OVERVIEW

In several important offshore and onshore oil exploration and production applications, long, tubular structures are held suspended in either vertical or catenary-shaped positions in a water head that often extends for several thousand feet. In such configurations, the submerged weight of the pipe must be supported at the top, resulting in significant build-up of axial tension in the structure. Although the tensile force decreases as the depth increases, there can be sections that simultaneously experience significant external pressure and axial tension. For commonly used line grade steels and pipe D/ts, tension can reduce the buckling and collapse pressures. Accordingly, these critical pressures must be reevaluated including the effect of tension.

For example, a pipeline being installed in deep water using the J-lay method (Figure 2.19) can have sections in which the effect of tension on the collapse pressure can be significant. The same is true for either straight or catenary production risers shown in Figures 2.5 2.9. Tubular tendons used in tension-leg platforms (Figure 2.6) are similarly affected, in some cases even more critically.

Even more importantly, collapse under combined axial tension and external pressure is the governing design loading for casing installed down-hole, both onshore and offshore. Figure 7.1 shows schematically an example of an offshore well with its many tubular components. The well shown starts at a water depth of about 3,000 ft (914 m) and goes down to 17,000 ft (5,200 m) below sea level. Telescoping tubulars with progressively decreasing diameters comprise the well. A production...