Development of an Alternative Criterion for Residual Strength of Corrosion Defects in Moderate- to High-Toughness Pipe

This paper presents the development of a new, simplified criterion, known as PCORRC, for prediction of the remaining strength of corrosion defects in moderate- to high-toughness pipeline steels that fail by plastic collapse. Comparisons against an experimental database indicate that, when toughness is sufficient, the PCORRC criterion reliably predicts the remaining strength of blunt defects using only the maximum depth and maximum length of the defects with less excess conservatism than existing criteria. The value of PCORRC is demonstrated in comparisons that show it capable of reducing excess conservatism significantly in the class of defects that fail by plastic collapse, potentially resulting in significant reductions in pipeline maintenance and repair costs. This new criterion was developed at Battelle under sponsorship of the Line Pipe Research Supervisory Committee of PRC international. The new simplified criterion was developed from a finite-element software analysis model. The analysis software was applied in a parametric investigation to evaluate the influence of geometry and material characteristics on the remaining strength of corrosion defects in moderate- to high-toughness steels that fail by plastic collapse. The model development and parametric investigations demonstrated that: • The failure of this class of defects is controlled by the ultimate tensile strength rather than yield strength or flow stress; • Defect depth and length are the most critical defect geometry variables; • Defect width and material strain hardening are of lesser importance.