Page 289 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

13/266 Stations and Surface Facilities
Table 13.4 Components and their equivalent surface areas fully explained here. Based on 100 points maximum (safest
situation = 100 points), as with the other indexes, the external
Component Equivalent area ft2) forces index assesses risks from possible outside forces
related to
Piping (above ground) 1
Tanks 2 Traffic
Tank bottom 5 Weather
Dresser coupling 2000
Other mechanical coupling 200 Successive reactions.
Pump seal, tandem 50
Pump seal, single 100 Trafic
Already corrodedbmaged material 20
Atmospheric corrosion hot spots 5 The potential for damage by outside force increases with
Pump (per horsepower) 10 increasing activity levels, which include the type, frequency,
Valves 10 intensity, complexity, and urgency of station activities. This
Penalty for buried component 0.5
also includes the qualifications of personnel who are active in
the station, weather conditions, lighting, third-party access,
traffic barriers, security, and a third-party awareness/damage
Table 13.4 also shows that the equivalency designers prevention program.
believe that buried components are twice as problematic as Vehicle impact against some facility component is a threat.
above ground. A penalty is assigned for buried or otherwise The type of vehicular traffic, the frequency, and the speed of
difficult to inspect portions of the facility. While buried por- those vehicles determine the level of threat. Vehicle movements
tions enjoy a reduced risk from external forces and fire, on inside and near the station should be considered, including
balance it is felt that the inability to inspect and the increased
opportunity for more severe corrosion, warrants a penalty. Aircraft
This is contrary to the case of cross-country pipelines where, Trucks
on balance, buried components are thought to present a Railtraffic
reduced risk. The penalty assigned to station buried facilities Marine traffic
results in increasing the equivalent surface area by 50%, in the Passenger vehicles
example table above. Maintenance vehicles (lawn mowers, etc.).
A good way to develop these relationships in the absence of
actual failure data is to ask station maintenance experts collec- Vehicles might be engaged in loadinghnloading operations,
tively questions such as “From a maintenance standpoint, how station maintenance, or may simply be operating nearby.
much piping would you rather have than one pump seal?” This Traffic flow patterns within the station can be considered: Is
puts the issue in perspective and allows the group to come up the layout designed to reduce chances of impact to equipment?
with the equivalencies needed. Use of signs, curbs, barriers, supervising personnel, operations
The scale should be flexible since knowledge will change by personnel unfamiliar with the station (perhaps remote access
over time. Changes to the equivalent lengths can automatically by nonemployee truckers), lighting, and turn radii are all consid-
convert into new risk scores if arobust computer model is used. erations. With closer facility spacing, larger surface areas, and
The equivulent surface ureu is numerically scaled from the poor traffic control, the potential for damage increases.
highest to lowest among stations and facilities to be assessed. Type and speed of vehicles can be assessed as a momentum
That is, the largest equivalent area station sets the high mark on factor, where momentum is defined in the classic physics sense
the reIative scale. The low mark can be taken at 0 or the smallest of vehicle speed multiplied by vehicle mass (weight).
station, depending on model resolution needs. Momentum can be assessed in a quantitative or qualitative
The equivalent surface area factor-the ratio of the station’s sense, with a qualitative approach requiring only the assign-
score to the highest score of any facility to he evaluated-is ment of relative categories such as high, medium, and low
then used to adjust the index sum. So, if the index sum for two momentum. The frequency can be similarly judged in a relative
facilities tuns out to be exactly equal, then the one with the sense. Note that relative frequency scales can and should be dif-
larger equivalent surface areu will show a higher failure proha- ferent for different vehicle types. For example, a high fre-
bility level. The exact amount of impact that the equivulent sur- quency of aircraft might be two or three planes per hour,
face areu has on the index sum is a matter ofjudgment. Saying whereas a high frequency for trucks might be several hundred
that the most complex station will have a failure probability of per hour (on a busy highway). For each type of vehicle, the fre-
50% more than the least complex or that the failure rate is 10 quency can be combined with the momentum to yield a point
times higher than the least complex station are both justifiable score. Where the potential for more than one type of vehicle
decisions, depending on the station types, operator experience, impact exists, the points are additive.
historical data, etc. The mathematics is therefore left to the Where protective measures such as barrier walls or protec-
evaluator to determine. tive railings have been installed, the momentum component for
the respective vehicle can be reduced. Similarly, natural barri-
External forces index ers such as distance, ditches, and trees can be included here.
This is consistent with the physical reality ofthe situation, since
For surface facilities, the third-party damage index can be the barrier will indeed reduce the momentum before the impact
replaced by the external forces index. This index is more to the facilities occurs.