Seismic risk assessment for oil and gas pipelines - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 694

For pipeline load conditions produced by an imposed displacement, rela-
tively large strains can be accepted provided the pipeline is in good condi-
tion and the girth welds are capable of developing gross-section yielding of
the pipe. For situations where the pipeline is subjected to high longitudinal
compression strains from a combination of axial and bending loads, there
is a potential for the development of local buckling of the pipe wall.
While continuum analyses hold the promise of eliminating many of the
simplistic representations of soil-pipe interaction using pipe elements and
soil springs, several signifi cant obstacles remain to be overcome before
continuum analysis methods can be considered superior to pipe element
and soil spring representations for routine engineering applications:
• It is typically necessary to represent several hundred meters of pipeline
in the analytical model which results in an unwieldy large model that
may take days to run using normally available computational resources.
• The complexity of the model makes it much more diffi cult to extract
results of interest and incorporate relatively minor changes (e.g., change
of soil cover or pipe diameter).
• The ability to model large relative displacements is often not possible
without an effi cient means to reformulate the model mesh.
• Continuum models are generally not capable of capturing fl ow and
fracture behavior and the development of slip planes in the soil sur-
rounding the pipeline.
• Modeling of the soil in a continuum models requires soil properties not
normally available and often requires calibration of the analytical mate-
rial model.
• The fi delity of results from continuum models is likely to be no greater
than what is obtained from simple soil spring models, since available
test data that could provide a basis for validation do not include infor-
mation on the state of stress within the soil and at the pipe-soil
interface.
25.8 Consequences of pipeline damage
The protocol developed for the California Department of Education (2007)
provides a good overview of a relatively simple consequence assessment
process based upon the ALOHA program that is generally available to the
public (NOAA, 2011). Consequences of damage to an oil or gas pipeline
are typically related to exposure to thermal radiation due to a pool fi re, jet
fi re, or fl ash fi re from a vapor cloud ignition. The consideration of explosion
from natural gas release is highly unlikely unless unique conditions exist
that would allow accumulation of gas near the ground without ignition,
confi nement of the gas cloud, and presence of an ignition source in the zone