Bending Stress in Pipeline Elastic bends


I am working on a buried 10 inch pipeline ( ASME B31.8) , I have noticed that Auto pipe does not consider the bending stresses in the pipe due to large diameter elastic bends ( 1200 m). it only reports the stressses due to pressure , temperature and gravity . can any one help ?



  • Hello SHK,

    I apologize, but I do not understand your question.  What load case are you expecting to see bending stresses for in your model of a large radius bend?

    I created a simple model with a large radius bend and was able to see bending stresses for  operating, sustained, occasional,etc.. load cases.

    Please be more specific.


    Mike Dattilio

    Bentley TSG Support Analyst


  • In most cases these initial stresses are ignored as are circumferential weld stresses. Similarly, for buried pipe the overburden soil load will add stresses which often are analyzed separately. These overburden stresses were recently supported in  AutoPIPE for some codes in which case they are added to other sustained stresses In addition to additional checks to insure that the pipe will not buckle under the soil load alone.  It is worth pointing out that the overburden stresses act against the initial cold bending stresses.

    The way to account for the elastic bending stresses is to calculate them manually and add them to the sustained stress. The moment created by bending can be calculated by E.I/R where E is the elastic pipe material modulus,  I is the pipe moment of inertia and R is the bend curvature radius. You can build a simple cantilever pipe model and apply this moment to the free end in a User case to get the cold bending stress. This bending stress can then be manually added to the maximum sustained stress in the long radius bend and the results compared to the sustained allowable. Note that you may not need to add it to expansion stress range since this is a one time event and would not reverse. However it can be added to operating cases as in B31.3 Appendix P, if that option is being used.


  • You can also calculate the cold bend stress using a pipe with two rigid anchors on both sides and apply a rotation equal to pipe span length times divided by bend radius or  theta = L/R in radians which can be converted to degrees. This rotation is applied to one of the end anchors under U1 user case.