Pipeline Collapse Methodology for Ultra-Deepwater

The objective of this paper is to summarize current ultra-deepwater (i.e. up to 3,500 meters water depth) pipeline mechanical design methodologies in the Gulf of Mexico (GOM), and the rest of the world. The standard mechanical design for ultra-deepwater pipelines in the GOM is based on API RP 1111. API code also has been used for deepwater projects in west Africa. DNV code OS-F101 was mostly used for deepwater projects in offshore Brazil and Europe. Some pipeline designs in the GOM have started to incorporate parts of the DNV design methodology. A discussion of collapse only design and combined loading (i.e. pressure + bending) design will be presented. The buckle arrestors shall be designed along with the ultra-deepwater pipeline mechanical design. The best design criteria are obtained from physical full-scale collapse testing. The comparison of the physical test data and collapse calculations using the DNV and API codes will be presented. It was found that the conservatism still exists within collapse prediction for ultra-deepwater pipeline using modern design codes such as DNV OS-F101 and API RP 1111. Recommendations of the mechanical design methodologies for the ultra-deepwater pipeline are presented.