
different ways (Rose, 2009):
• End of Physical Life – pipe actually fails (collapses)
• End of Service Life – pipe no longer performs at level required by stakeholders (e.g.
customers and regulators)
• End of Economic Life – pipe in its current management and operating environment
ceases to be the lowest cost alternative to satisfy a specified level of performance or
service at an acceptable level of risk
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