Page 186 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Adjustments to scores 71163
Table 7.14 Matrix for evaluating ability of leak detection systems to nance) of additional valves would far outweigh the possible
detect various leak rates benefits, and also imply that such valves may actually intro-
*, duce new hazards.
Leak detection system TI" T,oo TI000
C. Sensing devices. Part of the equation in response time is the
Mass balance for facility first opportunity to take action. This opportunity depends on
(SCADA and manual) the sensitivity of the leak detection. All leak detection will
Patrol have an element ofuncertainty, from the possibility of crank
Overline surveys
Acoustic monitoring phone calls to the false alarms generated by instrumentation
SCADA alarms failures or instrument reactions to pipeline transients. This
SCADA-based computational uncertainty must also be included in the following item.
methods D. Reaction times. If an operator intervention is required to ini-
SCADA-based mass balance tiate the proper response, this intervention must be assessed
Staffing of surface facilities in terms of timeliness and appropriateness. A control room
Passerby reporting operator must often diagnose the leak based on instrument
Other
readings transmitted to him. How quickly he can make this
diagnosis depends on his training, his experience, and the
check valves may reduce the draining or siphoning to a spill at a level of instrumentation that is supporting his diagnosis.
lower elevation. Included in this section should be automatic Probable reaction times can be judged from mock emer-
shutoffs ofpumps, wells, and other pressure sources. Redundancy gency drill records when available. The evaluator can incor-
should be included in all such systems before risk-reducing porate his incorrect operations index ratings (training,
credit is awarded (see Chapter 6, Incorrect Operations Index). SCADA, etc.) into this section also. If the control room can
remotely operate equipment to reduce the leak, the reaction
B. Valve spacing. Close valve spacing may provide a benefit in time is obviously improved. Travel time by first responders
reducing the spill amount. This must be coupled with the must otherwise be factored in. If the pipeline operator has
most probable reaction time in closing those valves. provided enough training and communications to public
emergency response personnel so that they may operate
Discounting failure opening size and pressure, the two com- pipeline equipment, response time may be improved, but
ponents of a release volume from a liquid line are (1) the con- possibly at the expense of increased human error potential.
tinued pumping that occurs before the line can be shut down Public emergency response personnel are probably not able
and (2) the liquid that drains from the pipe after the line has to devote much training time to a rare event such as a
been shut down. The former is only minimally impacted by pipeline failure. If the reaction is automatic (computer-gen-
additional valves-perhaps only helping to stop momentum erated valve closure, for instance) a sensitivity is necessarily
effects from pumping if a valve is rapidly closed (but poten- built in to eliminate false alarms. The time it takes before the
tially generating threatening pressure waves ). The main role of shut down device is certain of a leak must be considered.
additional valving, therefore, seems to be in reducing drain vol-
umes. Because a pipeline is a closed system, hydraulic head
andor a displacement gas is needed to affect line drainage. '%ea of Opportunity " Limitinghctions
Hilly terrain can create natural check valves that limit hydraulic As noted previously, the area of opportunity can sometimes
head and gas displacement of pipeline liquids. be limited by protecting or removing vulnerable receptors, by
Concerns with the use of additional block valves include costs removing possible ignition sources, or by limiting the extent of
and increased system vulnerabilities from malfunctioning com- the spilled product.
ponents andor accidental closures, especially where automatic
or remote capabilities are included. For unidirectional pipelines, A. Evacuation. Under the right conditions, emergency response
check valves (preventing backflow) can provide some conse- personnel may be able to safely evacuate people from the
quence minimization benefits. Check valves respond almost spill area. To do this, they must be trained in pipeline emer-
immediately to reverse flow and are not subject to most of the gencies. This includes having pipeline maps, knowledge of
incremental risks associated with block valves since they have the product characteristics, communications equipment, and
less chance of accidental closure due to human error or, in the the proper equipment for entering to the danger area (breath-
case of automatidremote valves, failure due to system malhc- ing apparatus, fire-retardant clothing, hazardous material
tions. Their failure rate (failure in a closed position) is uncertain. clothing, etc.). Obviously, entering a dangerous area in an
Studies of possible benefits of shorter distances between attempt to evacuate people is a situation-specific action. The
valves of any type produce mixed conclusions. Evaluations of evaluator should look for evidence that emergency respon-
previous accidents can provide insight into possible benefits ders are properly trained and equipped to exercise any rea-
of closer valve spacing in reducing consequences of specific sonable options after the situation has been assessed. Again,
scenarios, By one study of 336 liquid pipeline accidents, such the criteriamust include the time factor. Credit is given when
valves could, at best, have provided a 37% reduction in damage the risk can be reliably reduced by 50% due to appropriate
[76]. Offsetting potential benefits is the often substantial costs emergency response actions.
of additional valves and the increased potential for equipment B. Blockades. Another limiting action in this category is to
malfunction, which may increase certain risks (surge potential, limit the possible ignition sources. Preventing vehicles from
customer interruption, etc.). Rusin and Savvides-Gellerson entering the danger zone has the double benefit of reducing
[76] calculate that the costs (installation and ongoing mainte- human exposure and reducing ignition potential.