Dent strain and stress analyses and implications concerning API RP 1183 - Part I: Background for dent geometry and strain analyses during contact and re-rounding

Abstract

API RP 1183 was developed through industry collaboration to manage the threat posed by dents. It provides screening and more detailed techniques designed to manage single peak smooth dents. For more complex scenarios such as kinked and skewed dents its practices rely on numerical analysis.

This paper is the first of four that considers issues that arise when, consistent with API RP 1183, the axial and transverse profiles of dents are used as the basis for dent geometry and strain analyses. Part I presents background concepts and discusses the numerical details and other modeling that underpin API RP 1183. Part II presents a series of examples that amplify the concerns foreshadowed in Part I. Part III considers the cyclic loading of dents, and the viability of the dent stress and fatigue analyses that underlie those practices of API RP 1183, while Part IV focusses on the numerical and modeling aspects.

It becomes apparent from Part I that the benefits of the shell-element formulation adopted to simulate tens of thousands of dents has glossed over some key aspects that lead to significant unconservative errors, or lead to gaps in its dent management. Likewise, the broad utility of its global regression equations was found prone to significant err. The analysis of single peak dents with smooth profiles based on their axial and transverse profiles as outlined in API RP 1183 was found to incorrectly categorize dents, mis-predict their severity. Finally, a path toward resolution was noted.