Crack Shape Development in Fatigue Growth Assessment for Pipelines

摘要

Assessment of fatigue crack growth for pipelines is critical to evaluate the effects of operational pressures acting on flaws and predict the remaining service life. Under pressure cycling, cracks propagate continuously until they reach a critical size, resulting in a pipeline leak or rupture. When the crack grows, the crack shape and size evolve and it is important to characterize these changes to accurately predict fitness. Currently, it is typical to only consider growth in crack depth when modeling pressure cycling-induced fatigue. In some cases, neglecting the effects of crack shape or aspect ratio under crack growth may result in inaccurate predictions for remaining service life and ultimately a reduced margin of safety. Developing a full understanding of crack shape development during crack growth can be crucial for integrity management to more accurately estimate the remaining service life and prevent pipeline leaks or ruptures. In this work, crack aspect ratio change was studied for pipelines undergoing pressure cycling. The effects of initial crack aspect ratio, pipeline diameter and wall thickness, and loading conditions on the crack shape development were investigated. A new methodology for fatigue crack growth assessment is demonstrated. The study provides a refinement to fatigue crack growth assessment with the potential for more accurate prediction of remaining service life for pipelines.