Summary
Advanced well-design methods based on risk assessment of actual failure
mechanisms require accurate formulas for burst, collapse, yield, and fracture.
Moreover, these strength formulas should be generalized to account for the
combined internal pressure, external pressure, and axial load that well
tubulars experience.
This paper describes the development of a set of formulas for burst strength
[i.e., the failure envelope and the design limit for oil country tubular goods
(OCTG) under internal overpressure and any axial tension or axial compression].
Phenomena covered are ductile rupture, pipe necking, and local pipe-wall
wrinkling, thus spanning the first and second quadrant in the
effective-axial-load/pressure-differential-load space.
This set of formulas is based on a large-strain, elastic/plastic, 3D
formulation of pipe equilibrium, deformation, and buckling that has been solved
analytically in closed form for the situation of combined loads. The formulas
describe features such as a maximum internal-pressure load (rupture), a maximum
axial-tension load (necking), and local buckling of a pipe under axial
compression (wrinkling).
Approximate burst-strength formulas are presented that together span the
entire axial-load range and closely match the more complex, exact model
predictions.
The joint American Petroleum Institute/International Organization for
Standardization SC5 Work Group 2B (API/ISO SC5 WG2B) tasked with modernizing
the API 5C3 property equations has incorporated the approximate burst-strength
formulas presented in this paper into the new ISO TR 10400/API TR
5C3 document (API 2008; ISO 2007).
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
14 July 2006
- Meeting paper published:
25 September 2006
- Revised manuscript received:
19 September 2009
- Manuscript approved:
6 November 2009
- Published online:
22 April 2010
- Version of record:
22 September 2010
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