Grant: Collaborative Research and Development Grants

Near-neutral pH environmentally assisted corrosion (NNPHEAC) represents a substantial cost to Canadian pipeline companies and hence to Canadian consumers. NNPHSCC is controlled from an integrity management point of view by in-line inspection for oil pipelines or by hydrostatic testing for gas pipelines. Either of these techniques provides protection from in-service failures for a number of years and then the process has to be repeated. The testing cycle is particularly troublesome for gas pipelines since only quite large flaws that fail at hydrotest stress are detected by the hydrostatic testing technique. These procedures are also enormously expensive. The re-inspection interval or re-test interval is currently determined based on empirical models, which are rather imprecise. Recent investigation at the University of Alberta has found that the crack growth behavior of pipeline steels in near-neutral pH environments is consistent with that of true corrosion-fatigue, and crack growth rate da/dN can be correlated with a single mathematical term that is incorporated with all possible measurable variables pertinent to crack growth. In collaboration with engineers from TransCanada Pipelines and Spectra Energy, this project is aimed to achieve the following objectives: 1) To extend crack growth rate models to the growth of small/short/shallow cracks and the growth of cracks by crack coalescence, accounting for environmental, mechanical, and metallurgical effects. 2) To develop/update predictive pipeline integrity models to include the above crack growth rate models and to incorporate probabilistic variations and all uncertainties in the input data for more reliable predictions. 3) To establish sound scientific basis for various existing practices/methods used in pipeline integrity management including methods for determining re-inspection/re-test intervals, criterion of pipeline steels selections, measures for crack growth control, and prioritization of risk management.