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Repair Sleeve Testing and Validation

Full encirclement repair sleeves are very often used for repairing pipelines. When pipelines are externally corroded or damaged, repair sleeves provide the hoop stress reinforcement necessary to allow the pipeline to continue operating at high pressures. So the good news is that sleeves can be added to repair a damaged pipeline. Unfortunately, the bad news is that sleeves have to end somewhere. If a buried pipeline with an added sleeve is subject to differential soil settlement or ground motion, the ends of the sleeve generate a substantial discontinuity in the bending stiffness of the pipeline cross section. Such discontinuities may concentrate bending deformations with the potential to either wrinkle the carrier pipe or damage the pipe-sleeve welds.

The project included the analytical evaluation of repair sleeved designs used in the Trans-Alaska Pipeline System (TAPS) for Alyeska Pipeline Service Company. Finite element analysis of repair sleeve configurations was conducted including wrinkling capacity evaluation and weld fracture assessment. Simulations of field settlement demand scenarios were followed by design and planning of an experimental evaluation of pipe-sleeve configurations.

In order to validate the analytical work, SSD planned and directed a series of full-scale tests of fillet welded pipe-sleeve configurations. The tests, which were conducted on 48-inch diameter by 0.462-inch thick pipe sections, included the application of internal pressure and axial forces to simulate fully restrained conditions. Lateral loading was then applied through four-point bending up to, and beyond wrinkling of the specimens. Examples of the wrinkled pipe from these tests are shown in Figures 1 and 2.

At the completion of the experimental program, analytical correlation studies were also conducted to calibrate PIPLIN analysis models.  This effort led to the development of a wrinkling segment analysis method that allows for accurate prediction of pipe wall wrinkling of the TAPS pipeline, with and without sleeves. The wrinkling segment method involves the user of nonlinear anisotropic material stress-strain relationships and pipeline models which include large displacement effects and strength loss. The results from this method are practical because they can be used in conjunction with a pipeline monitoring program based on "smart" geometry pigs.

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