Page 146 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Design 6/123
last.” The important thing is that the equipment fails in a mode Example 6.3: Scoringsafety systems (Case C)
that leaves the system in the least vulnerable condition.
Three examples follow of the application of this point In this example, a supplier delivers product via a high-pres-
schedule. sure pump into a pipeline section that relies on a downstream
section’s reliefvalve to prevent overpressure. The supplier has a
pressure switch at the pump site to stop the pump in the event of
Example 6.1 : Scoring safety systems (Case A) high pressure. The pipeline owner inspects the pump station
owner’s calibration and inspection records for this pressure
In the pipeline section considered here, a pump station is
present. The pump is capable of overpressuring the pipeline. To switch. The pump station owner remotely monitors the pump
prevent this, safety devices are installed. A pressure-sensitive station operation 24 hours per day.
switch will stop the pump and allow product to flow around Conditions present Points
the station in a safe manner. Should the pressure switch
fail to stop the pump, a relief valve will open and vent the B 3
entire pumped product stream to a flare in a safe manner. This F-G - 2.5
station is remotely monitored by the transmission of appropri- Total points = 0.5
ate data (including pressures) to a control room that is manned
24 hours per day. Remote shutdown of the pump from this Note that in this case credit is not given for a relief valve not
control room is possible. Communications are deemed to be in the section being evaluated. The evaluator has decided that
98% reliable. the downstream relief valve does not adequately protect the
pipeline section being assessed.
~ ~ ~~~~~
Condition\ present Pornrr Note also that no points are given for the supplier’s remote
monitoring. Again, the evaluator has made the decision to sim-
C 6 plify-he does not wish to be evaluating suppliers’ systems
E 3
Total points = 9 beyond the presence of direct overpressure shutdown devices
located at the site. Finally, note that the evaluator has awarded
Note that two levels of safety are present (pressure switch points for the pipeline owner’s inspection of the suppliers’
and relief valve). and that full credit is given to the remote capa- maintenance records. He feels that. in this case. an amount of
bilities only after communication effectiveness is assessed risk reduction is achieved by such inspections.

Example 6.2: Scoring safety sjstems (Case B) A4. Material selection (62 pts)
For this example, a section of a gas transmission pipeline has The evaluator should look for evidence that proper materials
a supplier interconnect. This interconnect leads directly to a were identified and specified with due consideration to all
producing gas well that can produce pressures and flow rates stresses reasonably expected. This may appear to be an obvious
which can overpressure the transmission pipeline. Several lev- point, but when coupled with ensuring that the proper material
els of safety are present at the well site and under the control of is actually installed in the system, a number of historical fail-
the producer. The producer has agreed by contract to ensure ures could have been prevented by closer consideration of this
that the transmission pipeline owner is protected from any dam- variable. The evaluator should find design documents that con-
aging pressures due to the well operation. The pipeline owner sider all anticipated stresses in the pipeline components. This
monitors flow rates from the producer as well as pressures on would include concrete coatings, internal and external coat-
the pipeline. This monitoring is on a 24-hour basis, but no ings, nuts and bolts, all connecting systems. supports, and the
remote control is possible. structural (load-bearing) members of the system. Documents
should show that the corrosion potential, including incompati-
ble material problems and welding-related problems, was con-
Conditionspresen I Points
sidered in the design.
Most importantly, a set of control documents should
C 6
E 1 exist. These control documents, normally in the form of pipeline
G -3 specifications, give highly detailed data on all system compo-
Total points = 4 nents, from the nuts and bolts to the most complex instrumenta-
tion. The specifications will address component sizes, material
Note that credit is given for condition C even though the compositions, paints and other protective coatings. and any spe-
pipeline owner has no safety devices of his own in this section. cial installation requirements. Design drawings specify the loca-
The fact that the devices are present warrants points; the fact tion and assembly parameters of each component.
that they are not under the owner’s control negates some of When any changes to the pipeline are contemplated the control
those points (condition G). Also, while contractual agreements documents should be consulted. All new and replacement materi-
may be useful in determining liabilities ufier an accident, they als should conform to the original specifications or the specifica-
are not thought to have much impact on the risk picture. If the tions must be formally reviewed and revised to allow different
owner takes an active role in ensuring that the safety devices are materials. By rigidly adhering to these documents, the chance
properly maintained, condition F would replace G. yielding a of mistakenly installing incompatible materials is reduced.
total point score of 5. A management-of-change (MOC) process should be in place.