July 2014 - Piping Loads at Heat Exchangers

Well this year seems to have flown in with lots of piping courses completed including Milan and Dubai. Things have certainly slowed down here in Eastern Canada although the West and Maritimes seem to be pretty buoyant.

In traveling around the world giving piping courses I cannot help but notice that young designers and engineers are being thrown into design work without adequate training. This seems to be a universal problem as larger EPC
companies are downloading much of the detail engineering to maximize their profits.

Training costs time and money and all projects now are being fastracked.

This months’ tips


  • A heat exchanger is fixed at one end and free to slide at the other to permit free expansion of the exchanger.
  • Generally it is assumed that the exchanger would be located with the channel end pointing away from the piperack or any other obstruction to tube withdrawal.
  • If cooling water is going through the tubes the exchanger is generally fixed at the channel end.
  • Conversely if the hot fluid is passing through the tubes then the exchanger is sliding at the channel end.
  • This is to minimize differential expansion between the piping and exchanger.
  • Here again, the limiting values for applied forces and moments are laid down by the manufacturers. The exchanger will be designed in all probability to T.E.M.A. standards so that its shell will have to comply with the A.S.M.E. Unfired Pressure Vessel Code. This in turn means that there are strictly limited values for the stresses in the exchanger shell local to the nozzles carrying the piping loads. Again the manufacturer will dictate his allowables.
  • It is not generally appreciated by the average designer that there is an effective stress intensification at a nozzle of the order 5; therefore a bending stress in the piping at the nozzle of 5000 psi will produce a bending stress in the exchanger shell plate in the order 25,000 psi.
  • This leads to the following rough guide:
  • Resultant maximum force:        200 lbs/inch nom. dia.
  • Bending moments - Equivalent to a bending stress in standard wall pipe between 4000 and 5000 psi.