Pipelines comprised of materials manufactured prior to about 1980 are more likely than those comprised of newer materials to contain manufacturing or transportation-induced defects. These defects may become enlarged and fail in service because of pressure-cycle-induced fatigue crack growth. While such defects do not account for a large number of service failures, they clearly are a potential threat to pipeline integrity. In fact, the current U.S. pipeline integrity management regulations require seam-integrity assessments for certain types of pipe materials that appear to be particularly susceptible to this risk. To manage the risk of failure from pressure-cycle-induced fatigue a pipeline operator may need to cany out periodic seam-integrity assessments via either hydrostatic testing or in-line inspection using a reliable crack-detection tool. The appropriate period for reassessment depends on the sizes and growth rates of potential defects that may still exist (just-surviving defects) after an initial hydrostatic test or in-line inspection. The pressure cycles applied to the pipeline may cause the just-surviving defects to grow at a rate inherent in the material and its environment. Long-established principles can be used to predict the times to failure if the effective crack growth rate is known. A pipeline operator can use these principles to plan timely re-assessments to prevent failures. This paper describes one approach to predicting reassessment intervals. This approach has evolved over a period of more than 10 years. The authors have discovered some pitfalls and blind alleys that can lead to inappropriate predictions. The purpose of the paper is to show that while the well-known and widely available basic principles are sound, their application to pipeline integrity management requires an in-depth understanding of the particular pipeline being subject to assessment.
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