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  Title Longitudinal stress in buried pipelines near bends or end caps
  Author(s) Dr Fan Zhang and Michael Rosenfeld  
  Abstract ACCURATE ESTIMATION OF THE LONGITUDINAL STRESS is frequently required for the engineering critical assessment (ECA) of girth welds or the integrity analysis of pipelines including defects with considerable circumferential extension. The stress in a buried pipeline near a bend or an end cap is determined by the combined loads from internal pressure and thrust force, thermal deformation, and the resistance of the surrounding soil. The equations for longitudinal stresses in pipeline design standards are derived for straight pipe segments and cannot be used to estimate the longitudinal stresses near bends or end caps. A numerical approach, such as finite element analysis (FEA), can be used to accurately calculate these stresses on a case-by-case basis but can be expensive for assessment of multiple bends or end caps locations. In this paper, analytical solutions for the longitudinal stresses in a buried pipeline near a bend or an end cap were derived. The solutions were then verified by FEA. A sensitivity analysis was also conducted with the model to explore the influence of the length of the bend or the end cap and the dependence of the stress on the angle of the bend. Two frequently used simplified assumptions were also checked. One is that “the stress reaches its highest value near a 90° bend” and the other is that “the stress near a bend can be conservatively estimated as one half of hoop stress”. The analytical solutions show that the two assumptions may not be valid at locations too close to a bend.  
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