Page 70 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Assessing third-party damage potential 3/49
In each classification of the above example, population Anchoring, fishing, and dredging activities, along with
density is a factor. More people in an area generally means dropped objects, pose the greatest third-party threats to sub-
more activity: fence building, gardening, water well construc- merged pipelines. To a lesser degree, new construction by
tion. ditch digging or clearing, wall building, shed con- open-cut or directional-drill methods may also pose a threat
struction, landscaping, pool installations, etc. Many of these to existing facilities. Dock and harbor constructions and
activities could disturb a buried pipeline. perhaps even offshore drilling activities may also be a
The disturbance could be so minor as to go unreported by the consideration.
offending party. As already mentioned, such unreported distur-
bances as coating damage or a scratch in the pipe wall are often Seismograph activi8
the initiating condition for a pipeline failure sometime in the
future. Of special note here is seismograph work or other activities
An area that is being renovated or is experiencing a growth involving underground detonations. As a part of exploratory
phase will require frequent construction activities. These may work, perhaps searching for oil or gas reservoirs, energy is
include soil investigation borings, foundation construction, transmitted into the ground and measured to determine infor-
installation of buried utilities (telephone, water, sewer, elec- mation about the underlying geology of the area. This usually
tricity, natural gas), and a host of other potentially damaging involves crews laying shot lines-rows of buried explosives
activities. Planned or observed development is therefore a good that are later detonated. The detonations supply the energy
indicator of increased activity levels. Local community land source to gather the information sought. Sometimes, instead of
development or planning agencies might provide useful infor- explosive charges, other techniques that impart energy into the
mation to forecast such activity. soil are used. Examples include a weight dropped onto the
Perhaps one of the best indicators of the activity level is the ground where the resulting shock waves are monitored and a
frequency of activity reports. These reports may come from vibration technique that generates energy waves in certain fre-
direct observation by pipeline personnel, patrols by air or quency ranges.
ground and telephone reports by the public or by other con- Seismograph activity can be hazardous to pipelines and the
struction companies. The one-call systems (these are discussed potential for such activity should be included in the risk assess-
in a later section), where they are being used, provide an excel- ment. The first hazard occurs ifholes are drilled to place explo-
lent database for assessing the level of activity, although they sives. Such drilling can, of course, place the pipeline in direct
might only be a lagging indicator; that is, they may show where jeopardy. Depth of cover provides little protection because the
past activity has occurred but not necessarily be indicative of holes may be drilled to any depth. The second hazard is the
future activity. shock waves to which the pipeline is exposed. When the explo-
The presence of other buried utilities logically leads to more sive(s) is detonated a mass of soil is accelerated. If there is not
frequent digging activity as these systems are repaired main- enough backup support for the pipeline, the pipe itself absorbs
tained and inspected. This increased exposure is perhaps par- the energy of the accelerating soil mass [29]. This adds to the
tially offset by a presumption that utility workers are better pipe stresses (Figure 3.5). Conceivably, a charge (or line of
versed in potential excavation damages than are some other charges) detonated far below the pipeline can be more damag-
industry excavators. If considered credible evidence of ing than a similar charge placed closer to the line but at the
increased risk, the density ofnearby buried utilities can be used same depth. An analysis must be performed on a case-by-case
as another variable in judging the activity level. basis to determine the extent of the threat.

Ground surface

moved by the detonation)

(this is moved against
the pipeline when charge
detonates)
Figure 3.5 Seismograph activity near pipelines.