Examination of Commercial Casing Collapse Strength Under Axial Loading

Collapse testing of commercial API grade 7-in. casing was conducted under combined external pressure and axial load. The measured collapse pressure was considerably higher than the API minimum value, especially for the large D/t ratio, as expected. For the casings of large D/t ratio, the measured collapse pressure was a little smaller than the theoretical value for ideal pipe and the axial stress had a slight effect on the collapse pressure. In the range of plastic collapse, the measured collapse pressure was not less than the yield pressure for ideal pipe except near the boundary of the elastic and plastic collapse ranges.