Predictive crack growth models for pipeline integrity and risk management - phase II

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Near-neutral pH Stress Corrosion Cracking (NNpHSCC) 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. Long term investigation at the University of Alberta has found that the crack growth behavior of pipeline steels in NNpH environments is consistent with that of corrosion-fatigue, and crack growth rate can be correlated with a single term that is incorporated with all possible measurable variables pertinent to crack growth.