Page 407 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

3821 Glossary
aspects of pipeline design, construction, and operation. The of failure) to a theoretical high of 400 (virtually no chance of
Office of Pipeline Safety (OPS) is the department within failure).
DOT charged with ensuring pipeline safety. In-line inspection (ILI). The use of an electronically instru-
Draindown. Quantity of product that will gravity flow- mented device, traveling inside the pipeline, to measure
drain-to the leak site after a pipeline rupture, based on characteristics of a pipe wall, especially the detection of
topography, pipeline diameter, pressure, valve location, and anomalies such as metal loss due to corrosion, dents, gouges,
response time. and cracks. Several ILI tool technologies are available, each
with relative strengths in terms of types of anomalies
EPA. Environmental Protection Agency. The regulatory detected, ability to characterize the anomaly, and accuracy.
agency of the U.S. government that is charged with regulat- Internal corrosion. Any form of corrosion that occurs on the
ing activities that may be harmful to the environment. inside wall of the pipe or internal surfaces of any pipeline
ERW. Electric resistance welding is a manufacturing process component.
for pipe. Although modern ERW pipe is considered to be
high quality, a low-frequency ERW process common before Landslides. The moderately rapid to rapid (on the order of I
about 1970 produced a longitudinal weld seam that is more foot per year or greater) downslope movement of earth by
susceptible to certain failure mechanisms. means of gravitational body stresses.
Leak. Loss of containment from a pipeline component; the
Failure. The point at which a structure is no longer capable of unintentional release of product from the pipeline. Although
serving its intended purpose. Although a pipeline that is the terms leak and spill are used interchangeably in this text,
actually leaking product is the most obvious indication of a distinction could be that a leak is any amount of product
failure, failure is often also defined as the point at which the escaping the pipeline, whereas a spill refers to the results of a
material is stressed beyond its elastic or yield point-it does leak-the final leaked volume and accumulation point, for
not return to its original shape. instance.
Fatigue. The process of repeated application and removal of Leak impact factor. A number that represents the overall
stress. Because fatigue can cause a failure to occur at a rela- consequence of a pipeline failure in the risk assessment
tively low stress level, materials that must resist such cycles methodology presented in this book. This factor is a score
of stress must be specially designed for this service. based on the product hazard and the dispersion factor. The
Flaw. A defect in the pipe wall that could be a threat to leak impact factor is divided into the sum of the four index
pipeline integrity. Examples include cracks, gouges, and values to arrive at the relative risk score.
metal loss.
Fracture toughness. The ability of a material to resist crack- MAOP. Maximum allowable operating pressure; also called
ing. Materials that are more ductile can absorb larger MAWP for maximum allowable working pressure. The high-
amounts of energy before cracks spread. Lead has high frac- est internal pressure to which the pipeline may be subjected
ture toughness; glass has low fracture toughness. based on engineering calculations, proven material proper-
ties, and governing regulations.
Girth weld. Welds of the circumferential seams where the
ends oftwo sections ofpipe are joined. Palustrine. The palustrine system was developed to group
the vegetated wetlands traditionally called by such names as
HAZ. Heat-affected zone. The area of metal around a weld marsh, swamp, bog, fen, and prairie, which are found
that has been metallurgically altered by the heat of the weld- throughout the United States. It also includes the small, shal-
ing process. This area is often more susceptible to cracking low, permanent, or intermittent water bodies often called
than the parent metal. ponds. Palustrine wetlands may be situated shoreward of
Hazard. A potential event that can lead to a loss of life, prop- lakes, river channels, or estuaries; on river flood plains; in
erty, income, etc. isolated catchments; or on slopes. They may also occur as
Hydrostatic pressure test (hydrotest). An integrity verifi- islands in lakes or rivers.
cation test involving the pressurization of the pipeline sys- Peak ground acceleration. The force related to the ground
tem with water to a level higher than its intended operating acceleration during a seismic event, expressed as a percent of
pressure in order to prove the system’s strength. The test one gravity. The peak acceleration is the maximum accelera-
pressure is held for several hours and carefully monitored to tion experienced by a particle during the course of an earth-
ensure that even very minor leaks are detected. quake motion and is used as a measure of seismic damage
potential.
Index. One of four general categories to which pipeline acci- Pig. A device designed to move through a pipeline for
dents can be attributed. Aspects of pipeline design, opera- purposes of cleaning, product separation, or information
tion, and environment are scored to arrive at numerical gathering. A pig is usually propelled by gas or liquid pres-
values for the third-party index, corrosion index, design sure behind the pig. The term pig is said to have originated
index, and incorrect operations index. from the sound the device makes as it moves through the
Index sum. A summary number from the risk model pipeline.
(Chapters 3 through 6) that represents an assessment of all Pressure relief valve. Also called a pop valve or a safety
variables that affect spill probability. Index sums vary valve, this class of mechanical safety device is designed to
between a theoretical low ofzero (extremely high probability operate at a predetermined pressure to reduce the internal