Abstract
The pipeline industry has long sought a unified near-neutral pH stress corrosion cracking (NNpHSCC) growth model, which fully describes salient growth elements. In response to this gap, the Pipeline Research Council International (PRCI) has funded a multi-year research project, partnering with the University of Alberta (Project SCC-2-12). With the project nearing completion, application of the proposed near-neutral pH stress corrosion cracking growth model to two operating pipelines with known populations of stress corrosion crack features is presented.
The remaining life of each crack feature detected by crack in-line inspection tools, under known loading, is calculated for two segments of operating pipelines in North America. The PRCI developed model, referred to as PipeOnline™, is compared to the legacy Enbridge linear growth and Paris Law models.
A calibration technique for correcting the length and depth of the ILI feature calls provided by the in-line inspection vendor is reviewed, which takes into account tool tolerance and corrects length and depth to more closely match field findings. Efficiency improvements gleaned from this calibration technique are illustrated. While this calibration methodology is unique to the pipeline operator, the method is reviewed to allow other operators to readily implement the technique if it is found to be warranted.
The PipeOnline model is tested for the post-calibration dimensions and compared to the legacy growth model. Each of the required inputs is defined, and methods of quantification are shown. Negligible growth thresholds are reviewed, and the truncation of stress cycles below the growth threshold is discussed. The strategy of deployment is shown, along with the proportion of features that are predicted to remain in dormancy.
Methods to account for mean stresses and load application frequency are presented. The resulting PipeOnline re-inspection interval is compared to that predicted by typical existing growth models and then contrasted with excavation results on the asset. Calibration of the governing equation coefficients with rationale for each term is proposed for the pipeline segments examined in the study, and recommendations made for potential implementation for other operators, along with follow-on research.
Mechanisms of High-pH and Near-Neutral-pH SCC of Underground Pipelines
