Pressure Cycle Fatigue: A Statistical Assessment Approach

Operational pressure cycle fatigue (PCF) is one of the integrity threats managed by pipeline operators. Usually, hazardous liquid pipeline operators are most interested in the effects of pressure cycles since these pipelines inherently experience more significant pressure cycles than natural gas pipelines. The parameters considered in the assessment of operational pressure cycles include pipe geometry (diameter and wall thickness), mechanical properties of the pipe, distribution of hypothetical defect sizes that may exist in the pipeline, and pressure cycles. In performing these assessments, the most conservative value for each parameter is commonly used for predicting a time to failure. As such, the results are inherently overly conservative. A statistical assessment method, PCFStat, has been developed to more appropriately model the input parameters used in the assessment of operational pressure cycle fatigue; especially for cases where the deterministic approach identifies relatively short remaining fatigue lives. A distribution of each of the input parameters is developed, and then a Monte Carlo simulation of these parameters is performed. The results produced by this analysis are then used to evaluate the probability of a failure (leak or rupture) for a defined time interval.Copyright © 2004 by ASME