Aiming at the complicated stress characteristics of bends in directly buried heating pipelines
a three-dimensional thermal-mechanical coupled finite element model was constructed in terms of soil spring model. The main affecting factors on stress distribution of directly buried bends were analyzed. A thermal-mechanical coupled finite element model for bend with reduced straight pipe lengths was given. The weights of thermal medium and covering soil were considered in the pipe-soil interaction of the model. The boundary conditions were exerted to the ends of two bend arms. The results indicate that buried elbows of bends bear peak stresses with considerably higher value due to temperature rise than due to internal pressure. The primary stress of buried bend decreases with the increasing pipe wall thickness and buried depth
while it increases with the increasing internal pressure and curvature radius. The secondary stress of buried bend decreases with the increasing pipe wall thickness
while it increases with the increasing internal pressure
buried depth
temperature rise
curvature radius and end displacements of bend arms. Vertical ovalization for pipe section is beneficial to the bend
but transverse ovalization is harmful. The ground load reduces the maximum equivalent stress in buried bend.
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