This paper proposes a tubular-design ellipse dependent on backup pressure (internal pressure for collapse and external pressure for burst), so that the latest American Petroleum Institute (API) collapse-resistance equations (API TR 5C32015) with dependence on internal pressure can be shown simultaneously on the same plot with the ellipse. Unlike the current ellipse used widely in the industry for casing-and-tubing design, which is approximate, the proposed ellipse is exact for collapse, burst, and axial loads. Without the proposed ellipse, use of the approximate ellipse will continue, requiring separate plots for the API collapse-resistance equations. Example cases demonstrate the advantages of the proposed ellipse, including increased accuracy. Results help clarify questions regarding the origin and use of the 2015 API collapse-resistance equations.

Keywords:
casing and cementing, strength, casing design, Derivation, backup pressure, pipe, abscissa, ellipse, load case, API collapse
Subjects:
Casing and Cementing, Casing design, Drilling Equipment, Information Management and Systems, Pressure Management
Copyright 2018, Society of Petroleum Engineers
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