Engineering guide
The TEB module calculates tubesheets of shell-and-tube heat exchangers to TEMA Section 5 (1999 edition) — the standard of the Tubular Exchanger Manufacturers Association, which serves worldwide as the reference for the mechanical design of shell-and-tube equipment. The various tubesheet configurations (integrally welded, gasketed, U-tube tubesheet, supported tubesheet) are covered via the corresponding TEMA curves, with and without an expansion joint in the shell.
The tubesheet is the most highly loaded component of the heat exchanger: it simultaneously carries the shell-side and tube-side pressures, the bolt loads and flange moments of the gasketed joints and — in units with two fixed tubesheets — the restraint forces from the differential thermal expansion of shell and tubes. TEMA captures this thermal restraint loading via the equivalent expansion pressure and the flange loading via equivalent bolting pressures, so that all load components are combined into one effective differential pressure.
The calculation is needed for every new design and reassessment of shell-and-tube heat exchangers to TEMA — frequently in parallel with the pressure vessel calculation to ASME Section VIII. Through the coupling to the add-on module TEM, the longitudinal stresses in shell and tubes can be verified in addition.
Scope
- ASME-TEB TEMA standards 1999
Typical workflow
Define configuration and load cases
First, the tubesheet configuration (curves U, H, etc. depending on edge restraint and support) and the load cases to be examined are defined: shell-side pressure, tube-side pressure, both together, each with and without thermal restraint loading, plus the bolting-up condition.
Determine material and temperature properties
For the tubesheet, shell and tubes, the allowable stresses, moduli of elasticity and coefficients of thermal expansion are determined from the applicable material charts at the respective design temperatures.
Calculate equivalent pressures
The differential thermal expansion between shell and tubes is converted into the equivalent expansion pressure (RCB-7.161); flange moments from the operating and bolting-up conditions yield the equivalent bolting pressures on the tube side and shell side (RCB-7.162). An existing expansion joint enters via its spring rate and the factor J and reduces the restraint forces.
Effective differential pressure and governing load case
From the operating pressures, expansion pressure and bolting pressures, the effective design pressures of the tubesheet are formed for all load case combinations; the value with the largest magnitude governs.
Determine required tubesheet thickness
With the governing pressure, the edge restraint factor F of the selected curve and the allowable stress, the required thickness is calculated from the bending and shear checks per TEMA; corrosion allowances and, where applicable, gasket groove depths are added.
Coupling to the longitudinal stress check
Optionally, the results are passed to the TEM module, which verifies the axial stresses in shell and tubes as well as the tube-to-tubesheet joint for the same load cases.
Frequently asked questions
What is the equivalent expansion pressure?
In units with two fixed tubesheets, shell and tubes expand differently — due to different temperatures and coefficients of thermal expansion. Since both are rigidly coupled through the tubesheets, restraint forces arise. TEMA converts this restraint loading into a fictitious pressure that produces the same tubesheet loading as the actual differential expansion. This allows the thermal load case to be treated with the same formulas as the pressure load cases.
When do I need an expansion joint in the shell?
When the equivalent expansion pressure loads the tubesheet thickness, the tube axial stresses or the tube-to-tubesheet joint beyond acceptable limits — typically at large temperature differences between shell and tubes or with material pairings of strongly differing thermal expansion (e.g. a carbon steel shell with austenitic tubes). The expansion joint lowers the restraint forces through its low spring stiffness; alternatively, U-tube or floating-head designs come into consideration, which release the differential expansion by design.
Why must several load case combinations be calculated?
Because the components do not always add unfavourably: shell-side and tube-side pressures act on the tubesheet in opposite directions, and the expansion pressure can relieve or load depending on the temperature distribution. A partial load case can therefore also govern — for instance tube-side pressure alone during start-up, before the shell has reached temperature. TEMA therefore requires the systematic investigation of all combinations, including the bolting-up condition with bolt preload.
What is the relationship between TEMA and ASME Section VIII (UHX)?
TEMA Section 5 is the historically established, semi-empirical method; ASME introduced with Part UHX an analytically more rigorous tubesheet calculation that models the elastic interaction of tubesheet, tube field, shell and channel more accurately. For code-stamped equipment to ASME, UHX is mandatory; TEMA remains widespread for comparison calculations, existing equipment and markets without a UHX requirement. The results can differ significantly, particularly for thin tubesheets.
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