PR-185-133739-R01 Quantifying Re-Rounding in Pipeline Damage Severity Models

The objective of this work was to quantify re-rounding effects on mechanically damaged pipelines. This was done to determine if curvature suffices to identify where the effects of re-rounding are localized. It also was done to establish a framework that could be calibrated through subsequent analysis as an input to guidelines for damage severity assessment. Recognizing the expanding role of ILI and related in-the-ditch evaluation tools to help size and characterize damage, brief consideration was also given to ongoing work within the PRCI Nondestructive Evaluation (NDE) Program. This was done regarding the use of such technologies to assess metallurgical changes in the damaged zone and their integration into model development and sensitivity analysis.

Key conclusions for the analysis completed for this project and its validation by comparison to full-scale data include:

- Re-rounding can cause significant nonlinear effects in otherwise simple pressure cycling, due in part to localized strain hardening and localized kink formation when it occurs within dents and/or gouges;

- Metal-loss due to gouging can be simply idealized without jeopardizing the utility of analysis of the effects of re-rounding, as shown by three validation cases benchmarked against full-scale test-ing;

- Re-rounding showed a first-order dependence on pipe geometry and pressure; and

- Curvature change appears adequate to quantify re-rounding, but is inadequate to quantify local damage severity in a Level 1 damage screening tool: this also requires consideration of membrane strain (stress) and wall thinning where it is evident.

The dependence of re-rounding on pipe geometry and pressure should be broadly quantified, with analyses to trend the role of membrane stress included to build the basis for an ILI-based model to screen damage severity.