Volume 37, Issue 6 (November 2009)
Fatigue Crack Growth Rates in Pipeline Steels Using Curved M(T) Specimens
This study presents fatigue data for two different ferrite-pearlite pipeline steels. A fatigue crack growth test for full-thickness curved pipeline samples was developed using a middle tension (M(T)) specimen. Also, finite element analyses (FEAs) were carried out to show the M(T) curvature effects on the fatigue crack growth results. The two steels showed similar fatigue crack growth rate (da/dN) behavior. However, the ferrite-pearlite steel without banding had slightly better fatigue properties than the ferrite-pearlite banded steel. Uncertainty in the fatigue crack growth rates was analyzed by attributing all the fatigue scatter to the Paris law parameter C. The FEA based simulations, based on curved geometries, of the compliance relationship more accurately predicted both fatigue crack growth data and true crack lengths. Nevertheless, the ASTM E647-05 compliance relationship accurately predicted the crack length for the M(T) geometry, although its use leads to slightly conservative fatigue crack growth trends and a slight overestimation of the true final crack length.