Recent developments in the offshore industry are resulting in an increasing demand for deep water pipelines. At greater water depths, the external pressure will be the governing parameter for wall thickness design, and the failure mode is collapse.
DNV’s reliability based standard, DNV-OS-F101, uses the collapse capacity model and corresponding safety factors calibrated in the SUPERB Joint Industry Project, finalized in the mid 1990’s. Since then, a vast amount of research on collapse capacity of deep water pipelines is performed, indicating that it is time to re-visit the design equation and safety factors currently in use.
This paper firstly summarizes the relevant collapse pressure equations for pipeline design. Secondly, the major points related to collapse capacity in SUPERB and DNV-OS-F101 are presented. Furthermore, results from an assessment of newer collapse tests of pipelines are described. Focus is on larger (UOE) pipes with D/t ratios less than 25, corresponding to water depths beyond 1000 m. The test results are compared to the outcome of earlier experimental projects. A difference between older and more recent tests is observed, with the newer having a considerably higher collapse capacity. Finally, a calibration of safety factors is performed, compared to existing factors and discussed.