Finite Element Analysis of Bell-and-Spigot Pipeline Connections Under Axial Compression

Under Axial Compression

by Stephanie Tsetseni

Diploma Thesis, July 2005

ABSTRACT

Welded slip pipeline joints have been employed successfully in the construction of large-diameter pipelines. They consist of a "belled" pipe end, into which a straight pipe end ("spigot") is inserted and welded, and are used as an alternative to straight butt-welded joints in water conduits, because of their lower construction cost. Failures at the vicinity of such joints have been observed either on the construction stage, or after strong earthquake action. Because of the bell, the stress path under axial compressive load has an eccentricity e, associated with pipe wall bending and, therefore, a considerable increase of longitudinal stress occurs, which results in pipeline failure. This failure occurs at a load level lower than the corresponding ultimate load level of the straight pipeline part. In the present work, the welded slip joint structural integrity under pure axial compressive loading is investigated using numerical simulations. The joint is modelled with nonlinear finite elements, accounting for elastic-plastic material behaviour of the connection, as well as for large displacements and buckling. In the present analysis, prior to the application of the axial load, the cold-expansion manufacturing procedure is simulated, so that the effects of residual stresses and deformations on the load carrying capacity are taken into account. Following a comparison with available experimental data, the finite element models are used to simulate the response of welded slip joints under compressive axial load, examining the effect of connection eccentricity and bell length . Furthermore, the effects of welding type and the influence of internal pressure on the axial capacity are also investigated. Failure modes of the joints are identified and an assessment of previously reported simplified design equations is conducted.

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