Page 238 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

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Table 10.2 Critical delivery parameters

Delivetypurumeter Pipehnefailure Pipeline hlockage Equipment failure Operator emir
Flow Any pipeline failure Buildup(paraffin, Valve closure; pump Miscalibration;
polyethylene, etc.) failure; relief valve improper procedure
on pipe walls opening; control valve
malfunction: false signal
Pressure Same Same Same Same
Temperature Heat exchanger failure Failure to adjust for
decreased flow rate

B2. Pipeline blockages This includes many safety devices that, while protecting the
system from overstressing, could also impact a delivery param-
Mechanisms exist that can restrict or totally block flow in a eter. An “unwanted action” of such devices was not covered in
pipeline but not lead to a failure of the pipe wall. Common the basic risk assessment model because such malfunctions do
blockages include paraffin or wax plugging as paraffinic not usually lead to pipeline failure. Therefore, this additional
hydrocarbons crystallize in the bulk fluid or on the pipe wall; risk item must be added when service interruption is being
hydrate formation as free water freezes in the flowing product evaluated.
stream; and scale deposits as salts, such as barium sulfate, crys- Where redundant equipment or bypasses exist and can be
tallize on the pipe wall. These mechanisms depend on a host of activated in a timely manner, risk is reduced.
variables such as chemical compositions, flowing conditions Weather outages or outages caused by natural events such
(pressure, temperature, velocity, etc.), and pipe wall condition. as hurricanes, earthquakes, fires, and floods are also consid-
While complete flow blockage would usually interrupt pipeline ered here as a type of equipment failure. When such occur-
service, partial blockages often cause pressure increases suffi- rences cause a pipeline failure, they are addressed in the
ciently high to increase operational costs or reduce flow rates to basic risk model. When they cause a service interruption
unacceptable levels. The rate of blockage formation may also (without a pipeline failure), the probability ofthe event can be
be an important variable. considered here. A common example is an offshore pipeline
A sample qualitative scale to evaluate the potential for block- system that is intentionally shut down whenever large storms
age follows. threaten.
High 0 pts Pressure und,flows regulating equipmen? Rotating equipment
Blockage will almost certainly occur if mitigating actions are such as pumps and compressors used to maintain specified
not regularly taken. The formation of the block can occur rel- flows and pressures is a potential source of specification viola-
atively quickly. tion. In such complex equipment, it is rare to not have
Medium 10 pts allowances for outages since they are more prone to failure. A
Conditions exist that may cause blockage. Contamination whole host of relatively minor occurrences will stop these
episodes can form blockages. devices in the interest of safety and prevention of serious equip-
Low 1.5 pts ment damage.
Remote possibility of conditions conducive to blockage forma-
tion. Blockage would be very slow in forming. Flow stopping devices Devices that will stop flow through a
Impossible 20 pts pipeline are potential causes of specification violations.
Even considering contamination potential, the product will not Mainline block valves, including emergency shut-in, auto-
form blockages in the pipe. matic, remote, and manual configurations are included here.
Corrective actions taken include When the product source is a subterranean well or reservoir,
any and all attached shut-in devices should be considered.
Monitoring via pressure profile, internal inspection device,
etc. Sufet?, sewices Relief valves, rupture disks, and other auto-
Cleaning (mechanical, chemical, or thermochemical) at fre- matic shutdowns will normally impact delivery parameters
quencies consistent with buildup rates and the effectiveness when they are tripped. Often, the more complicated the shut-
of the cleaning process down schemes, the greater the probability of unnecessary trig-
Inhibitors to prevent or minim.ize buildup. gering of the system. A sophisticated SCADA system can
provide quick detection of equipment failures and can be con-
These should be considered in assessing the blockage poten- sidered to be a potential prevention opportunity.
tial.
Equipmenf controlling other product properties Where tem-
53 Equipmenrfuilures perature or temperature-related properties such as density and
viscosity are critical customer requirements, malfunctions in
Any piece of equipment that could upset a delivery parameter heat exchangers, coolers, heaters, etc., are sources of specifica-
should be examined as a potentla1 cause of servlce interruption tion violation.