Limit & Shakedown Loads Determination For Locally Thinned Wall Pipe Branch Connection Subjected To Pressure And Bending Moments

In this paper the shakedown limit load for unreinforced locally thinned wall pipe branch connection is determined using the Simplified Technique. Loadings were considered to be internal pressure, as a steady load, with in-plane bending or with out-of-plane bending applied on the branch, as alternating loads. Two locations of local wall thinning were taken; one was on the run pipe opposite to the branch and other on the branch at the maximum tension stress side of the bending moment applied whether in in-plane or out-of-plane situation. Two Finite Element (FE) limit load models were used to verify the modeling of the pipe branch connection with its local wall thinning. First model results were compared with experimental data taken from the literature, and the second results were compared with numerical models taken also from the literature and also compared with API 579 "Fitness For Service" (FFS), part-five, level-two assessment procedure. First and second comparisons lead to good agreement but for API 579 comparison it was found that it is slightly changing with the depth of the local wall thinning but does not reflect the expected behavior of the limit load as the PEA models showed. For the results of the shakedown limit load analysis, Bree diagrams were constructed to show elastic, shakedown and plastic collapse regions. Then, comparison was made to show the effect of the local wall thinning depth and location on previous limits. Finally, the shakedown results were verified using the elastic-plastic ratcheting analysis of API 579, level three assessment and it showed successfully the shakedown, ratchefing and reversed plasticity regions. This verifications and results can prove that the Simplified Technique can be used as a level-three ratcheting assessment in API 579.