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Corrosion Monitoring & Inspection Glossary - D

  • Data Analysis: The process through which indications recorded in an in-line inspection are evaluated to classify, characterize, and size them.

  • 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.

  • 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.

  • Detect: To sense or obtain a measurable in-line inspection indication from an anomaly.

  • 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.

  • Detection Limit: The largest anomaly that could be missed (not the smallest anomaly that could be found) by an in-line inspection tool.

  • DeWaard-Milliams analysis: Predictive model based on the chemical reactions, mass transfer and corrosion rates where CO2 exists in a system.

  • Differential Pressure: The difference between the pressures behind and ahead of the in-line inspection tool - the actual propeller of the tool.

  • Diffusion: The passage of a substance into a body (e.g., hydrogen into steel).

  • Direct Measurement: Describes measurement of metal loss or corrosion rate.

  • Dirty Steel: A term used to denote steel containing a high number of nonmetallic inclusions.

  • 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.

  • Discrete Repair: A short segment of a system identified to be repaired.

  • Dissolution: The decomposition of a solid into parts.

  • Distribution Line: A gas pipeline other than a gathering line or transmission line.

  • Double Submerged Arc Weld (DSAW): Weld using filler metal passes on the inside and outside of the pipe.

  • Ductility: A measure of the capability of a material to be deformed plastically before fracturing.

  • 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.

Corrosion Inspection and Monitoring