Thick Walled Expansion Joint Methodology

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Dec 11, 2015
2 min read

This article provides methodology for designing a thick walled expansion joint. The calculations developed here are based primarily on the paper “Expansion Joints for Heat Exchangers” (also discussed in Design of Process Equipment) and the rules introduced in ASME Section VIII, Division I, 2001 Code, 2002 Addenda, Appendix 5.

Many of the symbols have been changed to more clearly represent values based on pressure or thermal expansion. The calculation of the axial rigidity was not clearly provided by any of the references; the equation used here was derived from the Kopp and Sayre method. The differential expansion per annular plate and the resultant axial rigidity were altered to consider multiple convolutions. The total differential thermal expansion was taken from part UHX.

Appendix 5 from the 2002 Addenda gives us some basis for determining cycle life. In 2003, the cycle life calculations were removed from the code book because the code writers thought that enforcing the use of the specific equations was unnecessary. The allowable stress criteria from Section VIII, Division I UG-23 is used, limiting membrane + primary bending stress to 1.5S and membrane + secondary bending to SPS. The current Appendix 5 also has a shell stress requirement on the straight flange sections if they exceed a certain length; this requirement is checked as well as other requirements on dimensions from Appendix 5. The stress calculations come from the paper mentioned above.

a diagram outlining the parts of a thick walled expansion joint

Additional Notes:

  1. The user may use an operating temperature as well as a design temperature for the expansion joint. Expansion joint material properties and allowable stresses will be determined from the temperature used for the loading case in question. The default for all calculations is to use design temperature. Even if the designer chooses to use operating temperature, there are calculations that still require the use of design temperature. See notes 3 and 6.
  2. All calculations are performed for both the new and the corroded condition.
  3. The calculation for the axial rigidity will be based on the design temperature only.
  4. For the purpose of determining the axial rigidity, the designer shall have the option to neglect the effect of the thinning allowance.
  5. There are 6 loading cases; each loading case will have a new and a corroded condition for a total of 12 cases. The 6 loading cases are: Pressure, Thermal, Pressure + Thermal, Pressure + Fatigue, Thermal + Fatigue, and Pressure + Thermal + Fatigue.
  6. The Pressure case is always performed using the design temperature.
  7. The Thermal and Pressure + Thermal cases may be performed using the operating temperature at the designer’s discretion.
  8. The determination of Sn and the pass/fail status for the loading cases that include Fatigue may be based on operating temperature at the designer’s discretion.
  9. The value of SPS is either 3S or 2SY, per the designer’s discretion.