(eBook Version) Need: The design of deep water pipelines must consider external pressure loading which is applied to the line during construction or in service when the line is evacuated. A collapse failure can occur due to this external pressure alone or external pressure in combination with tension or bending loads which are imparted to the line during construction. Thus, there is an incentive for research to more accurately define the failure envelope for combined external pressure, bending, and tension for offshore pipelines.
Benefit: Previous work at the University of Texas at Austin concentrated on small scale testing and theoretical work. The purpose of the work in this project was to perform large scale tests to verify the previous work, and in particular to test a limited amount of seam welded Double Submerged Arc Welded (DSAW) pipe to compare with widely available seamless data. Deepwater gaslines normally are in the 16-24" size range where DSAW and ERW (electric resistance welded) are the only available manufacturing processes. ERW pipe was not studied in this project.
Three main types of tests were performed by Stress Engineering Services, Inc. in this project. These were collapse only (16" pipe), collapse plus tension (6 5/8" pipe), and collapse plus bending (6 5/8" pipe). SES designed and had a multi purpose test vessel constructed to accommodate all three types of tests.
Result: There is fairly good general agreement between this large scale data and the small scale data (approximately 1" diameter pipe) taken at the University of Texas. Conventional design formulas do a respectable job in predicting collapse behavior. Formulas used for prediction were from Shell Pipeline, Timoshenko, and API 5C3 for casing and tubing.
