PR-214-104505-R02 Improved Methods for Estimating Remaining Fatigue Life of ERW Pipelines

While the general fracture mechanics methodology for calculating fatigue life is well documented and validated, its application in the definition of pipeline system fatigue lives have differed from field experience. The source and magnitude of the conservatism inherent in the calculated fatigue life estimates are a concern when establishing integrity management programs. Of particular interest are the fatigue life estimates used in the integrity management programs for ERW pipeline systems that are primarily concerned with pipe wall anomalies oriented along the pipe axis. This project was initiated to consider several elements of the fatigue life estimation process to identify if there were sources of conservatism that could be better managed to permit integrity management programs to produce life estimates with known levels of conservatism. The project considered:

- Ovality and misalignment stress concentration factors;

- Fatigue crack growth rate (da/dN) material performance; and

- Bulging correction factor.

Both experimental and numerical simulation techniques were used to consider the impact of these factors on rate of fatigue crack growth of pipeline axially oriented defects. The project results were compared to existing codified treatments to quantify the level of conservatism inherent in the current state of practice. Recommendations were provided to enhance the precision and manage conservatism in fatigue crack growth rate calculations used in integrity management.

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