Compatibility between API equations and design limits plots for ellipse and circle of plasticity
Master thesis
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Date
2020-07-01Metadata
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- Studentoppgaver (TN-IEP) [323]
Abstract
This project presents a methodology to superimpose the API uniaxial and triaxial
limits on the design limits plot. Complications due to a recent change of axis are
resolved, producing practical design limits plots that avoid the horizontal shift of
the API vertical limits, currently done by the industry. The commonly used slanted
ellipse is compared against an adaptation of the circle of plasticity in the form of a
horizontal ellipse, showing the convenience of this last one with examples.
After a new collapse formulation was introduced in API TR 5C3 in 2015, the hor-
izontal axis on the standard industry well tubular design limits plot changed. The
study evaluates this rede nition of the horizontal axis. One consequence of this
modi cation is a di culty plotting the API tension and compression limits. The
API horizontal limits (uniaxial burst and collapse) are found to be independent of
load case, while the API vertical design limits (uniaxial tension and compression)
are dependent on inside and outside tubular pressures. The approaches used by
commercial software and industry publications to solve this challenge are analyzed.
A new design methodology is developed to link API limits to the triaxial theory.
The main objective of the study is to establish a mathematical relationship between
API tubular design limits and the Von Mises triaxial theory. A methodology that
allows plotting the API uniaxial force limits on the design limit plot is developed.
The study also shows that the results obtained from the industry standard slanted
ellipse are identical to those obtained from the horizontal ellipse/circle and therefore
the new plotting methodology can be applied to the last one as well. A di erence
is that the slanted ellipse is based on zero axial stress datum while the horizontal
ellipse/circle uses neutral axial stress datum. The horizontal ellipse/circle is well
suited for calculations involving buckling, is compatible with the information used
in eld operations, and its formulations are less complicated than in the tilted ellipse,
therefore attention is called to it.
Description
Master's thesis in Petroleum engineering