A Science-Based Crack Growth Model for Buried Pipelines Undergoing High pH SCC (II) - Application

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Product Number: 51314-3617-SG

ISBN: 3617 2014 CP

Author: Baotong Lu

Publication Date: 2014

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The new crack growth model developed in Part I is applied to predict the crack growth behavior of pipelines for the gas or liquid transportation based on the typical parameters of environments loading spectra and crack geometry that were reported from field survey. In accord with the model the effect of environmental changes can be assessed with the anodic current density over the bare metal surface (ia*) which can be determined from the potentiodynamic measurement with a potential-scanning rate 1 V/min. It is found that the predictions based on the mean value of ia* determined from the experimental measurements are in reasonably good agreement with field experience. The crack growth in gas lines is dominated by stress corrosion cracking under sustained loading and is not very sensitive to the factors that can change the mechanical driving force of cracking. The remaining life of gas lines are a power function of ia* with an exponent -3. The crack growth in liquid lines is dominated by corrosion fatigue mechanism. The pipe-pressure fluctuation accelerates the stress corrosion cracking development significantly but the effect of loading consequence is likely negligible. The crack growth is less sensitive to environmental changes that in gas lines does. In addition the fatigue crack growth may also be an important component of crack velocity that should be considered in the life prediction. Finally the application procedure of the new model is outlined