3 Replies Latest reply on Jan 27, 2015 1:57 AM by Jared Conway

    Thermal Analysis of an Expansion Joint

    Craig Jameson

      I have flanged and flued expansion joint that I am trying to analyze and having difficulty with the thermal analysis.  The expansion joint has 6psi internal pressure and a temperature of 900 degrees F, material is 304SS.  I initially applied the 6psi in a static analysis to see the stress would be, and they indeed were ~16ksi.  I then wanted to add temperature, so I did a separate steady state thermal analysis at 900 degrees.  I told my static analysis to rerun using the new thermal analysis results to see what the changes were.  The stresses were astronomical (560ksi), so I removed the fixed constraints and told the model to "relief inertia" and "use soft springs" I also took the 6psi off of the model as well, just to see what the thermal stresses were alone.  I am still seeing over 560ksi stresses.  304SS still has an allowable stress in ASME at 900 degrees F and this is a replace "like-kind" expansion join.  So I know it works, I just not understanding why the thermal analysis is going wrong.  Any input would be greatly appreciated.

       

      I also tried attaching a pack and go of the file but it was too big.  So I attached the assembly and parts.

        • Re: Thermal Analysis of an Expansion Joint
          Bill McEachern

          The heat transfer analysis is only sensible if the distribution of temperature is of concern. Chances are that for thermal expansion type problems you can assume the joint thing is at uniform temp as well as the rest of the kit. Then temperature is available as a load and you can run it all in a single static analysis. sounds like your restraint system is not well chosen as it unsuitably stiff. I don't have time to open up you files - how a picture of your restraints?

            • Re: Thermal Analysis of an Expansion Joint
              Craig Jameson

              Thanks for the response Bill.  You answered one of my concerns already, I was wondering if I could just include the temperature as a load in a normal static analysis.  For the last model I ran, I didn't have any restraints on the model, I just told the model to use "Use Soft Springs" and "Relief Inertia".  This is the iteration I tried by setting the "initial temp @ zero strain" to 500 degrees F to see if that made a difference.  This was done in a static analysis only with the temp applied as a load.

            • Re: Thermal Analysis of an Expansion Joint
              Jared Conway

              I would test your methodology on a smaller assembly

               

              my guess is you got a large displacement error of some sort or the soft springs/inertial relief combos are causing results that don't make any sense. use real restraints.

               

              and start with just a static analysis with a temperature load instead of an imported thermal analysis, apply to the body