Triaxial evaluation of loads is used extensively for casing and tubing string design and analysis. The paper presents a method of determining the triaxially based collapse strength of casing and tubing subjected to simultaneous axial and internal pressure loads. The triaxially based collapse strength method was recently adopted by the American Petroleum Institute (API) and an addendum issued to API Technical Report 5C3 (TR 5C3). Casing and tubing subjected to combined loads have higher collapse strength than previous formulas predict.
Improvements in integral joint connections (IJC) for casing in the past decade have allowed operators to drill wells previously not feasible to drill for economic or technology reasons.
New integral joint connections can withstand greater loads, increasing their range of applications. The use of IJC casing can allow a slimmer well to be drilled, reducing total well costs.