Page 234 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Upset score 10121 1
The definition for service interruption contains reference to 84. Operator Error 20 pts
a time factor. Time is often a necessary consideration in a spec- C.InterventionAdjustment (IA) Up to 80% of [(8O ~ PSD) +
ification noncompliance. A customer’s system might be able to (460 - DPD)]
tolerate excursions for some amount of time before losses are Total Upset Score 0-540 pts
incurred. When assessing customer sensitivity to specification
deviations, the evaluator should compare tolerable excursion Note: As with the basic risk assessment model, higher num-
durations with probable durations. bers indicate a safer (less risk) situation. Point values are based
In the basic risk model, variable scoring is geared toward a on perceived frequency and severity of the variables. They are
pipeline failure, basically defined as leakage. Therefore, all not currently based on statistical evidence but rather on judg-
previously scored items in the basic risk assessment model will ments of variable importance relative to other variables that
be included in assessing the risk of service interruption. As pre- contribute to risk. For example, in the sample point scheme
viously noted, because a service interruption can occur for rea- shown above, the variable pipeline blockages plays approxi-
sons other than a pipeline leak, some index items must be mately the same role in risk as does depth of cover (as an aspect
revisited. Considerations unique to service interruptions will of failure potential in the Third-party Index). Figure 10.1,
be scored and added to the safety risk scores. When a pipeline shown earlier, illustrates the calculation of the service interrup-
failure will not necessarily lead to a service interruption, the tion risk.
assessment becomes more difficult. Once done, care should be
exercised in making comparisons--it may not be appropriate to 111. Upset score
compare the basic risk assessment with an expanded assess-
ment that includes service interruption risk. A. Product specification deviation (PSD)
In keeping with the philosophy ofthe basic risk model, risk is
calculated as the product of the interruption likelihood and Deliveries of products by pipeline are normally governed by
consequences: contracts that inciude specifications. Most specifications wiil
state the acceptable limits ofproduct composition as well as the
Service interruption risk = (upset score) x (impact factor) acceptable delivery parameters. Deviations from contract spec-
ifications can cause an interruption of service. When formal
The impact,/uctor represents the magnitude of potential con- contracts do not exist, there is usually an implied contract that
sequences arising from a service interruption. The upset score the product supplied will be in a condition that fits the cus-
IS the numerical score that combines all pertinent risk likeli- tomer’s intended use. When a city resident orders a connection
hood elements-both risk contributors and risk reducers. It to the municipal gas distribution system, the implied contract is
encompasses the two types of service interruptions (excur- that gas, appropriate in composition, will be supplied at suffi-
sions): (I) deviations from product specifications and (2) devi- cient flow and pressure to work satisfactorily in the customer’s
ations from specified delivery parameters. The upset score also heating and cooking systems. The product specification can be
captures any intervention possibilities, in which an event violated when the composition of the product changes. This
occurs along the pipeline, but an intervention protects the will be termed contamination and will cover all episodes where
customer from impact. significant amounts of unintended materials have been intro-
We now look at the upset score in more detail: duced into the pipeline product stream. Significant is defined in
the specifications.
lJpsetscore=(PSD+DPD)+(IA) Common contamination episodes in hydrocarbon pipelines
where involve changes in the following:
PSD =product specification deviation-the potential for the
product transported to be off-spec for some reason Hydrocarbon composition (fractions of methane, ethane,
DPD =delivery parameter deviation-the potential for some butane, propane, etc.)
aspect of the delivery to be unacceptable Btucontent
IA = intervention adjustment--the ability of the system to Water content
compensate or react to an event before the customer is Hydrocarbon liquids
impacted. This is a percentage that applies to the differ- CO,,H,S
ence between actual PSD and DPD scores and maxi- Solids (sand rust, etc.).
mum possible PSD and DPD scores.
Some of these contaminants are also agents that promote
Here is a breakdown ofthe PSD. DPD, and IA categories: internal corrosion in steel lines. To assess the contamination
potential, the evaluator should first study the sensitivity of the
A. Product Specification Deviation (PSD) &SO pts customers. The customer tolerance to hydrocarbon composi-
A 1. Product Origin 20 pts tion changes is the key to how critical this factor becomes in
A2. Product Equipment Malfunctions 20 pts preventing service interruptions. The customer specifications
A3. Pipeline Dynamics 20 pts should reflect the acceptable composition changes, although
A4. Other 20 pts there is often a difference between what can actually be toler-
B. Delivery Parameter Deviation (DPD) W60 pts ated versus what contract specifications allow. If this becomes
B 1. Pipeline Failures 400 pts a critical issue, interviews with the customer process experts
B2. Pipeline Blockages 20 pts may be warranted. When the customer is an unsophisticated
B3. Equipment Failures 20 pts user of the product, such as a typical residential customer who