Length Effects on Fatigue Behavior of Longitudinal Pipeline Dents

Abstract

Dent length has been shown to have a significant effect on the fatigue cracking behavior of pipeline dents. Long dents, which experience rerounding and center cracking, have a dramatically shorter fatigue life than otherwise similar short dents, which experience peripheral cracking and little rerounding. Because the fatigue lives of long dents are much shorter than those of short dents, both safety and economy would benefit from improvements in the ability to distinguish long dents from short dents. Based on experimental evidence, a transition between short and long dent behavior is shown to exist. Finite element models are used to further explore the nature of this transition by allowing the examination of cases not available in the experimental record and by permitting stress behavior to be studied. A parametric study is used to quantify the nature of the short dent to long dent transition for a range of cases. Relative dent lengths that bound short and long dent regions of behavior are proposed for these cases.