Multiple or stacked crack-like flaws can be found at longitudinal welds on vintage low frequency (LF) ERW pipeline by inspection technologies. These features may be a result of fabrication or degradation during service. The assessment of coplanar anomalies for fitness for service requires the evaluation of interaction, coalescence, and sizing of overall depth and length for multiple and/or stacked linear features. Available industrial codes provide rules to perform interaction and multiple flaw characterization; however, in some instances these general rules may result in more features requiring repairs than is actually required for a pipeline integrity program. This paper reviews interaction rules and models for linear features developed from published codes and industrial research with the objective of identifying areas for further development.

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