Reasons For Evaluating Only Corrosion Defects

Most third party damage is not stress-free
Impact by a trencher or auger induces local stress and deforms the pipe
Dissipation of this stress may not be instantaneous
Impact by a trencher or auger can cause a gouge and microcracks in the steel. The residual stress in the pipe can cause the micro cracks to propagate over time resulting in delayed failure when the micro-cracks reach critical depth.
It is for these reasons that the early B31G Criterion was not recommended for the evaluation of dents, dings, or gouges. The application of the criterion was limited to:
- Corrosion only on weldable pipeline steels
- Defects that have relatively smooth contours- i.e. loss due to corrosion
- Corroded areas that do not touch
Excluded were corroded areas in welds or grooves and gouges caused by mechanical damage. The objective was to evaluate structural integrity only under internal pressure, i.e., not secondary stresses.

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