MECHANICAL PERFORMANCE OF BURIED PIPELINE BENDS

Abstract eng:
Special pipeline components such as pipe elbows, bends are used to change the direction in pipeline alignment. These components are sensitive to imposed deformation and their structural behavior is associated with significant stress and strain concentration, which may lead to failure. On the other hand, the possibility of reducing the stresses induced in the pipeline by using flexible elbow components in the vicinity of a seismic fault location can result in the mitigation of geo-hazard action in the pipeline. In the present paper, the mechanical performance of buried steel pipeline bends is investigated. A rigorous finite element model is developed, which uses shell elements for the pipe and solid elements for the soil, and is calibrated through appropriate experimental testing, conducted at CSM facilities, Sardinia, Italy. Three elbow (deflection)angles are taken into accountequal to 90, 60 and 30 degrees. The ratio of radius over diameter is taken equal to 5 degrees referring to a ‘hot’ pipeline bend.The results show the influence of the elbow angle on the flexibility of the pipeline bend. The results are reported in the form of diagrams, providing the axial force versus the axial displacement at the pipeline bend end. This relationship can be employedas end condition, through appropriate nonlinear springs, in a finite element analysis of a buried steel pipeline against permanent ground deformation. The present work is aimed at proposing complementary provisions in existing guidelines for buried pipeline design in geo-hazard areas.

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