Many of the assessment procedures in API 579 / ASME FFS-1 require that flaws to be assessed must be located a minimum distance away from a Major Structural Discontinuity to ensure that the disruptions caused by the discontinuity do not adversely affect the conservatism of the calculations. Flaws in a cylinder with a Distance to Major Structural Discontinuity (Lmsd) less than 1.8*sqrt(Dt) are typically excluded from basic assessments, regardless of the type of discontinuity (or flaw) in question. This work explores the impact of a Local Thin Area (LTA) in a cylindrical shell as the discontinuity approaches a 2:1 ellipsoidal head. In this paper, the authors populated an Elastic-Plastic parametric study spanning a wide range of cylindrical thickness-to-diameter ratios (D/t), flaw sizes (both longitudinal and circumferential), materials, flaw severities, and proximity to both 2:1 ellipsoidal heads and hemispherical heads in order to characterize the responses. The results imply the existence of several classes of structural discontinuity, along with conditions under which some discontinuities might either act to support or de-stabilize a cylindrical shell against plastic collapse. The authors demonstrate that under supportive conditions, an LTA in a cylinder can approach certain discontinuities with negligible effects. In some cases, the limiting load reliably increases due to the interaction with the discontinuity. The work concludes with broader observations on discontinuity types and the circumstances under which those discontinuities might be found to be beneficial.

This content is only available via PDF.
You do not currently have access to this content.