Page 240 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Upset score 10/217
scored. In the service interruption risk, interventions to prevent reduced probability of the event causing customer upset. This is
events that lead to service interruptions are also scored early in an important distinction; see the example at the end of this
the assessment, but then another intervention possibility is fac- chapter. A qualitative scale to assign a value to the intervention
tored in. This reflects the opportunity for intervention after an adjustment follows.
episode has occurred that would otherwise lead to a service
interruption. In the risk numbers, this adjustment allows the Early detection is not always possible No adjustment
section score to partially “recover” from low points in episode awarded
likelihood. When the excursion is not detectable, reactionary intervention
In many pipeline systems for which an uninterruptible sup- is not possible. When some of the possible excursions are
ply is critical, extra provisions have been made to ensure that detectable, score according to the next category.
supply. These provisions allow for reactions to events that, if Early detectionlaction Up to 30%
not addressed, would cause service interruptions. Examples Maximum points are awarded when all excursion episodes are
include halting the flow of an offending product stream and detected early enough to allow action to be taken to prevent
replacing it with an acceptable product stream, blending of a or minimize customer interruption. This may be at a point
contaminant to reduce concentration levels, treating of a con- where contaminated product is prevented from entering the
taminant on-line, and notifying the customer so that alternate pipeline, or where product streams may be blended to reduce
supplies can be arranged. The reactions can be assessed in contaminate levels to appropriate concentrations, alternate
terms of their effectiveness in preventing service interruptions delivery equipment can be brought into play, or where alter-
after an event has occurred. nate sources can be routed to the customer. The reliability of
Even a pipeline failure will not necessarily cause a service detection must be considered here. The time to detect and
interruption. This would be the case if an alternative supply take action must include time to receive, interpret, and
could be found to replace the lost supply or the leak can be respond to the detection information. Indirect indications,
repaired with the pipeline in service. Note that in assessing the such as a pressure drop after an accidental valve closure,
effectiveness ofa reaction, a time variable may be important. A serve as detection mechanisms. Note that unusual events will
given reaction may prevent a service interruption for only a normally require more human analysis time before action is
certain amount of time beyond which the interruption will taken. Emergency drills can be a useful measure of detec-
occur. tionireaction times.
Note that by use of this adjustment factor, a high-probability
excursion that has a low probability of actually impacting the Often a point on the pipeline near the customer may have a
customer is recognized and scored differently than the same problem (such as a closed mainline valve) in which there would
event that is more likely to impact the customer. Some interven- not be enough time to make a meaningful early detection and
tions have already been included in assessing the upset score. notification. When some excursion types can be detected and
Reconsidering them here is acceptable as long as a consistent some may not be, or when detection is not reliable, no more
approach is used.The intervention adjustment is sensitive to the than 10% should be awarded.
section being evaluated.
System dynamics play a role in assessing interventions. Customer warning is sufficient 50%
Consideration should be given to systems that are more “for- to prevent an outage for that customer
giving” in that they are slower to react to an upset. An example These percentage points are awarded only when there exists a
of this is a high-pressure, large-volume gas system in which unique situation in which, by the action of notifying the cus-
outflows will only slowly depressure the system upon tempo- tomer of a pending specification violation, that customer can
rary loss of inflows. Contrast this with a small-volume liquid always take action to prevent an outage. Coupled with a reli-
system that is effectively “tight-lined (inflows balance out- able early detection ability, this allows an 80% (30% + 50%)
flows with no temporary imbalances tolerable). In this latter factor to reduce the service interruption potential. An exam-
case, reaction times are more critical. ple would be an industrial consumer with alternative sup-
To score the availability and reliability of interventions, add plies where, on notification, the customer can easily switch
percentages for all the mitigating actions that are present and to an alternate supply.
functioning. Note that these actions apply to any and all identi- Customer warning will minimize 10%
fied episodes of product specification deviation or delivery impact (but not always prevent an outage)
parameter deviation. If an action cannot reliably address excur- When a customer early warning is useful but will not always
sions of any type, then intervention credit is awarded only to the prevent an outage, these percentage points are awarded. An
benefiting excursion. For example, if an early detection system example would be an industrial user who, on notification of a
can find and allow reporting of a contamination episode, but pending service interruption, can perform an orderly shut-
there is no equivalent system to react quickly to a pipeline fail- down of an operation rather than an emergency shutdown
ure, then the intervention adjustment is only applied to the PSD. with its inherent safety and equipment damage issues.
Therefore, these percentages will be used to adjust scores for Almost every customer will benefit to some degree from
PSD and DPD independently. The percentage will apply to the early warning. Even residential gas users, given a few
difference between the actual PSD or DPD score and the maxi- moments notice before an outage, can make plans and
mum possible score, up to 80%. The means that the PSD andlor adjustments to better respond to the service interruption. The
DPD scores can recover from low point conditions up to 80% of customer’s ability to react to the notification should be meas-
the maximum possible points. Increasing points in this fashion ured assuming the most likely detectiodnotification time
does not indicate a reduced probability of the event, only the period.