Page 267 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

la244 Offshore Pipeline Systems
of suspected hydrocarbon fields whose exact location and A3. Atmospheric Coating 3%
extent are never precisely known. The costs to recover the B. Internal Corrosion 20?!
hydrocarbons and their value on the world market are similarly B1. Product Corrosivity 10%
estimated values only. Consequently, it is not unusual for a B2. Internal Protection 10%
pipeline to be abandoned for long periods of time until eco- C. Submerged Pipe Corrosion 70%
nomic conditions change to warrant its return to service or until C 1. Submerged Pipe Environment 20%
technology overcomes some obstacle that may have idled the C2. Cathodic Protection 25%
line. Many lines are ultimately placed in a service for which C3. Coating 25%
they were not originally designed. Pressures, flow rates, veloci-
ties, and the composition of the products transported change as Design Index I OP/o
new fields are added or existing fields cease production. A. Safety Factor 25%
Ownership of the pipelines can change as new operators feel B. Fatigue 15%
that they can increase the profitability of an operation. C. Surge Potential 1 0%
Another aspect of offshore pipeline operations is the higher D. Integrity Verification 25%
costs associated with most installation, operation, and mainte- E. Stability 25%
nance activities. When pipelines are placed in an environment
where man cannot live and work without special life-support Incorrect Operations Index 100%
systems, additional challenges are obvious. Inspection, mainte- A. Design 30%
nance, repair, and modification requires boats, special equip- B. Construction 20%
ment, and personnel with specialized skills. Such operations C. Operations 35%
are usually more weather limited and proceed at a slower pace D. Maintenance 15%
than similar onshore operations, again adding to the costs.
Offshore systems are often more vulnerable to weather- LeakZmpact Factor
related outages, even when no damage to equipment occu~s. ProductHazard
This is covered in the cost ofsentice interruption assessment in Dispersion
Chapter 10. Spill Score
As with onshore lines, historical safety data of offshore Receptors
pipeline performance are limited. We cannot currently make
meaningful correlations among all of the factors believed to Some modest changes to some risk variables should be made to
play a significant role in accident frequency and consequence. account for differences between the onshore and offshore
The factors can, however, be identified and considered in a pipelines, Examples of differences include external forces
more qualitative sense, pending the acquisition of more statisti- related to sea bottom stability, inspection challenges, ROW
cally significant data. For these reasons, and for the sake of issues, and potential consequences. However, most risk model
consistency, an indexing approach for offshore lines that paral- variables will be identical. Sample weightings are shown in the
lels the onshore pipeline analysis is often the most useful risk variable descriptions in this chapter. These are determined as
assessment option. discussed in Chapter 2. Weightings should be carefully ana-
Offshore pipeline systems are either transmission pipelines- lyzed by the risk evaluator (or risk model designer) and
long, larger-diameter pipelines going to shore--or pipelines changed when experience, judgment, or failure data suggests
associated directly with production-flow lines, gathering lines. different values are more appropriate.
For purposes of this risk assessment, the two categories are Risers, commonly defined as the portion of the pipeline from
treated the same. The scoring for the offshore risk model will par- the sea bottom up to the platform (sometimes including pig
allel very closely the onshore model for transmission lines traps and valves on the platform), can be evaluated as part of the
described in Chapters 3-7. Although this chapter is primarily pipeline system or alternatively, as part of a risk assessment for
aimed at ocean and sea environments, most concepts will apply structures like platforms. Note that abandoned facilities may
to some degree to pipeline crossings of rivers, lakes, and also be included in an assessment as a potential threat to public
marshes. safety if consequences from the facility are identified (naviga-
After customization, the offshore risk model could have the tion hazard for surface facilities, threat of flotation, etc.). In that
following items and associated weightings: case, the assessment variables will need to be modified to
reflect the probability and consequences of those particular
Third-party Damage Index IOO% hazards.
A. Depth of Cover 20%
B. Activity Level 25%
C. Aboveground Facilities 10% II. Third-party damage index
D. Damage Prevention 20%
E. Right-of-way Condition 5% Consistent with the definition in Chapter 3, the term third-party
F. Patrol Frequency 20% damage as it is used here refers to any accidental damages done
to the pipe by the activities of personnel not employed by the
Comsion Index 100% pipeline operator. Intentional damages are covered in the sabo-
A. Atmospheric Corrosion 10% tage module. Accidental damages done by pipeline personnel
AI. Atmospheric Exposures 5% are usually covered in the incorrect operutions index. In the
A2. AtmosphericType 2% case of offshore operations, external damage can be associated