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Data Analysis: The process
through which indications recorded in an in-line inspection are evaluated to
classify, characterize, and size them.
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Defect: An anomaly for
which an analysis indicates that a system is approaching failure as stresses
approach the specified minimum yield strength of the material.
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Dent: A local depression
in the surface of a material caused by mechanical damage that produces a gross
disturbance in the curvature of the pipe without reducing the pipe wall thickness.
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Detect: To sense or obtain
a measurable in-line inspection indication from an anomaly.
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Detection: The process
of obtaining an inspection signal that is recognized as coming from a defect
or anomaly. An in-line inspection tool can detect only those defects that produce
signals that are both measurable and recognizable. Not all defects are detectable
with all inspection systems.
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Detection Limit: The largest
anomaly that could be missed (not the smallest anomaly that could be found)
by an in-line inspection tool.
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DeWaard-Milliams analysis:
Predictive model based on the chemical reactions, mass transfer and corrosion
rates where CO2 exists in a system.
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Differential Pressure:
The difference between the pressures behind and ahead of the in-line inspection
tool - the actual propeller of the tool.
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Diffusion: The passage
of a substance into a body (e.g., hydrogen into steel).
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Direct Measurement: Describes
measurement of metal loss or corrosion rate.
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Dirty Steel: A term used
to denote steel containing a high number of nonmetallic inclusions.
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Disbonded Coating: Any
loss of bond between the protective coating and the steel pipe as a result of
adhesive failure, chemical attack, mechanical damage, hydrogen concentrations,
etc.
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Discrete Repair: A short
segment of a system identified to be repaired.
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Dissolution: The decomposition
of a solid into parts.
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Distribution Line: A gas
pipeline other than a gathering line or transmission line.
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Double Submerged Arc Weld (DSAW):
Weld using filler metal passes on the inside and outside of the pipe.
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Ductility: A measure of
the capability of a material to be deformed plastically before fracturing.
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Dummy Tool Run: Preliminary
run of an uninstrumented pig to verify safe passage of a fully instrumented
tool through a section of pipeline. Dummy runs can also be used to remove debris
from the inside of the pipeline.
